The spacecraft team is now adapting the system to develop the best plan for MESSENGER's extended mission, which begins next month.

Software engineers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., designed SciBox for the simulation and planning of mission scientific operations and for the generation of spacecraft and instrument commands.

"It is a flexible, adjustable suite of mission-simulation and command-generation tools that models spacecraft performance with high fidelity," explains APL's Teck Choo, the creator and architect of SciBox.

SciBox developers worked with the scientists responsible for MESSENGER's investigations to insert the requirements for all scientific observations into the software's decision routines.

During a planning run, SciBox examines the entire mission, locating the best opportunity for each scientific observation. Then, using a set of intertwined priorities constructed to minimize interference among observations, SciBox schedules the full set of observations for the entire mission.

Once the science and engineering teams verify the plan, SciBox produces the instrument commands, which are combined with telecommunication and power commands and then converted to binary format for transmission to the spacecraft. Because spacecraft pointing is integral to the observation plan, SciBox also plans attitude control maneuvers and produces those commands.

The SciBox planning system has increased the scientific return from MESSENGER in several ways. First, it has reduced the complexity involved in combining the more than 30 different sets of observations from the seven instruments and radio science.

"By hand, this intractable problem-to find a fully integrated schedule that accommodates all observations - would be nearly impossible to solve," states Mark Perry, the science lead for SciBox development. "With SciBox, the scientists can levy any and all types of requirements and constraints on the observations, no matter how intricate, and the SciBox implementation team can create an observing sequence to satisfy them."

SciBox also helped the team evaluate options. "With SciBox, scientists and planners can modify the observational parameters and evaluate the effect on the entire mission schedule," Perry says.

"Part of SciBox's output is an extensive set of reports that includes detailed lists, summary statistics, and hundreds of plots that facilitate evaluation of improvements and modifications. With that valuable information, MESSENGER scientists can conduct trades to identify the best approach."

SciBox can also respond quickly to changes in the mission or requirements. "SciBox can re-plan an entire mission in three hours, including the re-integration of all observations, the generation of commands, and the completion of reports," says Choo.

"If the orbit is slightly different from that expected, or if an instrument's optimal observing parameters change during the course of the mission, then we modify SciBox and re-run it."

These same SciBox features have also reduced the risks involved in achieving overall mission objectives. "By planning all the mission observations at once, scientists need not estimate the long-range effects of their requirements," Perry says. Many of the observing variables are run-time parameters, enabling trade studies without modifying the SciBox code, he explains.

With SciBox, planners can also easily investigate the effects of problems and then modify SciBox to develop a plan that is less sensitive to such problems. This rapid response capability minimizes the effect of mission changes by quick re-planning of the full mission.

The SciBox tool continues to evolve. Indeed, one of its advantages is the ease with which it accommodates changes. During MESSENGER's yearlong primary mission, as the science team has identified new observing opportunities, capability has been added to generate new and improved observations.

For the extended mission, the team developed a version of SciBox that incorporates all of the extended-mission observing requirements defined by MESSENGER's science team. The SciBox developers examined strategies for accomplishing the new observations and then worked with the scientists to resolve conflicts and ensure that all requirements are met.

The result, endorsed by the science team and scheduled to go into effect in March, is a packed plan that achieves a scientific return that exceeds extended mission requirements.

]]> Thu, 09 FEB 2012 08:59:15 AEST Katlenburg-Lindau, Germany (UPI) Dec 23, 2011 - Mercury, the smallest planet and the closest to the sun, has an unexpectedly weak magnetic field, and European researchers have fingered the sun as the culprit.

Planetary magnetic fields are generated by flows in the hot, liquid iron cores of rocky planets. Based on its size and density, Mercury should field strengths similar to those on Earth -- yet the planet's field is 150 times weaker than Earth's.

Researchers in Germany say the sun's solar wind -- a constant stream of charged particles -- plays a large role in that.

Mercury, at an average distance from the sun of 36 million miles -- around one third of the distance from Earth to the sun -- is much more exposed to these particles, they said.

"We must keep in mind that Mercury strongly interacts with the surrounding solar wind," researcher Daniel Heyner, lead author of the study published in Science, said in a release from the Max Planck Institute for Solar System Research.

This interaction drives strong electrical currents in the magnetosphere of the planet, creating magnetic fields that counteract and cancel the internal dynamo effect of the flowing iron core, scientists said.

"The dynamo process in Mercury's interior is almost nipped in the bud by the interaction," researcher Karl-Heinz Glassmeier at the Technische Universitat Braunschweig said.

]]> Thu, 09 FEB 2012 08:59:15 AEST Paris, France (ESA) Dec 12, 2011 - The BepiColombo Mercury Magnetospheric Orbiter Structural Model arrived at ESA's European Space Research and Technology Centre in the Netherlands on 7 November 2011, having been flown from Japan.

