Pluto looks to be a far cry from the dead body that many scientists had long presumed. As the New Horizons probe continues to report back from the fringes of the solar system, a word that Mr. Spock might have used sums up the reaction: fascinating.
The latest snapshots represent only 1 to 2 percent of the data collected in the flyby — many more gigabits have yet to be sent across the billions of miles of interplanetary space.
The images show an area at the center of now-famous heart-shaped feature, informally dubbed "Tombaugh Regio" after Pluto's discoverer, Clyde Tombaugh. The newest features to be revealed are Sputnik Planum (named after the first artificial satellite) — a vast ice plain segmented by troughs and hills of Norgay Montes after the Nepali Sherpa who, along with Edmund Hillary, was the first to scale Mount Everest.
NASA put together this animated flyby of the region:
"Who would have expected this kind of complexity?" Alan Stern, New Horizons principal investigator at the Southwest Research Institute (SwRI) in Boulder, Col., asked rhetorically at a NASA news conference.
"I am a little biased, but I think the solar system saved the best for last," he said.
Randy Gladstone, New Horizons co-investigator at SwRI in San Antonio said early data suggests that Pluto has a multi-layered atmosphere, with nitrogen at the highest level, methane in between and "heavier hydrocarbons" near the surface. Because of Pluto's lack of gravitational heft, the nitrogen is escaping into space at a prodigious rate, he said.
"We know the atmosphere is nitrogen, escaping because of the weak gravity," says Fran Bagenal, New Horizons co-investigator at the University of Colorado, Boulder. "What we think is happening is that it's energized by the solar wind and carried off into space."
"As it escapes, the atmosphere is ionized as it is picked up by the solar wind," she said referring to the stream of charged particles emitted by the Sun.
Jeffrey Moore, New Horizons co-investigator at NASA's Ames Research Center in Moffett Field, Calif., described the irregularly shaped features of Sputnik Planum as "vast craterless plains that have some story to tell."
"I am still having to remind myself to take deep breaths. The geology is just astounding," he said.
The region is thought to be only about 100 million years old, quite young on the 4.5 billion-year timescale of the solar system. The forces that shaped it might still be in play on Pluto.
What about Norgay Montes? Moore said: "We suspect either the hills were pushed up from beneath the surface ... or are erosion-resistant knobs," that remain as the rest of the surface has been eroded away, being turned directly from solid to gas.
There's also the matter of some tantalizing dark smudges that look similar to plumes found on Neptune's moon, Triton. But, Moore said, it's too soon to say whether they are being driven by Pluto's internal geology or the wind on the surface.
For the data that might answer that and other questions, the scientists still have a few months to wait as New Horizons continues its interplanetary data dump.
As NPR's Geoff Brumfiel reported earlier this week:
"Since its discovery in 1930, Pluto has revealed itself to be an oddball world. It's smaller than our own moon, and it orbits at an angle relative to the plane of the solar system. Because of its size and distance, even the Hubble Space Telescope could only make it out as a brown smudge, billions of miles away.
"With New Horizons, all that has changed. Scientists can now see craters and regions of dark-reddish ground. A large, white, heart-shaped feature on the equator is made of ice, though Pluto is so cold it's probably an ice of nitrogen or methane, rather than water. A new close-up of a small region on Pluto's surface also reveals towering ice mountains, up to 11,000 feet high."