Two objects lurking near Jupiter and once considered rocky asteroids have turned out to be comets made up mostly of ice and dirt.
Using the Keck II Laser Telescope in Hawaii, astronomers found that the two objects, 617 Patroclus and its companion, Menoetius, had a density of only 0.8 grams per cubic centimeters -- only a third that of rock.
Most likely, the researchers say, Patroclus and Menoetius are comets, which are typically composed mainly of water ice and therefore much less dense than asteroids.
The finding could mean that many or most of the asteroid-like objects hovering around Jupiter and known as Trojans are actually comets that originated much farther from the sun and which were captured by the giant gas planet when the solar system was still young.
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Perhaps that ought to have been expected. The Jovian Trojans are in the right area for comets to collect and not suddenly evaporate. I'll have to check on the energy requirements for a mission to there...seems like a great place to deliver a probe that can go from Trojan to Trojan and study...