New Delhi: In a latest, new compositional data from NASA’s New Horizons spacecraft reveals that the surface of Hydra, Pluto’s outermost small moon, is dominated by nearly pristine water ice.
According to NASA, the new compositional data, recently received on Earth, was gathered with the Ralph/Linear Etalon Imaging Spectral Array (LEISA) instrument aboard New Horizons spacecraft on July 14, 2015, from a distance of 150,000 miles (240,000 kilometers).
The new data, known as infrared spectra, shows the Hydra spectrum is similar to that of Pluto’s largest moon, Charon, which is also dominated by crystalline water ice.
But the data indicates that Hydra’s water-ice absorption bands are even deeper than Charon’s, suggesting that ice grains on Hydra’s surface are larger or reflect more light at certain angles than the grains on Charon.
(New compositional data from NASA’s New Horizons spacecraft reveal a distinct water-ice signature on the surface of Pluto’s outermost moon, Hydra. Pluto’s largest moon Charon measures 752 miles (1,210 kilometers across), while Hydra is approximately 31 miles (50 kilometers) long.) Image credits: NASA/JHUAPL/SwRI
Hydra is thought to have formed in an icy debris disk produced when water-rich mantles were stripped from the two bodies that collided to form the Pluto-Charon binary some 4 billion years ago. Hydra’s deep water bands and high reflectance imply relatively little contamination by darker material that has accumulated on Charon's surface over time.
Mission scientists are investigating why Hydra’s ice seems to be cleaner than Charon’s.
"Perhaps micrometeorite impacts continually refresh the surface of Hydra by blasting off contaminants,” said Simon Porter, a New Horizons science team member from Southwest Research Institute in Boulder, Colorado, “This process would have been ineffective on the much larger Charon, whose much stronger gravity retains any debris created by these impacts.”
Meanwhile, the New Horizons science team is looking forward to obtaining similar spectra of Pluto’s other small moons, for comparison to Hydra and Charon.
Hydra, was only discovered in 2005, along with Nix - second outermost of Pluto’s five moons - by scientists using data from the Hubble Space Telescope.