Pluto's New Moon, P4: Dwarf Planet Discovery

With all the attention places like Jupiter and Mars have been getting as NASA prepares to send two new probes their way, it's easy to forget that a spacecraft is currently heading toward the edge of the solar system at speeds exceeding 50,000 m.p.h. (80,000 km/h), aimed straight at Pluto. 

Even at that blistering speed, the New Horizons probe, launched back in 2006 before Pluto was downgraded from a fully certified planet to a dwarf planet, won't arrive until 2015.



But mission scientists don't want to waste a moment when it finally gets there, so they've been scouting ahead with the Hubble Space Telescope to see if there's anything unusual to photograph or any hazards to avoid — like rings, which could damage or even destroy a probe that smashes through them at a high speed.





The image that popped up in Hubble's gallery on June 28 didn't show any rings — but it did show that Pluto has a moon nobody knew about. Temporarily known as P4 until it's granted a real name, it joins Charon, discovered by a U.S. Naval Observatory telescope in 1978; and Nix and Hydra, spotted by Hubble in 2005. 

There's a good reason P4 escaped notice until now: its diameter, somewhere between 8 and 21 miles (13 and 33 km), makes it all but impossible to see from Earth.

"We always knew it was possible there were more moons out there," says Alan Stern of the Southwest Research Institute in Boulder, Colo., the principal investigator of the New Horizons mission and a co-discoverer of the new moon. "And lo and behold, there it was."


It almost wasn't, as far as the astronomers were concerned. Stern, along with planetary scientist Mark Showalter of the SETI Institute in Mountain View, Calif., put in a proposal about a year ago asking for some of Hubble's precious time to look for rings around Pluto.

"It must have rings, at least from time to time," says Stern. The reason: Nix and Hydra, like pretty much every other object in the solar system, get bombarded with meteorites or bits of comet every so often. "I guarantee that when we get there," says Stern, "we'll see craters."

Those impacts will throw particles of ice into space and those particles will form themselves into rings. "The only question," says Stern, "is how long they last." The Hubble folks, though, turned the scientists down. So they appealed, and the second time around their project was approved.

Showalter and Stern are not done yet. Along with several colleagues, they have submitted a second proposal to the Hubble time-allocation committee, which fields hundreds of such pitches per year.


Read more at: http://www.time.com