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Nov.
3, 2009: The MESSENGER spacecraft's third flyby of
the planet Mercury has given scientists, for the first time,
an almost complete view of the planet's surface and revealed
some dramatic changes in Mercury's comet-like tail.
"The
new images remind us that Mercury continues to hold surprises,"
says Sean Solomon, principal investigator for the mission
and director of the Department of Terrestrial Magnetism at
the Carnegie Institution of Washington.
The
probe flew by Mercury on Sept. 29th, executing a critical
gravity assist maneuver designed to help MESSENGER enter Mercury-orbit
in 2011. Despite shutting down temporarily because of a power
system switchover during a solar eclipse, the spacecraft's
cameras and instruments revealed 6 percent of the planet's
surface never before seen at close range, including this picturesque
region pocked by impact craters and molded by volcanic activity:
Above:
This enhanced-color view was created with a statistical technique
that highlights subtle color variations seen in the 11 filters
of MESSENGER's wide-angle camera. The colors are often related
to the composition of underlying material material. [more]
[larger
image]
The
bright region in the upper-right corner of the image surrounds
a suspected explosive volcanic vent. The 290-km-diameter double-ring
basin near the bottom of the image has a smooth interior that
may be the result of effusive volcanism.
"This
double-ring basin, seen in detail for the first time, is remarkably
well preserved," notes Brett Denevi, a member of the probe's
imaging team and a postdoctoral researcher at Arizona State
University. "The inner floor of this basin is even younger
than the basin itself and differs in color from its surroundings.
We may have found the youngest volcanic material on Mercury."
One
of the spacecraft's instruments conducted its most extensive
observations to date of Mercury's ultrathin atmosphere or
"exosphere." Material in the exosphere comes mainly
from the surface of Mercury, knocked aloft by solar radiation,
solar wind bombardment and meteoroid vaporization: diagram.
This wispy gaseous envelope is stretched by solar radiation
pressure into a long, comet-like tail, which seems to be changing
as Mercury moves around the sun.
"A
striking illustration of what we call 'seasonal' effects in
Mercury's exosphere is that the neutral sodium tail, so prominent
in the first two flybys, is now significantly reduced in extent,"
says participating scientist Ron Vervack of the Johns Hopkins
University Applied Physics Laboratory in Laurel, Md.
Above:
These illustrations show how Mercury's comet-like tail has
decreased in size since MESSENGER's 2nd flyby in Oct. 2008.
Click
here to view the original data. [more]
[larger
image]
"This
difference is related to expected variations in solar radiation
pressure as Mercury moves in its [elliptical orbit around
the sun]," adds Vervack. "Mercury's
exosphere is one of the most dynamic in the solar system."
The
observations also show that calcium and magnesium in the exosphere
exhibit different seasonal changes than sodium--a difference
that researchers do not yet fully understand. After MESSENGER
enters Mercury orbit in 2011, it can make a continuous study
of seasonal changes in all exospheric constituents. That will
provide key information on the relative importance of the
processes that generate, sustain, and modify Mercury's atmosphere.
Approximately
98 percent of Mercury's surface now has been imaged by NASA
spacecraft. After MESSENGER goes into orbit, it will see the
polar regions, which are the only remaining unobserved areas
of the planet.
Click
here for more images and data from the 3rd flyby.
Editor: Dr.
Tony Phillips | Credit: Science@NASA
| more
information |
| MESSENGER
-- home page
The
MESSENGER project is the seventh in NASA's Discovery
Program of low-cost, scientifically focused missions.
The Johns Hopkins University Applied Physics Laboratory
of Laurel, Md., designed, built and operates the spacecraft
and manages the mission for NASA's Science Mission Directorate
in Washington. Science instruments were built by the
Applied Physics Laboratory; Goddard; the University
of Michigan in Ann Arbor; and the University of Colorado
in Boulder. GenCorp Aerojet of Sacramento, Calif., and
Composite Optics Inc. of San Diego provided the propulsion
system and composite structure. |
|
