21 Lutetia: Groundbased Near-infrared Spectroscopy Prior The Rosetta Flyby
Abstract
The Roseta mission flyby of the asteroid 21 Lutetia was scheduled for July 10, 2010 and the event was accomplished with a brilliant success. 21 Lutetia has an "estimated” diameter of (98.3 ± 5.9) km and is the largest body in the main-belt ever visited until now by a space mission. The asteroid is located in the inner part of the main belt, in an orbit with low eccentricity and inclination (a=2.4348 a.u., e=0.16, i=3°.06). The large amount of colors and spectral data of Lutetia, and the polarimetric and radiometric albedoes are giving puzzling results, with non-unique solution of the asteroid taxonomy.
We present near-infrared observations in the 0.8-4 µm spectral range performed during the last opposition in 2010, a few months before the flyby of the Rosetta spacecraft. Our observations were obtained with SpeX/IRTF in remote observing mode from CODAM - Paris Observatory in March 1 and 2, April 15, and May 16, 2010. The data of March and May were obtained in remarkable weather conditions (humidity between 1 and 4% and no wind). Three spectra in Prism mode (0.8-2.5 micron) and four spectra in LXD mode (2.2-3.8 micron) will be presented together with the physical ephemeris of the asteroid. We reached a SNR of 200 in Prism mode and of about 80 in LXD mode. The North Pole geometry of the object covers almost all latitudes between +90° and -30°. These high S/N spectra show very important spectral homogeneity for Lutetia. The spectra are flat and independent of the Lutetia's rotational phase. In the 0.8-1.6 micron, 1.6-2.4 micron and 2.8-3.3 micron wavelength ranges, we do not see any absorption band at the 0.5% level. This implies a dry surface. This implies also that signature of silicates such olivine and iron-rich pyroxenes are not present on the asteroid surface.- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #42
- Pub Date:
- October 2010
- Bibcode:
- 2010DPS....42.4604B