By Irene Klotz
CAPE CANAVERAL, Florida (Reuters) - Mercury's origins may be very different from its sister planets, including Earth, based on early findings that show surprisingly rich deposits of sulfur on the ground, scientists said on Thursday.
Early findings from the first spacecraft to orbit Mercury is forcing scientists to rethink how the planet closest to the sun formed and what has happened to it over the past 4 billion years.
NASA's Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft -- nicknamed Messenger -- is three months into a planned year-long mission. It has also uncovered evidence of a lopsided magnetic field and regular bursts of electrons jetting through the magnetosphere.
"It's almost a new planet because we've never had this kind of observatory before," said lead researcher Sean Solomon of the Carnegie Institution of Washington, D.C.
Volcanoes appear to have played a rather large role in shaping Mercury, providing fresh material to fill its cratered face, but also possibly providing an unexpected supply of sulfur to the surface, a finding that suggests Mercury may have had different building blocks than Venus, Earth and Mars.
Scientists expected that Mercury, which is believed to have formed in the hottest, densest part of the original solar nebula, wouldn't have had the right temperatures to hang on to lighter-weight materials like sulfur.
"Elements like that are usually lost in space," Solomon said. "The fact that we see sulfur from the surface points strongly that we had sulfur gases coming out.
"All of our simple ideas ... a hot planet, easily depleted of volatiles ... are not turning out to be the simple story we thought," Solomon added.
New images from Messenger reveal a massive plain of ancient lava flow, the largest of which spans 400 million square kilometers, about half the size of the continental United States.
Another surprise was the planet's lopsided magnetic field, which is stronger in the north than the south. Scientists can't yet account for the asymmetry, but one theory is that the planet's magnetic field is in the processing of flipping.
Mercury is the only terrestrial body besides Earth that has a magnetic field and one of the prime goals of the Messenger mission is to figure out how Mercury, which sports a massive iron core, was assembled. Scientists believe Mercury's core, like Earth's, is responsible for generating its magnetic field
Messenger also has been monitoring regular outbursts of electrons in Mercury's magnetosphere. Hints of the phenomenon were first detected by NASA's Mariner 10 probe, which flew past Mercury in 1974.
"We're seeing these seeing these very dynamic phenomena in the magnetosphere. It's very surprising and energetic," Solomon said.
Still to come: measurements to reveal if Mercury hides ice insides its permanently shadowed craters.
(Editing by Cynthia Osterman)