An underground ocean once sloshed beneath the surface of Pluto, while winds ripped overtop, carving dune fields along the way, data from the New Horizons mission suggests.
NASA's New Horizons's spacecraft made its historic flyby of Pluto and its moons last July. Based on the images and data it has been sending back ever since, a new crop of scientific findings were published in the journal Science this week.
The surprising discoveries have included a very young and geologically active surface on Pluto, featuring ice volcanoes, floating hills, flowing glaciers, sprawling, evolving plains, and more of an atmosphere than scientists expected.
"What we see really has exceeded all of our collective expectations and imagination," said William McKinnon, a planetary scientist at Washington University in St. Louis, Mo., in an interview with CBC's Quirks & Quarks that airs Saturday. "It really shows that nature's imagination is better than our own."
The researchers now believe that both Pluto and its largest moon, Charon, once had a liquid layer beneath their icy surfaces.
"We think on the insides of these bodies were very cold ammonia rich oceans," said McKinnon, noting that ammonia is a "fantastic antifreeze" that can lower the freezing point of water by 100 C.
Charon's wild youth
New Horizon's observations suggest that Charon's ocean likely froze solid a couple of billion years ago and expanded like a bottle of soda in the freezer, bursting through and cracking the surface above. Besides those big cracks, the surface also shows lava plains covered in "some sort of ice lava," McKinnon said.
"Charon had a very geological vigorous youth, a wild youth, but it's pretty much slowed down."
But Pluto, with its larger size, has managed to retain enough heat to remain geologically active, with shifting glaciers and plains. The heat likely comes from radioactivity in rocks beneath Pluto's icy surface.
McKinnon says high resolution images of Pluto's huge central plain don't show a single impact crater, suggesting that recent geological activity has covered up marks like that.
"That really tells you that this is a very young terrain," he said. "And it's in motion now."
More massive atmosphere
And Pluto may have been even wilder a short time ago – the existence of dune fields and some of the erosion on Pluto's surface suggest it was once significantly windier.
"There's not really very much wind on Pluto now, but we are coming to the conclusion that Pluto's climate in the past supported a much more massive atmosphere," McKinnon said.
In fact, scientists had predicted that Pluto was in the process of losing what little atmosphere it has left, but that turns out not to be the case, he added. A frozen layer of hydrogen cyanide appears to be holding it all in.
Data will continue to trickle in from New Horizons until the fall. And next month, scientists will put in a proposal to extend the mission so they can study the spacecraft's next destination – a smaller, more ancient Kuiper Belt object that it will visit in 2018.