posted 08-03-2004 02:30 AM               

Mercury-Bound MESSENGER Launches From Cape Canaveral

NASA's MESSENGER — set to become the first spacecraft to orbit the planet Mercury — launched today at 2:15:56 a.m. EDT aboard a Boeing Delta II rocket from Cape Canaveral Air Force Station, Fla.

The approximately 1.2-ton (1,100-kilogram) spacecraft, designed and built by the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., was placed into a solar orbit 57 minutes after launch. Once in orbit, MESSENGER automatically deployed its two solar panels and began sending data on its status. Once the mission operations team at APL acquired the spacecraft's radio signals through tracking stations in Hawaii and California, Project Manager David G. Grant confirmed the craft was operating normally and ready for early system check-outs.

"Congratulations to the MESSENGER launch team for a spectacular start to this mission of exploration to the planet Mercury," said Orlando Figueroa, Deputy Associate Administrator for Programs in the Science Mission Directorate at NASA Headquarters, Washington. "While we celebrate this major milestone, let's keep in mind there is still a lot to do before we reach our destination."

"All the work that went into designing and building this spacecraft is paying off beautifully," Grant said. "Now the team is ready to guide MESSENGER through the inner solar system and put us on target to begin orbiting Mercury in 2011."

During a 4.9-billion mile (7.9-billion kilometer) journey that includes 15 trips around the sun, MESSENGER will fly past Earth once, Venus twice and Mercury three times before easing into orbit around its target planet. The Earth flyby, in August 2005, and the Venus flybys, in October 2006 and June 2007, will use the pull of the planets' gravity to guide MESSENGER toward Mercury's orbit. The Mercury flybys in January 2008, October 2008 and September 2009 help MESSENGER match the planet's speed and location for an orbit insertion maneuver in March 2011. The flybys also allow the spacecraft to gather data critical to planning a yearlong orbit phase.

Since MESSENGER is only the second spacecraft sent to Mercury — Mariner 10 flew past it three times in 1974-75 and gathered detailed data on less than half the surface — the mission has an ambitious science plan. With a package of seven science instruments MESSENGER will determine Mercury's composition; image its surface globally and in color; map its magnetic field and measure the properties of its core; explore the mysterious polar deposits to learn whether ice lurks in permanently shadowed regions; and characterize Mercury's tenuous atmosphere and Earth-like magnetosphere.

"It took technology more than 30 years, from Mariner 10 to MESSENGER, to bring us to the brink of discovering what Mercury is all about," said Dr. Sean C. Solomon, MESSENGER's principal investigator from the Carnegie Institution of Washington, who leads a science team of investigators from 13 institutions across the U.S. "By the time this mission is done we will see Mercury as a much different planet than we think of it today."

MESSENGER, short for MErcury Surface, Space ENvironment, Geochemistry, and Ranging, is the seventh mission in NASA's Discovery Program of lower cost, scientifically focused exploration projects. APL manages the mission for NASA's Office of Space Science, built the spacecraft and will operate MESSENGER during flight. MESSENGER is the 61st spacecraft built at APL.

"With MESSENGER on its way to Mercury, the reality is sinking in that in a few years, we will see things that no human has ever seen and know infinitely more about the formation of the solar system than we know today," said Dr. Michael D. Griffin, head of the APL Space Department.

posted 01-08-2008 12:33 AM               

MESSENGER Only One Week from Mercury

MESSENGER's mid-December trajectory correction maneuver (TCM) went so well that the mission's design and navigation teams have decided that a TCM scheduled for January 10 will not be needed.

"Cancellation of this maneuver is a demonstration of the near-perfect execution of TCM-19 just prior to the start of the holiday season," says Mission Systems Engineer Eric Finnegan of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

On January 9, MESSENGER's Mercury Dual Imaging System cameras will begin gathering pictures of Mercury as the probe zeros in on the planet. "With just one week to go before the flyby, the spacecraft is on target to encounter the planet at an altitude of 202 kilometers," Finnegan says. "All subsystems and instruments are operating nominally and configured for the start of the flyby sequence, except for the Mercury Laser Altimeter and part of the Gamma-Ray Spectrometer, which we'll turn on just before the flyby."

Over the next week, the team will make final flyby preparations and upload the final command sequences for the encounter.

"We are about to visit Mercury for the first time in more than 30 years, and we can't wait," says MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington. "In addition to providing the critical gravity assist that will move MESSENGER along its path toward Mercury orbit insertion in March 2011, this flyby will let us see parts of Mercury never before viewed by spacecraft. We'll be making close-in observations of the composition of Mercury's surface and atmosphere, and we'll be probing deeper into the planet's magnetosphere than we've ever been. We expect many surprises."

posted 01-10-2008 12:47 PM               

NASA Spacecraft to Make Historic Flyby of Mercury

On Monday, Jan. 14, a pioneering NASA spacecraft will be the first to visit Mercury in almost 33 years when it soars over the planet to explore and snap close-up images of never-before-seen terrain. These findings could open new theories and answer old questions in the study of the solar system.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, called MESSENGER, is the first mission sent to orbit the planet closest to our sun. Before that orbit begins in 2011, the probe will make three flights past the small planet, skimming as close as 124 miles above Mercury's cratered, rocky surface. MESSENGER's cameras and other sophisticated, high-technology instruments will collect more than 1,200 images and make other observations during this approach, encounter and departure. It will make the first up-close measurements since Mariner 10 spacecraft's third and final flyby on March 16, 1975. When Mariner 10 flew by Mercury in the mid-1970s, it surveyed only one hemisphere.

"This is raw scientific exploration and the suspense is building by the day," said Alan Stern, associate administrator for NASA's Science Mission Directorate, Washington. "What will MESSENGER see? Monday will tell the tale."

This encounter will provide a critical gravity assist needed to keep the spacecraft on track for its March 2011 orbit insertion, beginning an unprecedented yearlong study of Mercury. The flyby also will gather essential data for mission planning.

"During this flyby we will begin to image the hemisphere that has never been seen by a spacecraft and Mercury at resolutions better than those acquired by Mariner 10," said Sean C. Solomon, MESSENGER principal investigator, Carnegie Institution of Washington. "Images will be in a number of different color filters so that we can start to get an idea of the composition of the surface."

One site of great interest is the Caloris basin, an impact crater about 800 miles in diameter, which is one of the largest impact basins in the solar system.

"Caloris is huge, about a quarter of the diameter of Mercury, with rings of mountains within it that are up to two miles high," said Louise Prockter, the instrument scientist for the Mercury Dual Imaging System at the Johns Hopkins University Applied Physics Laboratory in Laurel. "Mariner 10 saw a little less than half of the basin. During this first flyby, we will image the other side."

MESSENGER's instruments will provide the first spacecraft measurements of the mineralogical and chemical composition of Mercury's surface. It also will study the global magnetic field and improve our knowledge of the gravity field from the Mariner 10 flyby. The long-wavelength components of the gravity field provide key information about the planet's internal structure, particularly the size of Mercury's core.

The flyby will provide an opportunity to examine Mercury's environment in unique ways, not possible once the spacecraft begins orbiting the planet. The flyby also will map Mercury's tenuous atmosphere with ultraviolet observations and document the energetic particle and plasma of Mercury's magnetosphere. In addition, the flyby trajectory will enable unique particle and plasma measurements of the magnetic tail that sweeps behind Mercury.

Launched Aug. 3, 2004, MESSENGER is slightly more than halfway through its 4.9-billion mile journey. It already has flown past Earth once and Venus twice. The spacecraft will use the pull of Mercury's gravity during this month's pass and others in October 2008 and September 2009 to guide it progressively closer to the planet's orbit. Insertion will be accomplished with a fourth Mercury encounter in 2011.

The MESSENGER project is the seventh in NASA's Discovery Program of low-cost, scientifically focused space missions. The Applied Physics Laboratory designed, built and operates the spacecraft and manages the mission for NASA.

posted 01-10-2008 01:22 PM               

On January 9, 2008, the MESSENGER spacecraft snapped one of its first images of Mercury at a distance of about 2.7 million kilometers (1.7 million miles) from the planet.

The image was acquired with the Narrow Angle Camera, one half of MESSENGER's Mercury Dual Imaging System (MDIS) instrument. Mercury is about 4880 kilometers (3030 miles) in diameter, and this image has a resolution of about 70 kilometers/pixel (43 miles/pixel).

posted 01-13-2008 06:28 PM               

On Monday, January 14, 2008, at 19:04:39 UTC (2:04:39 pm EST), MESSENGER will pass a mere 200 kilometers (124 miles) above the surface of Mercury and will be the first spacecraft to visit Mercury in nearly a third of a century, since Mariner 10 flew by Mercury in 1974 and 1975.

Among the extensive scientific observations planned during the flyby is imaging a large portion of Mercury's surface that was not visible to the Mariner 10 mission.

MESSENGER's flyby will yield the first spacecraft images ever of these regions of Mercury's surface.

posted 01-14-2008 09:44 AM               

This image was taken on January 13, when the spacecraft was at a distance of about 760,000 kilometers (470,000 miles) from Mercury. Mercury is about 4880 kilometers (about 3030 miles) in diameter, and the smallest feature visible in this image is about 20 kilometers (12 miles) across.

posted 01-15-2008 10:23 PM               

MESSENGER's First Look at Mercury's Previously Unseen Side

When Mariner 10 flew past Mercury three times in 1974 and 1975, the same hemisphere was in sunlight during each encounter. As a consequence, Mariner 10 was able to image less than half the planet. Planetary scientists have wondered for more than 30 years about what spacecraft images might reveal about the hemisphere of Mercury that Mariner 10 never viewed.

On January 14, 2008, the MESSENGER spacecraft observed about half of the hemisphere missed by Mariner 10. This image was snapped by the Wide Angle Camera, part of the Mercury Dual Imaging System (MDIS) instrument, about 80 minutes after MESSENGER's closest approach to Mercury (2:04 pm EST), when the spacecraft was at a distance of about 27,000 kilometers (about 17,000 miles). The image shows features as small as 10 kilometers (6 miles) in size. This image was taken through a filter sensitive to light near the red end of the visible spectrum (750 nm), one of a sequence of images taken through each of MDIS's 11 filters.

Like the previously mapped portion of Mercury, this hemisphere appears heavily cratered. It also reveals some unique and distinctive features. On the upper right is the giant Caloris basin, including its western portions never before seen by spacecraft. Formed by the impact of a large asteroid or comet, Caloris is one of the largest, and perhaps one of the youngest, basins in the Solar System. The new image shows the complete basin interior and reveals that it is brighter than the surrounding regions and may therefore have a different composition. Darker smooth plains completely surround Caloris, and many unusual dark-rimmed craters are observed inside the basin. Several other multi-ringed basins are seen in this image for the first time. Prominent fault scarps (large ridges) lace the newly viewed region.

