[meteorite-list] Catch A Comet?

[Sterling K. Webb]

It seems that not only do comets impact Jupiter,
they may also become moons, temporary or
permanent, of the planet.

Wonder what it would take to get a "comet moon"
for the Earth?

Sterling K. Webb
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http://www.space.com/scienceastronomy/090914-jupiter-comet.html
Gotcha! Jupiter Turned Comet into a Moon 
By SPACE.com Staff

Jupiter already has an abundance of moons, 
but from 1949 to 1961 it had another, temporary 
satellite in the form of a comet trapped in the 
gas giant's gravitational grip.

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, astronomers announced 
today.

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 is the third longest.

The discovery was presented today at the European 
Planetary Science Congress in Potsdam by David 
Asher of Armagh Observatory in Northern Ireland.

An international team led by Katsuhito Ohtsuka 
of the Tokyo Meteor Network 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.

But Kushida-Muramatsu was different: The team 
used recent observations tracking the comet over 
nine years to calculate hundreds of possible orbital 
paths for it 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.

"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," Asher said.

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," Asher said.

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," 
Asher said.

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.