In the coming weeks, the four components that make up the Mercury Composite Spacecraft will be prepared for integration into their launch configuration in preparation for an acoustic and mechanical test campaign.

The BepiColombo Mercury Magnetospheric Orbiter (MMO) Structural Model (SM) arrived at ESA's European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands, on 7 November 2011, having travelled by road from Amsterdam Airport Schiphol.

The spacecraft, which is being developed and built by the Japan Aerospace Exploration Agency (JAXA), was flown from their facility at Sagamihara, Japan.

Once the transport container had been cleaned and transferred to the 'XMM' cleanroom in the ESTEC Test Centre, it was left overnight to reach thermal equilibrium with its surroundings.

On 8 November, the transport container was opened and the MMO's internal shock recorders were inspected to ensure that the dynamic environment experienced by the spacecraft during transport had remained within specifications.

An overhead crane and lifting device were used to move the MMO from its transport container base onto its handling trolley, after which it was moved to the 'Rosetta' cleanroom to join the other components of the Mercury Composite Spacecraft (MCS).

In parallel with the unpacking of the MMO, the Mercury Planetary Orbiter (MPO) was undergoing alignment checks after completion of its thermal balance test and the removal of its thermal blankets.

In the coming weeks, the MMO, the MPO, the Mercury Transfer Module (MTM) and the Magnetospheric Orbiter Sunshade and Interface Structure (MOSIF) will be prepared for integration to form the MCS, the configuration in which they will be launched and travel to Mercury.

The BepiColombo Mission
BepiColombo is Europe's first mission to Mercury. It is scheduled to launch in 2014 and arrive at Mercury in late 2020. It will endure temperatures in excess of 350C and gather data during a one-year nominal mission, with a possible one-year extension.

The mission comprises two spacecraft: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). During the journey to Mercury, the MMO will be shielded from the Sun by the Magnetospheric Orbiter Sunshield and Interface Structure (MOSIF), which also provides the interface between the MMO and the MPO.

The fourth component of the composite spacecraft stack is the Mercury Transfer Module (MTM), whose primary task is to provide solar-electric propulsion for the journey to Mercury.

BepiColombo is a joint mission by ESA and the Japan Aerospace Exploration Agency (JAXA), executed under ESA leadership. The Prime Contractor for BepiColombo is Astrium GmbH.

]]> Thu, 09 FEB 2012 08:59:15 AEST Annapolis, MD (SPX) Nov 16, 2011 - 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 November 9, 2011, 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: What are the sources of surface volatiles on Mercury?

How late into Mercury's history did volcanism persist?

How did Mercury's long-wavelength topography change with time?

What is the origin of localized regions of enhanced exospheric density at Mercury?

How does the solar cycle affect Mercury's exosphere and volatile transport?

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."

]]> Thu, 09 FEB 2012 08:59:15 AEST Huntsville AL (SPX) Oct 25, 2011 - NASA's MESSENGER spacecraft has discovered strange hollows on the surface of Mercury. Images taken from orbit reveal thousands of peculiar depressions at a variety of longitudes and latitudes, ranging in size from 60 feet to over a mile across and 60 to 120 feet deep. No one knows how they got there.

"These hollows were a major surprise," says David Blewett, science team member from the Johns Hopkins University Applied Physics Laboratory.

"We've been thinking of Mercury as a relic - a place that's really not changing much anymore, except by impact cratering. But the hollows appear to be younger than the craters in which they are found, and that means Mercury's surface is still evolving in a surprising way."

Mars Reconnaissance Orbiter spotted similar depressions in the carbon dioxide ice at Mars' south pole, giving that surface a "swiss cheese" appearance. But on Mercury they're found in rock and often have bright interiors and halos.

"We've never seen anything quite like this on a rocky surface."

If you could stand in one of these "sleepy" hollows on Mercury's surface, you'd find yourself, like Ichabod Crane, in a quiet, still, haunting place, with a black sky above your head.

"There's essentially no atmosphere on Mercury," explains Blewett. "And with no atmosphere, wind doesn't blow and rain doesn't fall. So the hollows weren't carved by wind or water. Other forces must be at work."

As the planet closest to the Sun, Mercury is exposed to fierce heat and extreme space weather. Blewett believes these factors play a role.

A key clue, he says, is that many of the hollows are associated with central mounds or mountains inside Mercury's impact craters.

These so-called "peak rings" are thought to be made of material forced up from the depths by the impact that formed the crater. Excavated material could be unstable when it finds itself suddenly exposed at Mercury's surface.

"Certain minerals, for example those that contain sulfur and other volatiles, would be easily vaporized by the onslaught of heat, solar wind, and micrometeoroids that Mercury experiences on a daily basis," he says.

"Perhaps sulfur is vaporizing, leaving just the other minerals, and therefore weakening the rock and making it spongier. Then the rock would crumble and erode more readily, forming these depressions."

