Hubble Space Telescope Observations of 3200 Phaethon At Closest Approach

Abstract

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 $\sim$1\degr~of the orbital plane, providing extra sensitivity to low surface brightness caused by scattering from a large-particle trail. We placed an upper limit to the apparent surface brightness of such a trail at 27.2 magnitudes arcsecond${}^{-2}$, corresponding to an in-plane optical depth $\le 3\times 10^{-9}$. No co-moving sources brighter than absolute magnitude 26.3, corresponding to circular equivalent radius $\sim$12 m (albedo 0.12 assumed), were detected. Phaethon is too hot for near-surface ice to survive. We briefly consider the thermodynamic stability of deeply-buried ice, finding that its survival would require either a very small (regolith-like) thermal diffusivity ($<10^{-8}$ m${}^2$ s${}^{-1}$), or the unexpectedly recent injection of Phaethon (timescale $\lesssim$ 10${}^6$ yr) into its present orbit, or both.

Improved the discussion of optical depth calculation and corrected an error in the previous version. 28 pages, 5 figures, Astronomical Journal, in press

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Cited by in corpus (14)

• Arecibo Radar Observations of Near-Earth Asteroid (3200) Phaethon During the 2017 Apparition
• Parker Solar Probe Observations of a Dust Trail in the Orbit of (3200) Phaethon
• Asteroid (3200) Phaethon: colors, phase curve, limits on cometary activity and fragmentation
• High Resolution Thermal Infrared Imaging of 3200 Phaethon
• Thermal Alteration of Labile Elements in Carbonaceous Chondrites
• Continued PSP/WISPR Observations of a Phaethon-related Dust Trail
• Formation, Structure, and Detectability of the Geminids Meteoroid Stream
• Thermal Alteration and Differential Sublimation Can Create Phaethons "Rock Comet" Activity and Blue Color
• Electrostatic Dust Ejection From Asteroid (3200) Phaethon With the Aid of Mobile Alkali Ions at Perihelion
• Perihelion Activity of (3200) Phaethon Is Not Dusty: Evidence from STEREO/COR2 Observations
• Thermal radiation pressure as a possible mechanism for losing small particles on asteroids
• WISE/NEOWISE Multi-Epoch Imaging of the Potentially Geminid-related Asteroids: (3200) Phaethon, 2005 UD and 1999 YC
• Asteroid-Meteoroid Complexes
• A Fireball and Potentially Hazardous Binary Near-Earth Asteroid (164121) 2003 YT${}_1$