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The atmospheric influence, size and possible asteroidal nature of the July 2009 Jupiter impactor

Orton, G. S. and Ingersoll, A. P. and Lai, S. (2011) The atmospheric influence, size and possible asteroidal nature of the July 2009 Jupiter impactor. Icarus, 211 (1). pp. 587-602. ISSN 0019-1035.

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Near-infrared and mid-infrared observations of the site of the 2009 July 19 impact of an unknown object with Jupiter were obtained within days of the event. The observations were used to assess the properties of a particulate debris field, elevated temperatures, and the extent of ammonia gas redistributed from the troposphere into Jupiter’s stratosphere. The impact strongly influenced the atmosphere in a central region, as well as having weaker effects in a separate field to its west, similar to the Comet Shoemaker-Levy 9 (SL9) impact sites in 1994. Temperatures were elevated by as much as 6 K at pressures of about 50–70 mbar in Jupiter’s lower stratosphere near the center of the impact site, but no changes above the noise level (1 K) were observed in the upper stratosphere at atmospheric pressures less than ~1 mbar. The impact transported at least ~2 × 10^(15) g of gas from the troposphere to the stratosphere, an amount less than derived for the SL9 C fragment impact. From thermal heating and mass-transport considerations, the diameter of the impactor was roughly in the range of 200–500 m, assuming a mean density of 2.5 g/cm^3. Models with temperature perturbations and ammonia redistribution alone are unable to fit the observed thermal emission; non-gray emission from particulate emission is needed. Mid-infrared spectroscopy of material delivered by the impacting body implies that, in addition to a silicate component, it contains a strong signature that is consistent with silica, distinguishing it from SL9, which contained no evidence for silica. Because no comet has a significant abundance of silica, this result is more consistent with a “rocky” or “asteroidal” origin for the impactor than an “icy” or “cometary” one. This is surprising because the only objects generally considered likely to collide with Jupiter and its satellites are Jupiter-Family Comets, whose populations appear to be orders of magnitude larger than the Jupiter-encountering asteroids. Nonetheless, our conclusion that there is good evidence for at least a major asteroidal component of the impactor composition is also consistent both with constraints on the geometry of the impactor and with results of contemporaneous Hubble Space Telescope observations. If the impact was not simply a statistical fluke, then our conclusion that the impactor contained more rocky material than was the case for the desiccated Comet SL9 implies a larger population of Jupiter-crossing asteroidal bodies than previously estimated, an asteroidal component within the Jupiter-Family Comet population, or compositional differentiation within these bodies.

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Orton, G. S.0000-0001-7871-2823
Ingersoll, A. P.0000-0002-2035-9198
Additional Information:© 2011 Elsevier Inc. Received 19 February 2010; revised 18 October 2010; accepted 19 October 2010. Available online 27 October 2010. We are grateful to the staffs of (i) the Infrared Telescope Facility, operated by the University of Hawaii under Cooperative Agreement number NCC 5-538 with the National Aeronautics and Space Administration, (ii) the Gemini North and Gemini South Observatories, operated by the Associated of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership, and (iii) the ESO Very Large Telescope (Paranal Observatories) without whom this work could not have taken place. The individual relevant program identifications for each observatory were cited in Section 2. We are particularly gratefully for their resourcefulness of the Gemini Telescope and Very Large Telescope personnel in responding to our requests for rapid access to telescope time. The research described in this paper that was performed by GSO, PAY-F, KHB, BMF, PC, and TM was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. LNF was supported by partially by a Glasstone Research Fellowship at the University of Oxford, and by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by Oak Ridge Associated Universities through a contract with NASA. During the course of this research N.R. and G.V. were NASA Undergraduate Research Program (USRP) fellows; Z.G., E.O. and S.L. were Caltech Summer Undergraduate Research Fellows. We thank many for helpful discussions, particularly E. Asphaug, D. Blaney, B. Bézard, M. Boslough, D. Crawford, L. Dones, A. J. Friedson, J. Goguen, J. Harrington, W. McKinnon, D. Korycansky, H. Levison, C. Palotai, J. Spencer, R.A. West and K. Zahnle.
Funding AgencyGrant Number
University of Oxford Glasstone Research FellowshipUNSPECIFIED
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:Jupiter; Impact processes; Infrared observations; Comets; Asteroid
Record Number:CaltechAUTHORS:20110302-114034979
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Official Citation:G.S. Orton, L.N. Fletcher, C.M. Lisse, P.W. Chodas, A. Cheng, P.A. Yanamandra-Fisher, K.H. Baines, B.M. Fisher, A. Wesley, S. Perez-Hoyos, I. de Pater, H.B. Hammel, M.L. Edwards, A.P. Ingersoll, O. Mousis, F. Marchis, W. Golisch, A. Sanchez-Lavega, A.A. Simon-Miller, R. Hueso, T.W. Momary, Z. Greene, N. Reshetnikov, E. Otto, G. Villar, S. Lai, M.H. Wong, The atmospheric influence, size and possible asteroidal nature of the July 2009 Jupiter impactor, Icarus, Volume 211, Issue 1, January 2011, Pages 587-602, ISSN 0019-1035, DOI: 10.1016/j.icarus.2010.10.010. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22613
Deposited By: Jason Perez
Deposited On:03 Mar 2011 03:39
Last Modified:20 Aug 2017 00:58

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