MESSENGER has indeed proven Mercury unexpectedly rich in sulfur. That in itself is a surprise that's forcing scientists to rethink how Mercury was formed.

The prevailing models suggest that either (1) very early in Solar System history, during the final sweep-up of the large planetesimals that formed the planets, a colossal impact tore off much of Mercury's rocky outer layering; or (2) a hot phase of the early Sun heated up the surface enough to scorch off the outer layers.

In either case, the elements with a low boiling point - volatiles like sulfur and potassium - would have been driven off.

But they're still there.

"The old models just don't fit with the new data, so we'll have to look at other hypotheses."

To figure out how the planets and Solar System came to be, scientists must understand Mercury.

"It's the anchor at one end of the Solar System. Learning how Mercury formed will have major implications for the rest of the planets. And MESSENGER is showing that, up to now, we've been completely wrong about this little world in so many ways!"

What other surprises does Mercury hold? The sleepy hollows of the innermost planet may be just the beginning.

]]> Thu, 09 FEB 2012 08:59:15 AEST Laurel MD (SPX) Oct 26, 2011 - The MESSENGER spacecraft successfully completed its fourth orbit-correction maneuver to increase the period of the spacecraft's orbit around the innermost planet from 11 hours 46 minutes to a precise 12 hours.

MESSENGER was 198 million kilometers (123 million miles) from Earth when the 159-second maneuver began at 6:12 p.m. EDT. Mission controllers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., verified the start of the maneuver about 11 minutes, 1 second later, when the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station outside Goldstone, Calif.

This is the fourth of five maneuvers planned for the primary orbital phase of the mission to keep orbital parameters within desired ranges for optimal scientific observations.

MESSENGER's orbital velocity was changed by a total of 4.2 meters per second (9.4 miles per hour) to make the corrections essential for continuing the planned measurement campaigns.

Most of the instruments were placed in a passive state during the burn, but the instruments were reconfigured at 7:05 p.m. EDT to resume scientific observations of the planet.

MESSENGER Mission Systems Engineer Eric Finnegan, of APL, said the engine burn was executed as planned. "The team was well-prepared for the maneuver, and MESSENGER is right where it needs to be to continue revealing new details about Mercury," he said.

The next orbit-correction maneuver is scheduled for December 5.

]]> Thu, 09 FEB 2012 08:59:15 AEST Paris (ESA) Oct 18, 2011 - Thermal-balance testing of the BepiColombo Mercury Planetary Orbiter Structural and Thermal Model, which has been under way in ESA's Large Space Simulator since 20 September, has been successfully completed. During these tests the conditions the spacecraft will encounter during the cruise to Mercury and while in orbit have been simulated, and a number of tests to characterise the spacecraft performance under some worst-case scenarios have been carried out.

'Dry run' in the Large Space Simulator
Following the installation of the Mercury Planetary Orbiter (MPO) Structural and Thermal Model (STM) in the Large Space Simulator (LSS) at ESA's Test Centre in Noordwijk, the Netherlands on 31 August and the completion of all the necessary preparations, a 'dry run' was conducted on 13 September to verify the performance of the spacecraft, its instrumentation, and the gimbal stand / spin box and levelling table that support, orient, rotate and level the spacecraft during testing.

The dry run was performed with the LSS top cover open; the MPO was illuminated with just one of the nineteen 25-kW lamps that make up the solar simulator.

In order to reach the radiation intensity that the orbiter will experience in orbit around Mercury, the 121 hexagonal mirror segments that produce the beam have been adjusted to produce a converging beam rather than the standard parallel beam.

To allow the wall of the LSS to cope with the increased beam intensity while continuing to simulate the cold of space, an additional shroud has been installed.

Pump down and cold calibration
After the dry run, the LSS top hatch was closed and vacuum pumping commenced on 20 September. Once a vacuum of around 10-5 mbar had been achieved, liquid nitrogen started to be pumped through the shrouds of the chamber walls to cool the interior of the LSS down to less than -173 degrees C (100 K). Once cool-down was completed, the steady state under cold conditions (referred to as 'cold calibration') was achieved and baseline data were acquired.

Cruise and orbit
On 22 September, simulation of the initial cruise phase of MPO's journey to Mercury began. This was followed, the next day, by the intermediate cruise phase; testing under in-orbit conditions followed, beginning on 26 September with conditions at aphelion and then moving on to perihelion. Particular attention has been paid to conditions at perihelion, where the MPO will be most strongly illuminated.

Investigations of the spacecraft's thermal performance during entry into and exit from eclipse have also been also carried out through 'snapshots' at various attitudes (for example, rotation of 45 degrees with the Sun on the +Y/-X faces and tilting of 30 degrees with the Sun on the +Z/+Y faces).

Around 4000 litres of liquid nitrogen are consumed per hour during testing, so a steady stream of tankers have been arriving to replenish the 100 000-litre on-site storage capacity.

