Book ChapterDOI
The cometary impactor flux at the Earth
Paul R. Weissman
- Vol. 247, pp 171-180
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TLDR
For the Earth-crossing Halley-type comets, the mean impact probability for long-period comets is 2.4× 10−9 per comet per perihelion passage, with a most probable encounter velocity of 53.5 km sec−1 as discussed by the authors.Abstract:
Comets account for a small but very significant fraction of impactors on the Earth. Although the total number of Earth-crossing comets is modest as compared with asteroids, the more eccentric and inclined orbits of the comets result in much higher encounter velocities with the planet. Additionally, some Earth-crossing comets are significantly larger than any current near-Earth asteroids (NEAs); comets 1P/Halley and C/1995 O1 Hale-Bopp are good examples of this. Thus, the most energetic impacts on the Earth likely result from comets and not NEAs. The mean impact probability for long-period comets is 2.4× 10−9 per comet per perihelion passage, assuming the perihelion distribution of Everhart (1967), with a most probable encounter velocity of 53.5 km sec−1. There are 21 known Earth-crossing Jupiter-family comets with a mean impact probability of 1.6× 10−9 per comet per year and a most probable encounter velocity of 17.0 km sec−1. For the 16 known Earth-crossing Halley-type comets the mean impact probability is 1.2× 10−10 per year with a most probable encounter velocity of 51.3 km sec−1. The poor knowledge of the size distribution of cometary nuclei makes it difficult to estimate actual impact energies at this time, though that situation is slowly improving, in particular for the Jupiter-family comets.read more
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Journal ArticleDOI
Does Europa have a subsurface ocean? Evaluation of the geological evidence
Robert T. Pappalardo,M. J. S. Belton,H. Herbert Breneman,Michael H. Carr,Clark R. Chapman,Geoffrey C. Collins,Tilmann Denk,Sarah A. Fagents,Paul Geissler,Bernd Giese,Ronald Greeley,Richard Greenberg,James W. Head,Paul Helfenstein,Gregory V. Hoppa,S. D. Kadel,Kenneth P. Klaasen,James E. Klemaszewski,K. Magee,K. Magee,Alfred S. McEwen,Jeffrey M. Moore,William B. Moore,Gerhard Neukum,Cynthia B. Phillips,Louise M. Prockter,Gerald Schubert,David A. Senske,David A. Senske,R. J. Sullivan,B. R. Tufts,Elizabeth P. Turtle,Robert Wagner,K. K. Williams +33 more
TL;DR: In this article, the authors summarize the geological evidence regarding an extant subsurface ocean, concentrating on Galileo imaging data and assess nine pertinent lines of geological evidence: impact morphologies, lenticulae, cryovolcanic features, pull-apart bands, chaos, ridges, surface frosts, topography, and global tectonics.
Journal ArticleDOI
Cratering rates on the Galilean satellites.
TL;DR: It is found that most, probably more than 90%, of the craters on the Galilean satellites are caused by the impact of Jupiter-family comets (JFCs), these are comets with short periods, in generally low-inclination orbits, whose dynamics are dominated by Jupiter.
Journal ArticleDOI
The Evolution of Long-Period Comets
Paul Wiegert,Scott Tremaine +1 more
TL;DR: In this article, the authors study the evolution of long-period comets by numerical integration of their orbits, a more realistic dynamical approach than the Monte Carlo and analytic methods previously used to study this problem.
Journal ArticleDOI
The rate of small impacts on Earth
TL;DR: In this article, the atmospheric behavior of iron and stony bodies over the mass range 1-10^12 kg (size range 6 cm-1 km) was modeled taking into account deceleration, ablation, and fragmentation.
Oort Cloud Formation and Dynamics
TL;DR: In this paper, the orbital distribution of known comets and the cometary fading problem are discussed, as well as the population and mass of the Oort cloud, including the hypothetical inner Oort clouds.