1I/2017 U1 (‘Oumuamua) is Hot: Imaging, Spectroscopy, and Search of Meteor Activity

Quan-Zhi Ye (叶泉志)1,2, Qicheng Zhang3, Michael S. P. Kelley4, and Peter G. Brown5,6
Astrophysical Journal Letters 851, L5 Link to Article [DOI: 10.3847/2041-8213/aa9a34]
1Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
2Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
4Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
5Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
6Centre for Planetary Science and Exploration, The University of Western Ontario, London, ON N6A 5B8, Canada

1I/2017 U1 (‘Oumuamua), a recently discovered asteroid in a hyperbolic orbit, is likely the first macroscopic object of extrasolar origin identified in the solar system. Here, we present imaging and spectroscopic observations of ‘Oumuamua using the Palomar Hale Telescope as well as a search of meteor activity potentially linked to this object using the Canadian Meteor Orbit Radar. We find that ‘Oumuamua exhibits a moderate spectral gradient of $10 \% \pm 6 \% \,{(100\mathrm{nm})}^{-1}$, a value significantly lower than that of outer solar system bodies, indicative of a formation and/or previous residence in a warmer environment. Imaging observation and spectral line analysis show no evidence that ‘Oumuamua is presently active. Negative meteor observation is as expected, since ejection driven by sublimation of commonly known cometary species such as CO requires an extreme ejection speed of ~40 m s−1 at ~100 au in order to reach the Earth. No obvious candidate stars are proposed as the point of origin for ‘Oumuamua. Given a mean free path of ~109 ly in the solar neighborhood, ‘Oumuamua has likely spent a very long time in interstellar space before encountering the solar system.

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