The heaters that simulate the thermal dissipation of the electronics units and those that warm critical components during eclipse are powered by external power sources during testing. Temperature data, obtained using thermocouples, are acquired by the thermal data handling system that is part of the LSS.

Two infrared cameras are used to monitor the spacecraft's multi-layer insulation and items external to the satellite that face the Sun simulator.

To maintain realistic conditions for the heat pipe network, which is designed to work in the microgravity of Mercury orbit, the satellite is kept levelled by adjusting the levelling table and acquiring readings from on-board tilt meters.

Non-nominal attitude - testing the worst-case scenario

In addition to simulating the nominal case, a series of tests have been carried out to investigate the thermal behaviour of the MPO in the event that its nominal attitude in orbit is temporarily lost. Loss of attitude might result in parts of the spacecraft that are not intended to be exposed to intense solar radiation being illuminated until its nominal attitude can be restored. These tests will demonstrate that the spacecraft structure and thermal control systems can withstand such unintended exposure.

Two particular cases of 'loss of attitude' were replicated: in the first scenario the situation where a loss of attitude results in the Sun being orthogonal to the MPO radiator was simulated by rotating the spacecraft so that the radiator was directly exposed to sunlight for 10 seconds, and then rotating the spacecraft back to its original position - to simulate the restoration of attitude control.

The second scenario simulated a loss of attitude that results in sunlight directly passing through the louvres onto the radiator.

For this test the Sun was temporarily switched off - by closing the shutters on the Sun simulator - the spacecraft was rotated so that the radiator was in front of the Sun simulator and then tilted by 30 degrees towards the large 5-metre door on the LSS, in other words, facing away from the Sun so that when the shutter was opened sunlight passed through the louvres onto the radiator. After 50 seconds of exposure the shutter was closed, simulating the spacecraft return to nominal attitude.

Warm up and pressure recovery
With the completion of the thermal-balance tests on 6 October, cooling of the LSS was gradually reduced and the satellite and chamber were allowed to return to ambient temperature; this took about 1.5 days.

On 8 October, once the warm up was complete, the vacuum pumps were stopped and the pressure was restored to normal atmospheric levels using gaseous nitrogen and air over the course of about 8 hours. The MPO STM will soon be removed from the LSS and preparations will begin for the next phase of testing.

Next stages
A number of deployable appendages and antennas will be installed on the MPO and deployment shock tests will be performed. The physical properties of the spacecraft - mass, centre of gravity, moment of inertia about all three axes - will be measured to confirm that they match the design values.

The MPO will then be ready for integration into the Mercury Composite Spacecraft (MCS) - the configuration in which the MPO, the Mercury Magnetospheric Orbiter (MMO), the Mercury Transfer Module (MTM) and the Magnetospheric Orbiter Sunshade and Interface (MOSIF) will be launched and travel to Mercury. The next phase of testing will include mechanical and acoustic testing of the MCS to qualify the structures for the dynamic mechanical environment specified by the launcher authority.

]]> Thu, 09 FEB 2012 08:59:15 AEST Paris, France (ESA) Oct 14, 2011 - Thermal-balance testing of the BepiColombo Mercury Planetary Orbiter Structural and Thermal Model, which has been under way in ESA's Large Space Simulator since 20 September, has been successfully completed. During these tests the conditions the spacecraft will encounter during the cruise to Mercury and while in orbit have been simulated, and a number of tests to characterise the spacecraft performance under some worst-case scenarios have been carried out.

'Dry run' in the Large Space Simulator
Following the installation of the Mercury Planetary Orbiter (MPO) Structural and Thermal Model (STM) in the Large Space Simulator (LSS) at ESA's Test Centre in Noordwijk, the Netherlands on 31 August and the completion of all the necessary preparations, a 'dry run' was conducted on 13 September to verify the performance of the spacecraft, its instrumentation, and the gimbal stand / spin box and levelling table that support, orient, rotate and level the spacecraft during testing.

The dry run was performed with the LSS top cover open; the MPO was illuminated with just one of the nineteen 25-kW lamps that make up the solar simulator. In order to reach the radiation intensity that the orbiter will experience in orbit around Mercury, the 121 hexagonal mirror segments that produce the beam have been adjusted to produce a converging beam rather than the standard parallel beam. To allow the wall of the LSS to cope with the increased beam intensity while continuing to simulate the cold of space, an additional shroud has been installed.

Pump down and cold calibration
After the dry run, the LSS top hatch was closed and vacuum pumping commenced on 20 September. Once a vacuum of around 10-5 mbar had been achieved, liquid nitrogen started to be pumped through the shrouds of the chamber walls to cool the interior of the LSS down to less than -173 degrees C (100 K). Once cool-down was completed, the steady state under cold conditions (referred to as 'cold calibration') was achieved and baseline data were acquired.

