Updates MESSENGER Mission News

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MESSENGER team members will be discussing these new findings in a news conference at NASA Headquarters on June 16, 2011, at 1 p.m.
I'm guessing thats EDT?

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NASA:
June 16, 2011​
MESSENGER Provides New Data about Mercury

After nearly three months in orbit about Mercury, MESSENGER's payload is providing a wealth of new information about the planet closest to the Sun, as well as a few surprises.

The spacecraft entered orbit around Mercury on March 18, 2011 UTC, becoming the first spacecraft ever to do so. Tens of thousands of images of major features on the planet — previously seen only at comparatively low resolution — are now available in sharp focus. Measurements of the chemical composition of Mercury's surface are providing important clues to the origin of the planet and its geological history. Maps of the planet's topography and magnetic field are revealing new clues to Mercury's interior dynamical processes. And scientists now know 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.

This week, MESSENGER completed is first perihelion passage from orbit, its first superior solar conjunction from orbit, and its first orbit-correction maneuver. "Those milestones provide important context to the continuing feast of new observations that MESSENGER has been sending home on nearly a daily basis,” offers MESSENGER Principal investigator Sean Solomon of the Carnegie Institution of Washington.


A Surface Revealed in Unprecedented Detail

Among the fascinating features seen in MESSENGER flyby images of Mercury were bright, patchy deposits on some crater floors. Without high-resolution images to obtain a closer look, these features remained a curiosity. New targeted Mercury Dual Imaging System images at up to 10 meters per pixel reveal these patchy deposits to be clusters of rimless, irregular pits varying in size from hundreds of meters to several kilometers. These pits are often surrounded by diffuse halos of higher-reflectance material, and they are found associated with central peaks, peak rings, and rims of craters.

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Targeted color imaging: Degas crater​
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"The etched appearance of these landforms is unlike anything we've seen before on Mercury or the Moon,” says 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 have a relatively young age and may suggest a more abundant than expected volatile component in Mercury's crust.”


Mercury's Surface Composition

The X-ray Spectrometer (XRS) — one of two instruments on MESSENGER designed to measure the abundances of many key elements on Mercury — has made several important discoveries since the orbital mission began. The magnesium/silicon, aluminum/silicon, and calcium/silicon ratios averaged over large areas of the planet's surface show that, unlike the surface of the Moon, Mercury's surface is not dominated by feldspar-rich rocks.

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Major-element composition of Mercury surface materials​
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XRS observations have also revealed substantial amounts of sulfur at Mercury's surface, lending support to prior suggestions from ground-based telescopic spectral observations that sulfide minerals are present. This discovery suggests that the original building blocks from which Mercury was assembled may have been less oxidized than those that formed the other terrestrial planets, and it has potentially important implications for understanding the nature of volcanism on Mercury.


Mapping of Mercury's Topography and Magnetic Field

MESSENGER's Mercury Laser Altimeter has been systematically mapping the topography of Mercury's northern hemisphere. After more than two million laser-ranging observations, the planet's large-scale shape and profiles of geological features are both being revealed in high detail. The north polar region of Mercury, for instance, is a broad area of low elevations. The overall range in topographic heights seen to date exceeds 9 kilometers.

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Magnetic field lines differ at Mercury's north and south poles​
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Two decades ago, Earth-based radar images showed that around both Mercury's north and south poles are deposits characterized by high radar backscatter. These polar deposits are thought to consist of water ice and perhaps other ices preserved on the cold, permanently shadowed floors of high-latitude impact craters. MESSENGER's altimeter is testing this idea by measuring the floor depths of craters near Mercury's north pole. To date, the depths of craters hosting polar deposits are consistent with the idea that those deposits occupy areas in permanent shadow.


Energetic Particle Events at Mercury

One of the major discoveries made by Mariner 10 during the first of its three flybys of Mercury in 1974 were bursts of energetic particles in Mercury's Earth-like magnetosphere. Four bursts of particles were observed on that flyby, so it was puzzling that no such strong events were detected by MESSENGER during any of its three flybys of the planet in 2008 and 2009. With MESSENGER now in near-polar orbit about Mercury, energetic events are being seen almost like clockwork.

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Locations of energetic electron events relative to Mercury’s magnetic field​
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"We are assembling a global overview of the nature and workings of Mercury for the first time,” adds Solomon, "and 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."


For more supporting materials, visit: http://messenger.jhuapl.edu/news_room/presscon9.html.


