Hyperactivity and Dust Composition of Comet 103P/Hartley 2 during the EPOXI Encounter

David E. Harker, Charles E. Woodward, Michael S.P. Kelley, Diane H. Wooden

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Abstract

Short-period comet 103P/Hartley 2 (103P) was the flyby target of the Deep Impact eXtended Investigation on 2010 November 4 UT. This comet has a small hyperactive nucleus, i.e., it has a high water production rate for its surface area. The underlying cause of the hyperactivity is unknown; the relative abundances of volatiles in the coma of 103P are not unusual. However, the dust properties of this comet have not been fully explored. We present four epochs of mid-infrared spectra and images of comet 103P observed from Gemini-South +T-ReCS on 2010 November 5, 7, 21 and December 13 UT, near and after the spacecraft encounter. Comet 103P exhibited a weak 10 μm emission feature ≃1.14 ± 0.01 above the underlying local 10 μm continuum. Thermal dust grain modeling of the spectra shows the grain composition (mineralogy) was dominated by amorphous carbon and amorphous pyroxene with evidence for Mg-rich crystalline olivine. The grain size has a peak grain radius range of a peak ∼ 0.5-0.9 μm. On average, the crystalline silicate mass fraction is ≃0.24, fairly typical of other short-period comets. In contrast, the silicate-to-carbon ratio of ≃0.48-0.64 is lower compared to other short-period comets, which indicates that the flux measured in the 10 μm region of 103P was dominated by amorphous carbon grains. We conclude that the hyperactivity in comet 103P is not revealing dust properties similar to the small grains seen with the Deep Impact experiment on comet 9P/Tempel 1 or from comet C/1995 O1 (Hale-Bopp).

Original languageEnglish (US)
Article number199
JournalAstronomical Journal
Volume155
Issue number5
DOIs
StatePublished - May 2018

Bibliographical note

Funding Information:
Data discussed in this manuscript are based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). D.E.H. and C.E.W. acknowledge support for this work from the National Science Foundation grant AST-0706980. D.E.H., C.E.W., and D.H.W. also acknowledge partial support for this work from NASA Planetary Astronomy Grant RTOP 344-32-21-04. D.E.H. and M.S.K. acknowledge support from NASA Planetary Astronomy Grants NNX13AH67G, NNX09AF10G. D.E.H., C.E.W., D.H.W., and M.S.K. acknowledge partial support for this work from NASA Emerging Worlds Grant NNX16AD33G. The authors also thank the Gemini Observatory staff for their support in conducting these observations as well as an anonymous referee whose comments improved the manuscript.

Funding Information:
Data discussed in this manuscript are based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CON-ICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). D.E.H. and C.E.W. acknowledge support for this work from the National Science Foundation grant AST-0706980. D.E.H., C.E.W., and D.H.W. also acknowledge partial support for this work from NASA Planetary Astronomy Grant RTOP 344-32-21-04. D.E.H. and M.S.K. acknowledge support from NASA Planetary Astronomy Grants NNX13AH67G, NNX09AF10G. D.E.H., C.E.W., D.H.W., and M.S.K. acknowledge partial support for this work from NASA Emerging Worlds Grant NNX16AD33G. The authors also thank the Gemini Observatory staff for their support in conducting these observations as well as an anonymous referee whose comments improved the manuscript. Software: Astropy (Astropy Collaboration et al. 2013). Facility: Gemini:South (TReCS).

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.

Keywords

  • comets: general
  • comets: individual (103P/Hartley 2)

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