Cruise and orbit
On 22 September, simulation of the initial cruise phase of MPO's journey to Mercury began. This was followed, the next day, by the intermediate cruise phase; testing under in-orbit conditions followed, beginning on 26 September with conditions at aphelion and then moving on to perihelion. Particular attention has been paid to conditions at perihelion, where the MPO will be most strongly illuminated.

Investigations of the spacecraft's thermal performance during entry into and exit from eclipse have also been also carried out through 'snapshots' at various attitudes (for example, rotation of 45 degrees with the Sun on the +Y/-X faces and tilting of 30 degrees with the Sun on the +Z/+Y faces).

Around 4000 litres of liquid nitrogen are consumed per hour during testing, so a steady stream of tankers have been arriving to replenish the 100 000-litre on-site storage capacity.

The heaters that simulate the thermal dissipation of the electronics units and those that warm critical components during eclipse are powered by external power sources during testing. Temperature data, obtained using thermocouples, are acquired by the thermal data handling system that is part of the LSS.

Two infrared cameras are used to monitor the spacecraft's multi-layer insulation and items external to the satellite that face the Sun simulator.

To maintain realistic conditions for the heat pipe network, which is designed to work in the microgravity of Mercury orbit, the satellite is kept levelled by adjusting the levelling table and acquiring readings from on-board tilt meters.

Non-nominal attitude - testing the worst-case scenario
In addition to simulating the nominal case, a series of tests have been carried out to investigate the thermal behaviour of the MPO in the event that its nominal attitude in orbit is temporarily lost. Loss of attitude might result in parts of the spacecraft that are not intended to be exposed to intense solar radiation being illuminated until its nominal attitude can be restored.

These tests will demonstrate that the spacecraft structure and thermal control systems can withstand such unintended exposure.

Two particular cases of 'loss of attitude' were replicated: in the first scenario the situation where a loss of attitude results in the Sun being orthogonal to the MPO radiator was simulated by rotating the spacecraft so that the radiator was directly exposed to sunlight for 10 seconds, and then rotating the spacecraft back to its original position - to simulate the restoration of attitude control.

The second scenario simulated a loss of attitude that results in sunlight directly passing through the louvres onto the radiator. For this test the Sun was temporarily switched off - by closing the shutters on the Sun simulator - the spacecraft was rotated so that the radiator was in front of the Sun simulator and then tilted by 30 degrees towards the large 5-metre door on the LSS, in other words, facing away from the Sun so that when the shutter was opened sunlight passed through the louvres onto the radiator. After 50 seconds of exposure the shutter was closed, simulating the spacecraft return to nominal attitude.

Warm up and pressure recovery
With the completion of the thermal-balance tests on 6 October, cooling of the LSS was gradually reduced and the satellite and chamber were allowed to return to ambient temperature; this took about 1.5 days. On 8 October, once the warm up was complete, the vacuum pumps were stopped and the pressure was restored to normal atmospheric levels using gaseous nitrogen and air over the course of about 8 hours. The MPO STM will soon be removed from the LSS and preparations will begin for the next phase of testing.

Next stages
A number of deployable appendages and antennas will be installed on the MPO and deployment shock tests will be performed. The physical properties of the spacecraft - mass, centre of gravity, moment of inertia about all three axes - will be measured to confirm that they match the design values. The MPO will then be ready for integration into the Mercury Composite Spacecraft (MCS) - the configuration in which the MPO, the Mercury Magnetospheric Orbiter (MMO), the Mercury Transfer Module (MTM) and the Magnetospheric Orbiter Sunshade and Interface (MOSIF) will be launched and travel to Mercury. The next phase of testing will include mechanical and acoustic testing of the MCS to qualify the structures for the dynamic mechanical environment specified by the launcher authority.

]]> Thu, 09 FEB 2012 08:59:15 AEST Nantes, France (SPX) Oct 14, 2011 - MESSENGER scientists will highlight the latest results on Mercury from MESSENGER observations obtained during the first six months (the first Mercury solar day) in orbit. These findings were presented in 30 papers and posters as part of a special session of the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society in Nantes, France.

Scientists will also look ahead to MESSENGER observations still to come and to the dual-spacecraft BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency later this decade.

"This is the first major scientific meeting at which MESSENGER orbital observations are being presented to the scientific community," says MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington.

"As the first spacecraft to orbit our solar system's innermost planet, MESSENGER continues to reveal new surprises every week. It is timely to sum up what we've learned so far and to seek feedback from our international colleagues across planetary science on our interpretations to date."

After three successful flybys of Mercury, the MESSENGER spacecraft entered orbit about the innermost planet on March 18, 2011. The orbital phase of the mission is enabling the first global perspective on the planet's geology, surface composition, topography, gravity and magnetic fields, exosphere, magnetosphere, and solar-wind interaction.

Studying Mercury can help astrobiologists understand the diversity of rocky bodies that potentially exist in the Universe. This information is important in determining where best to hunt for habitable worlds around distant stars. Mercury can also provide clues about how our own planet, Earth, formed and evovled into the habitbable world we know today.

