A European probe is tracking a rocky asteroid, where it will
make a pit stop next month on the way to its main comet target.
The European Space Agency's (ESA) Rosetta probe, which launched
in March 2004, is on a 10-year mission to hunt down the distant comet 67/P
Churyumov-Gerasimenko. But on the way, the spacecraft is due to fly by two
asteroids, the first of which is Steins.
This week, Rosetta began using its cameras to visually track
the asteroid, in order to measure its orbit accurately enough to steer in for a
close flyby.
"The orbit of Steins, with which Rosetta will
rendezvous on 5 September, closing to a distance of 800 km [500 miles], is only
known thanks to ground observations, but not yet with the accuracy we would
like for the close flyby," said Gerhard Schwehm, Rosetta mission manager at
the ESA's European Space Astronomy Centre near Madrid, Spain.
For the next three weeks, Rosetta is programmed to photograph
Steins twice a week. As it gets closer it should begin observing the asteroid
daily.
"As Rosetta's distance from Steins decreases, the
precision of the measurements for Steins' orbit will increase even further,
allowing us the best possible trajectory corrections later on before closest
approach, especially in early September," said Sylvain Lodiot, from the
Rosetta Flight Control Team at the European Space Operations Centre in
Darmstadt, Germany.
As the spacecraft nears Steins, it will also measure how the
asteroid's brightness varies over time, which will reveal more information
about its shape and rotation.
By studying the
asteroid, researchers hope to uncover secrets of its composition, rotation
and how it interacts with the charged particles streaming off the sun, called
the solar wind.
Rosetta previously swung
by Earth in November 2007 and March 2005, and passed Mars in February 2007.
The maneuvers gave the spacecraft gravitational boosts, as well as good
photo-ops. Rosetta plans to make a third and last swing by Earth in November
2009. The spacecraft is also slated to fly
by the asteroid Lutetia in June 2010.
The mission is the first designed to orbit and land on a
comet. When it finally arrives at 67/P Churyumov-Gerasimenko, slated for 2014,
Rosetta plans to map the comet's surface to select a touchdown site for its
lander, Philae. The vehicle is due to operate from the surface for at least a
week, sending back data and high resolution pictures of the icy comet as it
nears the sun.
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