Since their discovery by the Hubble Space Telescope in 2005, Pluto's tiny moons Nix and Hydra have been mere distant specks of reflected light. But with new observations transmitted back to Earth by NASA's New Horizons mission, that has all changed.
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Blasting through the Pluto system at around 31,000 miles per hour on July 14, New Horizons was able to quickly image the dwarf planet's moons as it made its rapid close encounter, coming within 7,750 miles of Pluto's surface. By now, we are becoming very familiar with Pluto's and largest moon Charon's beautifully detailed geology, but the smaller moons have yet to be so well defined.
However, that's beginning to change, in new imagery showcased on Tuesday.
Shown here are Nix and Hydra, the second and third Pluto moons to be discovered after Charon. Nix's color has been enhanced and an intriguing region has been revealed, appearing reddish. According to NASA, the moon is "jelly bean-shaped," around 26 miles (42 kilometers) long and 22 miles (36 kilometers) wide.
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This reddish region has piqued mission scientists' interest, and they already speculate that this region may be the site of a large impact crater, but they have to be patient and wait for the spacecraft to send more data.
"Additional compositional data has already been taken of Nix, but is not yet downlinked. It will tell us why this region is redder than its surroundings," said Carly Howett, New Horizons mission scientist with the Southwest Research Institute, in Boulder, Colo. "This observation is so tantalizing, I'm finding it hard to be patient for more Nix data to be downlinked."
In addition to Nix, New Horizons also sent an observation of Hydra made by the spacecraft's Long Range Reconnaissance Imager (LORRI) from a distance of 143,000 miles (231,000 kilometers). This observation reveals an irregularly shaped moon around 34 miles (55 kilometers) long and 25 miles (40 kilometers) wide with what appear to be two large craters and some variation in surface composition.
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"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 Ted Stryk, mission science collaborator from Roane State Community College in Tennessee.
In addition to Charon, Nix and Hydra, two more moons, Kerberos and Styx - also discovered by Hubble in 2011 and 2012, respectively - are known to orbit Pluto. And as the months go by, planetary scientists will be keen to see more images of Pluto's extended satellite family beamed back to Earth, helping us better understand the nature of this fascinating region of the Kuiper belt.