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January
21, 2008: "Discoveries are at hand!" That's
what members of the MESSENGER science team are saying after
their spacecraft flew past Mercury on Jan. 14th at a distance
of only 124 miles. The historic flyby netted 500 megabytes
of data (now safely downloaded to Earth) and more than 1200
photos covering nearly six million square miles of previously
unseen terrain.
"We're
inundated with data—it's wonderful," says mission scientist
and planetary geologist Scott Murchie of the Johns Hopkins
Applied Physics Lab.
One
of the first images beamed back from the spacecraft revealed
a side of Mercury researchers have been waiting three decades
to see:
Above:
New terrain on Mercury revealed by MESSENGER's cameras during
the Jan. 14, 2008, flyby. Caloris Basin is circled. [more]
The
cratered expanse pictured above was mostly in darkness 30
years ago when NASA's Mariner 10 spacecraft made the first
and (until now) only flybys of Mercury. Last week, MESSENGER
caught the terrain in sunlight for the first time.
At
first glance, the photo seems to show little more than a wasteland
of craters, but researchers are excited.
"These
are fantastic images," says Murchie. For one thing, "we've
gotten our first good look at Caloris Basin," the biggest
known impact crater on Mercury and one of the biggest craters
in the entire solar system.
In
the mid-1970s, Mariner 10 caught a tantalizing glimpse of
the basin's edge, a ring of shadowed mountains thrown up long
ago by some catastrophic impact. A comet or asteroid had smashed
Mercury and gouged a crater bigger than the state of Texas.
What was inside? No one could say.
"Big
impacts are revealing," says Murchie. "They're natural
drill holes that expose the interior of the planet—which of
course we're dying to see."
MESSENGER
snapped the picture that geologists had long wanted: Caloris
in its entirety, a top-down view in broad daylight—and the
results were surprising. Many experts expected the interior
of Caloris Basin to be dark, like the dark 'seas' of hardened
lava that fill major impact basins on the Moon and give anthropomorphic
form to the "Man in the Moon." Instead, Caloris
is bright inside and pitted with regions of interesting color.
Color
is something MESSENGER excels at. "Color reveals mineralogy,"
says Murchie. "Two of the instruments onboard MESSENGER
are able to map the surface of Mercury in wavelengths ranging
from ultraviolet across the visible spectrum to near-infrared.
We're calibrating the data now and plan to release some full-color
images soon."
Right:
Typical of the images returned by MESSENGER, this horizon
shot shows the beautifully shadowed crater named Sholem Aleichem.
[more]
Another
early highlight of the flyby are ridges geologists call lobate
scarps: photo.
These are fractures in Mercury's crust formed, perhaps, as
a result of planetary shrinkage. (Think wrinkles on a raisin.)
What could cause a rigid, rocky planet to shrink? Billions
of years ago, "Mercury may have undergone a period of
contraction as its molten core cooled," suggests Murchie.
High-resolution MESSENGER photos of Mercury's scarps will
allow geologists to test this and other ideas.
Other
snapshots of note include a telephone-shaped
crater, Mercury's
Antarctic, and a
"fresh" crater with many secondary crater
chains. Browse the
gallery for more.
"We're
leaving no stone unturned," says Murchie. In all, there
are 110+ scientists, students and engineers sifting through
the harvest of photography, spectroscopy, laser radar echoes
and magnetic field measurements from the Jan. 14th flyby.
Discoveries are sure to ensue.
And
remember, he says, "this is just the first of three flybys"
in preparation for orbit insertion in 2011. The next encounters
are scheduled for Oct. 2008 and Sept. 2009. More than a third
of Mercury's surface has yet to be photographed and those
flybys will fill in many gaps. Meanwhile, researchers are
fully occupied.
Stay
tuned for updates from Science@NASA.
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Author: Dr.
Tony Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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