Ice on Mercury
Mercury is as close to the sun as any planet in our solar system can go. It has to be hot there. One would expect boiling lava for example. So can water ice be present? The answer is surprisingly yes. Twenty years ago, radar observations from Earth revealed small, highly reflective areas close to Mercury's poles, suggesting the presence of ice (along with vast expanses of ancient lava). Now, NASA's MESSENGER spacecraft, which has orbited Mercury since March 2011, has confirmed that these radar-bright patches neatly coincide with deep crater floors near the poles that never receive any sunlight at all.
MESSENGER scientists on October 6 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 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 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.
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.
For further information: http://www.nasa.gov/home/hqnews/2011/sep/HQ_11-330_Messenger_Images.html or http://www.spacedaily.com/reports/MESSENGER_Team_Presents_New_Mercury_Findings_at_Planetary_Conference_999.html or http://www.europlanet-eu.org/outreach/index.php?option=com_content&task=view&id=229&Itemid=41