Large, bright plains on the surface of Mercury hint of a violent, volcanic past, according to the latest scientific findings from the Mercury Messenger probe operated by Johns Hopkins Applied Physics Laboratory.
Findings supporting volcanic activity, a liquid magnetic core and a dearth of iron among surface minerals were reported in 11 articles published today in the journal Science. The findings digest 55 hours of images taken during the probe?s first flyby of Mercury in January as Messenger maneuvers for its ultimate orbit around the planet in 2011.
“Some of those images have resolved debates that have gone on for 30 years,” said Sean Solomon, principal investigator with the Carnegie Institution of Washington.
Some thought that like the moon, Mercury?s plains formed when material ejected by large impacts settled in low areas in smooth “ponds.”
Others said the plains material came from erupted lava, but the absence of volcanic vents or other volcanic features in images from that mission preserved the mystery.
Higher-resolution images returned by Messenger showed the plains were formed by material ejected by volcanoes 3 to 4 billion years ago, said James W. Head III, professor of geological sciences at Brown University.
Researchers also found the solar system?s closest planet to the sun has a dipole magnetic field generated by a liquid outer core with no significant magnetic features on the surface, according to the articles.
Large fault lines, visible as straight-line cliffs and scarps, cut across circular craters, proving the existence of a shrinking planetary crust, Solomon said.
Most planets are cooling and contracting over time, Head said. Mercury?s 2,400-kilometer radius has shed 1 to 2 kilometers in the last 30 years by conservative estimates.
Other discoveries include measurements of Mercury?s extremely thin atmosphere.
“Air particles are more likely to collide with the planet?s surface than with each other,” Head said. “Our atmosphere is billions of times more dense.”
