Mass Loss, Destruction and Detection of Sun-grazing and -impacting Cometary Nuclei

TL;DR

This paper develops analytic models to describe the destruction mechanisms of sun-grazing comets near the Sun, identifying regimes of sublimation, ablation, and explosion, and predicting observable signatures of these events.

Contribution

It introduces simple analytic solutions for comet mass loss processes near the Sun, providing a framework to estimate destruction regimes and observable phenomena, complementing numerical models.

Findings

Most sun-grazers are destroyed sublimatively.

Larger impactors with small perihelion are ablated or explode depending on parameters.

Nuclei are destroyed above the photosphere, producing flare-like events.

Abstract

[Abridged] Sun-grazing comets almost never re-emerge, but their sublimative destruction near the sun has only recently been observed directly, while chromospheric impacts have not yet been seen, nor impact theory developed. Employing simple analytic models to describe comet destruction near the Sun and to enable the estimation of observable signatures, we find analytic solutions for the mass as a function of distance from the Sun, for insolation sublimation, impact ablation and explosion. Sun-grazers are found to fall into three regimes based on initial mass and perihelion: sublimation-, ablation-, and explosion-dominated. Most sun-grazers are destroyed sublimatively, and our analytic results are similar to numerical models. Larger masses (>10^11g) with small perihelion (q<1.01Rsun) ablation dominates but results are sensitive to nucleus strength, Pc, and entry angle to the vertical, phi. Nuclei with initial mass >~10^10g (Pc/10^6 (dyne/cm^2) sec (phi))^3 are fully ablated before exploding, though the hot wake itself explodes. For most sun-impactors sec(phi)~1. For small perihelion the ablation regime applies to moderate masses ~10^13-16 g impactors unless Pc is very low. For higher masses, or smaller perihelia, nuclei reach higher densities where ram pressure causes catastrophic explosion. For perihelion < 1.01Rsun, initial mass > 10^11 g nuclei are destroyed by ablation or explosion (depending on phi and Pc) in the chromosphere, producing flare-like events with cometary abundance spectra. For all plausible masses and physical parameters, nuclei are destroyed above the photosphere.