Jupiter Captured Comet for 12 Years in Last Century

http://www.spaceflightnow.com/news/n0909/14comet/

Jupiter captured comet for 12 years in last century
EUROPEAN PLANETARY SCIENCE CONGRESS NEWS RELEASE
September 14, 2009

Comet 147P/Kushida-Muramatsu was captured as a temporary moon of
Jupiter
in the mid-20th century and remained trapped in an irregular orbit for
about twelve years.

There are only a handful of known comets where this phenomenon of
temporary satellite capture has occurred and the capture duration in
the
case of Kushida-Muramatsu, which orbited Jupiter between 1949 and
1961,
is the third longest. The discovery will be presented at the European
Planetary Science Congress in Potsdam by Dr. David Asher on Monday 14
September.

An international team led by Dr. Katsuhito Ohtsuka modeled the
trajectories of 18 "quasi-Hilda comets", objects with the potential to
go through a temporary satellite capture by Jupiter that results in
them
either leaving or joining the "Hilda" group of objects in the asteroid
belt. Most of the cases of temporary capture were flybys, where the
comets did not complete a full orbit. However, Dr. Ohtsuka's team used
recent observations tracking Kushida-Muramatsu over nine years to
calculate hundreds of possible orbital paths for the comet over the
previous century. In all scenarios, Kushida-Muramatsu completed two
full
revolutions of Jupiter, making it only the fifth captured orbiter to
be
identified.

Dr. Asher said, "Our results demonstrate some of the routes taken by
cometary bodies through interplanetary space that can allow them
either
to enter or to escape situations where they are in orbit around the
planet Jupiter."

Asteroids and comets can sometimes be distorted or fragmented by tidal
effects induced by the gravitational field of a capturing planet, or
may
even impact with the planet. The most famous victim of both these
effects was comet D/1993 F2 (Shoemaker-Levy 9), which was torn apart
on
passing close to Jupiter and whose fragments then collided with that
planet in 1994. Previous computational studies have shown that
Shoemaker-Levy 9 may well have been a quasi-Hilda comet before its
capture by Jupiter.

"Fortunately for us Jupiter, as the most massive planet with the
greatest gravity, sucks objects towards it more readily than other
planets and we expect to observe large impacts there more often than
on
Earth. Comet Kushida-Muramatsu has escaped from the giant planet and
will avoid the fate of Shoemaker-Levy 9 for the foreseeable future",
said Dr. Asher.

The object that impacted with Jupiter this July, causing the new dark
spot discovered by Australian amateur astronomer Anthony Wesley, may
also have been a member of this class, even if it did not suffer tidal
disruption like Shoemaker-Levy.

"Our work has become very topical again with the discovery this July
of
an expanding debris plume, created by the dust from the colliding
object, which is the evident signature of an impact. The results of
our
study suggest that impacts on Jupiter and temporary satellite capture
events may happen more frequently than we previously expected," said
Dr.
Asher.

The team has also confirmed a future moon of Jupiter. Comet
111P/Helin-Roman-Crockett, which has already orbited Jupiter three
times
between 1967 and 1985, is due to complete six laps of the giant planet
between 2068 and 2086.