^1,2Jaramillo, E.A.,³Royle, S.H.,^4,5Claire, M.W.,^1,3Kounaves, S.P.,³Sephton, M.A.
Geophysical Research Letters 46, 3090-3098 Link to Article [DOI: 10.1029/2018GL081335]
¹Department of Chemistry, Tufts University, Medford, MA, United States
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
³Department of Earth Science and Engineering, Imperial College London, London, United Kingdom
⁴School of Earth and Environmental Sciences and Centre for Exoplanet Science, University of St. Andrews, Saint Andrews, United Kingdom
⁵Blue Marble Space Institute of Science, Seattle, WA, United States

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^1,2,3Wang, Y.,^2,3Hsu, W.,⁴Guan, Y.
Scientific Reports 9, 5727 Link to Article [DOI: 10.1038/s41598-019-42224-8]
¹Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210034, China
²The State Key Laboratory of Lunar and Planetary Science/Space Science Institute, Macau University of Science and Technology, Taipa, China
³CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Nanjing, 210034, China
⁴Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, United States

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¹Duczmal-Czernikiewicz, A.,¹Muszynski, A.,²Runka, T.,³Golebiewska, B.,¹Michalska, D.,
⁴Karwowski, L.
Przeglad Geologiczny 67, 156-158 Link to Article [DOI: 10.7306/2019.6]
¹Instytut Geologii, Uniwersytet Im. Adama Mickiewicza W Poznaniu, ul.Bogumila Krygowskiego 12, Poznan, 61-680, Poland
²Instytut Badan Matcrialowych I Inzynierii Kwantowcj, Politechnika Poznanska, ul. Piotrowo 2, Poznan, 61-138, Poland
³AGH Akademia Gorniczo-Hutnicza, Katedra Mineralogii, Geochemii Petrografii i Geochemii, al. Mickiewicza 30, Krakow, 30-059, Poland
⁴Uniwersytet and Slaski, Katedra Geochemii, Mineralogii i Petrografii, ul. Bqdzinska 60, Sosnowiec, 41-205, Poland

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^1,2,3Tobase, T.,¹Yoshiasa, A.,¹Komatsu, T.,¹Maekawa, T.,¹Hongu, H.,⁴Okube, M.,⁴Arima, H.,⁴Sugiyama, K.
Physics and Chemistry of Minerals (in Press) Link to Article [DOI: 10.1007/s00269-019-01030-4]
¹Graduate School of Science and Technology, Kumamoto University, Kumamoto, 860-8555, Japan
²Université de Lorraine, CRM2, UMR 7036, Vandoeuvre-les-Nancy, 54506, France
³CNRS, CRM2, UMR 7036, Vandoeuvre-les-Nancy, 54506, France
⁴Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan

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Quanzhi Ye (叶泉志)^1,2 et al. (>10)
Astrophysical Journal Letters 874, L16 Link to Article [DOI: 10.3847/2041-8213/ab0f3c]
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

Main-belt asteroid (6478) Gault unexpectedly sprouted two tails in late 2018 and early 2019, identifying it as a new active asteroid. Here we present observations obtained by the 1.2 m Zwicky Transient Facility survey telescope that provide detailed time-series coverage of the onset and evolution of Gault’s activity. Gault exhibited two brightening events, with the first one starting on 2018 October 18 ± 5 days and a second one starting on 2018 December 24 ± 1 days. The amounts of mass released are 2 × 10⁷ kg and 1 × 10⁶ kg, respectively. Based on photometric measurements, each event persisted for about a month. Gault’s color has not changed appreciably over time, with a pre-outburst color of g _PS1 − r _PS1 = 0.50 ± 0.04 and g _PS1 − r _PS1 = 0.46 ± 0.04 during the two outbursts. Simulations of dust dynamics shows that the ejecta consists of dust grains of up to 10 μm in size that are ejected at low velocities below regardless of particle sizes. This is consistent with non-sublimation-driven ejection events. The size distribution of the dust exhibits a broken power law, with particles at 10–20 μm following a power law of −2.5 to −3.0, while larger particles follow a steeper slope of −4.0. The derived properties can be explained by either rotational excitation of the nucleus or a merger of a near-contact binary, with the latter scenario to be statistically more likely.

Jan T. Kleyna¹ et al. (>10)
Astrophysical Journal Letters 874, L20 Link to Article [DOI: 10.3847/2041-8213/ab0f40]
¹Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA

On 2019 January 5 a streamer associated with the 4–10 km main belt asteroid (6478) Gault was detected by the ATLAS sky survey, a rare discovery of activity around a main belt asteroid. Archival data from ATLAS and Pan-STARRS1 show the trail in early 2018 December, but not between 2010 and 2018 January. The feature has significantly changed over one month, perfectly matching predictions of pure dust dynamical evolution and changes in the observing geometry for a short release of dust around 2018 October 28. Follow-up observations with the Hubble Space Telescope(HST) show a second narrow trail corresponding to a brief release of dust on 2018 December 30. Both releases occurred with negligible velocity. We find the dust grains to be fairly large, with power-law size distributions in the 10⁻⁵−10⁻³ m range and power-law indices of ~−1.5. Three runs of ground-based data find a signature of ~2 hr rotation, close to the rotational limit, suggesting that the activity is the result of landslides or reconfigurations after Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) spin-up.