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Pluto may have had lakes and flowing rivers once

A near-sunset view of the rugged, icy mountains and flat ice plains extending to Pluto’s horizon. (NASA/JHUAPL/SwRI)
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At a news conference at the Lunar and Planetary Science Conference on Monday, NASA scientists made it clear that we're not even close to being done puzzling out Pluto's weird little secrets. It's been more than eight months since the historic New Horizons flyby gave us an unprecedented look at that distant little dwarf planet, but the scientific findings are just starting to roll in.

"As planetary scientists, what the data revealed did not surprise us. It shocked us," NASA's Planetary Science Division Director Jim Green said during the Monday briefing. "What a beautiful system to study."

Pluto might have an ocean beneath its surface

Just days after a new glut of papers was published using New Horizons data, the researchers shared some of their more speculative findings – including the fact that Pluto probably hosted liquid lakes and rivers once.

In fact, they say, there might still be liquid nitrogen flowing beneath the surface.

“We see what for all the world looks to a lot of our team like a former lake,” Alan Stern, who leads the New Horizons team, said during the news conference.

Stern and the rest of the team suspect that Pluto's mountainous terrain – formed by water ice that freezes as hard as bedrock on the frigid world – has been carved by liquid nitrogen flows.

Pluto has brilliant blue skies and frozen water

It's possible that Pluto's extreme seasons (its axis is incredibly tilted) mean that the conditions are still right for liquid nitrogen once in awhile.

And a little bit more about those seasons: It turns out that the tropics of Pluto (yes, the tropics of Pluto) are kind of wonky. The dwarf planet is angled on a 120 degree axis (Earth is at 23 degrees), which looks something like this:

That tilt means that most of Pluto is "tropical" – meaning the sun passes directly overhead in these regions. But plenty of the planet is also "arctic," meaning that the sunlight there is finicky, plunging that region into long periods of light or darkness as is the case in our own Arctic Circle. Weirdly, there are spots where these qualities overlap – which means that parts of Pluto are both arctic and tropical.

In theory, the dwarf planet's extreme tilt might have caused just enough of a warm-up and pressure increase to allow nitrogen (or some other element) to form liquid. And if we're lucky, some of the data still beaming down from New Horizons will help scientists to prove it.

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