Encyclopedia of Astrobiology

2011 Edition
| Editors: Muriel Gargaud, Ricardo Amils, José Cernicharo Quintanilla, Henderson James (Jim) CleavesII, William M. Irvine, Daniele L. Pinti, Michel Viso

Gravitational Focusing

Reference work entry
DOI: https://doi.org/10.1007/978-3-642-11274-4_670


Gravitational focusing refers to the enhancement in the likelihood that two particles will collide, due to their mutual gravitational attraction. Without gravity, the probability of a collision scales with the cross-sectional area of the two particles, but with gravity, particles that may have missed each other may be drawn together. In other words, the particles have effective cross-sectional areas larger than their physical cross sections. This enhancement is quantified as 1 + (vesc/vrel)2, where vesc is the particle’s escape speed and vrel is the relative velocity of the two particles. Gravitational focusing is important during planet formation, as it decreases the time needed to form planets and encourages larger particles to grow more quickly.

See also

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© Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  1. 1.Astronomy DepartmentUniversity of WashingtonSeattleUSA