NASA: RELEASE : 11-186 - NASA Spacecraft Confirms Theories, Sees Surprises at Mercury
 

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NASA Spacecraft Confirms Theories, Sees Surprises at Mercury

June 16th,2011


WASHINGTON -- 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.

For more information about the mission, visit:


http://www.nasa.gov/messenger
 

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NASA Spacecraft Confirms Theories, Sees Surprises at Mercury
Article was already linked at the bottom of the previous post.
 

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American Institute of Aeronautics and Astronautics Honors MESSENGER Team Leaders



The Mid-Atlantic Section of the American Institute of Aeronautics and Astronautics (AIAA) has named MESSENGER team members Peter Bedini and Eric Finnegan as Engineering Manager of the Year and Engineer of the Year, respectively, for 2011. Bedini and Finnegan, both of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., will be honored at an awards dinner later this month.



Bedini is the MESSENGER Project Manager. In that role he oversees all aspects of the mission, including oversight of spacecraft engineering activities; coordination with the mission science leads, the Principal Investigator, and NASA management; delivery of data to the Planetary Data System; and operation of the spacecraft during its cruise to and orbit around Mercury.



The past year presented many special management challenges as the spacecraft entered its final year of cruise operations and as the MESSENGER team prepared for the orbital phase of the mission through a series of flight tests, operational rehearsals, and readiness reviews.



Bedini is credited with “skillfully and artfully” managing these activities, which culminated in a successful Mercury orbit insertion on March 18, 2011, making MESSENGER the first spacecraft ever to orbit the solar system’s innermost planet.



Finnegan is the MESSENGER Mission Systems Engineer. According to AIAA, Finnegan “demonstrated outstanding multi-disciplinary technical ability, leadership, and the ability to remain calmly focused on the ‘big picture’ on one of the most complex planetary missions that JHU/APL has undertaken.”



He is credited with establishing the overall operational requirements for mission execution during the cruise and on-orbit phases of the MESSENGER mission, and with leading the team of engineers and scientists through the design, review, and execution of all spacecraft mission events.



Finnegan supervised the MESSENGER team through the successful completion of four planetary flybys, four large-scale deep-space maneuvers, and the critical orbit insertion burn on March 18, 2011. In 2010, during the final year of the more than six-year cruise, he developed an overall plan for the verification of the on-orbit operations of the spacecraft and led his team through an extensive set of preparation, analysis, independent review, and testing activities. At the conclusion of these exercises, he and his team had demonstrated 10 simulated weeks of on-orbit operations and executed, via computer simulation, all 52 weeks of spacecraft and instrument commanding, providing high-fidelity verification of the tools and procedures that are currently being used by the MESSENGER spacecraft at Mercury.



“For more than four years, Peter and Eric have overseen, respectively, the MESSENGER project and its engineering team,” says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “Throughout that time, each of them has demonstrated an extraordinarily high level of professional dedication, exceptional attention to all aspects of the mission, and outstanding skill at managing a large team. That there is now and for the first time a spacecraft operating successfully in orbit about Mercury is in no small part the result of the sustained efforts of these two superbly skilled leaders.”




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MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 18, 2011, to begin a one-year study of its target planet. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.


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MESSENGER Mission News
July 27, 2011
http://messenger.jhuapl.edu/


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MESSENGER Makes Another Successful Orbit Adjustment The MESSENGER spacecraft continued to fine-tune its orbit around Mercury yesterday afternoon when mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., successfully executed the second orbit-correction maneuver of the mission.

The 3-minute, 8-second engine burn stretched the spacecraft’s orbit around the innermost planet from 11 hours 48 minutes to a precise 12 hours. This second of an expected five maneuvers planned for the mission’s primary orbital phase began at 5:20 P.M. EDT, and used approximately 1.9 kilograms of fuel.

“MESSENGER’s first orbit-correction maneuver, which took place in June, reset the periapsis altitude of the orbit to 200 km, but also shortened the orbital period. This second maneuver has reset the period to its nominal value of 12 hours,” says APL’s Peter Bedini, MESSENGER project manager.

MESSENGER Mission Systems Engineer Eric Finnegan, of APL, said the engine burn was “on target and a sweet success. We’re precisely where we need to be to continue to capture amazing data from Mercury’s surface.” The next orbit-correction maneuver is scheduled for September 7 and will lower the periapsis altitude from about 470 kilometers back to 200 kilometers.


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MMESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 17, 2011 (March 18, 2011 UTC), to begin a yearlong study of its target planet. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.
 

