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The 3-4 μm Spectra of Jupiter Trojan Asteroids

Brown, M. E. (2016) The 3-4 μm Spectra of Jupiter Trojan Asteroids. Astronomical Journal, 152 (6). Art. No. 159. ISSN 0004-6256. doi:10.3847/0004-6256/152/6/159.

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To date, reflectance spectra of Jupiter Trojan asteroids have revealed no distinctive absorption features. For this reason, the surface composition of these objects remains a subject of speculation. Spectra have revealed, however, that the Jupiter Trojan asteroids consist of two distinct sub-populations that differ in the optical to near-infrared colors. The origins and compositional differences between the two sub-populations remain unclear. Here, we report the results from a 2.2–3.8 μm spectral survey of a collection of 16 Jupiter Trojan asteroids, divided equally between the two sub-populations. We find clear spectral absorption features centered around 3.1 μm in the less-red population. Additional absorption consistent with that expected from organic materials might also be present. No such features are see in the red population. A strong correlation exists between the strength of the 3.1 μm absorption feature and the optical to near-infrared color of the objects. While, traditionally, absorptions such as these in dark asteroids are modeled as being due to fine-grain water frost, we find it physically implausible that the special circumstances required to create such fine-grained frost would exist on a substantial fraction of the Jupiter Trojan asteroids. We suggest, instead, that the 3.1 μm absorption on Trojans and other dark asteroids could be due to N–H stretch features. Additionally, we point out that reflectivities derived from WISE observations show a strong absorption beyond 4 μm for both populations. The continuum of 3.1 μm features and the common absorption beyond 4 μm might suggest that both sub-populations of Jupiter Trojan asteroids formed in the same general region of the early solar system.

Item Type:Article
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URLURL TypeDescription Paper
Brown, M. E.0000-0002-8255-0545
Additional Information:© 2016 The American Astronomical Society. Received 2015 October 14; revised 2016 May 20; accepted 2016 May 27; published 2016 November 11. We thank Andy Rivkin and Josh Emery for illuminating conversations about the nature of 3 μm absorptions in dark asteroids. Discussions with the Keck Institute for Space Studies "In Situ Science and Instrumentation for Primitive Bodies" study group, including Jordana Blacksberg, Bethany Ehlmann, John Eiler, Robert Hodyss, Ahmed Mahjoub, Michael Poston, and Ian Wong have been extremely valuable to the interpretation of these data. This research was supported by Grant NNX09AB49G from the NASA Planetary Astronomy Program. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The author wishes to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:minor planets, asteroids: general – planets and satellites: composition
Issue or Number:6
Record Number:CaltechAUTHORS:20161024-083653238
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Official Citation:M. E. Brown 2016 AJ 152 159
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71373
Deposited By: Tony Diaz
Deposited On:24 Oct 2016 15:49
Last Modified:11 Nov 2021 04:44

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