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

John Brown   Submitted: 2011-07-07 16:04

Context. Incoming sun-grazing comets almost never re-emerge, but nofinal destruction event has ever been observed, nor sunimpactordestruction theory developed.
Aims. We seek analytic models of comet nucleus destruction at the sun,to estimate impact signature dependence on incident massMo and perihelion q.Methods. We approximate evaporative mass loss rates by heatingrate/latent heat of sublimation and obtain analytic estimates forM(r) versus q and distance r for evaporation processes alone -insolation sublimation and, for the first time, impact ablation.Insolationdominates above 1.01Rsun (density n below 2.5E11/cc). Below 1.01Rsun,ablation overwhelms insolation, since n(r) rises exponentially.Nuclei with Mo(1-q/1.01Rsun)**1.5 below 1E10 g are totally ablatedbefore ram pressure matters. This shallow entry angleregime applies to the great majority of sun-grazers but any highmass/steep entry nuclei penetrate to n above 2.5E14/cc where soaringram pressure drives catastrophic explosion like large masscomet-planet impacts.
Results. Close sun-grazers fall sharply into three (Mo,q) regimes:insolation-, ablation-, and explosion-dominated. Our analytic insolationregime results are similar to previous numerical models. Nuclei of Moexceeding 1E11 g either survive insolation to r=1.01Rsunand re-emerge or, for q below 1.01Rsun, enter the atmosphericcollisional regime where behavior depends on Mo and entry angle phi.For the shallow angle impacts of most sun-grazers, all but theheaviest nuclei ablate totally before exploding, though the hot wakeitself explodes. For steep entry, all masses explode before totalablation, creating an airburst and fireball. These explosions resemblesolar flares and should be observable.
Conclusions. Analytic descriptions indicate the (Mo,q) regimes wheresublimation, ablation and explosion dominate destruction ofsun-grazer/-impactor comets. Extended insolative destruction near thesun is hard to observe. Nuclei with q below 1.01Rsun and Moabove 1E11 g are destroyed catastrophically by ablation or explosion(depending on Mo(cos phi)**3) in the chromosphere, producingfireballs with properties comparable to solar flares but with cometaryabundance spectra. Only nuclei more massive than 1E17 g canever reach the photosphere before exploding.

NOTE ADDED 7/7/11- Shortly after thispaper was resubmitted (21/6/11) to A&A, actualobservations of destruction of a sun-grazer comet today were reportedby Shryver - see www.lmsal.com/ schryver/

Authors: J.C. Brown, H.E. Potts, L.J. Porter & G. le Chat
Projects: None

Publication Status: A & A Submitted
Last Modified: 2011-07-07 16:05
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Mass Loss, Destruction and Detection of Sun-grazing & -impacting Cometary Nuclei

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