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Up close and personal with an asteroid

The Rosetta orbiter makes its second swing past a relic of the early solar system

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On July 10 the European Space Agency’s Rosetta orbiter will whiz past the biggest asteroid ever visited by a spacecraft. Cruising past the main belt asteroid 21 Lutetia at a cool 54,000 kilometers per hour, the orbiter and its lander will make rare up-close observations of the 114-kilometer-wide rock.

Since 2004, Rosetta has traveled about 5 billion kilometers on its way to the comet Churyumov-Gerasimenko, where it is scheduled to arrive in 2014. But first, the orbiter is squeezing in visits to two asteroids in the main asteroid belt between the orbits of Mars and Jupiter. Asteroids are rocky material leftover from the early days of our solar system, and thus clues to our solar system’s past. Only eight other asteroids in the main asteroid belt have been imaged in detail among the hundreds of thousands that exist.

On September 5, 2004, Rosetta flew within 800 kilometers of the asteroid 2867 Steins and took the first close-up snapshots of this rare E-type asteroid. A high-resolution camera captured detailed images of craters peppering the surface. Other instruments on board got data on the mass, density, subsurface temperature and composition of this primordial rock.

Rosetta will get similar images and data from Lutetia a different class of asteroid. Scientists aren’t sure yet whether Lutetia is an M-class asteroid (made mostly of nickel and iron) or the common C-type. Data gathered on the flyby will help determine asteroid’s composition.

Rosetta will come within 3,169 km of 21 Lutetia at about 1:45 EDT on July 10. Instruments will have a brief two-hour window in which to capture high-resolution images of the crater-filled surface and gather other data. Rosetta will use magnetometers and gas analyzers to try to detect a magnetosphere and exosphere around the asteroid. From this, scientists should be able to determine its age.

The Hubble Space Telescope helped prepare for this weekend’s flyby by gathering information about Lutetia’s surface reflectivity and searching for satellites or dusty debris nearby. Hubble saw nothing potentially harmful to Rosetta, which boosted mission planners’ confidence in planning this weekend’s encounter. After the flyby, the results from Rosetta’s instruments will be compared with Hubble’s findings to provide a more comprehensive view of this puzzling asteroid.

The first images will be beamed back around 11:00 p.m. local time Saturday night to an expectant media crowd at the European Space Operations Centre in Darmstadt, Germany. As they wait for the images, the crowd will be treated to a garden barbecue and showing of the Germany-Uruguay World Cup match.

Further Reading

Stay in touch with the flyby as it happens by visiting the Rosetta blog. [Go to]

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