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clean up & uniformity
|color=gray<ref name=color>Stern, S. A., Mutchler, M. J., Weaver, H. A., and Steffl, A. J. "[http://arxiv.org/abs/astro-ph/0605014 The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006]." ''Astronomical Journal'', submitted April 29, 2006. Accessed April 17, 2008.</ref>
|color=gray<ref name=color>Stern, S. A., Mutchler, M. J., Weaver, H. A., and Steffl, A. J. "[http://arxiv.org/abs/astro-ph/0605014 The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006]." ''Astronomical Journal'', submitted April 29, 2006. Accessed April 17, 2008.</ref>
|albedo=0.04<ref name=color/><ref>An assumed value</ref>
|albedo=0.04<ref name=color/><ref>An assumed value</ref>
}}'''Hydra''' is the third or outermost [[moon]] of the [[dwarf planet]] [[Pluto]]. It was discovered by the Hubble Space Telescope Pluto Companion Search Team in May of 2005.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/pluto.html Pluto]." <http://www.nineplanets.org/> Accessed January 22, 2008.</ref><ref name=IAUdisc>"[http://cfa-www.harvard.edu/iau/special/08625.pdf IAU Circular No. 8625]." [[International Astronomical Union]], October 31, 2005. Accessed April 17, 2008.</ref><ref name=hubble>"[http://hubblesite.org/newscenter/archive/releases/2005/19/ NASA's Hubble Reveals Possible New Moons Around Pluto]." News Release STScl-2005-19, ''Hubble Site'', October 31, 2005. Accessed April 17, 2008.</ref>
}}'''Hydra''' is the third or outermost [[moon]] of the [[dwarf planet]] [[Pluto]]. It was discovered by the Hubble Space Telescope Pluto Companion Search Team in May 2005.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/pluto.html Pluto]." <http://www.nineplanets.org/> Accessed January 22, 2008.</ref><ref name=IAUdisc>"[http://cfa-www.harvard.edu/iau/special/08625.pdf IAU Circular No. 8625]." [[International Astronomical Union]], October 31, 2005. Accessed April 17, 2008.</ref><ref name=hubble>"[http://hubblesite.org/newscenter/archive/releases/2005/19/ NASA's Hubble Reveals Possible New Moons Around Pluto]." News Release STScl-2005-19, ''Hubble Site'', October 31, 2005. Accessed April 17, 2008.</ref>
== Discovery ==
== Discovery ==
== Physical characteristics ==
== Physical characteristics ==
The Hubble Space Telescope's instruments have not been able to resolve Hydra sufficiently to measure its diameter. 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.<ref name=team2/> Nor has any instrument been able to resolve its sidereal day. Hydra is somewhat brighter than its companion moon Nix, and so might be the larger of the two, but this is not proved.<ref name=color/>
The Hubble Space Telescope's instruments have not been able to resolve Hydra sufficiently to measure its diameter. 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.<ref name=team2/> Nor has any instrument been able to resolve its sidereal day. Hydra is somewhat brighter than its companion moon Nix, and so might be the larger of the two, but this is not proved.<ref name=color/>
The [[New Horizons]] space probe, launched in 2006, will visit Hydra and its companions in February of 2015. This will represent the earliest opportunity to study Hydra in detail.
The [[New Horizons]] space probe, launched in 2006, will visit Hydra and its companions in February 2015. This will represent the earliest opportunity to study Hydra in detail.
== Companion satellites ==
== Companion satellites ==