New Horizons has been sending back stunning images of Pluto and its system for a while now. As we’ve collectively feasted on them, they've given researchers a chance to study the ex-planet and its satellites in unprecedented detail. The first results of that work are now out, and while some of the conclusions are expected, there is plenty of new information and detail.

The paper containing those details, published in the journal Science, covers more than just Pluto itself—it also examines the curious geology of Charon, its largest moon, and an unexpected result from its two smaller moons, Hydra and Nix. It details the search for extra moons, or even rings, in the system. Spoiler alert: none was found.

We’ll take you through the results on all of these bodies, starting with the main show: Pluto itself.

Pluto

One easily detectable feature of a celestial body is its shape, which can provide essential clues about its evolution. When a hot, still-forming body spins quickly on its axis, it doesn’t maintain its spherical shape. Instead, it starts to flatten out, looking more and more like a pancake. Many bodies are affected by this process, including the Earth itself, which is technically not a sphere but an “oblate spheroid.”

Pluto, however, turns out to be mostly a sphere. Any deviation from that shape could be no larger than a one percent difference between Pluto’s horizontal and vertical axes. The dwarf planet could have been spinning quickly due, say, to the formation of the moon Charon, which could have left evidence in the form of Pluto’s shape. That seems not to have happened.

That doesn’t necessarily mean the quick spin-up didn’t happen, though. The researchers speculate that this might be because Pluto remained warm and deformable during or after this process and re-established a spherical shape afterward.

The lay of the land

Pluto also has an interesting geography—and geology—that provides further insight. Not only is it covered in land masses worthy of any science fiction convention, but it has a remarkable variety of features, including a water ice crust.

Naming conventions

Someone clearly had fun naming places on Pluto. Once you’ve visited the Cthulhu Regio, you may be banished to Tartarus Dorsa, but you simply shall not pass the Balrog Macula! Someone clearly had fun naming places on Pluto. Once you’ve visited the Cthulhu Regio, you may be banished to Tartarus Dorsa, but you simply shall not pass the Balrog Macula! Charon goes even further. If you're planning a vacation to Charon, you can journey to Mordor Macula, but not before you’ve made a pilgrimage to Spock Crater in the Vulcan Planum, crossed the Tardis Chasma in Gallifrey Macula, and turned to the dark side of the Vader Crater. And no one heard you scream in Nostromo Chasma. And let's not forget Skywalker Crater, Organa Crater, Serenity Chasma, Kubrick Mons, and so on. While the naming scheme may not fit with the Greek and Roman mythology theme of the bodies themselves (Pluto is the Roman god of the underworld, and its moons are all associated with the underworld as well), it does have its merits.



One surprising conclusion we previously described is the planet’s recent geological activity. Researchers expected a dwarf planet to simply be too small to hold on to its heat from formation and too bereft of radioactive materials to produce new heat. The tidal forces from Charon fall short of producing enough heat to keep Pluto churning up to geologically recent times, if not to today.

Yet Pluto’s mountain ranges speak of tectonic activity, while its vast plains show recent remodeling. One region in particular, the Sputnik Planum, has large plains that have far fewer impact craters than the surrounding regions.

Since the objects responsible for these craters are largely from the Kuiper Belt (a ring of bodies of which Pluto is a member) researchers are able to model how often, on average, Pluto should be impacted. Rewinding this picture, the researchers calculated how long it would take for that area to reach its present distribution of craters. They found it should take a few hundred million years, which is likely when the plains came into existence, cooled from material that had welled up due to geological activity.

Atmosphere

Due to the REX instrument on New Horizons, researchers have gotten the first direct measurements of the lower atmosphere’s temperature and pressure.

The atmospheric pressure is somewhat lower than expected from Earth-based observations. It’s currently unclear whether this is because the atmosphere is shrinking, which is the opposite of what we'd observed prior to New Horizons’ arrival, or whether the pressure was always this low, and there’s some discrepancy between the two measurement techniques that creates an error.

New Horizons also discovered the presence of a haze extending up to about 150 kilometers above the dwarf planet’s surface. One possibility is that the haze is the result of interactions between ions (charged particles) in space and molecules on the planet's surface. Alternatively, the formation mechanism could involve dust from meteors.

The atmosphere also has somewhat less methane than expected, is slightly cooler than expected, and has new components not expected: acetylene and ethylene. Overall, the atmosphere is largely stagnant, at least from an altitude of 50 to 300 kilometers above the surface.