LAUREL, Md.NASA has released the first of many images taken during New Horizons' close encounter with dwarf planet Pluto.
And they are, in a word, astounding.
The images include a high-res view of a small patch near Pluto’s equator, in which mountains made of water ice rise 11,000 feet above what appears to be a young, active surface. Charon, Pluto’s largest moon, has also emerged in surprising detail. And then there’s the first image of Hydra, one of the system’s four small moons. Already, these images are challenging views about how small, icy worlds work.
“I think the whole system is amazing,” says New Horizons principal investigator Alan Stern. “This system is something wonderful.”
Now that Pluto is in the spacecraft’s past, the team is beginning to dig through the stream of data New Horizons will send to Earth over the next 16 months. Those observations, the first of which arrived at 5:50 a.m. on July 15, include information about Pluto’s atmosphere and composition, as well as the system’s four small moons. (Learn more about the historic mission to Pluto on the National Geographic Channel.)
A World Unlike Any Other
Early images showed that Pluto is a mottled, champagne-colored world that doesn’t look like anything else in the solar system—even if its reddish hue does somewhat resemble Mars. (New Horizons also found that Pluto is bigger than we thought.)
Pluto's surface, which we’ve been wondering about for 85 years, is unique. The world is covered in dramatically different terrains, some smooth, some cratered and bumpy. The new Pluto image reveals a portion of the planet with large mountains looming over a surface that looks relatively young—so young, in fact, that it suggests the planet is still geologically active.
“We have not yet found a single impact crater on this image,” says team member John Spencer. “Pluto has been bombarded by other objects in the Kuiper Belt. Craters happen. We think it has to be probably less than 100 million years old… it might be active right now.”
Pluto also varies in brightness. Smeared near the planet’s equator is an extremely bright, heart-shaped region the team is now informally calling Tombaugh Regio, after the man who discovered Pluto in 1930.
“We could see the heart very far from Pluto,” Stern said. “You could see that shining like a beacon, and because it’s the brightest and most prominent feature on the planet, that’s why we want to call it Tombaugh Regio.”
Hugging that heart on either side are splotches that are about as dark as anything can get. The heart’s halves appear to be made from different ingredients, but the team doesn’t yet understand the geology of the whole region.
“It’s kind of a coincidence that these things have similar [brightness],” said team member Will Grundy of Lowell Observatory.
It’s also not clear why the heart appears to be so smooth, or “absurdly featureless,” as Spencer called it. Studying its boundaries should provide a hint about what’s going on, and whether the smoother terrains are elevated or sunken.
“I expected it would be complicated and fascinating, but I had no idea it would be this complicated and this fascinating,” Grundy says. “All of the scientists are absolutely thrilled.”
And then there’s Charon, Pluto’s mega-moon.
“Pluto and Charon look very different,” Stern said. “Now we can see how dramatically different they really are.”
Together, the two bodies comprise a binary planet. They whirl around a point in the space between them, performing a cosmic dance in which they perpetually stare at one another. While scientists expected Charon to be intriguing, they weren’t prepared for the image that came back today.
“It’s a small world with deep canyons, troughs, cliffs, dark regions that are still slightly mysterious to us,” said deputy project scientist Cathy Olkin. “There is so much interesting science going on in this image alone.”
Charon has an enigmatic dark pole that could be made of materials that escaped from Pluto. Team members are informally referring to that area as Mordor, Olkin said.
The moon is also cracked—and some of those cracks are enormous, as much as five or six miles deep. What’s more, Charon’s surface is not ancient and completely cratered, as scientists had anticipated. Instead, the moon’s sparsely cratered face looks surprisingly young, suggesting that it might also be an active world.
In 1930, Clyde Tombaugh discovered Pluto when he compared this image (with Pluto circled) with another taken six days earlier and noticed the bright speck had moved.
Scientists think Charon formed from a giant impact with primordial Pluto, and that debris from the collision eventually coalesced and formed the pair’s four smaller moons, called Nix, Hydra, Kerberos, and Styx.
Hydra has now been seen for the first time, though it still looks like a pixelated blob. But team members figured out that the moon is 27 miles (43 kilometers) long.
“The surface of Hydra is surprisingly large,” says project scientist Hal Weaver. “That can only mean that Hydra’s surface is probably composed primarily of water ice.
Pluto's four moons were recently discovered to be chaotically rotating—in other words, they’re tumbling in orbit rather thin spinning. Altogether, the Pluto system is like a complex, shrunken planetary system, and scientists hope that by unlocking Pluto’s secrets, they’ll learn more about how planetary systems form and evolve.