Hydra is the fifth nearest and second- largest known moon of the dwarf planet Pluto. It was discovered along with Nix in June 2005, and was visited along with Pluto by New Horizons in July 2015. Young (23 February 2006).
Steffl, A. J.; Mutchler, M. J.; Weaver, H. A.; Stern, S. A.; Its diameter is estimated to be 61-167 kilometers. Compared to Pluto and its large moon Charon, at 2,360 and 1,210 kilometers in diameter respectively, Nix (inner moon) and Hydra (outer moon) are tiny, estimated to be only 40 to 160 kilometers across.
Hydra is lighter by 25 % than Nix, suggesting a 10 - 15% indicating larger diameter, assuming an equal albedo of the two moons. After the discovery in the summer of 2005, with images from the Hubble Space Telescope, the two newly discovered moons were observed in September 2005 by the Keck and the
The diameter has a calculated range of between 61 km and 167 km, depending on the albedo—and current instruments cannot adequately resolve the albedo, either. Hydra is somewhat brighter than its companion moon Nix, and so might be the larger of the two, but this is not proved. Under the current simulations, Hydra is on the same side of Pluto as Charon, Nix, however, on the other side, but closer to the probe. The orbit of the next inner moon Kerberos has an approximately 7000 km radius less;
The orbital period is close to a 1:6 orbital resonance with Charon, the deviation is 0.3 %. Hydra is the farthest moon of Pluto.It was found along with Nix in June, 2005 by the Hubble Space Telescope's Pluto Companion Search Team, which is composed of Hal A. Weaver, Alan Stern, Max J. Mutchler, Andrew J. Steffl, Marc W. Buie, William J. Merline, John R. Spencer, Eliot F. Young, and Leslie A. If it is not a real resonance, there is a hypothesis that originated such a near- resonance before the current outward migration of Charon. The exact value of the diameter could not be determined so far as the albedo (albedo ) of the surface is unknown. Stern, S. A.; Mutchler, M. J.; Weaver, H. A.; and Steffl, A. J.
Pre-discovery data from Hubble observations in 2002-3 inferred that Nix was the brighter moon. Hydra is likely analogous to the theory on the origin of the Moon, the product of large collision of a predecessor of Pluto with another pluto large body of the Kuiper Belt, which formed the moon, Charon, while debris fell into outer orbits around Pluto, this follows the moon Hydra formed. For spectral investigations Hydra was in contrast to the reddish Pluto in a similarly neutral gray color as Charon and Nix. Its diameter is estimated to be 61-167 kilometers. It is the second largest moon of Pluto, being slightly larger than Nix.Hydra was discovered along with Nix by the Pluto Companion Search Team in June 2005. Hydra orbits the common center of mass of the Pluto -Charon system in a prograde, slightly elliptical orbit at an average distance of 62,745 km ( 64,780 km distance from Pluto's center, about 56.18 Pluto radii ). Temporary names in H. A. Weaver; S. A. Stern, M. J. Mutchler, A. J. Steffl, M. W. Buie, W. J. Merline, J. R. Spencer, E. F. Young and L. A. If the albedo equal to that of Charon ( 0.372 ) may be, this would amount to 61 km, with an albedo of 0.04, corresponding to the darkest Kuiper Belt objects, 167 km.
In addition, the names Nix and Hydra correspond to the initials of the spacecraft
Hydra and Nix, however, were included in the monitoring program afterwards. Nix and Charon orbiting Pluto on even narrower lanes. Hydra's surface is probably covered with water ice. Since the discovery of Hydra and Nix and the fourth moon Kerberos was not confirmed at the start of the probe, they were not planned in the mission.