NASA’s New Horizons spacecraft has provided its first views of Nix and Hydra – the small moons of Pluto.
Nix (identified by a orange diamond) and Hydra (yellow diamond) are visible in the images taken by the New Horizons spacecraft. Image credit: NASA / Johns Hopkins APL / Southwest Research Institute.
Hydra (S/2005 P1) and Nix (S/2005 P2) were detected using the images taken by the Advanced Camera for Surveys on NASA’s Hubble Space Telescope in May, 2005.
Hydra, the outermost known moon of Pluto, has been calculated to have a diameter of between 61 and 167 km.
Nix is about 25 percent fainter than Hydra, so could be a 10 to 15 percent smaller than Hydra, assuming they have the same surface reflectivity.
Hydra orbits Pluto every 38 days at a distance of 64,700 km, while Nix orbits every 25 days at a distance of 48,700 km.
The new long-exposure images from the New Horizons offer best view yet of these two moons.
Pluto’s two other small moons, Styx and Kerberos, are still smaller and too faint to be seen by New Horizons at its current range to Pluto; they will become visible in the months to come.
“It’s thrilling to watch the details of the Pluto system emerge as we close the distance to the spacecraft’s July 14 encounter,” said Dr John Spencer, a scientist with the Southwest Research Institute and New Horizons science team member.
“This first good view of Nix and Hydra marks another major milestone, and a perfect way to celebrate the anniversary of Pluto’s discovery.”
These are the first of a series of long-exposure images that will continue through early March, with the purpose of refining the team’s knowledge of the moons’ orbits.
Each frame is a combination of five 10-second images, taken with New Horizons’ Long-Range Reconnaissance Imager (LORRI) using a special mode that combines pixels to increase sensitivity at the expense of resolution.
At left, Nix and Hydra are just visible against the glare of Pluto and its large moon Charon, and the dense field of background stars. The bright and dark streak extending to the right of Pluto is an artifact of the camera electronics, resulting from the overexposure of Pluto and Charon.
The right-hand image has been processed to remove most of Pluto and Charon’s glare, and most of the background stars. The processing leaves blotchy and streaky artifacts in the image, and also leaves a few other residual bright spots that are not real features, but makes Nix and Hydra much easier to see.
