COURTESY DAVID THOLEN
This image combines 16 exposures, with the contrast adjusted to show Pluto's new satellites Nix, left, and Hydra, right, as the small dots in the upper right. Both Nix and Hydra are about 5,000 times fainter than Pluto, thus both Pluto and Charon are washed out in this image. The Pluto system moved with respect to the background stars during the one hour of observations, leaving the stars trailed in this image.
Pluto close up
A UH astronomer finds a unique way get a better look than the Hubble telescope
In the suburbs of the solar system, Earth's distant cousins are a small, unruly bunch that do not even merit the designation of planet.
But these celestial misfits have come into closer focus thanks to a University of Hawaii astronomer using a novel imaging system atop Mauna Kea.
University of Hawaii astronomer Dave Tholen said his photos of Pluto and its satellites from the one of the Keck Telescopes are sharper than those from the Hubble Space Telescope.
That is not a small boast, since the atmosphere tends to blur images of stars and planets -- a problem that the orbiting Hubble does not have.
Removing the twinkle from stars or tiny, distant objects like Pluto requires adaptive optics -- instruments that compensate for the turbulence in the atmosphere.
Tholen used such as system on a Keck telescope during the early evening of Sept. 5.
"The natural seeing was better than average that night, more sensitive wave-front 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 in a recent release.
His images are about 20 times sharper than images taken of Pluto 30 years ago, he said.
Tholen had been looking at Hubble's observations of Pluto's system to help answer questions about the nature and mass of Charon, a large satellite discovered in 1978, and the smaller moons, Nix and Hydra, discovered in 2005.
But his own pictures of Pluto and its satellites could yield the information he is seeking.
"The masses are very high on our list of goals," he said in an e-mail from Orlando, Fla., where he was attending the annual American Astronomical Society Division for Planetary Sciences meeting.
"We'd also like to determine if the satellites are in a state of resonance with one another."
The gravity of Pluto and Charon have locked the pair into a mutual spin-orbit, much like a dumbbell. Nix and Hydra also weigh in, creating multiple orbital rhythms, or periodicities.
Tholen took 16 images during one hour on the telescope and combined them to form a single image. He hopes to get more pictures of the Pluto system of the same quality so Nix and Hydra can be tracked completely around Pluto several times.
"By making extremely precise measurements of the satellites' positions, we will determine their masses by detecting the tiny displacements caused by their mutual gravitational attraction," he said. "Once the masses are in hand, we'll be able to say something more definitive about how big these new satellites are."
Nix and Hydra have been estimated to be less than 62 miles in diameter, compared with about 751 miles for Charon and 1,426 for Pluto.
Among those interested in the images are scientists planning the 2015 visit to Pluto by NASA's New Horizons spacecraft, which passed Jupiter in February.
"Something as simple as selecting the proper exposure time to snap images of Nix and Hydra with New Horizons depends on knowing how big they are and how reflective their surfaces are," Tholen said. "One of our goals is to have those answers well in advance of the flyby."
Tholen said he asked for time on the Keck telescope to supplement Hubble's data and test the feasibility of doing the research from the ground.
He said the results were so spectacular that he has requested many more observations starting in about April. "If similarly successful to the Sept. 5 observations, then we'll have the 400-day coverage needed to look for those periodicities."