Predicting the size and shape of an asteroid at a distance

Astronomers have used the ESO Very Large Telescope (VLT) in conjunction with other telescopes, adaptive optics technology and an advanced computer program, to accurately predict the size and shape of an asteroid 200 million km from Earth. As the asteroid, (21) Lutetia, is only 100 km across, the challenging Earth-based observations were equivalent to trying to measure the size and shape of a large baked potato at a distance of about 200 km. Each of the approximately 300 snapshots shows the asteroid as little more than a small blob, but by combining all of them the team were able to reconstruct a three-dimensional model of Lutetia.

This comparison between the model images (right) and high-resolution photographs of Lutetia taken by ESA’s Rosetta spacecraft during a fly-by in July 2010 (left) shows convincingly the accuracy of the predictions. The combination of large Earth-based telescopes, adaptive optics technology and advanced computer code is an extremely powerful way to study asteroids.