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http://messenger.jhuapl.edu/news_room/details.php?id=181

MESSENGER Navigates Second Hot Season, Executes Third Orbit-Correction Maneuver

Today the MESSENGER spacecraft emerged unscathed from the second of four “hot seasons” expected to occur during its one-year primary mission in orbit around Mercury. Hours later, mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., successfully executed a maneuver to adjust the spacecraft’s trajectory.

“Operating MESSENGER in Mercury orbit is a bit like driving a high-performance automobile on a challenging track with continuously varying road conditions and unpredictable changes in weather,” says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “Our road track is three-dimensional, our environment imposes extreme variations in temperature every 12 hours, and our weather comes from space. Nonetheless, our spacecraft is resilient, our operations team is experienced at handling all the needed maneuvers, and we’re continuing to learn how to squeeze as much science as possible from our orbital observations.”

This hot season began on August 9 and lasted nearly one month. During that time, the closest approach of the spacecraft to Mercury was on the sunlit side of the planet. MESSENGER’s sunshade reached temperatures as high as 350°C during this season, and its solar panels had to be turned off the Sun for short periods during each orbit to protect them from overheating.

Within this second hot season there was a period — from August 20 to August 29 — in which the spacecraft experienced an eclipse during the portion of each orbit when it passed through the shadow of the planet. For eclipses that last longer than 35 minutes, the probe’s battery cannot power the full science payload, and some instruments must be turned off for a brief period.

Even with the challenges of operating the satellite in these extreme orbital environments, the team was able to fine-tune the system to increase the scientific data return from Mercury, says MESSENGER Systems Engineer Eric Finnegan, of APL.

“We went into the first hot season with very conservative assumptions for the spacecraft’s response to the Mercury environment,” says Finnegan. “To conserve energy, only one of MESSENGER’s seven instruments was allowed to operate continuously throughout that season. As it turned out, the battery performed superbly, and there was sufficient energy margin to allow two additional instruments to maintain continuous measurements throughout the entire eclipse season.” In addition to the Gamma-Ray Spectrometer, the Neutron Spectrometer and the Magnetometer remained on continuously through the second hot season.

Having weathered the hot season, MESSENGER engineers immediately turned to the task of adjusting the spacecraft’s orbit around Mercury. This third of five expected orbit-correction maneuvers lowered the periapsis altitude from about 470 kilometers back to 200 kilometers.

“MESSENGER’s orbit is continuously changing, so correction maneuvers are scheduled throughout the year to ensure that the orbital parameters remain within the desired ranges for the planned science observations,” says MESSENGER Project Manager Peter Bedini. “This was the second time that the periapsis altitude — the closest approach of the spacecraft to the planet — has been reset to 200 kilometers. One more such correction is planned for the primary mission, and that event is presently scheduled to take place in early December.”

The 2-minute, 46-second engine burn began at 15:08 UTC (11:08 a.m. EDT) and reduced the period of the spacecraft's orbit around the innermost planet from 12 hours to 11 hours 46 minutes. The next orbit-correction maneuver, designed to restore the orbital period to 12 hours, is scheduled for October 24.

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MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 17, 2011 (March 18, 2011 UTC), to begin a yearlong study of its target planet. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.
 

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MESSENGER Mission News
September 8, 2011
http://messenger.jhuapl.edu/

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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 at http://pds.nasa.gov/subscription_service/SS-20110908.html, and all of the MESSENGER data archived at the PDS thus far are available at http://pds.nasa.gov. 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 http://messenger.jhuapl.edu/ and http://www.nasa.gov/messenger.

“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.”

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MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 17, 2011 (March 18, 2011 UTC), to begin a yearlong study of its target planet. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

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NASA:
Sept. 27, 2011​
MEDIA ADVISORY : M11-207
NASA Spacecraft Reveals New Details Of Planet Mercury; Science Journal Has Embargoed Details Until 2 p.m. EDT on Sept. 29


WASHINGTON -- NASA will host a media teleconference at 2 p.m. EDT [18:00 UTC] on Thursday, Sept. 29, to discuss new data and images from the first spacecraft to orbit Mercury.

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft conducted fifteen laps through the inner solar system for more than six years before achieving the historic orbit insertion on March 18.

