July 14th, 2012 by James Ayre
The recent discovery of a new moon around Pluto has now raised the number of confirmed moons up to five.
The newly discovered moon is estimated to be around 6 to 15 miles across, and of an irregular shape. It follows a circular orbit with a 58,000-mile-diameter around Pluto. And it is thought to be co-planar with the other satellites in the system.
“On July 11, 2012, astronomers announced that a fifth moon had been discovered orbiting the dwarf planet. Researchers using NASA’s Hubble Space Telescope found the moon. The discovery comes almost exactly one year after Hubble spotted Pluto’s fourth moon, a tiny body currently called P4.”
The researchers are intrigued that such a small planet has such a complex collection of satellites.
“The moons form a series of neatly nested orbits, a bit like Russian dolls,” said team lead Mark Showalter of the SETI Institute in Mountain View, Calif.
Pluto’s entire moon system is thought to have formed by a collision between Pluto and a similar-sized body early in the history of the solar system. The collision threw out material that coalesced into the family of satellites orbiting Pluto. There may be even more moons to discover.
Scientists using Hubble discovered a fourth moon in 2011. This moon is estimated to be 8 to 21 miles (13 to 34 km) in diameter. P4’s orbit is between the orbits of Nix and Hydra.
The newly discovered P4 and P5 moons provide some clues on how the Pluto system may have formed and evolved. The currently favored theory is that all of Pluto’s moons are relics of a giant collision between Pluto and a large Kuiper belt object billions of years ago.
Pluto’s largest moon, Charon, is almost half the planet’s size. “Discovered in 1978, it was named Charon after the demon who ferried souls to the underworld in Greek mythology. The huge size of Charon (648 miles or 1,043 km in diameter) sometimes leads scientists to refer to Pluto and Charon as a double dwarf planet or binary system. Pluto’s diameter is 1,430 miles (2,302 km).”
“Pluto and Charon are just 12,200 miles (19,640 km) apart, less than the distance by flight between London and Sydney. Charon’s orbit around Pluto takes 6.4 Earth days, and one Pluto rotation — a Pluto day — also takes 6.4 Earth days. This means Charon hovers over the same spot on Pluto’s surface, and the same side of Charon always faces Pluto, a phenomenon known as tidal locking.”
“Compared with most of solar system’s planets and moons, the Pluto-Charon system is tipped on its side in relation to the sun. Also, Pluto’s rotation is retrograde compared to the other worlds — it spins backwards, from east to west.”
“In 2005, as scientists photographed Pluto with the Hubble Space Telescope in preparation for the New Horizons mission — the first spacecraft to visit Pluto and the Kuiper Belt — they discovered two other tiny moons of Pluto, now dubbed Nix and Hydra. These are two to three times farther away from Pluto than Charon, and they are thought to be just 31 to 62 miles (50 to 100 kilometers) wide each.”
These new discoveries should help scientists navigate the New Horizons spacecraft through the Pluto system in 2015. NASA’s New Horizons spacecraft will be the first to do a close flyby of the distant world.
“The team is using Hubble’s powerful vision to scour the Pluto system to uncover potential hazards to the New Horizons spacecraft. Moving past the dwarf planet at a speed of 30,000 miles per hour, New Horizons could be destroyed in a collision with even a BB-shot-size piece of orbital debris.”
“The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system,” said Harold Weaver of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.
“The inventory of the Pluto system we’re taking now with Hubble will help the New Horizons team design a safer trajectory for the spacecraft,” added Alan Stern of the Southwest Research Institute in Boulder, Colo., the mission’s principal investigator.
“Provisionally designated S/2012 (134340) 1, the latest moon was detected in nine separate sets of images taken by Hubble’s Wide Field Camera 3 on June 26, 27, 29, and July 7 and 9.”
“In the years following the New Horizons Pluto flyby, astronomers plan to use the infrared vision of Hubble’s planned successor, NASA’s James Webb Space Telescope, for follow-up observations. The Webb telescope will be able to measure the surface chemistry of Pluto, its moons, and many other bodies that lie in the distant Kuiper Belt along with Pluto.”
Image Credits: NASA; ESA; M. Showalter, SETI Institute
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