Other images obtained during the flyby will reveal surface features in color and in much more detail. Collectively, these images and measurements made by other MESSENGER instruments will soon provide a detailed global view of the surface of Mercury, yielding key information for understanding the formation and geologic history of the innermost planet.

posted 01-16-2008 01:30 PM               

As MESSENGER approached Mercury on January 14, 2008, the spacecraft's Narrow-Angle Camera on the Mercury Dual Imaging System (MDIS) instrument captured this view of the planet's rugged, cratered landscape illuminated obliquely by the Sun. The large, shadow-filled, double ringed crater to the upper right was glimpsed by Mariner 10 more than three decades ago and named Vivaldi, after the Italian composer. Its outer ring has a diameter of about 200 kilometers (about 125 miles). MESSENGER's modern camera has revealed detail that was not well seen by Mariner 10, including the broad ancient depression overlapped by the lower-left part of the Vivaldi crater. The MESSENGER science team is in the process of evaluating later images snapped from even closer range showing features on the side of Mercury never seen by Mariner 10. It is already clear that MESSENGER's superior camera will tell us much that could not be resolved even on the side of Mercury viewed by Mariner's vidicon camera in the mid-1970s.

This MESSENGER image was taken from a distance of about 18,000 kilometers (11,000 miles), about 56 minutes before the spacecraft's closest encounter with Mercury. It shows a region roughly 500 kilometers (300 miles) across, and craters as small as 1 kilometer (0.6 mile) can be seen in this image.

posted 01-18-2008 09:53 AM               

Bob Strom had begun to lose hope.

A veteran of NASA's Mariner 10 mission to Mercury in the 1970s, he was bursting with questions that the Mariner flybys had raised about the little planet but couldn't answer.

"I've been hoping for another Mercury mission for 30 years, practically," said Strom, an expert on impact craters. But for decades, NASA seemed unable to make it happen.

"I really thought... I'd never live to see Mercury again," he said.

But he did.

This week, NASA's Messenger spacecraft whizzed past Mercury and sent back more than 1,200 photos and measurements from the sun's nearest neighbor, and Strom was in the thick of it.

At 74, he is the only member of the old Mariner 10 team serving on the Messenger science team. He has been holed up in the mission's Science Operations Center, at the Johns Hopkins University's Applied Physics Lab near Laurel, marveling over the new data from Mercury.

posted 07-04-2008 09:51 AM               

NASA Reveals New Discoveries From Mercury

Scientists have argued about the origins of Mercury's smooth plains and the source of its magnetic field for more than 30 years. Now, analyses of data from the January 2008 flyby of the planet by the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft have shown that volcanoes were involved in plains formation and suggest that its magnetic field is actively produced in the planet's core.

Scientists additionally took their first look at the chemical composition of the planet's surface. The tiny craft probed the composition of Mercury's thin atmosphere, sampled charged particles (ions) near the planet, and demonstrated new links between both sets of observations and materials on Mercury's surface. The results are reported in a series of 11 papers published in a special section of Science magazine July 4.

The controversy over the origin of Mercury's smooth plains began with the 1972 Apollo 16 moon mission, which suggested that some lunar plains came from material that was ejected by large impacts and then formed smooth "ponds." When Mariner 10 imaged similar formations on Mercury in 1975, some scientists believed that the same processes were at work. Others thought Mercury's plains material came from erupted lavas, but the absence of volcanic vents or other volcanic features in images from that mission prevented a consensus.

Six of the papers in Science report on analyses of the planet's surface through its reflectance and color variation, surface chemistry, high-resolution imaging at different wavelengths, and altitude measurements. The researchers found evidence of volcanic vents along the margins of the Caloris basin, one of the solar system's youngest impact basins. They also found that Caloris has a much more complicated geologic history than previously believed.

The first altitude measurements from any spacecraft at Mercury also found that craters on the planet are about a factor of two shallower than those on Earth's moon. The measurements also show a complex geologic history for Mercury.

Mercury's core makes up at least 60 percent of its mass, a figure twice as large as any other known terrestrial planet. The flyby revealed that the magnetic field, originating in the outer core and powered by core cooling, drives very dynamic and complex interactions among the planet's interior, surface, exosphere and magnetosphere.

Remarking on the importance of the core to surface geological structures, Principal Investigator Sean Solomon at the Carnegie Institution of Washington said, "The dominant tectonic landforms on Mercury, including areas imaged for the first time by MESSENGER, are features called lobate scarps, huge cliffs that mark the tops of crustal faults that formed during the contraction of the surrounding area. They tell us how important the cooling core has been to the evolution of the surface. After the end of the period of heavy bombardment, cooling of the planet's core not only fueled the magnetic dynamo, it also led to contraction of the entire planet. And the data from the flyby indicate that the total contraction is a least one-third greater than we previously thought."

The flyby also made the first-ever observations of the ionized particles in Mercury's unique exosphere. The exosphere is an ultrathin atmosphere in which the molecules are so far apart they are more likely to collide with the surface than with each other. The planet's highly elliptical orbit, its slow rotation and particle interactions with the magnetosphere, interplanetary medium and solar wind result in strong seasonal and day-night differences in the way particles behave.

posted 09-30-2008 04:32 PM               

Space Scientists Set for Second Spacecraft Flyby of Mercury

NASA's MESSENGER spacecraft, which is toting an $8.7 million University of Colorado at Boulder instrument to measure Mercury's wispy atmosphere and blistering surface, will make its second flyby of the mysterious, rocky planet Oct. 6.

Traveling at a mind-blowing 4.2 miles per second, the spacecraft will dip within 124 miles of Mercury and image much of the surface never before seen by spacecraft. As MESSENGER pulls away from the planet it will view a region seen at high resolution only once before -- when NASA's Mariner 10 spacecraft made three flybys in 1974 and 1975, said Senior Research Associate William McClintock, a mission co-investigator from CU-Boulder's Laboratory for Atmospheric and Space Physics.

Launched in August 2004, MESSENGER will make the last of three passes by Mercury -- the closest planet to the sun -- in October 2009 before finally settling into orbit around it in 2011. The circuitous, 4.9 billion-mile-journey to Mercury requires more than six years and 15 loops around the sun to guide it closer to Mercury's orbit. McClintock led the development of CU-Boulder's Mercury Atmospheric and Surface Composition Spectrometer, or MASCS, miniaturized to weigh less than seven pounds for the arduous journey.

The craft is equipped with a large sunshade and heat-resistant ceramic fabric to protect it from the sun, and more than half of the weight of the 1.2-ton spacecraft at launch consisted of propellant and helium. "We are almost two-thirds of the way there, but we still have a lot of work to do," said McClintock. "We are continually refining our game plan, including developing contingencies for the unexpected."

The desk-sized MESSENGER spacecraft is carrying seven instruments -- a camera, a magnetometer, an altimeter and four spectrometers. Data from MASCS earlier this year during the first flyby Jan. 14 provided LASP researchers with evidence that about 10 percent of the sodium atoms ejected from Mercury's hot surface during the daytime were accelerated into a 25,000-mile-long sodium tail trailing the planet, McClintock said.

MESSENGER will take data and images from Mercury for about 90 minutes on Oct. 6, when LASP will turn on a detector in MASCS for its first look at Mercury's surface in the far ultraviolet portion of the light spectrum, said McClintock. The scanner will look at reflected light from Mercury's surface to better determine the mineral composition of the planet.

"We got some surprising results with our UV detector in January, and we hope to see additional surprises as we extend our observations further into the ultraviolet," he said.

The second Mercury flyby is slated for 2:40 a.m. MDT on Oct. 6. LASP Director Daniel Baker, also a co-investigator on the MESSENGER mission, is using data from the mission to study Mercury's magnetic field and its interaction with the solar wind. Mark Lankton is the LASP program manager for the MASCS instrument.

Dozens of undergraduates and graduate students will be involved in analyzing data over the next several years as information and images pour back to Earth from MESSENGER. Sean Solomon from the Carnegie Institution of Washington in Washington, D.C., is the MESSENGER principal investigator.

posted 10-06-2008 05:28 PM               

MESSENGER Flyby of Mercury

At a little after 4:40 a.m. EDT, MESSENGER skimmed 200 kilometers (124 miles) above the surface of Mercury in the second of three flybys of the planet. Initial indications from the radio signals indicate that the spacecraft continues to operate nominally. The spacecraft is now collecting images and other scientific measurements from the planet as it departs Mercury from the illuminated side, filling in the details of much of Mercury's surface not previously viewed by spacecraft.

Tomorrow at 1:14 a.m. EDT, the spacecraft will turn its high-gain antenna back toward Earth to start down-linking the data stored onboard. The first pictures from the flyby will be released around 10:00 a.m. on October 7, 2008. Additional information and features from this encounter will be available online.

posted 10-07-2008 11:03 AM               

Yesterday, at 4:40 am EDT, MESSENGER successfully completed its second flyby of Mercury. Today, at about 1:50 am EDT, the images taken during the flyby encounter began to be received back on Earth. The spectacular image shown here is one of the first to be returned and shows a WAC image of the departing planet taken about 90 minutes after the spacecraft's closest approach to Mercury.

The bright crater just south of the center of the image is Kuiper, identified on images from the Mariner 10 mission in the 1970s. For most of the terrain east of Kuiper, toward the limb (edge) of the planet, the departing images are the first spacecraft views of that portion of Mercury's surface.

A striking characteristic of this newly imaged area is the large pattern of rays that extend from the northern region of Mercury to regions south of Kuiper. This extensive ray system appears to emanate from a relatively young crater newly imaged by MESSENGER, providing a view of the planet distinctly unique from that obtained during MESSENGER's first flyby.

This young, extensively rayed crater, along with the prominent rayed crater to the southeast of Kuiper, near the limb of the planet, were both seen in Earth-based radar images of Mercury but not previously imaged by spacecraft.

As the MESSENGER team is busy examining this newly obtained view that is only a few hours old, data from the flyby continue to stream down to Earth, including higher resolution close-up images of this previously unseen terrain.

posted 10-09-2008 01:04 AM               

MESSENGER Sets Record for Accuracy of Planetary Flyby

By using solar sailing - rotating the spacecraft and tilting its solar panels to use the very small pressure from sunlight to alter the spacecraft's trajectory - MESSENGER navigators have achieved a new record for the smallest miss distance between the intended and actual closest approach distance during a flyby of a planet other than Earth.

