Pluto's Moon Hydra Coated in Nearly Pristine Water Ice

Posted on May 10, 2016

Pluto's icy moon Hydra

NASA's New Horizons researchers say data suggests that Pluto's moon Hydra is covered in nearly pristine water ice. The data was recently retrieved from New Horizons after being collected using the Ralph/Linear Etalon Imaging Spectral Array (LEISA) instrument on July 14, 2015, from a distance of 150,000 miles (240,000 kilometers).

NASA scientists say the data confirms hints picked up on images that show Hydra's highly reflective surface. The infrared spectra data shows what the researchers call "the unmistakable signature of crystalline water ice." It reveals a broad absorption from 1.50 to 1.60 microns and a narrower water-ice spectral feature at 1.65 microns. The chart below shows the data for Hydra and Charon compared to pure ice.

Charon and Hydra reflective data

The Hydra spectrum is similar to that of Charon (Pluto's largest moon) which is also dominated by crystalline water ice. Hydra's water-ice absorption bands are even deeper than Charon's. This suggests the ice grains on the surface of Hydra are larger or reflect more light at certain angles than the grains on Charon.

Simon Porter, a New Horizons science team member from Southwest Research Institute in Boulder, Colorado, says in a statement, "Perhaps micrometeorite impacts continually refresh the surface of Hydra by blasting off contaminants. This process would have been ineffective on the much larger Charon, whose much stronger gravity retains any debris created by these impacts."