New images of Pluto, sent back to Earth from NASA’s New Horizons spacecraft, are unveiling more surprises about the dwarf planet on the fringe of the observable solar system. Released over the last two days, the images are higher resolution than the ones released in July, when the spacecraft flew within 8,000 miles of Pluto’s surface. In the new set, landforms such as a chaotic patch of jumbled terrain, linear features resembling wind-sculpted dunes, and oozy nitrogen ice flows are sharp and in-focus.
When seen in silhouette, Pluto’s puffy nitrogen atmosphere, carved into hazy layers, steals the show. It’s even possible to see atmospheric rays that appear at dawn and dusk, as well as the bumpy, uneven outlines formed by features on Pluto’s surface (see image in the gallery above). In other words, we’re seeing Plutonian valleys, mountains and craters at twilight.
— Ian Regan (@IanARegan) September 11, 2015
(Bonus points for using crepuscular, one of my favorite words.)
Pluto’s geology is incredibly diverse, said Alan Stern, the mission’s principal investigator, during a Google hangout today. “I think it’s magical. It’s absolutely breathtaking.”
It’s not yet clear how the extreme diversity of Pluto’s surface has been shaped, but data sets downloaded over the next year should offer some clues. They’ll also tell us about the other members of Pluto’s family — its large moon Charon, and the four smaller satellites Nix, Hydra, Kerberos and Styx.
Images of Charon released yesterday are reinforcing a two-month-old idea about the moon’s activity: Even though it looks slightly more dead than Pluto — Charon is not as diverse geologically or compositionally, and doesn’t have a puffy atmosphere — the moon isn’t the lifeless, cratered sphere many scientists thought it would be.
“Charon has its own history,” Stern says. “There are faults, or other kinds of tectonic features on the surface — big canyons, clear evidence that there was some evolution on the surface, not just things bombarding it from the outside.”
Among other surprises revealed in July is the dark stain covering Charon’s north pole, which scientists think could be made of irradiated organic molecules that have wafted over from Pluto, writes Carly Howett of the Southwest Research Institute. As for Charon’s south pole? That’s still a complete mystery.
The best guess now is that the Pluto-Charon system formed from a giant impact not too unlike the collision that produced the Earth-moon system. Small shards of debris flung into space when the bodies collided eventually formed the four known smaller moons. Though tiny, those moons present their own questions, such as why — if they all formed from the same ingredients — one is peculiarly dark, while the others are bright. In fact, new images of Nix suggest it’s even brighter than some of the material on both Pluto and Charon, which presents a conundrum. The 30-mile-long moon also appears to have at least one enormous crater, surrounded by reddish material that may have been excavated from beneath the surface.
“Whether that’s an impact crater or something else is a little bit TBD,” Stern says. “It’s interesting that we don’t see a lot of other craters on its surface. We have some ideas about that, but it’s still early.”
For now, having more questions than answers is the norm. And that’s not only O.K., but pretty dang exciting.