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.

J. Martin Laming¹ et al. (>10)
Astrophysical Journal Letters 851, L12 Link to Article [DOI: 10.3847/2041-8213/aa9bf0]
¹Space Science Division, Naval Research Laboratory, Code 7684, Washington, DC 20375, USA

We compare element and isotopic fractionations measured in bulk solar wind samples collected by NASA’s Genesis mission with those predicted from models incorporating both the ponderomotive force in the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are consistent with the process of solar wind fractionation. Based on bulk wind measurements, we also consider in more detail the isotopic and elemental abundances of O. We find mild support for an O abundance in the range 8.75–8.83, with a value as low as 8.69 disfavored. A stronger conclusion must await solar wind regime-specific measurements from the Genesis samples.

Quan-Zhi Ye (叶泉志)^1,2, Qicheng Zhang³, Michael S. P. Kelley⁴, and Peter G. Brown^5,6
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 , 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.