[meteorite-list] MESSENGER Revealing More Details About Planet Mercury

[Ron Baalke]

Sept. 29, 2011

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Paulette Campbell 
Johns Hopkins University Applied Physics Laboratory, Laurel, Md. 
240-228-6792 
paulette.campbell at jhuapl.edu   


RELEASE: 11-330

NASA SPACECRAFT REVEALING MORE DETAILS ABOUT PLANET MERCURY

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

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

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

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

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

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

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

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

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

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

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

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

MESSENGER 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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