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Spitzer Observations of Interstellar Object 1I/‘Oumuamua

Trilling, David E. and Mommert, Michael and Hora, Joseph L. and Farnocchia, Davide and Chodas, Paul and Giorgini, Jon and Smith, Howard A. and Carey, Sean and Lisse, Carey M. and Werner, Michael and McNeill, Andrew and Chesley, Steven R. and Emery, Joshua P. and Fazio, Giovanni and Fernandez, Yanga R. and Harris, Alan and Marengo, Massimo and Mueller, Michael and Roegge, Alissa and Smith, Nathan and Weaver, H. A. and Meech, Karen and Micheli, Marco (2018) Spitzer Observations of Interstellar Object 1I/‘Oumuamua. Astronomical Journal, 156 (6). Art. No. 261. ISSN 1538-3881. doi:10.3847/1538-3881/aae88f.

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1I/'Oumuamua is the first confirmed interstellar body in our solar system. Here we report on observations of 'Oumuamua made with the Spitzer Space Telescope on 2017 November 21–22 (UT). We integrated for 30.2 hr at 4.5 μm (IRAC channel 2). We did not detect the object and place an upper limit on the flux of 0.3 μJy (3σ). This implies an effective spherical diameter less than [98, 140, 440] m and albedo greater than [0.2, 0.1, 0.01] under the assumption of low, middle, or high thermal beaming parameter η, respectively. With an aspect ratio for 'Oumuamua of 6:1, these results correspond to dimensions of [240:40, 341:57, 1080:180] m, respectively. We place upper limits on the amount of dust, CO, and CO2 coming from this object that are lower than previous results; we are unable to constrain the production of other gas species. Both our size and outgassing limits are important because 'Oumuamua's trajectory shows non-gravitational accelerations that are sensitive to size and mass and presumably caused by gas emission. We suggest that 'Oumuamua may have experienced low-level post-perihelion volatile emission that produced a fresh, bright, icy mantle. This model is consistent with the expected η value and implied high-albedo value for this solution, but, given our strict limits on CO and CO_2, requires another gas species—probably H_2O—to explain the observed non-gravitational acceleration. Our results extend the mystery of 'Oumuamua's origin and evolution.

Item Type:Article
Related URLs:
URLURL TypeDescription
Trilling, David E.0000-0003-4580-3790
Mommert, Michael0000-0002-8132-778X
Hora, Joseph L.0000-0002-5599-4650
Farnocchia, Davide0000-0003-0774-884X
Carey, Sean0000-0002-0221-6871
Lisse, Carey M.0000-0002-9548-1526
Chesley, Steven R.0000-0003-3240-6497
Fazio, Giovanni0000-0002-0670-0708
Fernandez, Yanga R.0000-0003-1156-9721
Harris, Alan0000-0001-7431-2013
Marengo, Massimo0000-0001-9910-9230
Weaver, H. A.0000-0003-0951-7762
Meech, Karen0000-0002-2058-5670
Micheli, Marco0000-0001-7895-8209
Additional Information:© 2018. The American Astronomical Society. Received 2018 July 13; revised 2018 October 4; accepted 2018 October 11; published 2018 November 14. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. We thank the SSC Director for approving these DDT observations and the SSC staff for rapidly implementing these observations with their usual technical excellence. Part of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. K.M. acknowledges support from NSF awards AST1413736 and AST1617015. Facility: Spitzer(IRAC). - Software: MOPEX (Makovoz et al. 2006), IRACproc (Schuster et al. 2006).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:comets: individual (1I&'Oumuamua) ; minor planets, asteroids: individual (1I&'Oumuamua) ; planetary systems
Issue or Number:6
Record Number:CaltechAUTHORS:20181115-105031850
Persistent URL:
Official Citation:David E. Trilling et al 2018 AJ 156 261
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90916
Deposited By: George Porter
Deposited On:15 Nov 2018 19:28
Last Modified:16 Nov 2021 03:36

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