Mercury's Global Magnetic Field
The magnetic and gravity fields of Mercury are the primary clues scientists have on the structure deep in the interior of the planet, which in turns helps develop general theories for how planets form and evolve. Orbital data reveal that Mercury's magnetic field is offset far to the north of the planet's center, by nearly 20% of Mercury's radius.

Relative to the planet's size, this offset is much more than in any other planet, and accounting for it will pose a challenge to theoretical explanations of the field.

"Although we don't know how to explain that yet - it is no doubt an important clue to the workings of Mercury's dynamo," says Brian Anderson, MESSENGER Deputy Project Scientist and a space physicist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

This finding has several implications for other aspects of Mercury, says Anderson, who co-authored several of the presentations in the MESSENGER session. "This means that the magnetic field in the southern hemisphere should be a lot weaker than it is in the north. At the north geographic pole, the magnetic field should be about 3.5 times stronger than it is at the south geographic pole.

"The big difference in northern and southern surface field strengths means that energetic particles, solar wind, and high-energy electrons will preferentially impact the surface in the south, and this situation should lead to asymmetries both in sources of atoms, ions, and molecules for Mercury's exosphere and in the discoloration of the surface by charged particle bombardment," he continues. "Both should occur more strongly in the south."

The Dynamics of Mercury's Exosphere
Mercury is surrounded by a tenuous exosphere of gas generated and maintained by the interaction of the space environment with the planet's surface. Measuring the composition and structure of the exosphere provides insight into how the space environment modifies the outermost layers of the planet's surface materials.

MESSENGER's observations during the flybys and orbit show that the current understanding of the nature of Mercury's exosphere is incomplete, says William McClintock, a MESSENGER mission co-investigator and senior scientist at the Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder.

"They show that distinctly different source and loss processes control the populations of the major constituents of sodium, magnesium, and calcium atoms in the exosphere," says McClintock.

Before MESSENGER, the prevailing theory suggested that material was released from the day side by solar wind and radiation. In this picture, lofted material then was carried to the night side by solar radiation pressure. MESSENGER measurements show that magnesium and calcium in the tail region are substantially more abundant than would be expected if they were produced in this way, he points out.

New magnetic field models, derived from MESSENGER's Magnetometer data, indicate that the planet's intrinsic field can couple with the interplanetary field to direct solar wind ions to the night side, sputtering material from non-illuminated surfaces.

But that source is too weak to explain the observed concentrations. Calcium also exhibits an unexplained enhanced concentration at the equator near dawn, a pattern that appears to be a persistent feature in the exosphere. Such dawn enhancements are not observed for magnesium, which is chemically similar to calcium.

The Evolution of Mercury's Geological and Surface Composition
After its first Mercury solar day in orbit, MESSENGER has nearly completed two of its primary global imaging campaigns: a monochrome map at 250 meters per pixel and an eight-color, 1 kilometer per pixel color map. Apart from small gaps, which will be filled in during the next solar day, these maps cover the entire planet under uniform lighting conditions ideal for assessing the form of Mercury's surface features as well as the color and compositional variations across the planet.

Flybys of Mercury by the MESSENGER and Mariner 10 spacecraft showed broad expanses of plains across the planet. There was strong evidence for a volcanic origin of many of these plains, indicating that volcanism played an important role in shaping Mercury's crust; but large regions of the planet remained unmapped, and the origin of many plains units had until now remained ambiguous.

"With images from MESSENGER's orbital mapping campaigns, as well as targeted high-resolution images, we can now begin to assess the origin of plains on a global basis, and - when combined with data from MESSENGER's X-Ray Spectrometer - their compositional variation," says Brett Denevi, a planetary scientist in APL's Space Department.

"We find that volcanic rocks dominate much of Mercury's crust, even in regions that are geologically complex and where impact cratering has destroyed many of the original surface features."

The X-Ray Spectrometer collects compositional information averaged over relatively large regions on Mercury's surface, and signals diagnostic of the heavier elements are received only during times of high solar activity. For regions where geologic mapping and detailed compositional information are both available, many of the large-scale volcanic units on Mercury are seen to be basaltic. Basalts are common volcanic rocks on Earth and the Moon.

Variations in Surface Reflectance Spectra
Over the course of the first solar day in orbit, the Visible and Infrared Spectrograph (VIRS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) obtained over one million spectra of the surface from near one pole to the other and spanning all longitudes. VIRS observed all the major geologic units and structures, from large basins to small fresh-looking craters, and from average pains to hollows and possible pyroclastic materials.

Whereas the Mercury Dual Imaging System highlights the morphology and broad color characteristics of these materials, VIRS reveals greater details of the reflective properties of surface materials.

"One surprise that's been with us since the flybys is the apparent lack of iron in the silicate minerals of the rocks on the surface of the planet," says APL's Noam Izenberg, Instrument Scientist for the MASCS instrument on MESSENGER.

