ASTRONOMERS USING THE Hubble Space Telescope have discovered a fourth moon orbiting the icy dwarf planet Pluto. The tiny, new satellite, temporarily designated P4, was uncovered in a Hubble survey searching for rings around the dwarf planet.
The new moon is the smallest discovered circling Pluto. It has an estimated diameter of 13 to 34 km. By comparison, Charon, Pluto’s largest moon, is 1,043 km across, and the other moons, Nix and Hydra, are in the range of 32 to 113 km in diameter.
“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 km,” said Mark Showalter of the SETI Institute, who led this observing programme with Hubble.
Mission to 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. “Now that we know there’s another moon in the Pluto system, we can plan close-up observations of it during our flyby.”
Moons formed in a smash-up
The new moon is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Charon was discovered in 1978 at the US 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 smash-up flung material that coalesced into the family of satellites observed around Pluto.
Lunar rocks returned to Earth from the Apollo missions led to the theory that our moon was the result of a similar collision between Earth and a Mars-sized body 4.4 billion years ago.
Scientists believe material blasted off Pluto’s moons by micrometeoroid impacts may form rings around the dwarf planet, but the Hubble photographs have not detected any so far.
No sign of rings yet
“This surprising observation is a powerful reminder of Hubble’s ability as a general purpose astronomical observatory to make astounding, unintended discoveries,” said Jon Morse, astrophysics division director at NASA Headquarters in Washington.
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. The moon was not seen in earlier Hubble images because the exposure times were shorter.
There is a chance it appeared as a very faint smudge in 2006 images, but was overlooked because it was obscured.
Adapted from information issued by NASA. Images and graphics courtesy NASA / A. Feild (STScI) / ESA.
Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz
Like this story? Please share or recommend it…