Briefing participants are:
  • Ed Graykzeck, MESSENGER program manager, NASA Headquarters, Washington
  • James Head, III, professor of geological sciences, Brown University
  • David Blewett, MESSENGER participating scientist and staff scientist, Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Md.
  • Patrick Peplowski, staff scientist, APL
  • Thomas Zurbuchen, professor of space science and aerospace engineering, University of Michigan

{...}
 

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NASA:
Orbital Observations of Mercury Reveal Flood Lavas, Hollows, and Unprecedented Surface Details

September 29, 2011

After only six months in orbit around Mercury, NASA's MESSENGER spacecraft is sending back information that has revolutionized the way scientists think about the innermost planet. Analyses of new data from the spacecraft show, among other things, new evidence that flood volcanism has been widespread on Mercury, the first close-up views of Mercury's "hollows," the first direct measurements of the chemical composition of Mercury's surface, and the first global inventory of plasma ions within Mercury's space environment.

[table="head;width=450"]{colsp=2}
Click on images for details​

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A View Looking Down on the North Pole of Mercury (Center)
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An Example of a Large Crater (Tyagaraja, 97 km in Diameter) with a Floor Partially Covered by Large Numbers of Coalesced Hollows

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Schematic Illustration of the Operation of MESSENGER's Gamma-Ray Spectrometer (GRS)
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Schematic View of Mercury's Magnetosphere and Heavy Plasma Ion Flux
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The results are reported in a set of seven papers published in a special section of Science magazine on September 30, 2011.

"MESSENGER's instruments are capturing data that can be obtained only from orbit," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "We have imaged many areas of the surface at unprecedented resolution, we have viewed the polar regions clearly for the first time, we have built up global coverage with our images and other data sets, we are mapping the elemental composition of Mercury's surface, we are conducting a continuous inventory of the planet's neutral and ionized exosphere, and we are sorting out the geometry of Mercury's magnetic field and magnetosphere. And we've only just begun. Mercury has many more surprises in store for us as our mission progresses."

MESSENGER Reveals Flood Volcanism

For decades scientists had puzzled over whether Mercury had volcanic deposits on its surface. MESSENGER's three flybys answered that question in the affirmative, but the global distribution of volcanic materials was not well constrained. New data from orbit show a huge expanse of volcanic plains surrounding the north polar region of Mercury. These continuous smooth plains cover more than 6% of the total surface of Mercury.

The volcanic deposits are thick. "Analysis of the size of buried ‘ghost' craters in these deposits shows that the lavas are locally as thick as 2 kilometers" (or 1.2 miles), explains James Head of Brown University, the lead author of one of the Science reports. "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."

According to Head, the deposits appear typical of flood lavas, huge volumes of solidified molten rock similar to those found in the few-million-year-old Columbia River Basalt Group, which at one point covered 150,000 square kilometers (60,000 square miles) in the northwest United States. "Those on Mercury appear to have poured out from long, linear vents and covered the surrounding areas, flooding them to great depths and burying their source vents," Head says.

Scientists have also discovered vents, measuring up to 25 kilometers (16 miles) in length, that appear to be the source of some of the tremendous volumes of very hot lava that have rushed out over the surface of Mercury and eroded the substrate, carving valleys and creating teardrop-shaped ridges in the underlying terrain. "These amazing landforms and deposits may be related to the types of unusual compositions, similar to terrestrial rocks called komatiites, being seen by other instruments and reported in this same issue of Science," Head says. "What's more, such lavas may have been typical of an early period in Earth's history, one for which only spotty evidence remains today."

As MESSENGER continues to orbit Mercury, the imaging team is building up a global catalog of these volcanic deposits and is working with other instrument teams to construct a comprehensive view of the history of volcanism on Mercury.

Hollows on Mercury

Images collected by MESSENGER have revealed an unexpected class of landform on Mercury and suggest that a previously unrecognized geological process is responsible for its formation. Images collected during the Mariner 10 and MESSENGER flybys of Mercury showed that the floors and central mountain peaks of some impact craters are very bright and have a blue color relative to other areas of Mercury. These deposits were considered to be unusual because no craters with similar characteristics are found on the Moon. But without higher-resolution images, the bright crater deposits remained a curiosity.

Now MESSENGER's orbital mission has provided close-up, targeted views of many of these craters.

"To the surprise of the science team, it turns out that the bright areas are composed of small, shallow, irregularly shaped depressions that are often found in clusters," says David Blewett, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and lead author of one of the Science reports. "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. Many of the depressions have bright interiors and halos, and Blewett says the ones detected so far have a fresh appearance and have not accumulated small impact craters, indicating that they are relatively young.

