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科技英语新闻:Astronomers discover new moon around Pluto

2011-07-21来源:Xinhuanet

WASHINGTON, July 20 (Xinhua) -- Using the Hubble Space Telescope, astronomers have discovered a fourth moon orbiting the icy dwarf planet Pluto, the U.S. National Aeronautics and Space Administration (NASA) announced Wednesday in a statement. The tiny, new satellite, temporarily designated P4, was uncovered in a Hubble survey searching for rings around the dwarf planet.

P4 was first seen in a photo taken with Hubble's Wide Field Camera 3 on June 28. It was confirmed in subsequent Hubble pictures taken on July 3 and July 18. It is the smallest moon discovered around Pluto. It has an estimated diameter of 8 to 21 miles (13 to 34 km). By comparison, Charon, Pluto's largest moon, is 648 miles (1,043 km) across, and the other moons, Nix and Hydra, are in the range of 20 to 70 miles in diameter (32 to 113 km).

Two labeled images of the Pluto system taken by the Hubble Space Telescope's Wide Field Camera 3 ultraviolet visible instrument with newly discovered fourth moon P4 circled. The image on the left was taken on June 28, 2011. The image of the right was taken on July 3, 2011.

"I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles (5 billion km)," said Mark Showalter of the SETI Institute in California, who led this observing program with Hubble.

P4 is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Charon was discovered in 1978 at the U.S. Naval Observatory and first resolved using Hubble in 1990 as a separate body from Pluto.

The dwarf planet's entire moon system is believed to have formed by a collision between Pluto and another planet-sized body early in the history of the solar system. The smashup flung material that coalesced into the family of satellites observed around Pluto.

The finding is a result of ongoing work to support NASA's New Horizons mission, scheduled to fly through the Pluto system in 2015. The mission is designed to provide new insights about worlds at the edge of our solar system. Hubble's mapping of Pluto's surface and discovery of its satellites have been invaluable to planning for New Horizons' close encounter.

"This is a fantastic discovery," said New Horizons' principal investigator Alan Stern of the Southwest Research Institute in Colorado. "Now that we know there's another moon in the Pluto system, we can plan close-up observations of it during our flyby."