Dead Mercury had volcanoes
2008-10-30 08:41
Washington - While it seems like a
geologically dead planet today, early in its history tiny
Mercury may have been a cauldron of volcanic activity, Nasa
scientists said on Wednesday.
Data from the US space agency's car-sized Messenger
probe's latest close encounter with the planet nearest the sun
on October 6 is helping to settle a debate dating back to the
1970s over the role volcanoes played in Mercury's history.
Messenger sent back images showing extensive and deep lava
flows on the surface, including hardened lava more than 2km deep filling a crater 100km in diameter.
The unmanned spacecraft also detected a so-called "wrinkle
ridge," a long geological feature on Mercury's surface about 600 meters high apparently caused by long-ago
contraction of the planet as it cooled, the scientists said.
Second of three encounters
That's about twice as high as similar features seen on the
surface of Mars, according to Maria Zuber, a Massachusetts
Institute of Technology scientist working on the mission.
This was the second of three scheduled encounters before
Messenger enters into orbit around Mercury in 2011. It flew
past Mercury on January 14 and will return in September 2009.
Combined with data from January's fly-by, the new
observations suggest Mercury was gripped by volcanic activity
on a planetary scale, the scientists said.
"The bottom line is volcanism was very important in the
history of Mercury," Mark Robinson of Arizona State University,
another scientist working on the mission, told reporters.
Zuber said the widespread volcanism may have occurred 3.8
billion to 4 billion years ago. Mercury and the rest of the
solar system formed about 4.5 billion years ago.
"This shows that's there's a lot more volcanism than we see
on the surface of the moon, which has always been the planetary
body we've compared Mercury to," added Nasa scientist Marilyn
Lindstrom.
95% of planet mapped
Mercury's surface is a mixture of volcanic plains, craters
caused by bygone impacts with space rocks and winding cliffs.
Messenger mapped about 30% of Mercury's surface that
had never before been seen from a spacecraft, meaning about 95% of the planet has now been mapped.
The only previous occasions Mercury was visited by a
spacecraft were in 1974 and 1975, when Nasa's Mariner 10 flew
past it three times and mapped about 45% of its surface.
Messenger's January encounter covered another 20%.
With many scientists now classifying Pluto a dwarf planet,
Mercury is considered the solar system's smallest planet, a
third the size of Earth and only a bit larger than the moon.
Messenger, which stands for Mercury Surface, Space
Environment, Geochemistry and Ranging, was launched in 2004.