Pluto continues to baffle as New Horizons reveals 'astounding' complexity

Pluto is even more of an enigma than scientists had imagined, researchers said as NASA published Thursday the first official data results from the New Horizons spacecraft’s historic flyby within 7,800 miles of the bizarre dwarf planet, after nearly 10 years and 3.3 billion miles of travel.

“Pluto itself is incredibly complicated, much more so than we’ve seen in any small planet before,” said Alan Stern, planetary scientist at the Southwest Research Institute in Boulder, Colorado, and principal investigator for the New Horizons mission to Pluto. “We don’t know why.”

“The range of geological landforms on the surface is just astounding,” Stern said.

Not only does Pluto’s surface show a surprising variety of features — from weirdly smooth plains to ridge-like mountains — but that surface is actively changing, as described by Stern and others from the New Horizons team in a paper published Thursday in the journal Science.

Scientists are baffled as to what forces are causing what they say are curiously “new” alterations to a planet that formed about 4.5 billion years ago. They said Pluto’s surface has been resurfaced recently in geological terms, possibly affected by wind, tectonic activity or glaciers.

One area of interest is called the Sputnik Planum, a flat and icy plain that is about the size of Texas and has no craters at all.

“Craters are our thermometer,” Stern explained. If a surface has no or few craters — which form when objects like asteroids impact them — then it is considered very “young.”

Thus scientist said this icy feature most likely formed within the last 100 million years, only the most recent 2 percent of the planet’s age. 

This finding is puzzling, Stern said, because geophysics tells us that a planet of Pluto’s small size — New Horizons just revealed its largest radius to be about 737 miles — should have “cooled off” at this point.

“There is no source of energy that has been identified that would keep it running this long,” Stern said. “And yet it is.”

In recent decades, scientists knew the surface of Pluto contained frozen nitrogen, carbon monoxide and methane. But New Horizons has now detected what some scientists think is an ice-based “bedrock” of water below the crust, in a mountain range that lies on Sputnik Planum’s edge and might be made of icebergs.

Also, “liquid nitrogen could be sort of groundwater on Pluto,” William McKinnon, a New Horizons scientist at Washington University in St. Louis, told Science magazine. “It could be coursing through the ice crust, and it could perhaps undermine terrain and lead to the dislocation of crustal blocks.”

Some of the other initial findings transmitted by New Horizons are that Pluto is blanketed in a thick atmospheric haze, and it has less pressure than scientists previously thought.

“It’s just incredible how many puzzles there are from this flyby, and we’re only beginning to unravel it, of course,” Stern said.

New Horizons will continue to beam data from the flyby back to Earth through September 2016.

Distant Pluto has been cloaked in mystery it was discovered in 1930, and scientists have long thought the icy body a bit of an oddity compared to the other planets in the solar system. They were astonished to discover in 1992 that Pluto was actually the largest known body in an entire swarm of tiny planets called the Kuiper Belt, an icy region beyond Neptune’s orbit.

Now, the discovery that Pluto’s surface is young and volatile “suggests that other small planets of the Kuiper Belt, such as Eris, Makemake and Haumea, could express similarly complex histories that rival those of terrestrial planets,” the authors wrote. “Pluto’s diverse surface geology and long-term activity also raise fundamental questions about how it has remained active many billions of years after its formation.”