A NASA probe made its second Mercury flyby early Monday as it
closes in on the closest planet to the sun.
The MESSENGER spacecraft was due to pick up a gravitational
boost during the rendezvous today at 4:45 a.m. EDT (0845 GMT) that will help it
settle into orbit around Mercury in 2011. But scientists also directed
MESSENGER's cameras and sensors to capture new images and data from areas of
the planet that remained uncharted after its first
flyby on Jan. 14.
"Mercury has been a real anomaly in that, up until now,
we have not seen the
entire surface on one of the bodies closest to the Earth," said Sean
Solomon, MESSENGER's principal investigator at the Carnegie Institution of
Washington, during a teleconference last week.
At its closest approach, MESSENGER, short for MErcury
Surface, Space ENvironment, GEochemistry, and Ranging, was expected to swing
within 125 miles (200 km) of the planet's surface.
Mission controllers expected to lose contact with the
spacecraft at certain times while it twisted and turned for better views of
Mercury. MESSENGER also switched from solar to battery power for 17 minutes
while flying through the planetary shadow.
Scientists eagerly await the new images from
never-before-seen regions of Mercury, which add up to about 30 percent of the
planet's surface. The spacecraft was slated to snap 629 images specifically for
nine large image mosaics that will help scientists begin mapping
Mercury.
Researchers hope to begin receiving new data from MESSENGER
about 21 hours after it leaves Mercury's shadow, in the very early morning
hours of U.S. EDT on Tuesday.
MESSENGER is the first spacecraft in 33 years to encounter
Mercury up close since NASA's Mariner probe buzzed the planet three times in
1974 and 1975. The new spacecraft swung by Earth once and Venus twice since
launching in August 2004, and has now completed two of three Mercury flybys
before going into orbit around the planet.
Mission controllers saved on precious propellant by taking
advantage of the solar wind's force to alter the probe's trajectory. The flyby
solar sailing maneuvers marked the successful execution of a "3-D complex
exercise in threading the needle," Solomon said.
MESSENGER's first flyby on settled an old scientific debate
by showing how volcanoes
have shaped the planet's flat, smooth plains. It also detected Mercury's
magnetic field, which is shaped by the solar wind's bombardment into a tear
drop with the flat face toward the sun.
The second flyby today allowed the spacecraft to peer at the
opposite side of the planet.
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