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Scientists Observe Springtime Changes On One Of Saturn's Moons

Jun 23, 2014
Originally published on June 23, 2014 11:15 am

With its large sand dunes, rivers, big lakes and seas, Saturn's biggest moon is one of the most Earth-like planetary bodies in the solar system. But Titan is no place to call home.

The surface temperature is negative 290 degrees Fahrenheit, and each of its seasons lasts about seven Earth years. Sunsets on Titan would look orangey-brown, thanks to a thick haze that keeps light from reaching the surface. Water is scattered around as solid, icy pebbles.

It's one of Titan's northern seas that now has researchers excited — scientists say they're seeing the first signs of springtime changes even though the summer solstice is almost three years away.

The Ligeia Mare is named after a mythical siren who lured sailors to their deaths. It's cold, dark, and made of liquid natural gas. You could scoop some up and dunk it in the fuel tank of a bus.

"And up until now, we thought that it would be a quite flat and calm environment," says Jason Hofgartner, a graduate student in astronomy at Cornell University who has studied the landscape in images of Titan taken by the Cassini spacecraft, which has been orbiting Saturn for the past decade.

He and his colleagues were sifting through radar images, he says, when they noticed that "there was this essentially a bright spot, where there hadn't been a bright spot before. And then 16 days later, it wasn't there again."

Hofgartner and his fellow researchers write in the journal Nature that this bright spot coming and going is evidence of something moving in that ocean of natural gas.

NASA's chief scientist, Ellen Stofan, says the movement could be windblown waves, bubbles from something below, or even a chunk of pumice floating on the surface like a fluffy iceberg. Whatever the thing is, she says, it's a sign of the season changing. As Titan's northern hemisphere gets more sunlight, the atmosphere is warming. Spring is in the air.

"It's around now, with the seasons changing, that the winds should be picking up, temperatures changing a little bit," Stofan says. "So, we were starting to look. On these northern seas, are we going to see changes?"

This is the first confirmed observation of such change in the northern hemisphere. Stofan says that monitoring the changes through the season will help them understand more about Titan. It could also help explain more about Earth.

"These results are just incredibly exciting because it's showing that we have this dynamic world so far out in the solar system, where we can learn about oceanography and climate," Stofan says.

Titan's seas may be made of a bizarre material, but the physics governing them are the same as those on our own planet.

"It's behaving exactly the way water does here on Earth," Stofan explains. "What an opportunity to learn more about the liquid cycles that we have here on Earth. Now we've got somewhere to compare it to."

The researchers expect to see more signs of movement on Titan's seas as its summer approaches in 2017.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

RENEE MONTAGNE, HOST:

There's a moon that orbits around the planet Saturn called Titan. And its landscape is the most earth-like one in the solar system. Its seasons are much longer, though. Each one lasts about seven Earth years. In fact, for Titan, summer is still almost three years away. As NPR's of Rae Ellen Bichell reports, scientists are making first observations about springtime changes in Titan's northern seas.

RAYE ELLEN BICHELL, BYLINE: If he was on Titan, instead of in his lab at Cornell, Jason Hofgartner says here's what things look like.

JASON HOFGARTNER: Large sand dunes, rivers, big lakes and seas.

BICHELL: Hofgartner's a grad student in astronomy. He's studied Titan's landscape and images taken by the Cassini spacecraft. It's been orbiting Saturn for the past 10 years. He says, compared to Earth, Titan wouldn't be a very comfortable place to live.

HOFGARTNER: It's about 180 degrees colder.

BICHELL: That's in Celsius.

HOFGARTNER: And it would also be much darker. And that's because Titan has a very thick haze, almost like a very thick smog layer, that prevents light from reaching surface.

BICHELL: Making sunsets an orange-y brown. Water is scattered around as solid, icy pebbles. But it's Titan's seas that researchers got excited about recently. In particular, one in the North - the Ligeaia Mare, named after a mythical siren, who lured sailors to their deaths. It's very cold and it looks very dark.

HOFGARTNER: Like really - like a black liquid.

BICHELL: It's liquid natural gas. You could use it to run a bus.

HOFGARTNER: And up 'til now we think that it would be quite flat and a calm environment.

BICHELL: Smooth and glossy - but then Hofgartner and his colleagues were sifting through radar images.

HOFGARTNER: And noticed that there was - essentially a bright spot, where there hadn't been a bright spot before. And then 16 days later, it wasn't there again.

BICHELL: It had disappeared. In their paper in the journal Nature, Hofgartner and his colleagues say, this bright spot coming and going is evidence of something moving in that ocean of natural gas.

ELLEN STOFAN: That's what we have been waiting to see.

BICHELL: Ellen Stofan is NASA's chief scientist. The movement could be windblown waves, bubbles from something below or even a chunk of pumice, floating on the surface like a fluffy iceberg. Stofan says whatever the thing is it's a sign of the season changing. As Titan's northern hemisphere gets more sunlight, the atmosphere is warming. Spring is in the air.

STOFAN: So it's around now with the seasons changing, the winds should be picking up, temperatures changing a little bit. So we were starting to look. Are things on these northern seas - are we going to see changes?

BICHELL: This is the first one. Stofan says monitoring these changes, through the season, will help scientists understand more about Titan. But it could also help explain more about our planet.

STOFAN: These results are just incredibly exciting because it's showing that we have this dynamic world, so far out in the solar system, where we can learn about oceanography and climate.

BICHELL: Titan seas may be made of a bizarre material.

STOFAN: But it's behaving exactly the way all water does here on earth, so what an opportunity to learn more about the liquid cycles that we have here on earth. Now we've got somewhere to compare it to.

BICHELL: The researchers expect to see more signs of movement on Titans seas as its summer approaches in 2017. Rae Ellen Bichell, NPR News. Transcript provided by NPR, Copyright NPR.