- CAPE CANAVERAL, Fla.
(Reuters) -- A satellite that heads off to Mercury, the hottest planet
in the solar system, on Monday has NASA scientists buzzing because it is
expected to journey there and find, of all things, ice.
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- The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry
and Ranging) spacecraft takes off three decades after the last time NASA
took an up-close look at Mercury, where the temperature at noon is just
a shade under 900 degrees F.
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- The $427-million mission starts with lift-off aboard
a Boeing Delta 2 rocket scheduled for 2:16 a.m. EDT on Monday from the
Cape Canaveral Air Force Station in Florida, the space agency said.
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- If ice does exist on Mercury, it manages to stay out
of the sun, inside the shadowy interior of craters at the poles of the
nearly airless planet, where the temperature may not rise above minus -300
degrees F.
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- Radio telescopes on Earth have detected the signature
of ice in those craters, scientists say, though they caution it might also
be super-frozen silica or something else.
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- Equally intriguing is Mercury's composition. The planet
is about two-thirds iron and as dense as a planet the size of Earth, although
it is much smaller, scientists say. Mercury is slightly larger than the
Earth's moon.
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- MORE EARTH-LIKE?
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- "Did Mercury start off more Earth-like, then lose
its rocky exterior?" asked Sean Solomon of the Carnegie Institute
of Washington and principal scientist for the MESSENGER mission. Both long
exposure to solar winds or some giant impact might account for that, he
said.
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- "What are the processes that contributed to the
inner planets (Mercury, Venus, Earth and Mars) turning out so differently?"
To understand that "we really have to study the most extreme of those
outcomes, and that's Mercury," Solomon said.
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- MESSENGER will be the first satellite to visit Mercury
since Mariner 10 a generation ago. It photographed about 45 percent of
the planet's surface during three fly-bys in 1974 and 1975.
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- But Mariner was traveling too quickly to enter orbit
around Mercury, where MESSENGER will spend at least a year.
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- To do that, MESSENGER will be forced onto a long, meandering
path, 15 times around the sun, flying past Earth once, Venus twice and
Mercury itself three times, using planetary gravity to slow the craft with
each pass.
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- Finally, it will enter Mercury's orbit in 2011, almost
seven years after liftoff.
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- A direct flight would take just three months, NASA said,
but it would also take more fuel for braking maneuvers, which would have
required a bigger rocket than the Delta 2 and a higher mission price tag.
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- MESSENGER bristles with seven complex sensor systems.
Beside cameras, there are spectrometers for remote chemical analysis, magnetometers
to study Mercury's strong magnetic field and a laser altimeter to map the
planet's topography.
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- Protecting the equipment from the sun is a curved, rectangular
screen that will always face the sun. Sometime in 2012 or 2013, when its
fuel is depleted, MESSENGER is likely to crash onto the planet's surface.
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