NASA's New Horizons space probe has sent the first compositional data about the four satellites of Pluto. The new data are showing that Hydra's surface is covered by nearly pristine frozen water.
According to Space Coast Daily, the new compositional data received recently on Earth were taken from a distance of 150,000 miles (240,000 kilometers), on July 14, 2015. The data were gathered by the Ralph/Linear Etalon Imaging Spectral Array (LEISA) instrument.
The infrared spectral readings acquired almost 10 months ago had to stay stored in the onboard computer's memory until only recently. So far, only around half of the data from the Pluto flyby mission have been sent back and they are estimated that it will take months longer to send back the rest.
Geek Wire reports that the new data received from the New Horizons space exploration mission show that the surface of Pluto's outermost small moon, Hydra, is dominated by nearly pure water ice. This information is confirming previous hints that scientists had by studying New Horizons images showing a highly reflective surface on the Hydra moon.
The new infrared spectra data show the signature of crystalline water ice. The Hydra spectrum is similar to Charon, Pluto's largest moon. Previously, scientists received infrared spectra data that confirmed Charon is also dominated by crystalline water ice.
Hydra's water-ice absorption bands are even deeper than Charon's. This suggests that ice grains on Hydra's surface reflect more light at certain angles or are larger than the ice grains on Charon.
Scientists believe that Hydra have formed some 4 billion years ago in an icy debris disk produced from the collision of two planetary bodies that formed the Pluto-Charon binary. Hydra's high reflectance and deep water bands imply relatively little contamination by Charon's surface darker material. Now mission scientists are studying the reasons why Hydra's ice appears cleaner than Charon's.
Simon Porter of Southwest Research Institute in Boulder, Colorado, a New Horizons science team member, said that one of the possible reasons might consists in micrometeorite impacts that blasted off contaminants, continually refreshing the surface of Hydra. According to him, on the much larger Charon, this process would have been ineffective due to much stronger gravity that would retain any debris created by impacts.
