Asteroid in Jupiter's orbit goes its own way | Science News


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How Bizarre

Asteroid in Jupiter's orbit goes its own way

Object circles the solar system in the opposite direction as all the planets

1:00pm, March 29, 2017
a backwards asteroid orbit

IN REVERSE  Jupiter’s trip around the sun is accompanied by many asteroids (white), which travel in the same direction as the planet. But scientists have found one, Asteroid 2015 BZ509 (green), that orbits backward.

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One of Jupiter’s companions is a bit of a nonconformist.

The gas giant shares its orbit around the sun with a slew of asteroids, but scientists have now discovered one that goes against the flow. It journeys around the solar system in reverse — in the opposite direction of Jupiter and all the other planets. Asteroid 2015 BZ509 is the first object found that orbits in the same region as a planet but travels backward, researchers from Canada and the United States report March 30 in Nature.

The asteroid was discovered with the Pan-STARRS observatory in Hawaii in 2015, and the researchers made additional observations with the Large Binocular Telescope Observatory in Arizona.

Backward-going asteroids are rare — only 0.01 percent of known asteroids are in retrograde orbits. Until now, none were known to share a planet’s orbit. It was thought that asteroids going in reverse couldn’t coexist with a planet because interactions with the celestial body, twice each orbit, would knock the asteroid off track. But because 2015 BZ509 passes on alternating sides of Jupiter, the interactions cancel each other out, the researchers say. The first flyby in orbit pulls the asteroid outward, and the next tugs it inward — keeping the maverick asteroid in line.

The asteroid’s relationship with Jupiter is no short-term fling: The researchers determined that the two have shared an orbit for a million years.

LONE WOLF Jupiter shares its orbit with more than 6,000 Trojan asteroids (white), which travel in the same direction as the planet. But one of the planet’s companions is an outlier, traveling in the opposite direction. Planets and asteroids in this video have been enlarged to make them visible. © 2017 Western Univ., Athabasca Univ., Large Binocular Telescope Observatory


P. Wiegert, M. Connors and C. Veillet. A retrograde co-orbital asteroid of Jupiter. Nature. Vol. 543, March 30, 2017, p. 687. doi: 10.1038/nature22029.

Further Reading

A. Grant. Astronomers explain planets’ backward motion. Science News Online, November 1, 2013.

L. Grossman. Backward planets may have flipped into place. Science News. Vol. 177, May 8, 2010, p. 11.

R. Cowen. Extrasolar planets at full tilt. Science News. Vol. 176, September 12, 2009, p. 12.

C. Crockett. Earth has a tiny tagalong, and no, it’s not a moon. Science News. Vol. 190, July 23, 2016, p. 5.

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