NASA’s New Horizons probe is currently on course for the edge of the solar system, and scientists were using the Hubble telescope to make sure it had a clear path. To their surprise, they found a small object in orbit around Pluto that they had never seen before: a new moon called P5. The finding adds to last year’s discovery of the small moon P4, bringing Pluto’s total to five.
A plausible explanation for the myriad Plutonian moons, Showalter says, is that “this system began when something big hit Pluto billions of years ago—it created this big cloud of debris, most of which condensed to form Charon.” Some of the cast-off material, though, settled into stable orbits farther from Pluto and coalesced into smaller moons. “Essentially we’re just seeing the leftover debris,” Showalter says.
Pluto and its largest moon Charon make for an interesting system: Both objects orbit a shared center of mass that floats off in empty space. The system’s smaller moons, Nix, Hydro, P4, and now P5, each follow an orbit that is related to that of Charon, says Matson.
For P4 and P5, the team members are holding off on proposing names for now, just in case a P6 comes along. “It’s still a moving target, because we don’t know what might come along,” Showalter said. “I expect that in a month or two, we’ll have finished everything we’re going to find until New Horizons gets close.” Only then will the team seriously consider what the two (or more) moons will be named. If things stay as they are, P4 and P5 will probably be named after a pair of characters with Greek underworld connections, such as Orpheus and Eurydice.
New Horizons is hoping to buzz past Pluto in July, 2015, and the scientists think that the discovery of P5 indicates that there will likely be a lot more dust and rubble also floating in the area than they thought, which may mean a more cautious approach for the speeding probe.
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