[meteorite-list] MESSENGER Confirms Theories, Sees Surprises at Mercury

[Ron Baalke]

June 16, 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: 11-186

NASA SPACECRAFT CONFIRMS THEORIES, SEES SURPRISES AT MERCURY

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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