Nile-like River Found on Saturn’s Moon Titan

Bad Astronomy
The entire universe in blog form
Dec. 13 2012 8:00 AM

Alien Nile: River of Liquid Methane Seen on Saturn's Moon Titan

River of liquid methane and ethane on Saturn's moon Titan.
Turns out it's not just a river in Egypt after all: A long river on Saturn's moon Titan bears a striking resemblance to the Nile. Click to enalkanate.

Image credit: NASA/JPL–Caltech/ASI

The amazing astronomy news keeps on coming! This one is very cool: What appears to be a 400 kilometer long (240 mile long) river of liquid has been found near the north pole of Saturn’s moon Titan!

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

You can see the river in the picture here, which was taken in September 2012 by the Cassini spacecraft orbiting Saturn. The image is so long I decided, what the heck, I’ll let it run down the side of this entire article. The river appears dark against the lighter background of Titan’s surface. While this isn't the first river network seen on Titan, it's the longest, and this is the highest-resolution image ever made of one.

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Cassini has flown by Titan several times, making detailed observations of the giant moon. Titan is huge, bigger than the planet Mercury, and has a dense atmosphere made of nitrogen. The top of the atmosphere has a thick layer of haze, making it impossible to see the surface with visible light. Infrared can penetrate the murk, as can radar. Cassini has the capability to use both, and has been making maps of the surface for years. It’s found huge sand dunes, structures that look like volcanoes … and a series of smooth, dark regions at both poles that look very much like lakes.

Then, in 2009, proof of liquid lakes came when a reflected glint of sunlight was seen off one of those dark regions. This sort of reflection can only come off something highly reflective such as a liquid, confirming Titan has huge lakes filled with some kind of liquid.

But what liquid? On Titan it’s so cold that water is literally frozen as solid as rock. But other substances have much lower freezing points, such as ethane and methane (which are natural gases here on our toasty Earth). It’s been known for some time that hydrocarbons are plentiful on Titan, so ethane and methane are abundant and almost certainly what’s in those lakes.

In fact, on Titan those liquids act like water does here on Earth, evaporating into Titan’s atmosphere, blowing around, raining down, and starting the cycle over again. It’s been suspected rivers might exist, but this is the first one seen. Note how it looks dark and smooth, which is a distinguishing characteristic of the lakes seen as well.

The length of this river and the fact that it’s mostly straight imply the liquid is flowing along a crack in the surface of Titan, perhaps a fault line in the surrounding bedrock. You can see tributaries feeding into it as well, with it finally flowing into a lake at the top of the picture.

That’s just plain amazing. And it sets fire to the imagination: Life on Earth is based on carbon molecules and needs liquid water to survive. Ethane and methane are carbon-based, and liquid to boot. Scientists have speculated for years that Titan might be a good place to look for life—though at a temperature of -180 degrees Celsius (-290 degrees Fahrenheit) it would be a lot different from us and would probably operate at a much slower pace. Still, it’s fascinating to try to imagine what sort of life might possibly arise on such a distant, chilly, alien world.

But life or not, this is still a fantastic scientific find. The more we learn about the myriad of planets and moons in our solar system, the more amazed I am at their diversity, complexity, and ability to surprise us. Titan may be alien, but when I see a picture like this—a Nile river in miniature!—it’s hard not to think about how much we have in common with all these worlds.

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