The view of Pluto is great from up here

A University of Hawai'i's astronomer David Tholen has taken the clearest images ever from Earth of Pluto, its big moon Charon and its two smaller moons, Nix and Hydra.

Nix and Hydra were only discovered two years ago from the Hubble Space Telescope, but they stand out clearly in this image, pinpoints of light that are distinct from the streaked objects in the background. From left to right, they are Pluto, Charon, Nix and Hydra. Hydra appears slightly brighter than nix.

Nix and Hydra are about 5,000 times fainter than Pluto, and can't be clearly imaged with Pluto in the frame. As a result, Tholen combined images to create the picture that has all four of the objects in it.

Astronomers have been having fun naming this group. Pluto is the ruler of the underworld in Greek mythology. Charon is the skipper of the boat that carries human souls across the river Styx to Pluto's world.

Nyx, the goddess of the night, was Charon's mother. Astronomers used the spelling Nix because Nyx was taken. And Hydra, a serpent with nine heads, is the grisly guard of Pluto's dark terrain.

The image doesn't address the prickly issue of whether Pluto ought to be called a planet or not, but it certainly seems to have a lot of moons for something that's not.

Tholen, of the university's Institute for Astronomy, created the image after spending an hour focusing one of the twin Keck Telescopes atop Mauna Kea on Pluto. A bunch of things came together to help make the images even clearer than anything the Hubble Space Telescope could produce.

The Kecks are among the biggest light-gathering scopes in the world. He used adaptive optics, a technology that corrects for distortions of the Earth's atmosphere. And that Sept. 5 night was simply a really good night for a clear view of the sky, he said.

"Several favorable factors occurred simultaneously to yield these spectacular images of the Pluto system," Tholen said. "The natural seeing was better than average that night, more sensitive wavefront sensors were installed on the telescope, and Pluto was at its maximum brightness, thereby giving the improved adaptive optics system more light with which to work its magic," he said.

Tholen said he hopes to use information from the images to help learn more about Nix and Hydra, which are believed to be 100 kilometers (about 60 miles) or less in diameter. By contrast, Pluto is 2,300 kilometers and Charon 1,212 kilometers in diameter.

© 2007 Jan W. TenBruggencate

For more images and more information on the subject, see the Institute for Astronomy site www.ifa.hawaii.edu/info/press-releases/PlutoPictures/Pluto-Tholen-10-07.html