Early results from Rosetta (March 2006)

Early observations of asteroid Steins were performed using Rosetta’s OSIRIS camera in March 2006. Continuous coverage of the asteroid, lasting more than 24 hours was obtained at a phase angle of 41.7 degrees – this is larger than the maximum phase angle of Steins (30 degrees) that can be seen from Earth. Several hundred images covering four rotation periods without interruption, were acquired.

Light curve of asteroid (2867) Steins from OSIRIS data, March 2006. (Küppers et al., 2007)

Analysis of the data revealed that the light curve of (2867) Steins is double peaked with an amplitude of approximately 0.23 mag. The rotation period was determined to be 6.052 ± 0.007 hours which confirmed previous measurements obtained from ground. The continuous observations over four rotation periods exclude the possibility of period ambiguities. The asymmetry of the light curve implies an irregular shaped asteroid.

Status of asteroid (2867) Steins prior to the Rosetta fly-by

Asteroid (2867) Steins was discovered in 1969 by N. Chernykh at Nauchnyj, Crimea.  It is named after Karlis Augustovick Steins, former director of the Latvian University Astronomical Observatory who was known for his work on cometary cosmogony. It is located in the main asteroid belt between Mars & Jupiter and has been classified as an E-type asteroid based on its visual and near-infrared spectrum (Barucci et al 2005) and on its high albedo of 0.45 determined by Fornasier et al (2006).