"In rock-forming silicates, the primary materials of most planetary crusts, iron shows up as a characteristic absorption at infrared wavelengths, but such features have been completely absent in spectra from Mercury," says Izenberg.

"The infrared continues to show very little spectral variation indicative of distinct mineralogies, and we are working hard to tease out what we can."

An important chapter of the story, however, appears to be at ultraviolet wavelengths, he says. "Iron in rocks also has effects in this region of the spectrum as well, but those effects are less well studied and understood. However it is here that we see variations among, for example, fresh-looking craters, plains, hollows, pyroclastic deposits, and low-reflectance units."

According to Izenberg, the variations in the ultraviolet may reflect both iron content and the type of rocks that hold it and may provide hints at other materials, such as sulfur, which have characteristic ultraviolet reflectance signatures as well.

"Evidence from other instruments on MESSENGER, such as the X-Ray Spectrometer, corroborates low iron abundance near the surface and the presence of sulfur, so as our analyses advance we'll be working to correlate the findings across all instruments."

Looking Ahead
MESSENGER continues to send back data that illuminate Mercury's mysteries. The knowledge gained is already sharpening the mission goals of the dual-spacecraft BepiColombo mission, scheduled to launch to Mercury in 2014.

Members of the MESSENGER team met with BepiColombo scientists at Kyoto University in Japan last month to review the state of knowledge about Mercury and to present initial MESSENGER orbital results.

"We discussed many of the new findings that will be covered in the MESSENGER sessions today," says MESSENGER Project Scientist Ralph McNutt.

"BepiColombo team members presented new perspectives on surface mineralogy from recent high-temperature laboratory measurements and new theories for Mercury's formation and for the generation of Mercury's magnetic field. This meeting continued a dialogue, begun more than a decade ago, on the synergies of the two investigations and how ongoing MESSENGER measurements are informing the planning for BepiColombo operations."

]]> Thu, 09 FEB 2012 08:59:15 AEST Nantes, France (SPX) Oct 06, 2011 - MESSENGER scientists on Wednesday highlighted the latest results on Mercury from MESSENGER observations obtained during the first six months (the first Mercury solar day) in orbit. The findings were presented in 30 papers and posters as part of a special session of the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society in Nantes, Frances.

Scientists will also look ahead to MESSENGER observations still to come and to the dual-spacecraft BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency's later this decade.

"This is the first major scientific meeting at which MESSENGER orbital observations are being presented to the scientific community," says MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington.

"As the first spacecraft to orbit our solar system's innermost planet, MESSENGER continues to reveal new surprises every week. It is timely to sum up what we've learned so far and to seek feedback from our international colleagues across planetary science on our interpretations to date."

After three successful flybys of Mercury, the MESSENGER spacecraft entered orbit about the innermost planet on March 18, 2011. The orbital phase of the mission is enabling the first global perspective on the planet's geology, surface composition, topography, gravity and magnetic fields, exosphere, magnetosphere, and solar-wind interaction.

Mercury's Global Magnetic Field
The magnetic and gravity fields of Mercury are the primary clues scientists have on the structure deep in the interior of the planet, which in turns helps develop general theories for how planets form and evolve.

Orbital data reveal that Mercury's magnetic field is offset far to the north of the planet's center, by nearly 20% of Mercury's radius. Relative to the planet's size, this offset is much more than in any other planet, and accounting for it will pose a challenge to theoretical explanations of the field.

"Although we don't know how to explain that yet, it is no doubt an important clue to the workings of Mercury's dynamo," says Brian Anderson, MESSENGER Deputy Project Scientist and a space physicist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

This finding has several implications for other aspects of Mercury, says Anderson, who co-authored several of the presentations in the MESSENGER session.

"This means that the magnetic field in the southern hemisphere should be a lot weaker than it is in the north. At the north geographic pole, the magnetic field should be about 3.5 times stronger than it is at the south geographic pole.

"The big difference in northern and southern surface field strengths means that energetic particles, solar wind, and high-energy electrons will preferentially impact the surface in the south, and this situation should lead to asymmetries both in sources of atoms, ions, and molecules for Mercury's exosphere and in the discoloration of the surface by charged particle bombardment," he continues.

"Both should occur more strongly in the south."

The Dynamics of Mercury's Exosphere
Mercury is surrounded by a tenuous exosphere of gas generated and maintained by the interaction of the space environment with the planet's surface. Measuring the composition and structure of the exosphere provides insight into how the space environment modifies the outermost layers of the planet's surface materials.

MESSENGER's observations during the flybys and orbit show that the current understanding of the nature of Mercury's exosphere is incomplete, says William McClintock, a MESSENGER mission co-investigator and senior scientist at the Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder.

"They show that distinctly different source and loss processes control the populations of the major constituents of sodium, magnesium, and calcium atoms in the exosphere," says McClintock.

