 Mercury is shrinking - fact.
October 7, 2008 8:19 AM
By Will Dunham
WASHINGTON - A car-sized NASA spacecraft zoomed above the surface of Mercury on Monday, viewing rocky terrain never before seen up close on our solar system's sun-baked innermost planet, scientists said.
The MESSENGER probe flew as low as 195km near the equator of Mercury as part of its ongoing exploration of the planet nearest the sun, said project scientist Ralph McNutt of Johns Hopkins University Applied Physics Laboratory.
Initial images sent back to Earth showed newly discovered cliffs on Mercury's surface, with the bulk of the data to be transmitted tomorrow, McNutt said.
"This is all covering about 30 per cent of the planet that
has never been seen by a spacecraft before," McNutt said.
"As far as we can tell, everything executed just as it was
supposed to."
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.
McNutt said combining the data collected in January
with that expected from Monday's encounter should
give scientists a nice idea of the planet's topographical
features. The spacecraft snapped about 1,200 images
on its latest pass.
Data from the January fly-by showed that volcanic
activity played a key role in forging Mercury's surface
and that the planet has been shrinking more than
expected over time.
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 per
cent of its surface. MESSENGER's January encounter
covered another 20 per cent.
With the latest fly-by, at a speed of 23,000kmh, studying
an area about the same size as South America, only
about five per cent of the surface will remain unseen by
a spacecraft, McNutt said.
Mercury's surface is a mixture of plains, craters caused
by long-ago impacts with space rocks, and long, winding
cliffs like the ones seen on Monday.
MESSENGER, which stands for Mercury Surface, Space
Environment, Geochemistry and Ranging, was launched in
2004.
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 bigger than the moon.
Separately, NASA said a spacecraft due to study the
region where the outer edge of the solar system meets
interstellar space launches on October 19 from Kwajalein
Atoll in the Pacific.
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