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.
An Example of a Large Crater (Tyagaraja, 97 km in Diameter) with a Floor Partially Covered by Large Numbers of Coalesced Hollows. Image courtesy of NASA.
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, Maryland, 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, Alabama.
