Categories: BlogInfographicsMissionsNew HorizonsPluto

Pluto’s Moons Nix and Hydra Get Real / New Pluto Mountain Range Discovered

Pluto’s moon Nix (left), shown here in enhanced color as imaged by the New Horizons Ralph instrument, has a reddish spot that has attracted the interest of mission scientists. The data were obtained on the morning of July 14, 2015, and received on the ground on July 18. At the time the observations were taken New Horizons was about 102,000 miles (165,000 km) from Nix. The image shows features as small as approximately 2 miles (3 kilometers) across on Nix, which is estimated to be 26 miles (42 kilometers) long and 22 miles (36 kilometers) wide. Pluto's small, irregularly shaped moon Hydra (right) is revealed in this black and white image taken from New Horizons' LORRI instrument on July 14, 2015 from a distance of about 143,000 miles (231,000 kilometers). Features as small as 0.7 miles (1.2 kilometers) are visible on Hydra, which measures 34 miles (55 kilometers) in length. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Of course they’ve always been real worlds. They just never looked that way. We’ve only known of their existence since 2005, when astronomers with the Pluto Companion Search Team spotted them using the Hubble Space Telescope. Never more than faint points of light, each is now revealed as a distinct, if tiny, world.

“Before last week, Hydra was just a faint point of light, so it’s a surreal experience to see it become an actual place, as we see its shape and spot recognizable features on its surface for the first time,” said New Horizons mission science collaborator Ted Stryk.

Nix and Hydra compared to “giants” Pluto and its largest moon Charon. Pluto measures 1,473 miles in diameter and Charon 790 miles. A. Stern (SwRI) and Z. Levay (STScI)

Nix looks like a strawberry-flavored jelly bean, but that reddish region with its vaguely bulls-eye shape hints at a possible crater on this 26 miles (42 km) long by 22 miles (36 km) wide moon. Hydra, which measures 34 x 25 miles (55 x 40 km), displays two large craters, one tilted to face the Sun (top) and the other almost fully in shadow. Differences in brightness across Hydra suggest differences in surface composition.

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Now we’ve seen three of Pluto’ family of five satellites. Expect images of Pluto’s most recently discovered moons, Styx and Kerberos, to be transmitted to Earth no later than mid-October.

Formation of Pluto’s moons. 1: a Kuiper belt object approaches Pluto; 2: it impacts Pluto; 3: a dust ring forms around Pluto; 4: the debris aggregates to form Charon; 5: Pluto and Charon relax into spherical bodies. Smaller pieces became the irregularly-shaped moons Nix, Hydra, Kerberos and Styx. Credit: Wikipedia

All of Pluto’s satellites are believed to have been created in what’s now referred to as “The Big Whack”, a long-ago collision between Pluto and another planetary body. A similar scenario probably played out at Earth as well, leading to the formation of our own Moon. In Pluto’s case, most of the material pulled together to form Charon; the leftover chips became the smaller satellites. Their sizes are too small for self-gravity to crush them into spheres, hence their irregular shapes. The moons’ neatly circular orbits about Pluto suggest they formed together rather than being captured willy-nilly from the Kuiper Belt.

A newly discovered mountain range lies near the southwestern margin of Pluto’s Tombaugh Regio (Tombaugh Region), situated between bright, icy plains and dark, heavily-cratered terrain (left). This image taken on July 14, 2015 from a distance of 48,000 miles (77,000 km) and received on Earth on July 20. Features as small as a half-mile (1 km) across are visible.
Credits: NASA/JHUAPL/SWRI

Update: This just in. Take a look at this new close-up of Pluto that features a newly discovered mountain range in southwestern Tombaugh Regio. Sure looks like ice flows. This is a complex little dwarf planet!

Below we have a special treat just in this morning (July 22) — mosaics and montages of Pluto and family created by Damian Peach from New Horizons images. Be sure to click to see the hi-res versions. Enjoy!

Close up mosaic of a part of Tombaugh Regio created by Damian Peach using New Horizons imagery

The Pluto system with Charon (upper right), Nix and Hydra. Credit: NASA, Damian Peach

Views of Pluto during New Horizons’ approach. Credit: NASA/Damian Peach

Charon approach from New Horizons. Credit: NASA/Damian Peach

Bob King

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.