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标题：Hubble Space Telescope Observations of 3200 Phaethon at Closest Approach
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作者：David Jewitt ; Max Mutchler ; Jessica Agarwal 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2018
卷号：156
期号：5
页码：1-7
DOI：10.3847/1538-3881/aae51f
语种：English
出版社：American Institute of Physics
摘要：We present Hubble Space Telescope observations of the active asteroid (and Geminid stream parent) 3200 Phaethon when at its closest approach to Earth (separation 0.07 au) in 2017 December. Images were recorded within ∼1°of the orbital plane, providing extra sensitivity to low surface brightness caused by scattering from a large-particle trail. We placed an upper limit on the apparent surface brightness of such a trail at 27.2 mag arcsecond −2 , corresponding to an in-plane optical depth 3×10 −9 . No co-moving sources brighter than absolute magnitude 26.3, corresponding to circular equivalent radius ∼12 m (albedo 0.12 assumed), were detected. Phaethon is too hot for near-surface ice to survive. We briefly consider the thermodynamic stability of deeply buried ice, finding that its survival would require either a very small (regolith-like) thermal diffusivity (<10 −8 m 2 s −1 ), or the unexpectedly recent injection of Phaethon (timescale 10 6 years) into its present orbit, or both.
关键词：comets: general;meteorites, meteors, meteoroids;minor planets, asteroids: general