Hubble Uncovers Fourth Moon Around Pluto
Pluto may not have full planet status but the distant, icy rock at the fringe of the solar system has three more moons than Earth—scientists with the Space Telescope Science Institute (STSI) on Wednesday announced that they have discovered a fourth satellite orbiting the dwarf planet.
“I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than three billion miles,” Mark Showalter of the SETI Institute in Mountain View, Calif., who led a team mapping Pluto with the Hubble Space Telescope, said in a statement.
Pluto’s new moon has been temporarily designated P4. It’s the smallest of Pluto’s known satellites, with an estimated diameter of eight to 21 miles, according to its discoverers. Pluto’s largest moon, Charon is 746 miles across, while Nix and Hydra are between 20 and 70 miles in diameter.
Charon was discovered in 1978, while Nix and Hydra were spotted in Hubble images in 2005.
The discovery of P4 was the result of work being done to support NASA’s $700-million New Horizons mission, which aims to send a probe through the Pluto system in 2015. Pluto’s fourth moon was spotted while Hubble was being used to search for rings around the dwarf planet, scientists said.
“This is a fantastic discovery,” said Alan Stern of the Southwest Research Institute in Boulder, Calif., principal investigator on the New Horizons mission. “Now that we know there’s another moon in the Pluto system, we can plan close-up observations of it during our flyby.”
Scientists first spotted P4 in a photo taken with Hubble’s Wide Field Camera 3 on June 28, the STSI statement said. Its existence was confirmed in two more pictures taken on July 3 and July 18. It may also appear as “a very faint smudge” in Hubble images from 2006, according to the statement.
P4 is located between the orbits of Nix and Hydra, according to the STSI statement.
“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.