Volume 535, November 2011
|Number of page(s)||12|
|Section||Planets and planetary systems|
|Published online||10 November 2011|
Mass loss, destruction and detection of Sun-grazing and -impacting cometary nuclei⋆
1 School of Physics and Astronomy, University of Glasgow, G12 8QQ, UK
2 Max-Planck-Institut für Astrophysik, 85748 Garching, Germany
3 LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, 92190 Meudon, France
4 NCAR High Altitude Observatory, Boulder, CO 80303, USA
5 Astrophysics Research Group. Trinity College, Dublin (TCD), Ireland
Received: 30 August 2010
Accepted: 12 October 2011
Context. 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.
Aims. We seek simple analytic models of comet destruction processes near the sun, to enable estimation of observable signature dependence on original incident mass Mo and perihelion distance q.
Methods. Simple analytic solutions are found for M(r) versus q and distance r for insolation sublimation and, for the first time, for impact ablation and explosion.
Results. Sun-grazers are found to fall into three (Mo,q) regimes: sublimation-, ablation-, and explosion-dominated. Most sun-grazers have Mo too small (<1011 g) or q too large (>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 < 1.01R⊙,Mo > 1011 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.
Key words: Sun: flares / comets: general / Sun: general
This paper is dedicated to the memories of: Brian G. Marsden, world expert on minor bodies of the solar system and an irreplaceable friend and colleague; Gerald S. Hawkins who introduced me to the joys of this field in my (J.C.B.’s) first real (radar meteor) research experience at HSRAO/CfA in the summer of 1967.
© ESO, 2011
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