The close views of the asteroid (2867) Steins, obtained with the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) on Rosetta, have provided extensive new measurements of physical properties of the asteroid main belt. Steins is proving to be a pile of rubble rather inconsistent with the diamond shape has been shaped by the YORP effect. This is the first time that this effect is seen in the asteroid main belt. The results are reported by H. Uwe Keller and his colleagues in the edition of 08 January 2010 from Science magazine.
The closest approach of the asteroid was held at 18h38 UTC at a distance of 803 kilometers. About 60% of the surface has been solved in providing an overview of all single image from which a certain number of important physical properties can be deduced.
Little was known about the asteroid (2867) Steins when he was chosen in early 2004 as a target for a fly closer during the Rosetta mission. At this time, it was classified as an E-type asteroid based on its visual spectrum and near infrared and its high albedo. Later, ground-based observations have estimated a diameter of approximately 4.6 km and identified a period rotation of about 6 hours
The new images of OSIRIS show that Steins is a body flattened at the poles, like a brilliant diamond, with dimensions of 6.67 x 5.81 x 4.47 km. Its surface is mostly covered with shallow craters with some scattered larger craters smaller. Analysis of impact craters indicates a deficit of small craters (those with a diameter of less than 0.5 km) that Keller and his colleagues attributed to a reorganization of the surface resulting from the effect Yarkovsky-O’Keefe-Radzievskii – Paddack (YORP). The effect would have caused landslides that have caused the filling of craters smaller. This is the first time that the YORP effect is seen in the asteroid main belt.
An incident photon can also be absorbed by a molecule and then the photon energy is converted into an excitation of that molecule’s electron cloud. This type of interaction is sensitive to the internal structure of the molecule, since the laws of quantum mechanics only allow for the existence of a limited number of excited states of the electron cloud of any given chemical species. Each of these excited states has a defined energy; the absorption of the photon has to bridge the energy gap between the ground state (lowest energy state) and an allowed excited state of the electron cloud. Molecules can therefore be identified by their absorption spectrum: Their wavelength-dependent capacity for absorbing photons depends on the energy spacing of the states of their electron cloud. (Astronomers use absorption lines to determine the composition of stars, for example.) Molecules which strongly absorb visible light appear colored to the human eye and are therefore called “chromophores,” i.e. “carriers of color.”