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Hubble discovers
Pluto’s fourth moon

Posted: 20 July 2011

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Astronomers using the Hubble Space Telescope to look for potential rings around dwarf planet Pluto have instead uncovered a fourth moon orbiting the distant icy world.

The moon, currently assigned the temporary name P4, is the smallest of Pluto’s satellites – astronomers estimate that its diameter is between 13 and 34 kilometres. The largest moon Charon is 1,043km wide and Nix and Hydra are in the range of 32-113 kilometres. P4 is located between the orbits of Nix and Hydra.

Two images, taken about a week apart by NASA’s Hubble Space Telescope, show Pluto’s four moons, including the newly discovered member P4. Image: NASA, ESA, and M. Showalter (SETI Institute).

“I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than 5 billion kilometres,” says Mark Showalter of the SETI Institute, who led this Hubble observing program. The moon was first identified in a Wide Field Camera 3 image taken on 28 June, and confirmed in follow-up images snapped on 3 and 18 July. The new images had much longer exposure times than those previously taken of Pluto’s neighbourhood, which is why P4 has been overlooked until now.

The hunt for rings around Pluto stems from the idea that material blasted off Pluto’s moons by micrometeorite impacts may go into orbit around the planet. So far no evidence for the proposed ring has been identified, but the Hubble observations will continue to prime the New Horizons spacecraft for when it encounters the outer Solar System dwarf planets in 2015 for close-up investigation.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


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