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Jupiter borrowed a passing comet to make a moon for 12 years

comet 147P/Kushida-Muramatsu orbits around JupiterThe middle of the 20th century was an eventful time in terms of Earth's geopolitics. In the spring of 1949, the North Atlantic Treaty Organization (NATO) was taking shape, and simmering tensions in Korea hinted at the war that would begin there the following year. Twelve years later, in the summer of 1961, President John F. Kennedy was in his first year of office and had already committed the U.S. to reaching the moon before the decade was out.

A few hundred million miles away, during that same interval of years, Jupiter had its own share of the action. The gas giant passed the time by borrowing a comet called 147P/Kushida-Muramatsu to form a temporary satellite, holding onto it for two orbits. That's the conclusion, anyway, of a study presented yesterday (pdf) at the European Planetary Science Congress in Potsdam, Germany, by a team of researchers from Japan and the U.K.

A few other such Jovian events are known—in one case, the massive planet may have held onto its captive comet for more than half a century.

To uncover the 12-year rendezvous between Jupiter and Comet 147P/Kushida-Muramatsu, an icy body discovered in 1993, the research team, led by Katsuhito Ohtsuka of the Tokyo Meteor Network, tracked the orbits of likely comets back 100 years based on their known characteristics today.

From about May 1949 to July 1961, the group found, Comet 147P/Kushida-Muramatsu was pulled in by Jupiter's influence before escaping to its present orbit via a gravitationally stable zone known as a Lagrange point, where the gravitational influence of two bodies—in this case Jupiter and the sun—balance out.

The research on 147P/Kushida-Muramatsu was originally published in October 2008 in Astronomy & Astrophysics.

Modeled orbit of Comet 147P/Kushida-Muramatsu around Jupiter (at center of diagram): Ohtsuka/Asher

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