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Crystalline water ice on the Kuiper belt object (50000) Quaoar


The Kuiper belt is a disk-like structure consisting of solid bodies orbiting the Sun beyond Neptune1. It is the source of the short-period comets and the likely repository of the Solar System's most primitive materials2. Surface temperatures in the belt are low ( 50 K), suggesting that ices trapped at formation should have been preserved over the age of the Solar System. Unfortunately, most Kuiper belt objects are too faint for meaningful compositional study, even with the largest available telescopes. Water ice has been reported in a handful of objects3,4,5, but most appear spectrally featureless5,6. Here we report near-infrared observations of the large Kuiper belt object (50000) Quaoar, which reveal the presence of crystalline water ice and ammonia hydrate. Crystallinity indicates that the ice has been heated to at least 110 K. Both ammonia hydrate and crystalline water ice should be destroyed by energetic particle irradiation on a timescale of about 107 yr. We conclude that Quaoar has been recently resurfaced, either by impact exposure of previously buried (shielded) ices or by cryovolcanic outgassing, or by a combination of these processes.

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Figure 1: Albedo spectrum of Quaoar showing red optical continuum and distinct absorption bands at 1.5, 1.65 and 2.0 µm.
Figure 2: Near-infrared reflection spectrum of Quaoar (black) compared with a water-ice reflection spectrum10 (red).
Figure 3: Close-up of the reflection spectrum of Quaoar centred at 2.2 µm.
Figure 4: Near-infrared spectra of Pluto, Quaoar and Charon compared.


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This paper is based on observations at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We thank K. Aoki and B. Potter for help with CISCO/Subaru and C. Dumas, Y. Fernandez and T. Owen for helpful comments. This work was supported in part by a grant to D.C.J. from NASA.

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Correspondence to David C. Jewitt.

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Jewitt, D., Luu, J. Crystalline water ice on the Kuiper belt object (50000) Quaoar. Nature 432, 731–733 (2004).

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