Rosetta’s blind date with asteroid Lutetia
18 June 2010
ESA’s Rosetta comet-chaser is heading for a blind date with asteroid Lutetia. Like many first dates, Rosetta will meet Lutetia on a Saturday night. However, no one yet knows what Lutetia looks like up-close. The chances are that Lutetia’s face will be very ancient and marked by craters, since asteroids are chunks of rock left over from the formation of the planets.
Little is known about this mysterious member of the main asteroid belt, which orbits the Sun between Mars and Jupiter. However, Lutetia is certainly the largest asteroid yet visited by a spacecraft. At first it was thought to be about 95 km across, but only slightly elliptical (egg-shaped). A more recent estimate suggests that it may be much more elongated and up to 134 km wide. Continuous changes in its brightness make it clear that Lutetia is rotating and has a rough surface.
Another mystery involves what the asteroid is made of. Most measurements indicate that it is a ‘C-type’, which contains compounds of carbon. However, some studies suggest that it may be an ‘M-type’, rich in metals.
The answers to all these questions will come when Rosetta sweeps to within 3,200 km of the space rock on 10 July. Ground controllers are carefully tweaking the spacecraft’s path so that it will be able to send back around two hours of detailed images. The spacecraft will instantly begin beaming the data back to Earth and the first pictures will be released later that evening. Rosetta will then head for another first date – this time with comet Churyumov-Gerasimenko - with their exciting encounter expected in 2014.
