Animation of Rosetta's trajectory from 2 March 2004 to 9 September 2016 Rosetta·67P·Earth·Mars·21 Lutetia· 2867 Šteins
On 5 September 2008, the Rosetta space probe flew by Šteins at a distance of 800 km and a relatively slow speed of 8.6 km/s. Despite the short duration of this encounter (approximately 7 minutes in total), a great amount of data was obtained by the 15 scientific instruments operating on board the Rosetta spacecraft. This was the first of two planned asteroid flybys performed by the probe, the second being to the much larger 21 Lutetia in 2010. The timing of the fly-by meant that the asteroid was illuminated by the sun from the perspective of the spacecraft, making the transmitted images clear. The European Space Operations Centre streamed a press conference on Šteins later that day.
A study published in 2006 by astronomers at the European Southern Observatory showed that Šteins is an E-type asteroid with a diameter of approximately 4.6 kilometers. After the Rosetta flyby, the ESA described Šteins as a "diamond in the sky", as it has a wide body that tapers into a point. The wide section is dominated by the large Diamond crater with a diameter of 2.1 kilometers, which surprised scientists, who were at first amazed the asteroid survived such an impact, while later it turned out that the crater-to-body diameter ratio of 0.79 is in fact not abnormally large as it follows an already established trend. Besides its irregular in shape, it does not have any moons.
Diameter and albedo
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer and observations by the Spitzer Telescope, Šteins measures 5.16 and 4.92 kilometers in diameter and its surface has an albedo of 0.30 and 0.34, respectively. In 2012, the photographs of Šteins taken by Rosetta using stereophotoclinometry allowed scientists to determine that the asteroid's dimensions are 6.83 × 5.70 × 4.42 kilometers, which equates to a mean diameter in volume of 5.26 km. (Asteroid 129167 Dianelambert was later named for the scientist using this 3D-method.) The Collaborative Asteroid Lightcurve Link adopts an albedo of 0.34 and a diameter of 4.9 kilometers with an absolute magnitude of 13.36.
^ abWeissman, Paul R.; Lowry, Stephen C.; Choi, Young-Jun (August 2005). "CCD Photometry of Asteroid 2867 Steins: Flyby Target of the Rosetta Mission". American Astronomical Society. 37: 644. Bibcode:2005DPS....37.1528W.
^ abDotto, E.; Perna, D.; Fornasier, S.; Belskaya, I. N.; Barucci, M. A.; Shevchenko, V. G.; et al. (February 2009). "Photometric and spectroscopic investigation of 2867 Steins, target of the Rosetta mission. Ground-based results prior to the Rosetta fly-by". Astronomy and Astrophysics. 494 (3): L29–L32. Bibcode:2009A&A...494L..29D. doi:10.1051/0004-6361:200811340.
^Warner, Brian D. (September 2004). "Lightcurve analysis for numbered asteroids 301, 380, 2867, 8373, 25143, and 31368". The Minor Planet Bulletin. 31 (3): 67–70. Bibcode:2004MPBu...31...67W. ISSN1052-8091.