2004 EW95: A Phyllosilicate-bearing Carbonaceous Asteroid in the Kuiper Belt

Tom Seccull1, Wesley C. Fraser1, Thomas H. Puzia2, Michael E. Brown3, and Frederik Schönebeck4
Astrophysical Journal Letters 851, L12 Link to Article [DOI: 10.3847/2041-8213/aab3dc]
1Astrophysics Research Centre, Queen’s University Belfast, Belfast BT7 1NN, UK
2Institute of Astrophysics, Pontificia Universidad Católica de Chile, Av. Vincuña Mackenna 4860, 7820436, Santiago, Chile
3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
4Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg, Germany

Models of the Solar System’s dynamical evolution predict the dispersal of primitive planetesimals from their formative regions among the gas-giant planets due to the early phases of planetary migration. Consequently, carbonaceous objects were scattered both into the outer asteroid belt and out to the Kuiper Belt. These models predict that the Kuiper Belt should contain a small fraction of objects with carbonaceous surfaces, though to date, all reported visible reflectance spectra of small Kuiper Belt Objects (KBOs) are linear and featureless. We report the unusual reflectance spectrum of a small KBO, (120216) 2004 EW95, exhibiting a large drop in its near-UV reflectance and a broad shallow optical absorption feature centered at ~700 nm, which is detected at greater than 4σsignificance. These features, confirmed through multiple epochs of spectral photometry and spectroscopy, have respectively been associated with ferric oxides and phyllosilicates. The spectrum bears striking resemblance to those of some C-type asteroids, suggesting that 2004 EW95 may share a common origin with those objects. 2004 EW95 orbits the Sun in a stable mean motion resonance with Neptune, at relatively high eccentricity and inclination, suggesting it may have been emplaced there by some past dynamical instability. These results appear consistent with the aforementioned model predictions and are the first to show a reliably confirmed detection of silicate material on a small KBO.

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