On October 6, 2008, the probe flew 199.4 kilometers (123.9 miles) above the surface of the planet. "Our goal was to fly 200 kilometers from the planet's surface, and we missed that target by only 0.6 kilometers," explained MESSENGER Mission Design Lead Jim McAdams, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

That's pretty remarkable targeting, given that MESSENGER has travelled 668 million kilometers since its last deep space maneuver in March, McAdams says. "It's as if we shot an arrow from New York to a target in Los Angeles - nudged it three times mid-stream with a soft breath - and arrived within the width of the arrow's shaft at the target."

posted 05-01-2009 11:43 AM               

MESSENGER Spacecraft Reveals a Very Dynamic Planet Mercury

A NASA spacecraft gliding over the surface of Mercury has revealed that the planet's atmosphere, the interaction of its surrounding magnetic field with the solar wind, and its geological past display greater levels of activity than scientists first suspected. The probe also discovered a previously unknown large impact basin about 430 miles in diameter -- equal to the distance between Washington and Boston.

Analyses of these new findings and more are reported in four papers published in the May 1 issue of Science magazine. The data come from the Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft, known as MESSENGER. On Oct. 6, 2008, the probe flew by Mercury for the second time, capturing more than 1,200 high-resolution and color images of the planet. The probe unveiled another 30 percent of the planet's surface that had never been seen by previous spacecraft, gathering essential data for planning the remainder of the mission.

"This second Mercury flyby provided a number of new findings," said Sean Solomon, the probe's principal investigator from the Carnegie Institution of Washington. "One of the biggest surprises was how strongly the dynamics of the planet's magnetic field-solar wind interaction changed from what we saw during the first Mercury flyby in January 2008. The discovery of a large and unusually well preserved impact basin shows concentrated volcanic and deformational activity."

The spacecraft also made the first detection of magnesium in Mercury's thin atmosphere, known as an exosphere. This observation and other data confirm that magnesium is an important constituent of Mercury's surface materials.

The probe's Mercury Atmospheric and Surface Composition Spectrometer instrument detected the magnesium. Finding magnesium was not surprising to scientists, but seeing it in the amounts and distribution observed was unexpected. The instrument also measured other exospheric constituents, including calcium and sodium.

"This is an example of the kind of individual discoveries that the science team will piece together to give us a new picture of how the planet formed and evolved," said William McClintock, co-investigator and lead author of one of the four papers. McClintock, who is from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder, suspects that additional metallic elements from the surface, including aluminum, iron and silicon, also contribute to the exosphere.

The variability that the spacecraft observed in Mercury's magnetosphere, the volume of space dominated by the planet's magnetic field, so far supports the hypothesis that the great day-to-day changes in Mercury's atmosphere may be a result of changes in the shielding provided by the magnetosphere.

"The spacecraft observed a radically different magnetosphere at Mercury during its second flyby compared with its earlier Jan. 14 encounter," said James Slavin from NASA's Goddard Space Flight Center in Greenbelt, Md. Slavin is a mission co-investigator and lead author of one of the papers. "During the first flyby, important discoveries were made, but scientists didn't detect any dynamic features. The second flyby witnessed a totally different situation."

The spacecraft's discovery of the impact basin, called Rembrandt, is the first time scientists have seen terrain well exposed on the floor of a large impact basin on Mercury. Landforms such as those revealed on the floor of Rembrandt usually are buried completely by volcanic flows.

"This basin formed about 3.9 billion years ago, near the end of the period of heavy bombardment of the inner solar system," said Thomas Watters from the Smithsonian Institution in Washington, a participating scientist and lead author of one paper. "Although ancient, the Rembrandt basin is younger than most other known impact basins on Mercury."

Half of Mercury was unknown until a little more than a year ago. Globes of the planet were blank on one side. Spacecraft images have enabled scientists to see 90 percent of the planet's surface at high resolution. The spacecraft's nearly global imaging coverage of the surface after the second flyby gives scientists fresh insight into how the planet's crust was formed.

"After mapping the surface, we see that approximately 40 percent is covered by smooth plains," said Brett Denevi of Arizona State University in Tempe, a team member and lead author of a paper. "Many of these smooth plains are interpreted to be of volcanic origin, and they are globally distributed. Much of Mercury's crust may have formed through repeated volcanic eruptions in a manner more similar to the crust of Mars than to that of the moon."

Scientists continue to examine data from the first two flybys and are preparing to gather more information from a third flyby of the planet on Sept. 29.

"The third Mercury flyby is our final dress rehearsal for the main performance of our mission, the insertion of the probe into orbit around Mercury in March 2011," said Solomon. "The orbital phase will be like staging two flybys per day and will provide the continuous collection of information about the planet and its environment for one year. Mercury has been coy in revealing its secrets slowly so far, but in less than two years the innermost planet will become a close friend."

posted 09-28-2009 05:12 PM               

MESSENGER Spacecraft Prepares for Final Pass by Mercury

NASA's Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft known as MESSENGER will fly by Mercury for the third and final time on Sept. 29. The spacecraft will pass less than 142 miles above the planet's rocky surface for a final gravity assist that will enable it to enter Mercury's orbit in 2011.

Determining the composition of Mercury's surface is a major goal of the orbital phase of the mission. The spacecraft already has imaged more than 90 percent of the planet's surface. The spacecraft's team will activate instruments during this flyby to view specific features to uncover more information about the planet.

"This flyby will be our last close look at the equatorial regions of Mercury, and it is our final planetary gravity assist, so it is important for the entire encounter to be executed as planned," said Sean Solomon, principal investigator at the Carnegie Institution in Washington. "As enticing as these flybys have been for discovering some of Mercury's secrets, they are the hors d'oeuvres to the mission's main course -- observing Mercury from orbit for an entire year.

The spacecraft may observe how the planet interacts with conditions in interplanetary space as a result of activity on the sun. During this encounter, high spectral- and high spatial-resolution measurements will be taken again of Mercury's tenuous atmosphere and tail.

"Scans of the planet's comet-like tail will provide important clues regarding the processes that maintain the atmosphere and tail," said Noam Izenberg, the instrument's scientist at the Johns Hopkins University Applied Physics Laboratory, or APL, in Laurel, Md. "The Mercury Atmospheric and Surface Composition Spectrometer will give us a snapshot of how the distribution of sodium and calcium vary with solar and planetary conditions. In addition, we will target the north and south polar regions for detailed observations and look for several new atmospheric constituents."

As the spacecraft approaches Mercury, cameras will photograph previously unseen terrain. As the spacecraft departs, it will take high-resolution images of the southern hemisphere. Scientists expect the spacecraft's imaging system to take more than 1,500 pictures. Those images will be used to create a mosaic to complement the high resolution, northern-hemisphere mosaic obtained during the second Mercury flyby. The first flyby took the spacecraft over the eastern hemisphere in January 2008, and the second flyby took it over western side in October 2008.

"We are going to collect high resolution, color images of scientifically interesting targets that we identified from the second flyby," said Ralph McNutt, a project scientist at APL. "The spectrometer also will make measurements of those targets at the same time."

Two spacecraft maneuvers will improve the ability of the spacecraft's Neutron Spectrometer to detect low-energy neutrons sensitive to the abundances of iron and titanium on Mercury's surface. These two elements absorb neutrons and are critical to an understanding of how the planet and its crust formed. A combination of day and night measurements will enable scientists to test the influence that planetary surface temperature has on the neutron population. The data are important for interpreting measurements that will be made after the probe is in orbit around Mercury.

An altimeter will make a topographic profile along the instrument ground track of Mercury's surface. The data gathered will provide additional topography of Mercury's surface features for ongoing studies of the form and structure of its craters and large faults. The information also will extend scientists' equatorial view of Mercury's global shape and allow them to confirm the discovery made during the first and second flyby that Mercury's equatorial region is slightly elliptical.

The spacecraft has completed nearly three-quarters of its 4.9-billion-mile journey to enter orbit around Mercury. The trip includes more than 15 trips around the sun. In addition to flying by Mercury, the spacecraft flew past Earth in August 2005 and Venus in October 2006 and June 2007.

The project is the seventh in NASA's Discovery Program of low-cost, scientifically focused space missions. The spacecraft was designed and built by APL. The mission also is managed and operated by APL for NASA's Science Mission Directorate in Washington.

posted 10-01-2009 10:19 AM               

Mercury Flyby 3

MESSENGER successfully flew by Mercury Sept. 29, gaining a critical gravity assist that will enable it to enter orbit about Mercury in 2011 and capturing images of five percent of the planet never before seen. With more than 90 percent of the planet's surface already imaged, MESSENGER's science team had drafted an ambitious observation campaign designed to tease out additional details from features uncovered during the first two flybys. But an unexpected signal loss prior to closest approach hampered those plans.

At approximately 5:55 p.m., the spacecraft passed by Mercury at an altitude of 142 miles and at a relative velocity of more than 12,000 miles per hour according to Doppler residual measurements logged just prior to the closet approach point. As the spacecraft approached the planet, MESSENGER's Wide Angle Camera captured this striking view, which shows portions of Mercury's surface that had remained unseen by spacecraft even after the three flybys by Mariner 10 in 1974 and 1975 and MESSENGER's two earlier flybys in 2008.

Credit: NASA/JHU APL/Carnegie Institution

"This third and final flyby was MESSENGER's last opportunity to use the gravity of Mercury to meet the demands of the cruise trajectory without using the probe's limited supply of on-board propellant," says MESSENGER Mission Systems Engineer Eric Finnegan of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

A portion of the complicated encounter was executed in eclipse, when the spacecraft is in Mercury's shadow and the spacecraft - absent solar power - was to operate on its internal batteries for 18 minutes. Ten minutes after entering eclipse and four minutes prior to the closet approach point, the carrier signal from the spacecraft was lost, earlier than expected.

According to Finnegan, the spacecraft autonomously transitioned to a safe operating mode, which pauses the execution of the command load and "safes the instruments," while maintaining knowledge of its operational state and preserving all data on the solid-state recorder.

"We believe this mode transition was initiated by the on-board fault management system due to an unexpected configuration of the power system during eclipse," Finnegan says. MESSENGER was returned to operational mode at 12:30 a.m. with all systems reporting nominal operations. All on-board stored data were returned to the ground by early morning and are being analyzed to confirm the full sequence of events.

