for National Geographic News
Sixty years ago, Jupiter carried on a 12-year fling with an extra "moon" then casually cast it aside—and the gas giant will likely do it again within decades, scientists announced today.
In 1949 the massive planet's gravity pulled in comet 147P/Kushida-Muramatsu and held it in orbit until 1961, according to an international team led by Katsuhito Ohtsuka of the Tokyo Meteor Network.
The 1,300-foot-wide (400-meter-wide) comet's stint as a so-called temporary satellite was revealed when the researchers used calculations taken since the comet's 1993 discovery to determine the space rock's past course.
"We can be fairly sure that the comet orbited Jupiter once or twice before escaping it," said team member David Asher of the U.K.'s Armagh Observatory.
Temporary "Moon" Ended With a Bang
Only one temporary satellite has been observed falling prey to a planet's pull: comet Shoemaker-Levy 9, which broke apart and crashed into Jupiter in 1994. (See a Hubble Space Telescope picture of comet debris approaching Jupiter.)
A mysterious debris plume spotted on Jupiter this past July may have been caused by the spectacular impact of another such temporary satellite, Asher said.
Unlike those objects, comet Kushida-Muramatsu eventually escaped Jupiter's gravity. It currently circles the sun in the solar system's asteroid belt, between the orbits of Mars and Jupiter.
Before long, though, another comet is destined for moondom. Between 2068 and 2086, comet 111P/Helin-Roman-Crockett is expected to be captured and complete six laps around Jupiter, the astronomers say.
Earth Unlikely to Gain Extra Moon
It's doubtful that our own planet would have the gravitational pulling power to add a temporary satellite to the night sky, Asher said.
"There are examples of small objects that the Earth had captured and then escaped again, so it could in principal happen," Asher said.
"But with one of these larger objects—objects big enough to cause serious damage, were they to impact the Earth—fortunately they are much more likely to be captured by Jupiter"—sparing Earth a potential Armageddon.
Findings presented today at the European Planetary Science Congress in Potsdam, Germany.
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