VIRTIS Observations during Rosetta Flyby of 2867 Steins

Details VIRTIS Observations during Rosetta Flyby of 2867 Steins VIRTIS Observations during Rosetta Flyby of 2867 Steins

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusm.p12a..03c&link_type=abstract

American Geophysical Union, Spring Meeting 2009, abstract #P12A-03

Physics

5400 Planetary Sciences: Solid Surface Planets

Scientific paper

At present, several asteroids have been remotely observed by space probes; yet they present new surprises. On 5 September 2008, the Rosetta spacecraft encountered the asteroid 2867 Steins on its way to the comet 67P/Churyumov-Gerasimenko. This was the first of two planned asteroid flybys performed by the probe, the second being the much larger 21 Lutetia in July 2010. From ground-based observations, Steins was classified as an E-type asteroid. The designation is linked with the mineral enstatite, common in aubrite meteorites. Therefore, we are in presence of a differentiated object whose study can give information on the differentiation processes that took place in its parent body. We will discuss here this hypothesis in the light of the data acquired by the VIRTIS imaging spectrometer on board Rosetta, that collected resolved observation of Steins, performing spectroscopic measurements in both the visible and near-infrared ranges. In particular, we will describe the results of the observations performed in the 2 channels of VIRTIS, VIRTIS-M and VIRTIS-H. The VIRTIS -M channel is an imaging spectrometer covering the 0.25-5 micrometers spectral range with medium spectral resolution. Each pixel of the VIRTIS-M spectrometer consists of 864 spectral bands, allowing to measure surface reflectance with a spectral resolution of about 2 nm in the VIS and 10 nm in the IR. VIRTIS-H is a point spectrometer that reaches a high spectral resolution (about 1500) in a single aperture from 2 to 5 micrometers. Despite the difficulties for an imaging spectrometer to operate during a fast (8.616 km/s) and close (800 km) flyby, VIRTIS-M was able to acquire high signal/noise hyperspectral data of different regions of Steins. The spatial resolution on the asteroid's surface is of the order of 200 m/pix. VIRTIS-H acquired several unresolved spectra. Both channels were perfectly working: using this data set we have investigated the spectral behavior of the asteroid's surface, as well as its superficial temperature. Moreover, the asteroid was observed in high resolution by VIRTIS -H. Also from the data of VIRTIS H the temperature of the asteroid was measured. The analysis of the data of both channels revealed a substantial agreement, the observed value ranging between 200 and 230 K. The analysis of spectroscopic data is in substantial agreement with an average enstatitic-achondrite composition.

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