"Although the events did not transpire as planned, the primary purpose of the flyby, the gravity assist, appears to be completely successful," Finnegan adds. "Furthermore, all approach observing sequences have been captured, filling in additional area of previously unexplored terrain and further exploring the exosphere of Mercury."

"MESSENGER's mission operations and engineering teams deserve high commendation for their professional and efficient approach to last night's spacecraft safe-mode transition," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "They quickly diagnosed the initial problem, restored the spacecraft to its normal operating mode, and developed plans to recover as much of our post-encounter science observations as possible. Most importantly, we are on course to Mercury orbit insertion less than 18 months from now, so we know that we will be returning to Mercury and will be able to observe the innermost planet in exquisite detail."

Credit: NASA/JHU APL/Carnegie Institution

posted 11-03-2009 10:38 PM               

MESSENGER Spacecraft Reveals More Hidden Territory on Mercury

A NASA spacecraft's third and final flyby of Mercury gives scientists, for the first time, an almost complete view of the planet's surface and provides new scientific findings about this relatively unknown world.

The Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft, known as MESSENGER, flew by Mercury on Sept. 29. The probe completed a critical gravity assist to remain on course to enter into orbit around Mercury in 2011. Despite shutting down temporarily because of a power system switchover during a solar eclipse, the spacecraft's cameras and instruments collected high-resolution and color images unveiling another 6 percent of the planet's surface never before seen at close range.

Approximately 98 percent of Mercury's surface now has been imaged by NASA spacecraft. After MESSENGER goes into orbit around Mercury, it will see the polar regions, which are the only unobserved areas of the planet.

"Although the area viewed for the first time by spacecraft was less than 350 miles across at the equator, the new images reminded us that Mercury continues to hold surprises," said Sean Solomon, principal investigator for the mission and director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington.

Many new features were revealed during the third flyby, including a region with a bright area surrounding an irregular depression, suspected to be volcanic in origin. Other images revealed a double-ring impact basin approximately 180 miles across. The basin is similar to a feature scientists call the Raditladi basin, which was viewed during the probe's first flyby of Mercury in January 2008.

"This double-ring basin, seen in detail for the first time, is remarkably well preserved," said Brett Denevi, a member of the probe's imaging team and a postdoctoral researcher at Arizona State University in Tempe. "One similarity to Raditladi is its age, which has been estimated to be approximately one billion years old. Such an age is quite young for an impact basin, because most basins are about four times older. The inner floor of this basin is even younger than the basin itself and differs in color from its surroundings. We may have found the youngest volcanic material on Mercury."

One of the spacecraft's instruments conducted its most extensive observations to date of Mercury's exosphere, or thin atmosphere, during this encounter. The flyby allowed for the first detailed scans over Mercury's north and south poles. The probe also has begun to reveal how Mercury's atmosphere varies with its distance from the sun.

"A striking illustration of what we call 'seasonal' effects in Mercury's exosphere is that the neutral sodium tail, so prominent in the first two flybys, is 10 to 20 times less intense in emission and significantly reduced in extent," says participating scientist Ron Vervack, of the Johns Hopkins University Applied Physics Laboratory, or APL, in Laurel, Md. "This difference is related to expected variations in solar radiation pressure as Mercury moves in its orbit and demonstrates why Mercury's exosphere is one of the most dynamic in the solar system."

The observations also show that calcium and magnesium exhibit different seasonal changes than sodium. Studying the seasonal changes in all exospheric constituents during the mission orbital phase will provide key information on the relative importance of the processes that generate, sustain, and modify Mercury's atmosphere.

The third flyby also revealed new information on the abundances of iron and titanium in Mercury's surface materials. Earlier Earth and spacecraft-based observations showed that Mercury's surface has a very low concentration of iron in silicate minerals, a result that led to the view that the planet's crust is generally low in iron.

"Now we know Mercury's surface has an average iron and titanium abundance that is higher than most of us expected, similar to some lunar mare basalts," says David Lawrence, an APL participating mission scientist.

The spacecraft has completed nearly three-quarters of its 4.9-billion-mile journey to enter orbit around Mercury. The full trip will include more than 15 trips around the sun. In addition to flying by Mercury, the spacecraft flew past Earth in August 2005 and Venus in October 2006 and June 2007.

The spacecraft was designed and built by APL. The mission is managed and operated by APL for NASA's Science Mission Directorate in Washington.

posted 07-16-2010 01:56 PM               

MESSENGER Spacecraft Reveals New Information About Mercury

The first spacecraft designed by NASA to orbit Mercury is giving scientists a new perspective on the planet's atmosphere and evolution.

Launched in August 2004, the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft, known as MESSENGER, conducted a third and final flyby of Mercury in September 2009. The probe completed a critical maneuver using the planet's gravity to remain on course to enter into orbit around Mercury next year.

Data from the final flyby has revealed the first observations of ion emissions in Mercury's exosphere, or thin atmosphere; new information about the planet's magnetic substorms; and evidence of younger volcanic activity than previously recorded. The results are reported in three papers published online in the July 15 edition of Science Express.

The distribution of individual chemical elements that the spacecraft saw in Mercury’s exosphere varied around the planet. Detailed altitude profiles of those elements in the exosphere over the north and south poles of the planet were also measured for the first time.

"These profiles showed considerable variability among the sodium, calcium, and magnesium distributions, indicating that several processes are at work and that a given process may affect each element quite differently," said Ron Vervack, lead author of one of the papers and the spacecraft's participating scientist at the Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md.

Emission from ionized calcium in Mercury's exosphere was observed for the first time during the flyby. The emission was concentrated over a relatively small portion of the exosphere, with most of the emission occurring close to the equatorial plane.

During its first two flybys of Mercury, the spacecraft captured images confirming that the planet's early history was marked by pervasive volcanism. The spacecraft's third flyby revealed a new chapter in that history within an impact basin 180 miles in diameter that is among the youngest basins yet seen. The basin, recently named Rachmaninoff, has an inner floor filled with smooth plains that differ in color from their surroundings. These sparsely cratered plains are younger than the basin they fill and apparently formed from material that once flowed across the surface.

"We interpret these plains to be the youngest volcanic deposits we have yet found on Mercury," said Louise Prockter, one of the spacecraft's deputy project scientists at APL and lead author of one of the three papers. "Other observations suggest the planet spanned a much greater duration volcanism than previously thought, perhaps extending well into the second half of solar system history."

For the first time, the spacecraft revealed substorm-like build-up, or loading, of magnetic energy in Mercury's magnetic tail. The increases in energy measured in Mercury's magnetic tail were very large. They occurred quickly, lasting only two to three minutes from beginning to end. These increases in tail magnetic energy at Mercury are about 10 times greater than at Earth, and the substorm-like events run their course about 50 times more rapidly.

Magnetic substorms are space-weather disturbances that occur intermittently on Earth, usually several times per day, and last from one to three hours. Earth substorms are accompanied by a range of phenomena, such as the majestic auroral displays seen in the Arctic and Antarctic skies. Substorms also are associated with hazardous energetic particle events that can wreak havoc with communications and Earth-observing satellites.

"The extreme tail loading and unloading observed at Mercury implies that the relative intensity of substorms must be much larger than at Earth," said James A. Slavin, a space physicist at NASA's Goddard Space Flight Center in Greenbelt, Md., and a member of the spacecraft's science team and lead author of another paper.

The new measurements give fresh insight on the time duration of Mercury's substorms. Scientists await more extensive measurements when the spacecraft is in orbit.

"Every time we've encountered Mercury, we've discovered new phenomena," said Sean Solomon, the mission's principal investigator at the Carnegie Institution of Washington. "We're learning that Mercury is an extremely dynamic planet, and it has been so throughout its history. After MESSENGER has been safely inserted into orbit around Mercury next March, we'll be in for a terrific show."

In addition to flying by Mercury, the spacecraft flew past Earth in August 2005 and Venus in October 2006 and June 2007. Approximately 98 percent of Mercury's surface has been imaged by NASA spacecraft. After this spacecraft goes into orbit around Mercury for a yearlong study of the planet, it will observe the polar regions, which are the only unobserved areas of the planet.

The spacecraft was designed and built by APL. The mission is managed and operated by APL for NASA's Science Mission Directorate in Washington.

posted 03-15-2011 01:20 PM               

MESSENGER Primed for Mercury Orbit

After more than a dozen laps through the inner solar system and six planetary flybys, NASA's MESSENGER spacecraft will move into orbit around Mercury on at around 9 p.m. EDT on March 17, 2011. The durable spacecraft -- carrying seven science instruments and fortified against the blistering environs near the Sun -- will be the first to orbit the innermost planet.

"From the outset of this mission, our goal has been to gather the first global observations of Mercury from orbit," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "At the time of our launch more than six and a half years ago, that goal seemed but a distant dream. MESSENGER is now poised to turn that dream into reality."

Just over 33 hours before the main Mercury orbit insertion maneuver, two antennas from NASA's Deep Space Network -- one main antenna and one backup -- will begin to track the MESSENGER spacecraft continuously. At 6:30 p.m. EDT on March 17, the number of antennas tracking MESSENGER will increase to five -- four of these will be arrayed together to enhance the signal from the spacecraft, and a fifth will be used for backup.

At about 8 p.m., the solar arrays, telecommunications, attitude control, and autonomy systems will be configured for the main thruster firing (known as a "burn"), and the spacecraft, operating on commands transmitted last week from Earth, will be turned to the correct orientation for MESSENGER's Mercury orbit insertion maneuver.

To slow the spacecraft down sufficiently to be "captured" by Mercury, MESSENGER's main thruster will fire for about 15 minutes beginning at 8:45 p.m. This burn will slow the spacecraft by 1,929 miles per hour (862 meters per second) and consume 31 percent of the propellant that the spacecraft carried at launch. Less than 9.5 percent of the usable propellant at the start of the mission will remain after completing the orbit insertion maneuver, but the spacecraft will still have plenty of propellant for orbit adjustments during its yearlong science campaign.

After the burn, the spacecraft will turn toward Earth and resume normal operations. Data will be collected by Deep Space Network antennas and transferred to the Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., to be analyzed. It is expected that by 10 p.m. EDT, mission operators will be able to confirm that MESSENGER has been successfully captured into orbit around Mercury.

The maneuver -- which will be completed at a time that MESSENGER is more than 96 million miles from Earth -- will place the probe into an orbit that brings it as close as 124 miles to Mercury's surface. At 2:47 a.m. EDT on March 18, the spacecraft will begin its first full orbit around Mercury, and the probe will continue to orbit Mercury once every 12 hours for the duration of its primary mission.

