Hydra is the outermost of Pluto ’s known moon , and until now , we ’d only ever seen it as a faint pixel of sparkle . Today , planet Earth get its first real glance of this petite , oracular artificial satellite .
This never - before - seen view of Hydra ’s open was captured yesterday at a length of 645,000 kilometer , within hours of New Horizons closelipped approach path on the morning of July 14th , 2015 . Captured with the spacecraft ’s high - resolution , monochromatic LORRI camera at approximately 3.2 kilometers per pel , we ’re literally watching a point of light transform into a bonafide Sun Myung Moon . That is a big flaming slew .
For the first clip , we recognise the size of Hydra . It ’s about 48 km by 33 kilometer ( 27 miles by 20 mil ) , a definitely stretch , lopsided lump of rock and ice . It has an medium albedo , a luminance about halfway between Pluto and Charon . That means the aerofoil must be almost entirely frosty .
Nix and Hydra each orbit Pluto about once a month . Image acknowledgment : NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute
We think that Hydra is either the second or third - prominent moonshine of Pluto , but we wo n’t live for certain until tomorrow when we get our first eminent - solving at the other competition , Nix .
Hydra was let in in the first datum downlink betimes this morningafter the New Horizons probe restore liaison of late last Nox . But this is n’t the last facial expression we ’ll get at this little moon . From New Horizons Project Scientist and LORRI science operations lead Hal Weaver : “ New Horizons has finally nailed the basic physical properties of Hydra . We ’re going to see Hydra even better in the double yet to follow . ” We ’ll be getting a second feeling at the moonlight at just over 1 kilometer per pixel resolution later this workweek .
Charon might have been the first moonlight spotted in the Pluto system , but within the past decade , we ’ve added four additional satellites to the flock — Nix , Styx , Kerberos , and Hydra . We were already preparing to launch the New Horizons probe to Pluto when Hydra and Nix were identify in June of 2005 by the Hubble Space Telescope ’s ‘ Pluto Companion Search Team . ’ Kerberos was notice later on , in 2011 during a Hubble survey search for rings around Pluto , while teeny tiny small Styx was n’t spotted until July of 2012 , when the New Horizons team was conducting a lookup for potential hazards to the reconnaissance mission mission .
On June 21st , 2006 , the name ‘ Hydra ’ was attribute by the International Astronomical Union . Hydra , a nine - headed serpent from Greek mythology , pays double court to Pluto ’s then - tenure as the ninth satellite in our solar system ( Pluto was reclassify as a dwarf satellite in August 2006 ) , with the ‘ H ’ also indicating its discovery by Hubble .
Hydra orbits Pluto at roughly 64,800 kilometers ( 40,264 miles ) from the gravitative center ( barycenter ) of the system . Its nearly orbitual , prograde ambit is in the same plane as the moon Charon . Hydra is sometimes bright than the other oblong moon , Nix , suggesting that it is either larger or that the surface of the moon variegate in brightness .
Until the New Horizons flyby , astronomers had no direct measurements of Hydra ’s size . We had work out some very rough size of it estimates based on the presumptuousness that Hydra is the same brightness as Charon . That assumption , however , would imply Hydra is compositionally very standardized to Charon ( roughly a 50 / 50 mix of ice and rock ) , and we really had no good cause to expect that it is . There could be any number of appendage — collisions between planetary bodies , different ices or gases siphon off Pluto — that might make Pluto ’s organization compositionally divers , similarly to the Moon surrounding Jupiter , Saturn , and Neptune .
That Charon , Hydra and Nix are all comparatively the same brightness is simply the best guess we were able to make based on incredibly limited selective information . But with our first real image of Hydra , we can start up to make some more sophisticated reflection and hypotheses about what this enigma of a lunation is actually made of .
Despite the fact that we were really just guessing at Hydra ’s size before today , we were correct in supposing the moon is n’t massive enough to form a spheroid under its own gravity . Like Mars ’ moon Phobos , Hydra ( and Nix ) are rather oblong little things :
During the New Horizons mission to fly through the Pluto - Charon system , our previous best tone at the smaller moon Nix and Hydra was way back in February .
Pluto , Charon , Nix , and Hydra seen by the Hubble Space Telescope in 2006 . Image credit rating : NASA / ESA / H. Weaver / A. Stern
Heavy processing brings out Nix and Hydra more distinctly [ right ] while losing pesky details like desktop stars[left ] . range of a function credit : NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute
And here she is again , as revealed bit ago :
Fascinated by Hydra ? Hold onto your keyboard , nerd ! This is only the beginning . We ’ll be getting back even higher resolution images of Hydra in the coming solar day , and learning much , much more about Pluto ’s outermost known moon in the weeks and months ahead . We ’ll get our first downlink of Pluto ’s other oblong moon , Nix , later tonight , and see it within the next few twenty-four hour period .
Top image : Hydra close to 644,000 kilometers ( 400,000 mile ) away from New Horizons . credit entry : NASA / JHUAPL / SwRI
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