Pluto's satellite – Nix

Abstract

Before the launch of the "New Horizons" spacecraft, a special Hubble Space Telescope Pluto Companion Search Team was created. The members of this team believed that Pluto and its moon Charon could have other moons and, possibly, even rings. Any of these objects could prevent a safe passage through the Pluto system. In 2005, researchers began using the Hubble Space Telescope to search for moons around Pluto. As a result of analyzing the images obtained, in mid -July 2005, two previously unknown moons were dis covered around Pluto. A year later, the International Astronomical Union officially assigned them their own names, Nix and Hydra. The orbital radius for the smaller moon is about 48.71 thousand km. Calculations showed that Charon and these two moons are in an orbital resonance of 3:2:1. For the moons Nix and Hydra, the "New Horizons" space probe obtained fairly detailed images of its surface in July 2015. The satellite measures 49.8 km × 33.2 km × 31.1 km. It is the third largest satellite of Pluto, being only slightly smaller than Hydra. Nix is also the third -farthest satellite of Pluto. Nix moves erratically; the inclination of the satellite's axis and the period of rotation vary greatly over a short period of time. Due to its erratic rotation, Nix can even flip its axis of rotation from time to time. This erratic movement of the satellite is caused by the gravitational effects of Pluto and Charon. The erratic movement of Nix is further enhanced by its elongated shape. All of Pluto's satellites have circular orbits. And they all have very low orbital inclinations to Pluto's equator. Early remote observations of the satellite showed that Nix's surface has a reddish color. Other remote observations showed that Nix is spectrally neutral, similar to the other s mall satellites of Pluto. Nix also varied in brightness and albedo. It was believed that the brightness fluctuations were caused by the visibility of regions with different albedos on the surface of Nix. This was confirmed by close -up images obtained by th e "New Horizons" spacecraft. They showed the presence of a large reddish region on the surface of Nix, approximately 18 km across. This region is believed to be a large impact crater, where reddish material was ejected from under a layer of water ice on the surface of Nix. The water ice present on the surface of Nix should be responsible for its high reflectivity. Traces of frozen methane are also present on the surface of Nix. These may be the reason for the presence of reddish material on its surface; most likely, they may be tholins. To explain the resonances between the rotation periods of all Pluto's moons, it has been proposed to consider the influence of the gravitational field strength of the Pluto-Charon system.