"For the first two weeks of orbit, we'll be focused on ensuring that the spacecraft systems are all working well in Mercury's harsh thermal environment," says APL's Eric Finnegan, the MESSENGER Mission Systems Engineer. "Starting on March 23 the instruments will be turned on and checked out, and on April 4 the science phase of the mission will begin and the first orbital science data from Mercury will be returned."

While in orbit, MESSENGER's instruments will perform the first complete reconnaissance of the cratered planet's geochemistry, geophysics, geological history, atmosphere, magnetosphere, and plasma environment.

"The marathon cruise phase of the MESSENGER mission is nearing the finish line," says Solomon. "Like a seasoned runner, the MESSENGER team is positioned to break through the tape. We are extremely excited by the prospect that orbital operations will soon begin."

posted 03-16-2011 01:19 PM               

MESSENGER On Autopilot for Orbit Insertion

MESSENGER is now on autopilot, faithfully executing a detailed set of instructions required to achieve its historic rendezvous with Mercury tomorrow night.

At 8 a.m. Tuesday, all attitude re-orientations planned to control the probe's momentum accumulation and adjust its trajectory were successfully completed. MESSENGER turned to point its high-gain antenna back to Earth for the final stretch of continuous data monitoring until just before the start of Mercury orbit insertion.

The operations team at the Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md., has monitored on-board commanded vehicle re-configurations and has sent pre-defined ground commands to establish configurations for the burn.

The science instrument suite has recorded the last set of data for the cruise portion of the mission, and all instruments have been turned off. Although not in an operational mode, the Gamma-Ray Spectrometer has been left in its stand-by mode to ensure thermal stability of the delicate cryogenic cooler. The instruments will be tuned back on as part of orbital commissioning beginning on March 23.

"The navigation team is reporting that there has been little change from the previous targeting estimates, so the spacecraft is on the glide-slope for final approach to Mercury," says MESSENGER Systems Engineer Eric Finnegan.

posted 03-17-2011 02:47 PM               

MESSENGER Orbit Maneuver a "Go"

With less than six hours to go, MESSENGER is on schedule for its 8:45 p.m. (EDT) rendezvous with Mercury. "The command sequence containing instructions to maneuver MESSENGER into orbit about Mercury is now executing, the science instruments have been turned off, and the propulsion system is conditioned for its big show this evening," says MESSENGER Project Manager Peter Bedini.

The MESSENGER team at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., expects confirmation of orbit by 10 p.m. (EDT).

Coverage of the mission will begin at 8 p.m. (EDT) tonight at APL's Kossiakoff Auditorium. The event will include a mission overview by MESSENGER Project Scientist Ralph L. McNutt, Jr., and live commentary by other scientists and engineers. The event will be broadcast live via Webcast.

Note: This webcast cannot be viewed using Safari browser. Mozilla Firefox is recommended when viewing this webcast on a Mac.

posted 03-17-2011 08:03 PM               

• 7:49 p.m. CDT: MESSENGER ran the final autonomy system configurations before firing the engine.

• 7:54 p.m. CDT: Ignition of the main thruster of the MESSENGER spacecraft as it prepares to slow down and enter Mercury orbit.

• 8:09 p.m. CDT: Engine shutdown. Doppler data suggests orbital capture. Waiting on high-rate telemetry from MESSENGER to confirm.

• 8:21 p.m. CDT: MESSENGER turned its main antenna back toward Earth to reestablish full telemetry contact.

• 8:51 p.m. CDT: MESSENGER confirmed as first spacecraft to enter orbit around Mercury!

NASA'S MESSENGER Spacecraft Begins Historic Orbit Around Mercury

NASA's MESSENGER spacecraft successfully achieved orbit around Mercury at approximately 9 p.m. EDT Thursday. This marks the first time a spacecraft has accomplished this engineering and scientific milestone at our solar system's innermost planet.

"This mission will continue to revolutionize our understanding of Mercury during the coming year," said NASA Administrator Charles Bolden, who was at MESSENGER mission control at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., as engineers received telemetry data confirming orbit insertion. "NASA science is rewriting text books. MESSENGER is a great example of how our scientists are innovating to push the envelope of human knowledge."

At 9:10 p.m. EDT, engineers Operations Center, received the anticipated radiometric signals confirming nominal burn shutdown and successful insertion of the MESSENGER probe into orbit around the planet Mercury. NASA's MErcury Surface, Space ENvironment, Geochemistry, and Ranging, or MESSENGER, rotated back to the Earth by 9:45 p.m. EDT, and started transmitting data. Upon review of the data, the engineering and operations teams confirmed the burn executed nominally with all subsystems reporting a clean burn and no logged errors.

MESSENGER's main thruster fired for approximately 15 minutes at 8:45 p.m., slowing the spacecraft by 1,929 miles per hour and easing it into the planned orbit about Mercury. The rendezvous took place about 96 million miles from Earth.

"Achieving Mercury orbit was by far the biggest milestone since MESSENGER was launched more than six and a half years ago," said Peter Bedini, MESSENGER project manager of the Applied Physics Laboratory (APL). "This accomplishment is the fruit of a tremendous amount of labor on the part of the navigation, guidance-and-control, and mission operations teams, who shepherded the spacecraft through its 4.9-billion-mile journey."

For the next several weeks, APL engineers will be focused on ensuring the spacecraft's systems are all working well in Mercury's harsh thermal environment. Starting on March 23, the instruments will be turned on and checked out, and on April 4 the mission's primary science phase will begin.

"Despite its proximity to Earth, the planet Mercury has for decades been comparatively unexplored," said Sean Solomon, MESSENGER principal investigator of the Carnegie Institution of Washington. "For the first time in history, a scientific observatory is in orbit about our solar system's innermost planet. Mercury's secrets, and the implications they hold for the formation and evolution of Earth-like planets, are about to be revealed."

APL designed and built the spacecraft. The lab manages and operates the mission for NASA's Science Mission Directorate in Washington.

posted 03-29-2011 04:43 PM               

MESSENGER Sends Back First Image of Mercury from Orbit

MESSENGER has delivered its first image since entering orbit about Mercury on March 17.

It was taken today (March 29) at 5:20 a.m. EDT by the Mercury Dual Imaging System as the spacecraft sailed high above Mercury's south pole, and provides a glimpse of portions of Mercury's surface not previously seen by spacecraft.

The image was acquired as part of the orbital commissioning phase of the MESSENGER mission. Continuous global mapping of Mercury will begin on April 4.

Credit: NASA/JHU APL/Carnegie Institution of Washington

"The entire MESSENGER team is thrilled that spacecraft and instrument checkout has been proceeding according to plan," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "The first images from orbit and the first measurements from MESSENGER's other payload instruments are only the opening trickle of the flood of new information that we can expect over the coming year."

"The orbital exploration of the Solar System's innermost planet has begun."

Several other images will be available Wednesday, March 30, in conjunction with a media teleconference to discuss the initial orbital images taken from the first spacecraft to orbit Mercury.

posted 04-01-2011 12:01 PM               

First Color Image of Mercury from Orbit

The first image acquired by MESSENGER from orbit around Mercury was actually part of an eight-image sequence, for which images were acquired through eight of the WAC's eleven filters.

Here we see a color version of that first imaged terrain; in this view the images obtained through the filters with central wavelengths of 1000 nm, 750 nm, and 430 nm are displayed in red, green, and blue, respectively.

One of MESSENGER's measurement objectives is to create an eight-color global base map at a resolution of 1 km/pixel (0.6 miles/pixel) to help understand the variations of composition across Mercury's surface.

Credit: NASA/JHU APL/Carnegie Institution of Washington

posted 06-16-2011 10:06 PM               

NASA Spacecraft Confirms Theories, Sees Surprises at Mercury

NASA scientists are making new discoveries about the planet Mercury. Data from MESSENGER, the first spacecraft to orbit Mercury, is giving scientists important clues to the origin of the planet and its geological history and helping them better understand its dynamic interior and exterior processes.

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, or MESSENGER, has been orbiting Mercury since March 18. To date the spacecraft has provided tens of thousands of images showing detailed planetary features. The planet's surface previously had been seen only at comparatively low resolution but is now in sharper focus.

The spacecraft also has collected extensive measurements of the chemical composition of Mercury's surface and topography and gathered global observations of the planet's magnetic field. Data now confirm that bursts of energetic particles in Mercury's magnetosphere are a continuing product of the interaction of Mercury's magnetic field with the solar wind.

"We are assembling a global overview of the nature and workings of Mercury for the first time," said MESSENGER principal investigator Sean Solomon of the Carnegie Institution of Washington. "Many of our earlier ideas are being cast aside as new observations lead to new insights. Our primary mission has another three Mercury years to run, and we can expect more surprises as our solar system's innermost planet reveals its long-held secrets."

Flyby images of Mercury had detected bright, patchy deposits on some crater floors. Without high-resolution images to obtain a closer look, these features remained only a curiosity. Now new detailed images have revealed these patchy deposits to be clusters of rimless, irregular pits varying in size from several hundred feet to a few miles wide. These pits are often surrounded by diffuse halos of more reflective material and are found on central peaks, peak rings, and rims of craters.

"The etched appearance of these landforms is unlike anything we've seen before on Mercury or the moon," said Brett Denevi, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and a member of the MESSENGER imaging team. "We are still debating their origin, but they appear to be relatively young and may suggest a more abundant than expected volatile component in Mercury's crust."

One of two instruments on the spacecraft designed to measure the quantity of key chemical elements on Mercury has made several important discoveries since the orbital mission began. Elemental ratios averaged over large areas of the planet's surface show that Mercury's surface differs markedly in composition from that of the moon.

Observations have revealed substantial amounts of sulfur at Mercury's surface, lending support to prior suggestions from ground-based telescopic observations that sulfide minerals are present. This discovery suggests that the original building blocks from which Mercury formed may have been less oxidized than those that formed the other terrestrial planets. The result also hints that sulfur-containing gases may have contributed to past explosive volcanic activity on Mercury.

Topography data of Mercury's northern hemisphere reveal the planet's large-scale shape and profiles of geological features in high detail. The north polar region is a broad area of low elevations, whereas the overall range in topographic heights seen to date exceeds 5 miles (9 kilometers).

Two decades ago, Earth-based radar images showed deposits thought to consist of water ice and perhaps other ices near Mercury's north and south poles. These deposits are preserved on the cold, permanently shadowed floors of high-latitude impact craters. MESSENGER is testing this idea by measuring the floor depths of craters near Mercury's north pole. The craters hosting polar deposits appear to be deep enough to be consistent with the idea that those deposits are in permanently shadowed areas.

