What Scientists Have Discovered About Pluto (So Far)

Yesterday NASA released the first high-resolution photography of Pluto. Alan Stern, who leads the New Horizons mission as its principal investigator, described the data as “something wonderful.”

Members of the New Horizons team were hesitant to offer anything more than preliminary suspicions—the world is too weird and early information has been returned only from five instruments—but practically everything about the world and its system discovered thus far has proven surprising.

Perhaps the most significant scientific finding is that tidal heating is not essential to power ongoing geologic activity on icy worlds. (Pluto and Charon orbit a common point, always facing one another. Because they are in tidal equilibrium, tides are essentially removed from the equation.) This finding will fundamentally alter our understanding of planets.

Because Pluto appears to have few impact craters, we now think the surface of Pluto is young—less than 100 million years old. (A young surface is smooth; an old surface is cratered.) That’s much younger than the solar system. Active geologic processes can degrade terrain features and fill impact features. Pluto’s 11,000-foot-tall mountains are evidence of an icy bedrock and water ice.

The diversity of Pluto’s surface has left scientists on the New Horizons team stunned. “There’s a lot of depression on the science team,” Stern joked. “They don’t understand anything.”

Image Credit: NASA-JHUAPL-SWRI 

NEW NAMES AND BIG QUESTIONS

Informally, the New Horizons team has given names to newly discovered features on Pluto. The feature formerly called “the whale” is now Cthulhu. Balrog is an area of lumpy terrain. Pluto’s “heart” has been renamed Tombaugh Regio after the discoverer of Pluto, Clyde Tombaugh.

Its atmosphere has been a surprise too. Planetary scientists expected that Pluto would have an atmosphere a bit thicker than that of Triton, Neptune’s moon, and a troposphere and stratosphere like those of Earth. However, the New Horizons measurement of Pluto’s radius—it is larger than expected, and now known to be the ninth-largest body orbiting the sun—invalidated those suspicions.

“If there’s a troposphere on Pluto like Earth, it has to be very thin, which is extremely interesting from an atmospheric scientist’s perspective,” said Michael Summers, deputy lead of the New Horizons atmosphere theme team.  

Pluto’s atmosphere is always—and very quickly—escaping into space, making it utterly unique. “For an atmosphere that’s escaping like that, supersonically, into space, there's nothing like that in the solar system, except for the solar wind itself,” Summers said. The only local parallel is Earth—but 4.5 billion years ago. “Maybe studying this process on Pluto can help us understand what happened here."

Charon, Pluto’s largest moon, is also proving to be a scientific curiosity. “Charon just blew our socks off,” said Cathy Olkin, deputy project scientist of New Horizons. Smooth terrain on the new image suggests geologic activity. The mysterious dark north pole, nicknamed Mordor, is thought to be a thin veneer, the result of a crater having previously excavated the terrain. Canyons four to six miles deep have been revealed, as have a 600-mile series of cliffs.

“It is a small world with deep canyons, troughs, cliffs, dark regions that are still slightly mysterious to us,” Olkin said. “We’ve been saying Pluto did not disappoint. I can add: Charon did not disappoint, either.”

OUTBOUND FROM PLUTO

Though New Horizons’ discoveries travel back to Earth at the speed of light, distance limits its bandwidth to 2 kbps. It will take 16 months before the data arrives in its entirety—and data collection continues. The spacecraft is presently studying the “night side” of Pluto. The new vantage point of the Sun, behind the ninth classical planet, helps scientists study its atmosphere and search for such phenomena as rings.

Yesterday’s full-resolution image of Pluto answers a few questions but raises innumerable more, and will require decades of study. The biggest question of all, however, is whether a New Horizons mission extension will be funded by NASA. The probe has enough fuel to operate into the 2030s, and two candidate Kuiper Belt Objects have been selected for future exploration.