Pluto continues to blow away all expectations for what we thought this dwarf planet was going to look like. Fresh off the back of the discovery of icy mountains and frozen plains on its surface, a new view from New Horizons has revealed more mountains among filled-in craters.
The latest image is looking at a region toward the southwest of the heart-shaped Tombaugh Regio (Tombaugh Region). It was taken by the Long Range Reconnaissance Imager (LORRI) on New Horizons on July 14, 2015 from a distance of 77,000 kilometers (48,000 miles).
The mountains in the image are about 1.0 to 1.5 kilometers (0.5 to 1.0 mile) high, smaller than the earlier icy Norgay Montes (Norgay Mountains) spotted on Pluto. These latest mountains are about the same height as the Appalachian Mountains in the US.
Perhaps most interestingly, the image reveals previously scarce craters on the surface. The darker region seen here may date back billions of years, as opposed to other much lighter and younger areas on the surface such as Sputnik Planum, which is thought to be less than 100 million years old.
The craters, though, appear to be filled with a bright, sediment-like material, such as the crater to the lower left of the center of the image. The cause of activity that shifted this material on Pluto's surface is not yet known, but some have suggested that it may be the result of geological activity.
“There is a pronounced difference in texture between the younger, frozen plains to the east and the dark, heavily-cratered terrain to the west,” said Jeff Moore, leader of the New Horizons Geology, Geophysics and Imaging Team (GGI) at NASA’s Ames Research Center in Moffett Field, California, in a statement. “There’s a complex interaction going on between the bright and the dark materials that we’re still trying to understand.”
Also this week, NASA revealed the clearest views yet of two of Pluto’s moons, Nix and Hydra. Both of the moons are pale in comparison to Pluto’s largest moon, Charon. Nix is just 42 kilometers (26 miles) in length, while Hydra is 55 kilometers (34 miles) long. Charon is about 1,210 kilometers (750 miles) across.
Nix (left) and Hydra (right), as seen by New Horizons. NASA/JHUAPL/SWRI.
The images reveal an odd reddish region on Nix that NASA refers to as a “bulls-eye pattern.” Scientists think that this region may be a crater, but aren’t quite sure why it’s redder than its surroundings. “This observation is so tantalizing, I’m finding it hard to be patient for more Nix data to be downlinked,” said mission scientist Carly Howett, Southwest Research Institute, Boulder, Colorado in a statement.
The image of Hydra, meanwhile, reveals that it has an irregular shape that resembles the state of Michigan. Two large craters seem to be on its surface, one of which is in shadow, while the surface appears to have different compositions in the upper and lower portions.
With each new image, Pluto and its moons become more and more fascinating. By mid-October, we can expect the first ever images of the remaining two of the five moons to be seen, Styx and Kerberos. Until then, we’ll have to make do with analyzing the increasingly fascinating surface of Pluto and its imaged moons.