Mass loss, destruction and detection of sun-grazing and -impacting cometary nuclei

Results. Sun-grazers are found to fall into three (Mo,q) regimes: sublimation-, ablation-, and explosion-dominated. Most sun-grazers have Mo too small ( 1.01R⊙) to reach atmospheric densities (n > 2.5 × 10¹¹/cm³) where ablation exceeds sublimation.

Our analytic results for sublimation are similar to numerical models. For q 10 ¹¹ g, ablation initially dominates but results are sensitive to nucleus strength Pc = 10⁶P₆ dyne/cm² and entry angle φ to the vertical. Nuclei with Mo ≼ 10¹⁰(P6secφ)3 g are fully ablated before exploding, though the hot wake itself explodes.

For most sun-impactors secφ ≫ 1 (since q ~ r∗), so for q very close to r∗ the ablation regime applies to moderate g impactors unless P₆ ≼ 0.1. For higher masses, or smaller q, nuclei reach densities n > 2.5 × 10¹⁴P₆/cm³ where ram pressure causes catastrophic explosion. Conclusions.

Analytic descriptions define (Mo,q) regimes where sublimation, ablation and explosion dominate sun-grazer/-impactor destruction. For q ≺ 1.01R⊙,Mo ≽ 10¹¹ g nuclei are destroyed by ablation or explosion (depending on Mocos3φ/Pc) in the chromosphere, producing flare-like events with cometary abundance spectra. For all plausible Mo,q and physical parameters, nuclei are destroyed above the photosphere.