Since its discovery 85 years ago, Pluto has been nothing more than a tiny dot of light. Thanks to NASA’s New Horizons mission, this is no longer the case. After a 9.5 year, 3.5 billion mile journey, a spacecraft the size of a baby grand piano has revolutionized our understanding of the icy world. The first close-up images of the Pluto system are proving to be every bit as exciting as the science team had hoped. Principal investigator Alan Stern said in a media briefing today, “The Solar System definitely saved the best for last.”

With the data beamed down so far, everything we can now see of Pluto and its five moons is changing the way planetary scientists view these distant, icy worlds. Not only does Pluto harbor 11,000-foot mountains composed of frozen water ice, but its surface and the surface of its largest moon, Charon, are surprisingly devoid of large impact craters. This indicates to scientists that both bodies could be geologically active.

The mountains—thought to be no more than 100 million years old—are very young compared to the age of the Solar System, and their average height rivals that of the Rocky Mountains found here on Earth. It’s too early to determine how they formed, but their presence was a surprise to scientists. “This is one of the youngest surfaces we’ve ever seen in the Solar System,” said Jeff Moore of the New Horizons Geology, Geophysics, and Imaging Team (GGI) at NASA’s Ames Research Center in Moffett Field, California.

Mountains can be formed in many ways, and the team cannot definitively say how these came to be. But they can rule out tidal heating. There are no other large bodies near Pluto other than its largest moon, Charon, and since it is tidally locked with Charon, there is not a large heat exchange system between the two bodies. There must therefore be some other geologic process taking place.

Whatever provides the power, it could reshape the surface through possibilities that include geysers and or cryovolcanoes. Neither of these processes has been observed yet, but the team will be looking for evidence of them.

The latest data, released today, shows a zoomed-in view of a vast, smooth plain north of the mountains in an area unofficially dubbed “Tombaugh Regio” in honor of the man who discovered Pluto—Clyde Tombaugh. Moore went on to say, “This terrain is not easy to explain; however, the discovery of vast crater-less, very young plains on Pluto exceeds all pre-fly expectations.” The icy plains of Pluto seen in the image—unofficially named Sputnik Planum after the first satellite launched in space—resemble frozen mud cracks like we see here on Earth. This could be evidence for contraction of surface materials, like when mud dries and cracks, or even signs of convection below the surface. More data will be needed to tell.

The region is broken into irregular “polygons,” approximately 20 kilometers across; these are bordered by shallow troughs. Some of the troughs are filled with a dark surface material, while some harbor groups of hills. The hills could have been pushed up via interior processes, or they could be erosion-resistant features.

Adjacent to the hills are regions covered by small pits that scientists predict could have formed via sublimation—a process by which ice bypasses the liquid phase and goes directly from a solid to a gas. Another surprise was detected in the heart of Tombaugh Regio; the science team discovered a concentrated area of carbon monoxide ice. The team knew that Pluto contained carbon monoxide, but they were surprised to find the bulk of it concentrated in one location.

Scientists first detected Pluto’s atmosphere back in 2008, but the science team did not expect that the atmosphere extends 1,600 kilometers above the surface and tens of thousands of kilometers beyond Pluto, forming a tail as it’s stripped away by solar wind. The Solar Wind Around Pluto (SWAP) instrument detected an outflow of nitrogen ions that form a plasma tail behind the icy body, similar to the ones observed at Venus and Mars. The team estimates that as much as 500 tons of nitrogen is lost each hour as it escapes and is ionized, then carried away by the solar wind.

“This is just a first tantalizing look at Pluto’s plasma environment,” says co-investigator Fran Bagenal, University of Colorado, Boulder, who leads the New Horizons Particles and Plasma team. “We’ll be getting more data in August, which we can combine with the Alice and Rex atmospheric measurements to pin down the rate at which Pluto is losing its atmosphere. Once we know that, we’ll be able to answer outstanding questions about the evolution of Pluto’s atmosphere and surface and determine to what extent Pluto’s solar wind interaction is like that of Mars.”

During the flyby, New Horizons also observed Pluto’s small moons: Nix, Hydra, Styx, and Kerberos. So far, we only have a sneak peek at Hydra and at Nix. The new data confirms that Hydra is an irregular-shaped world and is estimated to span approximately 43 by 33 kilometers. Its surface reflects about 45 percent of the light that hits it, indicating that it is most likely covered in water ice.

Nix measures only 6 kilometers across, and the science team thinks the image we have shows us only one end of an elongated, football-shaped body spanning roughly 40 kilometers in diameter. Future images along with spectroscopic and stereo data, both still on the spacecraft, are expected to reveal more details about all of the small satellites.

In addition to the images of Pluto, Hydra, and Nix, NASA also released a stunning image of Charon showing never-before-seen details of its surface. Taken from a distance of 466,000 kilometers, the image reveals a younger surface than previously predicted, which indicates Charon is also geologically active. We see evidence of a dark crater—the team refers to as Mordor—cliffs and troughs, as well as a canyon 7 to 9 kilometers deep. To put that in perspective, the Grand Canyon in the United States is approximately 1.6 kilometers deep. Geologists are especially intrigued by an area called “the mountain and the moat,” which features a deep depression with a mountainous peak shooting up from the center.

"With the flyby in the rearview mirror, a decade-long journey to Pluto is over—but, the science payoff is only beginning,” said Jim Green, director of Planetary Science at NASA Headquarters in Washington. "Data from New Horizons will continue to fuel discovery for years to come.”

So far approximately 1 Gigabit of the 50 Gigabits of data collected has been downlinked from the spacecraft. The remaining data will be beamed to ground teams via NASA’s Deep Space Network (DSN) over the next 16 months. Stay tuned for more data and images as they become available.