Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Water Ice and Dust in the Innermost Coma of Comet 103P/Hartley 2   On November 4th, 2010, the Deep Impact eXtended Investigation (DIXI)
successfully encountered comet 103P/Hartley 2, when it was at a heliocentric
distance of 1.06 AU. Spatially resolved near-IR spectra of comet Hartley 2 were
acquired in the 1.05-4.83 micron wavelength range using the HRI-IR
spectrometer. We present spectral maps of the inner ~10 kilometers of the coma
collected 7 minutes and 23 minutes after closest approach. The extracted
reflectance spectra include well-defined absorption bands near 1.5, 2.0, and
3.0 micron consistent in position, bandwidth, and shape with the presence of
water ice grains. Using Hapke's radiative transfer model, we characterize the
type of mixing (areal vs. intimate), relative abundance, grain size, and
spatial distribution of water ice and refractories. Our modeling suggests that
the dust, which dominates the innermost coma of Hartley 2 and is at a
temperature of 300K, is thermally and physically decoupled from the
fine-grained water ice particles, which are on the order of 1 micron in size.
The strong correlation between the water ice, dust, and CO2 spatial
distribution supports the concept that CO2 gas drags the water ice and dust
grains from the nucleus. Once in the coma, the water ice begins subliming while
the dust is in a constant outflow. The derived water ice scale-length is
compatible with the lifetimes expected for 1-micron pure water ice grains at 1
AU, if velocities are near 0.5 m/s. Such velocities, about three order of
magnitudes lower than the expansion velocities expected for isolated 1-micron
water ice particles [Hanner, 1981; Whipple, 1951], suggest that the observed
water ice grains are likely aggregates.

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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: math
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: alg-geom
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The categories of this paper are: bayes-an
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: stat
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ph