By Frank D. Roylance , Sun reporter|July 04, 2008
Instruments aboard a Maryland-built spacecraft that soared past the planet Mercury in January have provided a real surprise: traces of water molecules in the hot little world's extremely thin atmosphere, scientists reported yesterday.
It's not clear where they came from yet, but astronomers suspect that the water molecules are being blasted from the planet's surface by the solar wind, along with ions of sodium, calcium and magnesium - all clues to the chemical composition of surface material.
"This water is clearly there," said Thomas H. Zurbuchen, a member of the Messenger science team from the University of Michigan, Ann Arbor.
The discovery is among the first formal findings from Messenger's initial flyby of Mercury, on Jan. 14. They're contained in 11 papers published today in the journal Science.
Although surface temperatures on the planet closest to the sun can soar to 750 degrees Fahrenheit, Zurbuchen said, some observations have suggested that water ice may persist in the cold, shaded recesses of polar craters. If the observations are right, the data are the first to confirm the presence of water on Mercury.
"It's very interesting," Zurbuchen said.
Messenger scientists said their data are also revealing a planet with a solid iron core, and an enormous outer core of molten iron. Motion in that outer core is generating a planet-wide magnetic field much like the one that protects life on Earth from deadly radiation from the sun and outer space.
But Messenger's data suggest the little planet is being raked by solar particles anyway, blowing surface material into a cometlike tail that extends far into space, away from the sun.
"Even though it appears the solar wind was relatively quiescent [during the flyby] we still see a strong signature in the tail," said William McClintock, a team member from the University of Colorado. "It's very exciting. I can't wait until orbital observations begin and we're able to monitor the tail's response ... on a daily basis."
As Mercury's core cools, and the molten iron condenses, the planet has been shrinking like a dried apple. And that has caused the titanic cliffs and faults Messenger photographed on its rocky surface. The shrinkage may be continuing today, scientists said.
Messenger has also found evidence that at least some of the bright, smooth plains visible on the planet's surface are volcanic lava flows rather than material ejected from meteor impact craters as some had theorized.
