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Project Progress

Evidence for the presence of hydrated silicates was reported at the surface of two outer solar system Kuiper Belt Objects (KBOs) by Lazzarin et al 2003 (AJ 125, 1554L) although further observations by the same group did not confirm this detection (de Bergh et al 2004, A&A 416, 791). Actual evidence for the presence of hydrated minerals on these types of objects will put strong constraints on the thermal history and on the physical conditions of the outer part of the solar system, and the state and history of water in these outer regions of our planetary system. The formation of hydrated silicates implies either the presence of liquid water (in the 273 – 400K range) at some point of the objects history or the presence of a rock/ice interface at 200 – 273 K. Both situations are not expected to take place routinely in the current Kuiper Belt region, where the surface of objects should be at an equilibrium temperature in the range 10-50K.

To tackle this question, we initiated a visible spectroscopic study with the 10m telescope Keck2 + LRIS-B in Hawaii, to look for the diagnostic wide absorption band around 600nm (Fe²⁺ to Fe³⁺ transition). We observed the two ambiguous objects as well as surveyed the surface of other KBOs. In parallel, Lysa Chizmadia is conducting some pioneer laboratory studies to understand the hydration of silicates at the interface rock/ice (as described in a separate project report)

None of the objects studied showed any evidence for the presence of hydrated silicates (from the resulting visible spectra). Additional lightcurve data was taken for the two ambiguous KBOs (with UH88 telescope) to estimate what fraction of the surface was actually sampled. Final results are almost ready and close to submission.