During the first of three Mercury flybys in1974, Mariner 10 discovered bursts of energetic particles in the planet's Earth-like magnetosphere. Four bursts of particles were observed on that flyby. Scientists were puzzled that no such strong events were detected by MESSENGER during any of its three flybys of the planet in 2008 and 2009. But now that the spacecraft is in near-polar orbit around Mercury, energetic events are being seen regularly.

The spacecraft was designed and built by APL. The lab manages and operates the mission for NASA's Science Mission Directorate (SMD) in Washington. The mission is part of NASA's Discovery Program, managed for SMD by the agency's Marshall Space Flight Center in Huntsville, Ala.

posted 09-08-2011 02:52 PM               

MESSENGER Team Delivers First Orbital Data to Planetary Data System

Data collected during MESSENGER's first two months in orbit around Mercury have been released to the public by the Planetary Data System (PDS), an organization that archives and distributes all of NASA's planetary mission data. Calibrated data from all seven of MESSENGER's science instruments, plus radio science data from the spacecraft telecommunications system, are included in this release.

"It's a real milestone for the first data ever obtained from orbit around Mercury to be available now in the PDS," says Nancy Chabot, Instrument Scientist for MESSENGER's Mercury Dual Imaging System (MDIS).

"Scientists around the world will use these data to better understand Mercury and the formation and evolution of our solar system as a whole," says Chabot, of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. "However, to me, one of the most exciting aspects of this release is that these data now in the PDS are just the first of much more to come. MESSENGER continues to send us new data practically every day!"

The science results from these instruments have already shed light on questions about Mercury that have lingered for more than three decades. Many of these results were highlighted in a June 16 press conference at NASA headquarters.

For instance, says MESSENGER Project Scientist Ralph McNutt of APL, "The imaging has highlighted the importance of volcanism in plains formation in the planet's history, and the geochemical remote sensing instruments are providing new insights into formation scenarios for the planet. Geophysics data are yielding new information on Mercury's internal structure, and data from the exosphere and magnetosphere instruments are giving us the first continuous view of Mercury's interaction with its local space environment.

"The availability of these data via PDS will allow scientists around the world to study the data and begin making even more connections and discoveries," McNutt adds.

Since the mid-1990s, NASA has required all of its planetary missions to archive data in the PDS, an active archive that makes available well-documented, peer-reviewed data to the research community. The PDS includes eight university/research center science teams, called discipline nodes, each of which specializes in a specific area of planetary data. The contributions from these nodes provide a data-rich source for scientists, researchers, and developers.

"PDS deliveries are the result of a concerted effort between the MESSENGER team and the PDS that starts well before the release to the public," says APL's Susan Ensor, MESSENGER's Science Operations Center lead. "Approximately 50 MESSENGER team members were actively involved in making this PDS delivery, including instrument team members, developers from Applied Coherent Technology Corporation, and Science Operations Center personnel."

Previous MESSENGER PDS deliveries included data from cruise and flybys of the Earth, Venus, and Mercury. The data for this delivery are archived and available online, and all of the MESSENGER data archived at the PDS thus far are available here. As of this release, MESSENGER will have delivered 1.1 terabytes of raw and calibrated data to the PDS, including more than 30,000 images (of which over 18,000 are from orbit).

The team will submit three more PDS deliveries at six-month intervals from MESSENGER's primary mission. "Improved calibrations will be incorporated in these future deliveries," Ensor says. "Advanced products, including Mercury maps, will be included in the final primary mission delivery in March 2013."

The MESSENGER team has created an innovative software tool with which the public can view data from this delivery. ACT-REACT-Quick Map provides a simple, interactive Web interface to MESSENGER data. Developed by Applied Coherent Technology Corporation, Quick Map allows users to examine global mosaics constructed with high-resolution images from this PDS delivery.

The tool also provides weekly updates of coverage for surface-observing instruments, as well as the status of specially targeted MDIS observations. Information is also available that can be used to locate MESSENGER data products at the PDS. QuickMap can be accessed via links on each of the MESSENGER websites at Johns Hopkins University Applied Physics Laboratory and NASA.

"The MESSENGER team is delighted to share the orbital observations of Mercury with the planetary science community and the public," adds MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "The first global exploration of our solar system's innermost planet is a wonderful adventure, and there are plenty of front-row seats for all to participate."

posted 09-29-2011 05:57 PM               

NASA Spacecraft Revealing More Details About Planet Mercury

NASA's MESSENGER spacecraft, the first to achieve orbit around Mercury, is providing scientists new information about the planet. The data show widespread flood volcanism similar to Earth, clearer views of Mercury's surface, the first measurements of its elemental composition, and details about charged particles near the planet.

MESSENGER, or the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, conducted 15 laps through the inner solar system for more than six years before achieving the historic orbit insertion March 18. The new results are reported in seven papers published in Science magazine.

"MESSENGER's instruments are capturing data that can be obtained only from orbit," says principal investigator Sean Solomon, of the Carnegie Institution of Washington. "Mercury has many more surprises in store for us as our mission progresses."

Scientists for decades had puzzled over whether Mercury had volcanic deposits on its surface. New data show a huge expanse of volcanic plains surrounding the planet's north polar region. These continuous smooth plains cover more than six percent of the planet's total surface. The deposits appear typical of flood lavas, or huge volumes of solidified molten rock similar to those found in the northwest United States.

"If you imagine standing at the base of the Washington Monument, the top of the lavas would be something like 12 Washington Monuments above you," said James Head of Brown University, the lead author of one of the papers.

Scientists also have discovered vents or openings measuring up to 16 miles (25 kilometers) across that appear to be the source of some of the large volume of very hot lava that has rushed across Mercury's surface carving valleys and creating teardrop-shaped ridges in the underlying terrain.

New images reveal landforms on Mercury suggesting a previously unrecognized geological process. Images of bright areas appear to be small, shallow, irregularly shaped depressions. The science team adopted the term "hollows" for these features to distinguish them from other types of pits seen on Mercury. Hollows have been found over a wide range of latitudes and longitudes, suggesting that they are fairly common across Mercury.

"Analysis of the images and estimates of the rate at which the hollows may be growing led to the conclusion that they could be actively forming today," says David Blewett of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., lead author of one of the reports.

Scientists also now have observations of the chemical composition of Mercury's surface. The information is being used to test models of Mercury's formation and further study the relationship between the planet's tenuous atmosphere and surface makeup. Chemical measurements reveal a higher abundance of potassium than previously predicted.

"These measurements indicate Mercury has a chemical composition more similar to those of Venus, Earth, and Mars than expected," says APL's Patrick Peplowski, lead author of one of the papers.

MESSENGER also has collected the first global observations of plasma ions-- mostly sodium -- in Mercury's magnetosphere, the volume of space near the planet dominated by Mercury's magnetic field. These results reveal that Mercury's weak magnetosphere provides the planet very little protection from the gusty solar wind, resulting is a very hostile surface environment with extremes in space weather.

"We were able to observe the formation process of these ions, and it's comparable to the manner by which auroras are generated in the Earth's atmosphere near polar regions," said Thomas Zurbuchen of the University of Michigan and lead author of one of the reports.

posted 11-15-2011 11:44 AM               

NASA Extends MESSENGER Mission

NASA has announced that it will extend the MESSENGER mission for an additional year of orbital operations at Mercury beyond the planned end of the primary mission on March 17, 2012. The MESSENGER probe became the first spacecraft to orbit the innermost planet on March 18, 2011.

"We are still ironing out the funding details, but we are pleased to be able to support the continued exploration of Mercury," said NASA MESSENGER Program Scientist Ed Grayzeck, who made the announcement on Nov. 9 at the 24th meeting of the MESSENGER Science Team in Annapolis, Md.

The spacecraft's unprecedented orbital science campaign is providing the first global close-up of Mercury and has revolutionized scientific perceptions of that planet. The extended mission will allow scientists to learn even more about the planet closest to the Sun, says MESSENGER Principal investigator Sean Solomon, of the Carnegie Institution of Washington.

"During the extended mission we will spend more time close to the planet than during the primary mission, we'll have a broader range of scientific objectives, and we'll be able to make many more targeted observations with our imaging system and other instruments," says Solomon. "MESSENGER will also be able to view the innermost planet as solar activity continues to increase toward the next maximum in the solar cycle. Mercury's responses to the changes in its environment over that period promise to yield new surprises."

The extended mission has been designed to answer six scientific questions, each of which has arisen only recently as a result of discoveries made from orbit:

1. What are the sources of surface volatiles on Mercury?
   
2. How late into Mercury's history did volcanism persist?
   
3. How did Mercury's long-wavelength topography change with time?
   
4. What is the origin of localized regions of enhanced exospheric density at Mercury?
   
5. How does the solar cycle affect Mercury's exosphere and volatile transport?
   
6. What is the origin of Mercury's energetic electrons?

"Advancements in science have at their core the evaluation of hypotheses in the light of new knowledge, sometimes resulting in slight changes in course, and other times resulting in paradigm shifts, opening up entirely new vistas of thought and perception," says MESSENGER Project Scientist Ralph McNutt, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "With the early orbital observations at Mercury we are already seeing the beginnings of such advancements. The extended mission guarantees that the best is indeed ‘yet to be' on the MESSENGER mission, as this old-world Mercury, seen in a very new light, continues to give up its secrets."

posted 11-30-2012 10:10 AM               

NASA spacecraft finds new evidence for water ice on Mercury

A NASA spacecraft studying Mercury has provided compelling support for the long-held hypothesis that the planet harbors abundant water ice and other frozen volatile materials within its permanently shadowed polar craters.

The new information comes from NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Its onboard instruments have been studying Mercury in unprecedented detail since its historic arrival there in March 2011. Scientists are seeing clearly for the first time a chapter in the story of how the inner planets, including Earth, acquired their water and some of the chemical building blocks for life.

"The new data indicate the water ice in Mercury's polar regions, if spread over an area the size of Washington, D.C., would be more than 2 miles thick," said David Lawrence, a MESSENGER participating scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and lead author of one of three papers describing the findings. The papers were published online in Thursday's edition of Science Express.

Spacecraft instruments completed the first measurements of excess hydrogen at Mercury's north pole, made the first measurements of the reflectivity of Mercury's polar deposits at near-infrared wavelengths, and enabled the first detailed models of the surface and near-surface temperatures of Mercury's north polar regions.

