The European Space Agency's Rosetta spacecraft captured the first images of an unusually bright object in the asteroid belt between Mars and Jupiter, in a flyby that got it as close as 800 km from it. The object was asteroid Steins, Rosetta's first nominal scientific target in its 11 ½ year mission to explore the nucleus of Comet 67P/Churyumov-Gerasimenko, ESA revealed.

The images, which were taken with the help of Rosetta's OSIRIS imaging system and VIRTIS infrared spectrometer, revealed what the agency called spectacular results: “Steins looks like a diamond in the sky,” said Uwe Keller, Principal Investigator for the OSIRIS imaging system from the Max Planck Institut Fuer Sonnensystemforschung, Lindau.

The asteroid presents a series of small craters, as well as two huge ones, possibly 2 kilometers in diameter, which suggests that the asteroid is very old. In order to establish the age of the asteroid, scientists began counting the number of craters on its surface, and found 23 of them. It is believed that the larger the number of craters, the older the asteroid.

Steins is a relatively small E-type asteroid with irregular shape, and a diameter of only 4.6 kilometers. Just like other asteroids in its class, Steins orbits in the inner part of the main asteroid belt between Jupiter and Mars, and possibly originates from the mantle of larger asteroids that have bee destroyed in the early history of the Solar System.

According to Gerhard Schwehm, Mission Manager for Rosetta, “it looks like a typical asteroid, but it is really fascinating how much we can learn from just the images. This is our first science highlight; we certainly have a lot of promising science ahead of us. I'm already looking forward to encountering our next diamond in the sky, the much bigger Lutetia.”