"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," Blewett says. "The old conventional wisdom was that ‘Mercury is just like the Moon.' But from its vantage point in orbit, MESSENGER is showing us that Mercury is radically different from the Moon in just about every way we can measure."

Mercury's Surface and Exospheric Composition, Up Close and Personal

Scientists are collecting data about the chemical composition of Mercury's surface that could not have been obtained without the sustained observing perspective that MESSENGER's orbit provides, and that information is being used to test models of Mercury's formation and shed light on the dynamics of the planet's exosphere.

Measurements of Mercury's surface by MESSENGER's Gamma-Ray Spectrometer (GRS) reveal a higher abundance of the radioactive element potassium, a moderately volatile element that vaporizes at a relatively low temperature, than previously predicted. Together with MESSENGER's X-Ray Spectrometer (XRS), it also shows that Mercury has an average surface composition different from those of the Moon and other terrestrial planets.

"Measurements of the ratio of potassium to thorium, another radioactive element, along with the abundance of sulfur detected by XRS, indicate that Mercury has a volatile inventory similar to Venus, Earth, and Mars, and much larger than that of the Moon," says APL Staff Scientist Patrick Peplowski, lead author of one of the Science papers.

These new data rule out most existing models for Mercury's formation that had been developed to explain the unusually high density of the innermost planet, which has a much higher mass fraction of iron metal than Venus, Earth, or Mars, Peplowski pointed out. Overall, Mercury's surface composition is similar to that expected if the planet's bulk composition is broadly similar to that of highly reduced or metal-rich chondritic meteorites (material that is left over from the formation of the solar system).

MESSENGER has also collected the first global observations of plasma ions in Mercury's magnetosphere. Over 65 days covering more than 120 orbits, MESSENGER's Fast Imaging Plasma Spectrometer (FIPS) made the first long-term measurements of Mercury's ionized exosphere.

The team found that sodium is the most important ion contributed by the planet. "We had previously observed neutral sodium from ground observations, but up close we've discovered that charged sodium particles are concentrated near Mercury's polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury's surface," notes the University of Michigan's Thomas Zurbuchen, author of one of the Science reports. "We were able to observe the formation process of these ions, one that is comparable to the manner by which auroras are generated in the Earth atmosphere near polar regions."

The FIPS sensor detected helium ions throughout the entire volume of Mercury's magnetosphere. "Helium must be generated through surface interactions with the solar wind," says Zurbuchen. "We surmise that the helium was delivered from the Sun by the solar wind, implanted on the surface of Mercury, and then fanned out in all directions.

"Our results tell us that Mercury's weak magnetosphere provides the planet very little protection from the solar wind," he continued. "Extreme space weather must be a continuing activity at the surface of the planet closest to the Sun."

"These revelations emphasize that Mercury is a fascinating world that is unmatched in the solar system," says Blewett. "We have barely begun to understand what Mercury is really like and are eager to discover what Mercury can tell us about the processes that led to formation of the planets as we see them today."

{...}



MESSENGER site:
NASA Press Release: RELEASE : 11-330 - NASA Spacecraft Revealing More Details About Planet Mercury

SPACE.com: Planet Mercury Full of Strange Surprises, NASA Spacecraft Reveals
 

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"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."
New unit of height? The Washington Monument. Used to be Nelson's Column when I was a lad.

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I'd say Library of Congress is a unit of volume, so about 2KOSP(Olympic Swimming Pool)?

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I'd say Library of Congress is a unit of volume, so about 2KOSP(Olympic Swimming Pool)?

N.
No, a Library of Congress would be a unit of data storage, but it's expanding fairly rapidly so pinning down an exact value is difficult.

Anyways, height has to be measured in Washington Monuments or Empire State Buildings on this side of the pond since few of us even know what Nelson's Column is. Even those that do don't really have a feel for how big it is. (I did see it when I visited London, though).
 

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Tricky, I doubt many people in the UK have been to Traflagar Square, so no real idea how tall Nelson's column is. I 've seen it, but still couldn't say(100')?

Dosen't really matter, as it and Waterloo Station were built just to annoy Napoleon, seems a bit of a waste now.

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Tricky, I doubt many people in the UK have been to Traflagar Square, so no real idea how tall Nelson's column is. I 've seen it, but still couldn't say(100')?
But people in the UK are still more likely to have seen photos of it, and even if you don't know how tall it is, the photos you've seen of it (or the real life views, if you've actually been there) are likely to contain familiar objects such as people to give a sense of perspective.
 
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