Short-term variability on the surface of (1) Ceres. A changing amount of water ice?
Authors:
D. Perna, Z. Kanuchova, S. Ieva, S. Fornasier, M. A. Barucci, C. Lantz, E. Dotto, G. Strazzulla
Image & caption:
Please click on image thumbnail to get more info:
Image caption::
Up: Ceres’ 3-μm spectra taken in 1987 (Jones et al. 1990), 2004
(Vernazza et al. 2005), 2005 (Rivkin et al. 2006). Down: the 2004/2005
spectral ratio and the spectrum of crystalline (150 K) water ice.
Description:
The dwarf planet (1) Ceres – target of the NASA Dawn mission – is the largest body in the asteroid main belt. Although several observations of this body have been performed so far, the presence of surface water ice is still questioned. We acquired new visible and near-infrared spectra at the Telescopio Nazionale Galileo (La Palma, Spain), and reanalyzed
literature spectra in the 3-μm region. We obtained the rotationally resolved spectroscopic observations of Ceres at visible wavelengths. Visible spectra taken one month apart at almost the same planetocentric coordinates show a significant slope variation (up to 3%/103 Å). A faint absorption centered at 0.67 μm, possibly due to aqueous alteration, is detected in a subset of our spectra. The various explanations in the literature
for the 3.06-μm feature can be interpreted as due to a variable amount of surface water ice at different epochs. The remarkable short-term temporal variability of the visible spectral slope and the changing shape of the 3.06-μm band can be hints of different amounts of water ice exposed on the surface of Ceres. This would agree with the recent detection by the Herschel Space Observatory of localized and transient sources of water vapor over this dwarf planet.
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