This
story was updated Sept. 29 at 7:20 p.m. EDT.
A NASA
spacecraft zoomed by Mercury Tuesday to snap pictures of the planet's uncharted
regions and fine-tune its path through the solar system, one that will
ultimately place the probe in orbit around the small, rocky world.
The
MESSENGER probe skimmed just 142 miles (228 km) above Mercury at its closest
approach as it whipped around the planet during the flyby, the last of three
designed to guide the spacecraft into orbit around the planet in 2011. The spacecraft
was expected to snap about 1,559 new
photographs of Mercury, some of regions never before observed up close.
"Radio signals received after the spacecraft
emerged from behind the planet indicate that the spacecraft is operating
nominally," said flight controllers at MESSENGER's
mission operations center at the Johns Hopkins Applied Physics Laboratory
(JHUAPL) in Laurel, Md., in a statement. "Its instruments are now collecting
images and other scientific measurements from the planet as it departs
Mercury."
The first
new images from the flyby are expected to be released on Wednesday.
MESSENGER
made its closest approach to Mercury at about 5:55 p.m. EDT (2155 GMT) when it
sped by at about 12,000 mph (19,312 kph). The probe
then flew behind Mercury, passing out of communications with Earth for about an
hour before restoring contact.
Mercury's
gravity was expected to slow MESSENGER by about 6,000 mph (9,656 kph) during the flyby and place it on track to enter orbit
in March 2011. MESSENGER snapped a photo
of the planet Sunday that revealed it as a half-lit, desolate-looking world
as seen from a distance of about 418,000 miles (672,000 km) away.
The $446
million spacecraft flew by Mercury twice in 2008 to map the planet in
unprecedented detail while using the rocky world's gravitational pull to refine
its flight path through space.
"A
planetary flyby is really like Christmas morning for scientists," said
MESSENGER principal investigator Sean Solomon of the Carnegie Institution of
Washington before the rendezvous. "We expect to be surprised and we expect to be delighted."
In all,
MESSENGER has photographed about 90 percent of Mercury's
surface and was expected to cover another 5 percent of unmapped terrain when it flew
by today. The spacecraft is the first probe to visit Mercury since NASA's
Mariner 10 mission in the mid-1970s.
Unlike MESSENGER's first two flybys - which revealed the first
close-up views of Mercury in decades - Tuesday's rendezvous was aimed at
observing specific points on
the planet's surface. The probe was commanded to target its camera eyes at interesting
craters, measure Mercury's magnetosphere and tenuous atmosphere, as well as
study the planet's odd, comet-like tail of trace gases.
"This is
the last look at Mercury's equatorial region, and it's the last time we fly
through the tail," Solomon said.
When
MESSENGER arrives in its final orbit around Mercury, it will begin a
long-awaited observation phase that will complete its new maps of the planet.
NASA launched MESSENGER - short for MErcury Surface,
Space ENvironment, GEochemistry,
and Ranging - in 2004. The probe swung
past Earth once and Venus twice before beginning its three Mercury flybys.
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