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Is That a Frozen Lake on Pluto?

Pluto may once have had lakes and river of liquid nitrogen on its surface. (NASA/JHUAPL/SwRI)
What looks like a frozen lake suggests Pluto may occasionally have liquids flowing on its surface. (NASA/JHUAPL/SwRI)

THE WOODLANDS, Texas—Liquids may have pooled and flowed on Pluto’s surface within the last million years – and they may do so again, scientists reported March 21 at the Lunar and Planetary Science Conference.

Though not a given, the presence of liquids on Pluto at any point is puzzling, given that average temperatures on the frozen world hover around -400 Fahrenheit. But, as NASA’s New Horizons team is learning, Pluto is anything but dead—or predictable.

“What the data revealed did not surprise us,” says NASA’s Jim Green. “It shocked us.”

Two lines of evidence suggest the dwarf world’s surface may occasionally be just a little bit wetter than it is now. One is based on how the planet’s atmospheric pressure changes during Pluto’s 248-year orbit, and the other comes from recent images sent home by the New Horizons spacecraft, which flew by Pluto in July 2015.

For starters, Pluto’s axis is tilted by about 120 degrees—it’s tipped so far over that its north pole actually points downward (as a comparison, Earth is tipped 23 degrees). As Pluto orbits the sun, it experiences some of the most extreme seasonal shifts in the solar system, with parts of it swinging between a half-century of nearly complete sunlight and a half-century of perpetual night.

When scientists simulated these seasonal changes over millions of years, taking into account how Pluto’s tilt can wobble just a bit, they realized that Pluto’s nitrogen atmosphere becomes dramatically thicker and thinner over millions of years.

A patch of crisscrossing gullies that could have been carved by liquids. (NASA/JHUAPL/SwRI)
A patch of crisscrossing gullies that could have been carved by liquids. (NASA/JHUAPL/SwRI)

“The pressure changes radically,” says New Horizons principal investigator Alan Stern. Today, he says, Pluto’s atmospheric pressure is “atypically low,” noting that at maximum it can be more than 20,000 times the current reading.

That means surface temperatures must be fluctuating enough to mess with the nitrogen on Pluto’s surface, driving it from a frozen solid into a gas. And sometimes, the temperature and pressure occasionally rise high enough for liquid nitrogen to flow on the surface.

The last time temperatures were sufficiently high to melt nitrogen was around 800,000 years ago, when Pluto’s orbital alignment led to its most extreme warm climate, says MIT’s Richard Binzel.

“The current Pluto is in an intermediate phase between its climate extremes,” Binzel says.

Next, as the New Horizons team studied the images coming back from the spacecraft, scientists started to spot surface features that looked as though they’d been carved by liquid. “We see for all the world what looks to a lot of our team like a former lake, a frozen lake,” Stern says. That lake, located just north of the smooth, bright icefield known as Sputnik Planum, measures about 20 miles from one end to the other. But there are also forking riverbeds and crisscrossing gullies that could have been sculpted by a similarly liquidy hand.

These branching features could be riverbeds sculpted by liquids on Pluto. (NASA/JHUAPL/SwRI)
These branching features could be riverbeds sculpted by liquids on Pluto. (NASA/JHUAPL/SwRI)

Though it’s not entirely clear what kind of liquid may occasionally trickle across the surface of a world billions of miles from the sun, nitrogen is a decent guess. Other possibilities include neon, molecular oxygen, or molecular helium, though it’s not likely those species are present in sufficient quantities to craft the observed features.

“This story, like the planet, is evolving,” Stern says.

Indeed, as tipped-over Pluto continues tracing its oval path around the sun, its temperature will continue to rise and fall, perhaps awakening that frozen nitrogen in another several million years and once again sending it tumbling through gullies and streambeds.


11 thoughts on “Is That a Frozen Lake on Pluto?

  1. Now *that* looks like a great place for a sporting game of hockey! Never in my 60 years did I ever think Pluto would be the fascinating place that it’s turned out to be. Pity only robots can visit it.

  2. is that a floater in my eye? is that a lake on pluto? are there monsters under my bed? does santa really fly?
    and other important questions. 😛

  3. In hindsight it seems common sense that for certain chemicals and elements “warm” – specifically warm enough to allow for liquids – is relative and that with temperatures fluctuating even just from -300 to -400 one could encounter an entirely similar yet different “geology” on a planet or dwarf planet, with some of the ices clearly taking on moving glacier qualities as well.

    Just like the Goldilocks zone for water, there’s other parts of a solar system where other elements are liquids and ices having their geologic impact where we thought it would be quiet, from the methane lakes of Titan to the glaciers, plains and frozen seas of Pluto

    Ironic that depending on what geological chemical components are present, even much warmer temperatures can be dead quiet compared to what’s happening on the edge of the Kuiper Belt


  4. pretty obvious that this is where an asteroid hit the planet and the energy of contact melted one or other or both, spilling over onto adjoining real estate, and allowing pooled rock (or whatever it is) to cool in solid form in crater….

  5. Why would you use Fahrenheit for mentioning temperature? If you can not avoid using Fahrenheit then you should also provide Celsius or Kelvin temperature value in a parenthesis.

    1. Its called He2 , its a bond between 2 helium atoms , a very weak bond that can only exist at very low cryogenic temperatures.

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