Pluto’s smaller moons, Nix and Hydra, have been showing off their surface features as new images from NASA’s New Horizons spacecraft bring them into much clearer focus.
The two moons are approximately the same size at an estimated 42 kilometres (26 miles) long and 36 kilometres (22 miles) across, however, the similarities between them end there. For one, Nix takes on a jelly bean-shape with a splattering of red while its companion moon, Hydra, is much more irregular in shape with a more grey and neutral shading. Nix was imaged by New Horizons’ Ralph instrument, while Hydra was snapped by the spacecraft’s LORRI (LOng-Range Reconnaissance Imager) instrument.
Astronomers are speculating that Nix’s bull’s-eye pattern is a crater but will need to get a much more closer look before they can certain. “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,” says New Horizons mission scientist Carly Howett of the Southwest Research Institute in Boulder, Colorado. “This observation is so tantalising, I’m finding it hard to be patient for more Nix data to be downlinked.”
Meanwhile Hydra, which the New Horizons team have likened to the state of Michigan because of its shape, appears to play host to at least two large craters, one of which is mostly in shadow. The moon’s upper portion looks much darker than then rest of the dwarf planet’s satellite, which suggests a possible difference in the composition of Hydra’s surface.
It was only last week that Hydra was just a faint point of light. “It’s a surreal experience to see [the moon] become an actual place, as we see its shape and spot recognisable features on its surface for the first time.” says Ted Stryk, a mission science collaborator, who is based at Roane State Community College in Tennessee.
Images of Pluto’s most recently discovered moons, Styx and Kerberos, are expected to be transmitted to Earth no later than mid-October.