Mercury’s composition makes it unique among the solar system’s rocky planets, new images and data from NASA’s MESSENGER spacecraft reveal. The spacecraft’s first three months in Mercury orbit also show that some craters on the sunbaked innermost planet are chilly enough to hold frozen water. Researchers announced these and other findings at a June 16 press briefing.
“Mercury is turning out to be unlike any place we’ve seen before,” said lead scientist Sean Solomon of the Carnegie Institution for Science in Washington, D.C.
The craft’s sharp images of the northern plains suggest that massive volcanic eruptions sculpted the region some 3.7 billion years ago, burying craters under several kilometers of lava.
By combining MESSENGER’s measurements of the depths of north polar craters with other data, scientists have confirmed that some of the craters’ floors never receive sunlight. These chilly regions happen to coincide with highly reflective zones, first observed by Earth-based radar 20 years ago, that have been interpreted as deposits of water ice.
MESSENGER, which will record data through next March, has also detected surprisingly high abundances of sulfur and potassium on Mercury’s surface. Both elements evaporate easily and were thought to have escaped Mercury during its hot formation or soon thereafter.
“This is changing our view of the origin of Mercury,” said Larry Nittler of the Carnegie Institution.