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Moons galore for dwarf planet

Pluto and its five moons

A Hubble Space Telescope image showing the five moons that orbit Pluto.
(Courtesy: NASA, ESA and M Showalter at the SETI Institute)

By Tushna Commissariat

The dwarf-planet Pluto is back in the news this week, as astronomers have discovered that it has a fifth icy moon orbiting it. The newly discovered moon, which was seen as a speck of light in nine separate sets of images taken by the NASA/ESA Hubble Space Telescope, apparently has a rather irregular shape, and is about 10–25 km across. With its 95,000 km diameter circular orbit around Pluto, the moon should lie within the same plane as Pluto’s other four moons.

“The moons form a series of neatly nested orbits, a bit like Russian dolls,” says Mark Showalter of the SETI Institute in the US, who was also the leader of the scientific team that discovered the new moon. The team was intrigued that a dwarf planet such as Pluto can have such a complex collection of satellites and says that the new moon could provide further clues towards understanding how Pluto’s system has formed and evolved.

Pluto’s largest moon, Charon, was discovered in 1978. Further observations in 2006, again made by Hubble, uncovered two additional small moons, Nix and Hydra, and the fourth moon, known only as P4, was found last year. The new moon has provisionally been called P5.

NASA’s New Horizons space probe, which is currently en route to Pluto, has a high-speed fly-by scheduled for 2015. It will return the first ever detailed images of the Pluto system, which is so small and distant that even Hubble can barely see the largest features on its surface.

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