Given its proximity to the sun, Mercury would seem to be an unlikely place to find ice. However, the tilt of Mercury's rotational axis is less than 1 degree, and as a result, there are pockets at the planet's poles that never see sunlight.

Scientists suggested decades ago there might be water ice and other frozen volatiles trapped at Mercury's poles. The idea received a boost in 1991 when the Arecibo radio telescope in Puerto Rico detected radar-bright patches at Mercury's poles. Many of these patches corresponded to the locations of large impact craters mapped by NASA's Mariner 10 spacecraft in the 1970s. However, because Mariner saw less than 50 percent of the planet, planetary scientists lacked a complete diagram of the poles to compare with the radar images.

Images from the spacecraft taken in 2011 and earlier this year confirmed all radar-bright features at Mercury's north and south poles lie within shadowed regions on the planet's surface. These findings are consistent with the water ice hypothesis.

The new observations from MESSENGER support the idea that ice is the major constituent of Mercury's north polar deposits. These measurements also reveal ice is exposed at the surface in the coldest of those deposits, but buried beneath unusually dark material across most of the deposits. In the areas where ice is buried, temperatures at the surface are slightly too warm for ice to be stable.

MESSENGER's neutron spectrometer provides a measure of average hydrogen concentrations within Mercury's radar-bright regions. Water ice concentrations are derived from the hydrogen measurements.

"We estimate from our neutron measurements the water ice lies beneath a layer that has much less hydrogen. The surface layer is between 10 and 20 centimeters [4-8 inches] thick," Lawrence said.

Additional data from detailed topography maps compiled by the spacecraft corroborate the radar results and neutron measurements of Mercury's polar region. In a second paper by Gregory Neumann of NASA's Goddard Flight Center in Greenbelt, Md., measurements of the shadowed north polar regions reveal irregular dark and bright deposits at near-infrared wavelength near Mercury's north pole.

"Nobody had seen these dark regions on Mercury before, so they were mysterious at first," Neumann said.

The spacecraft recorded dark patches with diminished reflectance, consistent with the theory that ice in those areas is covered by a thermally insulating layer. Neumann suggests impacts of comets or volatile-rich asteroids could have provided both the dark and bright deposits, a finding corroborated in a third paper led by David Paige of the University of California at Los Angeles.

"The dark material is likely a mix of complex organic compounds delivered to Mercury by the impacts of comets and volatile-rich asteroids, the same objects that likely delivered water to the innermost planet," Paige said.

This dark insulating material is a new wrinkle to the story, according to MESSENGER principal investigator Sean Solomon of Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y.

"For more than 20 years, the jury has been deliberating whether the planet closest to the sun hosts abundant water ice in its permanently shadowed polar regions," Solomon said. "MESSENGER now has supplied a unanimous affirmative verdict."

posted 03-13-2013 01:23 PM               

MESSENGER Has Imaged 100 Percent of Mercury

The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft, in orbit about Mercury for nearly two years, has finally imaged 100 percent of the planet. Until recently, explains Brett Denevi of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., MDIS images acquired from orbit collectively covered most (99.99%), but not all, of the surface. The recent downlink of an image of the north polar region now completes the picture.

"It's a huge accomplishment - we've gone from having more than half of the planet a complete mystery prior to MESSENGER to a full coverage that will enable a better understanding of the global processes that shaped Mercury's formation and evolution," says Denevi, the deputy instrument scientist for MDIS and a member of MESSENGER's Geology Discipline Group. "But we've still only seen just a tiny fraction of the planet at the highest resolution, and we are learning more daily from color images, reflectance spectra, geochemical measurements, and topographic information - none of which have anywhere close to 100% coverage, and all of which will be important aspects of a second extended mission at Mercury."

During its one-year primary mission, MESSENGER acquired 88,746 images and extensive other data sets. It is now nearing completion of a yearlong extended mission, during which the spacecraft has acquired more than 80,000 additional images and other measurements to support MESSENGER's science goals.

"Completing the initial imaging of the entire surface of our solar system's innermost planet is an important milestone," adds MESSENGER Principal Investigator Sean Solomon, of Columbia University's Lamont-Doherty Earth Observatory. "Those global images have produced many important discoveries about how Mercury's crust formed and evolved, but all of those discoveries have raised new questions. With ongoing and planned targeted observations, conducted synergistically with all of MESSENGER's instruments, we can look forward to further discoveries and new understanding."

posted 10-15-2014 06:32 PM               

MESSENGER Provides First Optical Images of Ice Near Mercury's North Pole

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has provided the first optical images of ice and other frozen volatile materials within permanently shadowed craters near Mercury's north pole. The images not only reveal the morphology of the frozen volatiles, but they also provide insight into when the ices were trapped and how they've evolved, according to an article published today in the journal, Geology.

Two decades ago, Earth-based radar images of Mercury revealed the polar deposits, postulated to consist of water ice. That hypothesis was later confirmed by MESSENGER through a combination of neutron spectrometry, thermal modeling, and infrared reflectometry. "But along with confirming the earlier idea, there is a lot new to be learned by seeing the deposits," said lead author Nancy Chabot, the Instrument Scientist for MESSENGER's Mercury Dual Imaging System (MDIS) and a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Above: Kandinsky crater is located near Mercury's north pole and shows evidence for hosting water ice. The floor of Kandinsky is in permanent shadow and never receives direct sunlight, keeping it very cold. However, by using sunlight scattered off the crater's walls and the WAC broadband clear filter, MDIS was able to capture this image that reveals the details of the shadowed surface! The WAC broadband image is shown on the left, outlined in yellow and overlain on an MDIS polar mosaic. The view on the right shows the same image but with the brightness and contrast stretched to show the details of the crater's shadowed floor. (NASA/JHU APL/Carnegie)

Beginning with MESSENGER's first extended mission in 2012, scientists launched an imaging campaign with the broadband clear filter of MDIS's wide-angle camera (WAC). Although the polar deposits are in permanent shadow, through many refinements in the imaging, the WAC was able to obtain images of the surfaces of the deposits by leveraging very low levels of light scattered from illuminated crater walls. "It worked in spectacular fashion," said Chabot.

The team zeroed in on Prokofiev, the largest crater in Mercury's north polar region found to host radar-bright material. "Those images show extensive regions with distinctive reflectance properties," Chabot said. "A location interpreted as hosting widespread surface water ice exhibits a cratered texture indicating that the ice was emplaced more recently than any of the underlying craters."

In other areas, water ice is present, she said, "but it is covered by a thin layer of dark material inferred to consist of frozen organic-rich compounds." In the images of those areas, the dark deposits display sharp boundaries. "This result was a little surprising, because sharp boundaries indicate that the volatile deposits at Mercury's poles are geologically young, relative to the time scale for lateral mixing by impacts," said Chabot.

"One of the big questions we've been grappling with is 'When did Mercury's water ice deposits show up?' Are they billions of years old, or were they emplaced only recently?" Chabot said. "Understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth."

Overall, the images indicate that Mercury's polar deposits either were delivered to the planet recently or are regularly restored at the surface through an ongoing process.

The images also reveal a noteworthy distinction between the Moon and Mercury, one that may shed additional light on the age of the frozen deposits. "The polar regions of Mercury show extensive areas that host water ice, but the Moon's polar regions -- which also have areas of permanent shadows and are actually colder -- look different," Chabot said.

"One explanation for differences between the Moon and Mercury could be that the volatile polar deposits on Mercury were recently emplaced," according to the paper. "If Mercury's currently substantial polar volatile inventory is the product of the most recent portion of a longer process, then a considerable mass of volatiles may have been delivered to the inner Solar System throughout its history."

"That's a key question," Chabot said. "Because if you can understand why one body looks one way and another looks different, you gain insight into the process that's behind it, which in turn is tied to the age and distribution of water ice in the Solar System. This will be a very interesting line of inquiry going forward."

posted 03-27-2015 06:46 PM               

MESSENGER Completes 4,000th Orbit of Mercury

On March 25, the MESSENGER spacecraft completed its 4,000th orbit of Mercury, and the lowest point in its orbit continues to move closer to the planet than ever before. The orbital phase of the MESSENGER mission, which was originally designed to collect data for one Earth year, just completed its fourth year of operation around Mercury. The mission has received a final extension to allow scientists to gather specific low-altitude data over an additional several weeks.

"When we completed our first Mercury flyby on January 14, 2008, after months of preparations and testing, we were amazed and perhaps even a little skeptical when the science team told us that the orbital phase could be characterized as two flybys of data collection every Earth day (and eventually three per day starting in April 2012)," said MESSENGER Mission Operations Manager Andy Calloway, of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. "Now that we have surpassed 4,000 orbits and more than 17 Mercury years since Mercury orbit insertion, we know just what was meant by that prediction."

"Thanks to requisite optimization tools and techniques — such as the SciBox science planning tool, customized downlink rate stepping during Deep Space Network contacts, and automated prioritization of data playback with the use of the Consultative Committee for Space Data Systems (CCSDS) file delivery protocol, to name just a few — we have captured more than 275,000 images and downlinked more than four Earth years of data from our comprehensive suite of instruments," he continued. "MESSENGER really is the little spacecraft that could."

Last week, mission operators conducted the first of five final adjustments to MESSENGER's orbit to delay the inevitable impact onto the surface of Mercury. During these last several weeks (for which the project uses the term XM2' hover campaign), the spacecraft is maintaining an unprecedented range of periapsis altitudes between 6 and 38 kilometers (3.7 to 24 miles) above Mercury's surface, allowing scientists to continue to collect and return novel data until the final moments before impact.

"The MESSENGER milestone of 4,000 orbits around Mercury in just over four years is a testament to the talent and dedication of the teams that designed, built, and operated a spacecraft for which the original plan was to complete about 740 orbits during a single year after Mercury orbit insertion," said APL's James McAdams, MESSENGER's Mission Design Lead Engineer. "An exemplary science team and supportive NASA sponsorship and oversight have made the most of the mission extensions, leading to numerous new insights into the processes that formed and subsequently transformed our solar system's nearest planet to the Sun."

posted 04-03-2015 11:18 AM               

Planned Maneuver Further Extends MESSENGER Orbital Operations

MESSENGER mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., conducted a maneuver yesterday to raise the spacecraft's minimum altitude sufficiently to extend orbital operations and further delay the probe's inevitable impact onto Mercury's surface.

The previous maneuver, completed on March 18, raised MESSENGER to an altitude at closest approach from 11.6 kilometers (7.2 miles) to 34.4 kilometers (21.4 miles) above the planet's surface. Because of progressive changes to the orbit over time in response to the gravitational pull of the Sun, the spacecraft's minimum altitude continued to decrease.

