April 30, 2009

Mercury Has A Magnesium Based Surface

NASA's live media teleconference held earlier today included a panel of experts working on the U.S. space program's MESSENGER instrument that discussed new data and findings revealed by the planet Mercury's makeup.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft's second flyby of the planet in October 2008 showed that the planet's atmosphere, magnetosphere, and geological past are all characterized by much greater levels of activity than astronomers originally thought.

The seven instruments carried aboard MESSENGER include a camera, a magnetometer, an altimeter and four spectrometers.

MESSENGER Principal Investigator Sean Solomon at the Carnegie Institution of Washington said the instruments second flyby of Mercury provided a number of new findings, such as how strongly the planet's magnetospheric dynamics changed from what they saw during the first Mercury flyby in January 2008.

Additionally, the first detection of magnesium in Mercury's exosphere and neutral tail provided scientists with confirmation that magnesium is an important constituent of Mercury's surface materials.

Magnesium is an element created inside exploding stars that is also found in many medicine cabinets on Earth.

Senior Research Associate William McClintock of CU-Boulder's Laboratory for Atmospheric and Space Physics said they had long suspected magnesium would be present, but they were surprised at its distribution and abundance.

"Detecting magnesium was not too surprising, but seeing it in the amounts and distribution we recorded was unexpected," said McClintock, a MESSENGER co- investigator who led the development of CU-Boulder's Mercury Atmospheric and Surface Composition Spectrometer, or MASCS.

"This is an example of the kind of individual discoveries that the MESSENGER team will piece together to give us a new picture of how the planet formed and evolved," he added.

The desk-sized MESSENGER spacecraft, which was developed and coordinated by a team of scientists at the University of Colorado at Boulder, also measured calcium and sodium levels in the exosphere during the Oct. 6 flyby and the team was again surprised by the findings.

"Since calcium and magnesium are chemically similar, we might expect them to have a similar distribution in Mercury's exosphere," McClintock said. "But they don't, and we don't yet understand why."

He said the team also suspects that other metallic elements from the surface such as aluminum, iron and silicon are also present in the exosphere, left over from a time in which they permeated the solar nebula when it was coalescing some 4.5 billion years ago during the shaping the planets.

The abundance of materials escaping from Mercury's surface is accelerated by solar radiation pressure to form a gigantic tail of atoms flowing away from the sun, McClintock said.

The team believes that the magnetospheric variability observed suggests the great day-to-day changes in Mercury's atmosphere may be due to changes in the shielding provided by the magnetosphere.

NASA scientists were also excited to discover the craft captured a previously unknown large impact basin some 430 miles in diameter that experts said would span the distance between Washington, D.C., and Boston.

Now being called "The Rembrandt Basin," the important landform was likely created by the collision of asteroid-scale objects early in planetary history some 3.9 billion years ago, near the end of the period of heavy bombardment of the inner Solar System.

Thomas Watters of the Smithsonian's National Air and Space Museum said the pattern of tectonic landforms in the Rembrandt basin is truly extraordinary.

"It is unlike anything we have seen before in other impact basins on Mercury, the Moon or Mars, or in basins formed on the icy moons of the outer planets," he added.

Brett Denevi, a MESSENGER team member at Arizona State University, said scientists have now seen 90 percent of the planet's surface at high resolution with image data from MESSENGER.

He said astronomers could now start to assess what this global picture can provide about the history of the planet's crustal evolution.

With the success of the first two flybys and data being prepared from a third flyby on September 29, 2009, scientists are learning more and more about what they're now referring to as "an amazingly dynamic planet".

In March 2011, the team plans to send the probe into orbit around Mercury for one year of continuous data collection.

Solomon said the orbital phase of the mission would be like staging two flybys per day. 

"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," he said.


Image 1: A mosaic of images collected by MESSENGER's Narrow Angle Camera as the spacecraft approached Mercury on October 6, 2008. The Rembrandt impact basin, 715 km in diameter, is seen at the center as night was falling across its eastern edge. An image similar to this one appears on the cover of the 1 May issue of Science magazine containing four articles on the latest results from that flyby. Credit: Image produced by NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington. Image reproduced courtesy of Science/AAAS.

Image 2: The Rembrandt impact basin was discovered by MESSENGER during its second flyby of Mercury in October 2008. Images show that the Rembrandt basin is remarkably well preserved. Most large impact basins on Mercury, the Moon, and other inner planets are flooded by volcanic flows that cover their entire floor. The number per area and size distribution of impact craters superposed on Rembrandt's rim indicates that it is one of the youngest impact basins on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Smithsonian Institution/Carnegie Institution of Washington


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