ESA’s Rosetta mission has has a long a interesting journey through the solar system on its way to its final target Comet Churyumov-Gerasimenko. Launched in 2004 the probe has completed flybys of Earth twice and Mars one and already visited an asteroid as well as taking some fantastic astro-images on the way.
Today it passes asteroid 21 Lutetia at a distance of about 3,000 km. The closest approach takes place at about 1645 BST but as it is happening at a distance of 450 million km from Earth it will take some time for the pictures to be returned and processed. It's unlikely we'll see anything on the web before ten o'clock tonight.
This image from the ESA Rosetta team shows the asteroid seen from the probe yesterday at a distance of 2 million km. More information and updates are available on the Rosetta Blog.
The asteroid itself is relatively large, about 100km in diameter and although classed as an 'M type' asteroid has some characteristics of the much older 'C type' asteroids. Hence there is a bit of a mystery for astronomers to solve from the data Rosetta returns. It is also a great opportunity to test out all the instruments before the final comet encounter in 2014.