Astronomy: Rosetta exposes water ice on
the surface of comet 67P
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Embargo
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London: Wednesday 13 January 2016 18:00 (GMT)
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New York: Wednesday 13 January 2016 13:00 (EST)
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Tokyo: Thursday 14 January 2016 03:00 (JST)
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Sydney: Thursday 14 January 2016 05:00 (AEDT)
The Rosetta spacecraft has identified exposed water ice on the nucleus of comet
67P/Churyumov–Gerasimenko, reports a study published online in Nature this week. Previous
research has confirmed the presence of water vapour in the nebulous cloud (coma) of comet
67P, and water is known to be the major constituent of cometary nuclei. However, large regions
of water ice have so far been conspicuously absent from surface observations of cometary
nuclei.
Gianrico Filacchione and colleagues used measurements taken by the VIRTIS-M instrument
onboard the Rosetta spacecraft to identify water ice at infrared wavelengths in a dusty region
called Imhotep, located on the nucleus of comet 67P. The authors make quantitative estimates of
water-ice abundance and grain size in this region, thereby revealing the presence of millimetresized pure water-ice grains — larger than those in all previous observations — and 50micrometre-sized grains, mixed with dark material.
Although vapour condensation is usually the mechanism behind the formation of the smaller,
micrometre-sized grains, the authors propose that the larger, millimetre-sized grains may have
arisen from occasional exposure of, and subsequent vapour diffusion in, ice-rich layers within the
comet, or the coalescing of smaller ice grains. These processes are consistent with the presence
of a layered structure in the nucleus of comet 67P, in which an outer dehydrated crust is
superimposed on water-ice-enriched layers.
Article and author details
1. Exposed water ice on the nucleus of comet 67P/ChuryumovGerasimenko
Corresponding Author
Gianrico Filacchione
INAF-IAPS, Rome, Italy
Email: gianrico.filacchione@iaps.inaf.it, Tel: +39 0645488454
DOI
10.1038/nature16190
Online paper*
http://nature.com/articles/doi:10.1038/nature16190
* Please link to the article in online versions of your report (the URL will go live after the embargo ends).
Geographical listings of authors
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France
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, Germany
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, Italy
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, Netherlands
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, Poland
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, Taiwan
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, United Kingdom
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& United States