A NASA
spacecraft has a date with Mercury next week for a flyby that will return the
first detailed views of the small planet in more than 30 years.
The
MESSENGER probe will skim just 124 miles (200 km) above Mercury's uncharted
hemisphere during its closest pass at 2:04 p.m. EST (1904 GMT) on Monday,
marking the first of ultimately three flybys to bleed off speed and enter orbit
around the planet.
"Our
spacecraft is lined up and ready to go," said Marilyn Lindstrom, NASA's
MESSENGER program scientist, in a Thursday briefing, adding that the probe has
already returned its first images of its target. "Mercury, here comes
MESSENGER."
Launched
in August 2004, MESSENGER — short for the bulky moniker MErcury Surface,
Space ENvironment, GEochemistry, and Ranging — is the first spacecraft to visit
Mercury since NASA's Mariner 10 probe swung past the planet three times between
1974 and 1975. But unlike its predecessor, MESSENGER will rendezvous with
Mercury four times, making three flybys before ultimately entering orbit in
2011 for a one-year science campaign.
The $446
million mission is aimed at probing the secrets of Mercury, ranging from its
wispy thin atmosphere to an unusually dense interior. The mission will also
generate the first maps of some 55 percent of the planet's rocky surface that
Mariner 10 missed during its three
planetary passes.
"More than
half the planet's never been seen before," said MESSENGER principal
investigator Sean Solomon, of the Carnegie Institution of Washington. "That
will change on Monday."
MESSENGER's
Mercury flyby actually begins in earnest around midday Sunday, when the probe
will turn itself away from Earth to bring its science instruments to bear on its
planetary target. The spacecraft will snap more than 1,200 photographs of Mercury
during its first rendezvous while a protective sunshade keeps its cameras and
other instruments at room temperature. The sun-facing side of the shade may
reach temperatures of 600 degrees Fahrenheit (315 degrees Celsius) or so,
researchers said.
For 14
minutes, the probe's power-generating solar panels will be in Mercury's shadow,
forcing the spacecraft to briefly rely solely on its batteries, said Eric
Finnegan, MESSENGER systems engineer. The probe will use the gravitational pull
of Mercury to slow its speed by about 5,000 miles per hour (8,046 kph) during
the flyby, he added.
MESSENGER
is expected to reestablish contact with Earth about midday on Tuesday, 22 hours
after the closest Mercury approach, and then beam back images to its eager
science team. The probe has already flown
past Earth once and Venus twice as it spiraled down the solar system on the
4.9 billion-mile (7.9 billion-kilometer) trek to Mercury.
"Now, we're just a few days away from our first glimpse of
Mercury in 33 years," said Solomon. "It is an understatement to say that the
science team is extremely excited."
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