Thermal Alteration and Differential Sublimation Can Create Phaethons "Rock Comet" Activity and Blue Color

TL;DR

This paper predicts that thermal alteration and sublimation near perihelion can cause Phaethon to exhibit 'rock comet' activity and develop a blue surface color, which can be tested through spectral observations and upcoming space missions.

Contribution

It introduces the idea that thermal effects can cause both activity and surface color changes in Phaethon-like objects, linking sublimation to spectral bluing.

Findings

Thermal alteration can produce gas release similar to sublimation.

Preferential removal of Fe and organics can blue the surface.

Predictions are testable via spectral observations and space missions.

Abstract

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 ~ 10$^{22}$ mol/sec at perihelion would also help greatly bluen Phaethon's surface via preferential thermal alteration and sublimative removal of surface Fe and refractory organics, known reddening and darkening agents. These predictions are testable by searching for signs of spectral bluening of the surfaces of other objects in Phaethon-like small perihelion orbits, and by in situ measurements of Phaethons surface and coma composition near perihelion with the upcoming DESTINY+ mission to Phaethon by JAXA.