Before MESSENGER, the prevailing theory suggested that material was released from the dayside by solar wind and radiation. In this picture, lofted material then was carried to the nightside by solar radiation pressure. MESSENGER measurements show that magnesium and calcium in the tail region are substantially more abundant than would be expected if they were produced in this way, he points out.

New magnetic field models, derived from MESSENGER's Magnetometer data, indicate that the planet's intrinsic field can couple with the interplanetary field to direct solar wind ions to the nightside, sputtering material from non-illuminated surfaces. But that source is too weak to explain the observed concentrations.

Calcium also exhibits an unexplained enhanced concentration at the equator near dawn, a pattern that appears to be a persistent feature in the exosphere. Such dawn enhancements are not observed for magnesium, which is chemically similar to calcium.

The Evolution of Mercury's Geological and Surface Composition
After its first Mercury solar day in orbit, MESSENGER has nearly completed two of its primary global imaging campaigns: a monochrome map at 250 meters per pixel and an eight-color, 1 kilometer per pixel color map.

Apart from small gaps, which will be filled in during the next solar day, these maps cover the entire planet under uniform lighting conditions ideal for assessing the form of Mercury's surface features as well as the color and compositional variations across the planet.

Flybys of Mercury by the MESSENGER and Mariner 10 spacecraft showed broad expanses of plains across the planet. There was strong evidence for a volcanic origin of many of these plains, indicating that volcanism played an important role in shaping Mercury's crust; but large regions of the planet remained unmapped, and the origin of many plains units had until now remained ambiguous.

"With images from MESSENGER's orbital mapping campaigns, as well as targeted high-resolution images, we can now begin to assess the origin of plains on a global basis, and-when combined with data from MESSENGER's X-Ray Spectrometer-their compositional variation," says Brett Denevi, a planetary scientist in APL's Space Department.

"We find that volcanic rocks dominate much of Mercury's crust, even in regions that are geologically complex and where impact cratering has destroyed many of the original surface features."

The X-Ray Spectrometer collects compositional information averaged over relatively large regions on Mercury's surface, and signals diagnostic of the heavier elements are received only during times of high solar activity.

For regions where geologic mapping and detailed compositional information are both available, many of the large-scale volcanic units on Mercury are seen to be basaltic. Basalts are common volcanic rocks on Earth and the Moon.

Variations in Surface Reflectance Spectra
Over the course of the first solar day in orbit, the Visible and Infrared Spectrograph (VIRS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) obtained over one million spectra of the surface from near one pole to the other and spanning all longitudes.

VIRS observed all the major geologic units and structures, from large basins to small fresh-looking craters, and from average pains to hollows and possible pyroclastic materials. Whereas the Mercury Dual Imaging System highlights the morphology and broad color characteristics of these materials, VIRS reveals greater details of the reflective properties of surface materials.

"One surprise that's been with us since the flybys is the apparent lack of iron in the silicate minerals of the rocks on the surface of the planet," says APL's Noam Izenberg, Instrument Scientist for the MASCS instrument on MESSENGER.

"In rock-forming silicates, the primary materials of most planetary crusts, iron shows up as a characteristic absorption at infrared wavelengths, but such features have been completely absent in spectra from Mercury," says Izenberg. "The infrared continues to show very little spectral variation indicative of distinct mineralogies, and we are working hard to tease out what we can."

An important chapter of the story, however, appears to be at ultraviolet wavelengths, he says. "Iron in rocks also has effects in this region of the spectrum as well, but those effects are less well studied and understood. However it is here that we see variations among, for example, fresh-looking craters, plains, hollows, pyroclastic deposits, and low-reflectance units."

According to Izenberg, the variations in the ultraviolet may reflect both iron content and the type of rocks that hold it and may provide hints at other materials, such as sulfur, which have characteristic ultraviolet reflectance signatures as well.

"Evidence from other instruments on MESSENGER, such as the X-Ray Spectrometer, corroborates low iron abundance near the surface and the presence of sulfur, so as our analyses advance we'll be working to correlate the findings across all instruments."

Looking Ahead
MESSENGER continues to send back data that illuminate Mercury's mysteries. The knowledge gained is already sharpening the mission goals of the dual-spacecraft BepiColombo mission, scheduled to launch to Mercury in 2014.

Members of the MESSENGER team met with BepiColombo scientists at Kyoto University in Japan last month to review the state of knowledge about Mercury and to present initial MESSENGER orbital results.

"We discussed many of the new findings that will be covered in the MESSENGER sessions today," says MESSENGER Project Scientist Ralph McNutt.

"BepiColombo team members presented new perspectives on surface mineralogy from recent high-temperature laboratory measurements and new theories for Mercury's formation and for the generation of Mercury's magnetic field. This meeting continued a dialogue, begun more than a decade ago, on the synergies of the two investigations and how ongoing MESSENGER measurements are informing the planning for BepiColombo operations."

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