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New Data from New Horizons Reveals Pure Water Ice on Pluto’s Moon Hydra

Hydra lives up to its name with its super-clean water ice.
Image: NASA,

When scientists discovered a tiny moon orbiting Pluto back in 2005, they named it Hydra in keeping with the general Greco-Roman underworld theme established in the Plutonian system.

But now, the New Horizons spacecraft, which flew by Pluto last summer, has found that Hydra's name is doubly fitting, thanks to its watery associations. The latest dispatch from the distant probe contains the first composition data about Pluto's four small satellites, and includes confirmation that Hydra is covered in pristine water ice, which explains why it is such a highly reflective world.


Images captured by New Horizons' array picked up the spectral fingerprints of unusually clean ice all over Hydra. By itself, that news is not surprising, as New Horizons has revealed that the Plutonian system is quite abundant in water ice. But for some reason, Hydra has some next-level snow purity on its slopes, which results in a much brighter surface than other moons, like Charon.

"Perhaps micrometeorite impacts continually refresh the surface of Hydra by blasting off contaminants," speculated Simon Porter, who works with the New Horizons science team, in a statement. "This process would have been ineffective on the much larger Charon, whose much stronger gravity retains any debris created by these impacts."

New compositional data from New Horizons. Image: NASA/JHUAPL/SwRI

The only way to find out will be to keep studying fresh data from New Horizons as it comes in. Though the probe is traveling ever deeper into the Kuiper belt, it is still processing and transmitting the wealth of information about Pluto and its moons during its brief flyby last July, so no doubt plenty of new discoveries are still headed down the pipeline.