The European Space Agency mission flew past the 4.6km-wide rock at a distance of about 800km, taking pictures and recording other scientific data. The information will be sent back to Earth for processing and will be released to the public on Saturday. The asteroid pass is a bonus for Rosetta. Its prime goal is to catch and orbit Comet 67P/Churyumov-Gerasimenko out near Jupiter in 2014.
Friday’s pass occurred about 360 million km from Earth, in between the orbits of Mars and Jupiter, in the asteroid belt. Closest approach to (2867) Steins – to give the rock its full designation – was timed for 1858 GMT. Rosetta was turned to give its instruments the best possible view of the target. Mission planners said the spacecraft would have flown past the rocky body at a relative speed of 8.6km/s. Both the probe and the asteroid would have been illuminated by the Sun, providing an excellent opportunity for science observations.
A radio signal was received from Rosetta at 2014 GMT, confirming a smooth fly-by. The probe was not expected to beam back its data haul until late on Friday. The mission will make another asteroid rendezvous as it works its way out to Jupiter.
The probe will visit the (21) Lutetia space rock on 10 June 2010, but from the larger distance of 3,000 km. Only a few asteroids have so far been observed up close. They have been shown to be very different in shape and size – ranging from a few km to over 100km across – and in their composition.
The rocks are often referred to as “space rubble” because they represent the leftovers that were never incorporated into planets when the Solar System formed 4.6 billion years ago. As with comets, they may contain very primitive materials that have not undergone the constant recycling experienced by, for example, Earth rocks. Rosetta data should therefore help researchers understand better how our local space environment has evolved over time. – bbc