Thermal alteration and differential sublimation can create phaethon’s “rock comet” activity and blue color

1C.M.Lisse,2.3J.K.Steckloff
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114995]
1Space Exploration Sector, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD, USA 20723
2Planetary Science Institute, Tucson, AZ 85719, USA
3Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, TX 78712, USA
Copyright Elsevier

In 2010 Jewitt and Li published a paper examining the behavior of “comet-asteroid transition object” 3200 Phaethon, arguing it was asteroid-like in its behavior throughout most of its orbit, but that near its perihelion, at a distance of only 0.165 AU from the sun, its dayside temperatures would be hot enough to vaporize rock (>1000 K, Hanus et al., 2016). Thus it would act like a “rock comet” as gases produced from evaporating rock were released from the body, in a manner similar to the more familiar sublimation of water ice into vacuum seen for comets coming within ~3 AU of the Sun. In this Note we predict that the same thermal effects that would create “rock comet” behavior with Qgas ~ 1022 mol/s at perihelion would also help bluen the surface via preferential thermal alteration and sublimative removal of surface Fe and refractory organics, known reddening and darkening agents. These predictions are testable by surveying other objects on Phaethon-like small perihelion orbits, and by in situ measurements from the upcoming DESTINY+ mission to Phaethon by JAXA.

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