At the time of yesterday's maneuver, MESSENGER was in an orbit with a closest approach of 5.5 kilometers (3.4 miles) above the surface of Mercury. With a velocity change of 2.96 meters per second (6.63 miles per hour), four of the spacecraft's 12 smallest monopropellant thrusters nudged the spacecraft to an orbit with a closest approach altitude of 27.5 kilometers (17.1 miles). This maneuver also increased the spacecraft's speed relative to Mercury at the maximum distance from Mercury, adding about 1.2 minutes to the spacecraft's eight-hour, 17.6-minute orbit period.

The second orbit-correction maneuver (OCM) in MESSENGER's low-altitude hover campaign, also called the extension of the second extended mission, OCM-14 is the first propulsive course correction since December 2006 to use the two small thrusters that point sunward from the sunshade center panel. This view shows MESSENGER's orientation at the start of the maneuver.

MESSENGER was 200.6 million kilometers (124.6 million miles) from Earth when the 6.7-minute maneuver began at about 4:30 p.m. EDT. Mission controllers at APL verified the start of the maneuver 11.2 minutes later, after the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station in Goldstone, Calif. The next maneuver, on April 6, will again raise the spacecraft's minimum altitude, allowing scientists to continue to collect images and data from MESSENGER's instruments. The 3.8 days between OCM-14 and OCM-15 will be the shortest time between any two MESSENGER maneuvers.

posted 04-07-2015 05:08 PM               

Latest Maneuver Illustrates Critical Role Telecommunications System Plays in Delaying MESSENGER's Mercury Impact

MESSENGER's orbit-correction maneuver on April 6 was a nail biter. It was the 15th such maneuver since the spacecraft entered orbit about Mercury in 2011, and the third in a series of increasingly risky "burns" designed to delay MESSENGER's inevitable impact onto Mercury's surface. Each maneuver illustrates the critical role that the spacecraft's radio frequency (RF) telecommunications system plays in its operation.

The RF telecommunications system is used to receive operational commands at the spacecraft from Earth, and to transmit data acquired in making science observations, and data indicative of spacecraft health, from the spacecraft to Earth. The RF subsystem also supports MESSENGER navigation by providing precise observations of the spacecraft's Doppler velocity and range in the line of sight to Earth.

The system consists of redundant General Dynamics Small Deep Space Transponders, solid-state power amplifiers, phased-array antennas, and medium- and low-gain antennas. The phased-array antennas, the first electronically steered antennas ever to be used in deep space, have no moving parts, thus reducing the likelihood of failure in the extreme thermal environment of Mercury. These antennas are designed to work at the 350 degrees Celsius ambient temperature.

Onboard Insight

"The RF system provides our only insight into what's going on aboard the spacecraft," explained MESSENGER Communications Engineer Dipak Srinivasan, of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. Such situational awareness is particularly important as the team attempts — in a series of increasingly risky maneuvers — to raise the spacecraft's minimum altitude sufficiently to extend orbital operations as long as possible.

"We use data from the RF system to confirm whether a maneuver has started and completed properly," he said. "We can also look at the change in the signal's frequency -- caused by the spacecraft's changing motion and the resulting Doppler effect -- to provide instantaneous assessments on the maneuver status."

The frequent, almost back-to-back orbit-correction maneuvers (OCMs) of MESSENGER's "hover campaign" present a challenge to the RF system. "During OCMs, the spacecraft has to be oriented in a way that best supports the propulsion system and keeps the sunshade between the Sun and the spacecraft's thermally sensitive payload," Srinivasan added. "This requirement means that communications can suffer when we are forced to use our low-gain antennas to support communications with Earth. In such situations, the signal strength we receive on the ground is quite low, so we must optimize our ground configuration to maintain communications throughout the burn."

The Latest Maneuver

MESSENGER was nearly at its farthest point from Mercury in its eccentric orbit about the planet when Monday's maneuver was executed. The burn raised the spacecraft's minimum altitude above Mercury from 13.1 kilometers (8.1 miles) to 25.7 kilometers (16.0 miles). It increased the spacecraft's speed relative to Mercury and also added about 0.55 minutes to the spacecraft's eight-hour, 18.9-minute orbit period. Four of the 12 smallest monopropellant thrusters imparted a change in velocity of 1.77 meters per second (3.97 miles per hour).

The operation used all of MESSENGER's remaining usable hydrazine propellant from the small auxiliary fuel tank. It was completed over its final six minutes with helium pressurant being expelled through the same thrusters that were used with the first part of the maneuver.

Although no problems were reported during the maneuver, the usable propellant was depleted sooner than predicted. The MESSENGER flight operations team is planning a "clean-up" maneuver for April 8 (with a backup scheduled for April 11) that will again use helium pressurant to put the spacecraft back on schedule for OCM-16 on April 14.

Solar Conjunction Adds to the Thrill

The spacecraft is about to enter a superior solar conjunction, during which Mercury and MESSENGER will be on the far side of the Sun from Earth. "As we approach superior solar conjunction, the RF signal has to travel through more of the solar plasma," Srinivasan explained. "The plasma causes scintillations in the signal, disrupting it in both phase and amplitude. This phenomenon introduces noise in our received signal, deteriorating our signal-to-noise ratio and making it harder to decode the information from the spacecraft. As the angle between the spacecraft and Sun gets smaller and smaller, the signal eventually drops out completely, and we won't pick it up again until the spacecraft emerges from behind the Sun on the other side."

Having an OCM just before a superior solar conjunction is cutting it close, he admits. "Conjunctions always cause a slight worry, as the Sun prevents us from contacting the spacecraft for relatively long periods of time. But we have several conjunctions and maneuvers under our belt and we are confident the spacecraft will pull through okay," he said. "Fortunately, we have a proven fault-protection system on board, as well as seasoned mission operations and engineering teams ready to solve problems that may arise."

"Our engineering team continues to pull rabbits out of this mission's hat," said MESSENGER Deputy Principal Investigator Larry Nittler, of the Carnegie Institution of Washington. "Their efforts to keep our little spacecraft going long past all original expectations are truly heroic. They are working to keep the craft flying at low altitudes for a few extra weeks — fighting against the gravitational pull of the Sun — with empty fuel tanks, by blowing helium into space. The observations we make these last few weeks will add importantly to the long list of scientific discoveries from this amazing mission."

posted 04-16-2015 09:31 PM               

NASA Spacecraft Achieves Unprecedented Success Studying Mercury

After extraordinary science findings and technological innovations, a NASA spacecraft launched in 2004 to study Mercury will impact the planet's surface, most likely on April 30, after it runs out of propellant.

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft will impact the planet at more than 8,750 miles per hour (3.91 kilometers per second) on the side of the planet facing away from Earth. Due to the expected location, engineers will be unable to view in real time the exact location of impact.

On Tuesday, mission operators in mission control at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, completed the fourth in a series of orbit correction maneuvers designed to delay the spacecraft's impact into the surface of Mercury. The last maneuver is scheduled for Friday, April 24.

"Following this last maneuver, we will finally declare the spacecraft out of propellant, as this maneuver will deplete nearly all of our remaining helium gas," said Daniel O'Shaughnessy, mission systems engineer at APL. "At that point, the spacecraft will no longer be capable of fighting the downward push of the sun's gravity."

Although Mercury is one of Earth's nearest planetary neighbors, little was known about the planet prior to the MESSENGER mission.

"For the first time in history we now have real knowledge about the planet Mercury that shows it to be a fascinating world as part of our diverse solar system," said John Grunsfeld, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. "While spacecraft operations will end, we are celebrating MESSENGER as more than a successful mission. It's the beginning of a longer journey to analyze the data that reveals all the scientific mysteries of Mercury."

The spacecraft traveled more than six and a half years before it was inserted into orbit around Mercury on March 18, 2011. The prime mission was to orbit the planet and collect data for one Earth year. The spacecraft's healthy instruments, remaining fuel, and new questions raised by early findings resulted in two approved operations extensions, allowing the mission to continue for almost four years and resulting in more scientific firsts.

One key science finding in 2012 provided compelling support for the hypothesis that Mercury harbors abundant frozen water and other volatile materials in its permanently shadowed polar craters.

Data indicated the ice in Mercury's polar regions, if spread over an area the size of Washington, would be more than two miles thick. For the first time, scientists began seeing clearly a chapter in the story of how the inner planets, including Earth, acquired water and some of the chemical building blocks for life.

A dark layer covering most of the water ice deposits supports the theory that organic compounds, as well as water, were delivered from the outer solar system to the inner planets and may have led to prebiotic chemical synthesis and, thusly, life on Earth.

"The water now stored in ice deposits in the permanently shadowed floors of impact craters at Mercury's poles most likely was delivered to the innermost planet by the impacts of comets and volatile-rich asteroids," said Sean Solomon, the mission's principal investigator, and director of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York. "Those same impacts also likely delivered the dark organic material."

In addition to science discoveries, the mission provided many technological firsts, including the development of a vital heat-resistant and highly reflective ceramic cloth sunshade that isolated the spacecraft's instruments and electronics from direct solar radiation – vital to mission success given Mercury's proximity to the sun. The technology will help inform future designs for planetary missions within our solar system.

"The front side of the sunshade routinely experienced temperatures in excess of 300° Celsius (570° Fahrenheit), whereas the majority of components in its shadow routinely operated near room temperature (20°C or 68°F)," said Helene Winters, mission project manager at APL. "This technology to protect the spacecraft's instruments was a key to mission success during its prime and extended operations."

The spacecraft was designed and built by APL. The lab manages and operates the mission for NASA's Science Mission Directorate. The mission is part of NASA's Discovery Program, managed for the directorate by the agency's Marshall Space Flight Center in Huntsville, Alabama.

posted 04-30-2015 02:30 PM               

End of MESSENGER: First probe to orbit Mercury impacts planet

The first spacecraft to orbit Mercury, the planet closest to the Sun, is no more.

On Thursday (April 30), NASA's MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft impacted the small planet at more than 8,750 miles per hour (14,080 kilometers per hour). The probe hit the planet at about 3:26 p.m. EDT (1926 GMT) on the side facing away from the Earth, leaving a crater about 52 feet (16 meters) across, based on pre-impact estimates.

The collision came as a result of MESSENGER depleting its propellant after almost 11 years. Mission controllers at the Johns Hopkins University Applied Physics Laboratory in Maryland, exhausted the last of the craft's reserves with an orbit correction maneuver last Friday (April 24).

See here for discussion about NASA's MESSENGER mission at Mercury.