The Pluto system with Pluto and Charon in the center. Nix and Hydra can be seen on the top right. (c) David Tholen
Read The fact that the dwarf planet Pluto is not easy to observe shows already his late discovery: It was not until 1930, the 2, 300-kilometer-diameter celestial body was detected on images of the Lowell telescope in the US state of Arizona. Researchers at the University of Hawaii have even succeeded in photographing the two tiny moons Nix and Hydra, discovered only in 2005 by the Hubble Space Telescope, from Earth. "Several favorable factors came together to enable these spectacular images of the Pluto system, " said David Tholen, who photographed the dwarf planet on September 5 with the twin telescopes of the Keck Observatory on Mauna Loa, Hawaii: "The visibility was better as usual, better instruments were installed at the telescope and Pluto was seen at maximum brightness. "

The Keck telescope has so-called adaptive optics. An adjustable mirror and special sensors eliminate the distortions that cause turbulence in the atmosphere. Thanks to this new technology, the images of the Keck telescope are sometimes sharper than those of the Hubble Space Telescope. Tholen shot a total of 16 pictures of the dwarf planet and its three moons over a period of one hour. The tiny satellites Nix and Hydra, whose luminosity is about a five-thousandth of Plutos, but were only visible by combining all 16 images.

"It is our intention to make further shots of the system of similar quality to track several rounds of Nix and Hydra around Pluto, " says Tholen. So far, the size and mass of the little satellites are not known exactly. "Extremely precise orbit rules allow us to determine their mass and perhaps their size, " Tholen hopes.

Planet researchers estimate that Nix and Hydra are less than a hundred kilometers in size. Apart from the two chunks, Pluto still has the moon Charon, which has a diameter of 1, 200 kilometers and was discovered in 1978. The latest Pluto images are particularly interesting for the scientists involved in NASA's New Horizons mission: if they know how big and bright Nix and Hydra are, they can choose suitable camera settings in advance. New Horizons will reach Pluto 2015. display

Ute Kehse

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