Jupiter's comet family
Jupiter's comet familyA comet family whose distribution of aphelion distances (the comets' farthest points from the Sun) correlates with the mean distance of the planet Jupiter. Its members have aphelion distances of 4–8 AU. Jupiter is capable of substantially changing the orbits of comets that happen to pass close by. Brooks 2 passed within two Jovian radii of Jupiter's surface in July 1886. Its period and aphelion distance were changed from 31 years and 14 AU to 7 years and 5.4 AU. The formation of the family is caused by such gravitational perturbations. Jupiter is also capable of throwing comets out of its family into long-period orbits (using a process similar to the one used to deflect spacecraft out of the Solar System). Over 90% of the Jovian family move in direct orbits. Comets with periods less than 10 years have a mean inclination to the ecliptic of 12°. After a comet has been captured by Jupiter it will take another 200 to 400 orbits (depending on perihelion distance) before it decays completely. No comet can remain in the Jupiter family for more than about 4000 years so the family is being replenished continually.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006