No. 17 for Jupiter: Discovery of Tiny Moon Is Reported

Astronomers say they have found a 17th moon orbiting Jupiter. If confirmed, the 3-mile-diameter moon would be the smallest-known satellite of a major planet and the first Jovian moon discovered in 21 years.

“When you realize that you were the first person to lay eyes on something that had not been seen before, that’s kind of a good feeling,” University of Arizona astronomer Jeff Larsen, who made the first observations of the moon in October, said in Saturday’s Arizona Daily Star.

Larsen works with the university’s Spacewatch project, which uses a 79-year-old Kitt Peak, Ariz., telescope to survey the solar system for comets and asteroids. Project workers usually avoid the region around Jupiter because the solar system’s largest planet is bright and reflected light can swamp the telescope’s sensitive electronic detectors.

The Smithsonian Astrophysical Observatory in Cambridge, Mass., confirmed the find. For now, the object is designated S/1999 J1.

Among Jupiter’s 16 moons, half are smaller than 32 miles in diameter. Mars has the smallest confirmed moon, Deimos, which is about 7.5 miles in diameter. Earth’s moon is 2,160 miles in diameter.

Jupiter is currently too close to the sun to allow follow-up observations, but it should be accessible within the next couple of months, said University of Arizona planetary scientist Robert S. McMillan, principal investigator of Spacewatch.