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Detection of ice and organics on an asteroidal surface


Recent observations, including the discovery1 in typical asteroidal orbits of objects with cometary characteristics (main-belt comets, or MBCs), have blurred the line between comets and asteroids, although so far neither ice nor organic material has been detected on the surface of an asteroid or directly proven to be an asteroidal constituent. Here we report the spectroscopic detection of water ice and organic material on the asteroid 24 Themis, a detection that has been independently confirmed2. 24 Themis belongs to the same dynamical family as three of the five known MBCs, and the presence of ice on 24 Themis is strong evidence that it also is present in the MBCs. We conclude that water ice is more common on asteroids than was previously thought and may be widespread in asteroidal interiors at much smaller heliocentric distances than was previously expected.

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Figure 1: The reflectance spectra of 24 Themis are well fitted by a mixture of ice-coated pyroxene grains and amorphous carbon.
Figure 2: Organic material is present on the surface of 24 Themis.


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This work was supported by the NASA Planetary Astronomy programme. A.S.R. is a visiting astronomer at the IRTF, which is operated by the University of Hawaii under cooperative agreement no. NNX-08AE38A with NASA, Science Mission Directorate, Planetary Astronomy programme. All the observations used in this publication were obtained at the IRTF. We would like to thank the telescope operators of the IRTF for their efforts.

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A.S.R. performed all of the telescopic observations and reduced all of the data, including the thermal flux removal. J.P.E. performed the spectral modelling of the ice and organics and performed spectral library searches. The authors contributed equally to interpretation and analysis.

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Correspondence to Andrew S. Rivkin.

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The authors declare no competing financial interests.

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Supplementary Information

This file contains Supplementary Information and Data comprising: Consideration of alternate explanations for 3.1-µm absorption, Supplementary References, Supplementary Table S1 and Supplementary Figures S1-S4 with legends. (PDF 2547 kb)

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Rivkin, A., Emery, J. Detection of ice and organics on an asteroidal surface. Nature 464, 1322–1323 (2010).

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