Asteroid Steins seen from a distance of 800 km, taken by the OSIRIS imaging system from two different perspectives. The effective diameter of the asteroid is 5 km, approximately as predicted. At the top of the asteroid (as shown in this image), a large crater, approximately 1.5-km in size, can be seen. Scientists were amazed that the asteroid survived the impact that was responsible for the crater.
Artist’s impression of Rosetta as it flies by asteroid Steins
ESA’s Rosetta spacecraft flew by asteroid (2867) Steins on 5 September 2008 at 20:58 CEST, ground received time (= spacecraft time CEST + 20 minutes), with a closest approach distance of 800 km.
Steins was Rosetta’s first nominal scientific target. The spacecraft encountered the asteroid in the course of its first incursion into the main asteroid belt located between the orbits of Mars and Jupiter, while on its way to Comet 67P/Churyumov-Gerasimenko.
The study of asteroids is extremely important because they represent samples of Solar System material at different stages of evolution – key to understanding the origin of our own planet and of our planetary neighbourhood.
Artist’s impression of Rosetta as it flies by asteroid Steins
ESA/image by C.Carreau
Asteroid Steins observed by Rosetta
Four images of Asteroid (2867) Steins taken by the OSIRIS Narrow Angle Camera. The second, third, and fourth image, from bottom to top, were taken approximately 5, 10, and 15 hours after the first image, respectively. For the whole duration of the observation Steins stayed within the circle, demonstrating the excellent tracking capability of Rosetta.
Asteroid Steins seen by Rosetta's Navigation Camera "A"
Asteroid Steins is the tiny white dot in the centre of the two concentric circles, as seen by Rosetta's Navigation Camera "A" in the morning of 4 August, when the spacecraft was approximately 24 mn kms from Steins; this was only the first in a series of steadily better images as Rosetta closed the range.
On this day, the asteroid was still fainter than the nominal detection limit of the camera. The larger surrounding white spots are stars; almost all other small white spots are artefacts from the camera's CCD sensor (known as 'pixel dark current'), which considerably degrades the quality of the image. The asteroid was found within 3 arcseconds of its predicted position.
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