River networks on Titan point to a puzzling geologic history

Jul 20, 2012 by Jennifer Chu
Images from the Cassini mission show river networks draining into lakes in Titan's north polar region. Image: NASA/JPL/USGS

For many years, Titan’s thick, methane- and nitrogen-rich atmosphere kept astronomers from seeing what lies beneath. Saturn’s largest moon appeared through telescopes as a hazy orange orb, in contrast to other heavily cratered moons in the solar system.

In 2004, the Cassini-Huygens spacecraft — a probe that flies by as it orbits Saturn — penetrated Titan’s haze, providing scientists with their first detailed images of the surface. Radar images revealed an icy terrain carved out over millions of years by rivers of liquid methane, similar to how rivers of water have etched into Earth’s rocky continents.

While images of Titan have revealed its present landscape, very little is known about its geologic past. Now researchers at MIT and the University of Tennessee at Knoxville have analyzed images of Titan’s river networks and determined that in some regions, rivers have created surprisingly little erosion. The researchers say there are two possible explanations: either erosion on Titan is extremely slow, or some other recent phenomena may have wiped out older riverbeds and landforms.

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“It’s a surface that should have eroded much more than what we’re seeing, if the river networks have been active for a long time,” says Taylor Perron, the Cecil and Ida Green Assistant Professor of Geology at MIT. “It raises some very interesting questions about what has been happening on Titan in the last billion years.”

A paper detailing the group’s findings will appear in the Journal of Geophysical Research-Planets. What accounts for a low crater count?

Compared to most moons in our solar system, Titan is relatively smooth, with few craters pockmarking its facade. Titan is around four billion years old, about the same age as the rest of the solar system. But judging by the number of craters, one might estimate that its surface is much younger, between 100 million and one billion years old.

What might explain this moon’s low crater count? Perron says the answer may be similar to what happens on Earth.

“We don’t have many impact craters on Earth,” Perron says. “People flock to them because they’re so few, and one explanation is that Earth’s continents are always eroding or being covered with sediment. That may be the case on Titan, too.”

For example, plate tectonics, erupting volcanoes, advancing glaciers and river networks have all reshaped Earth’s surface over billions of years. On Titan, similar processes — tectonic upheaval, icy lava eruptions, erosion and sedimentation by rivers — may be at work.

But identifying which of these geological phenomena may have modified Titan’s surface is a significant challenge. Images generated by the Cassini spacecraft, similar to aerial photos but with much coarser resolution, are flat, depicting terrain from a bird’s-eye perspective, with no information about a landform’s elevation or depth. 

“It’s an interesting challenge,” Perron says. “It’s almost like we were thrown back a few centuries, before there were many topographic maps, and we only had maps showing where the rivers are.”

Charting a river’s evolution

Perron and MIT graduate student Benjamin Black set out to determine the extent to which river networks may have renewed Titan’s surface. The team analyzed images taken from Cassini-Huygens, and mapped 52 prominent river networks from four regions on Titan. The researchers compared the images with a model of river network evolution developed by Perron. This model depicts the evolution of a river over time, given variables such as the strength of the underlying material and the rate of flow through the river channels. As a river erodes slowly through the ice, it transforms from a long, spindly thread into a dense, treelike network of tributaries.

Black compared his measurements of Titan’s river networks with the model, and found the moon’s rivers most resembled the early stages of a typical terrestrial river’s evolution. The observations indicate that in some regions have caused very little erosion, and hence very little modification of Titan’s surface.

“They’re more on the long and spindly side,” Black says. “You do see some full and branching networks, and that’s tantalizing, because if we get more data, it will be interesting to know whether there really are regional differences.”

Going a step further, Black compared Titan’s images with recently renewed landscapes on Earth, including volcanic terrain on the island of Kauai and recently glaciated landscapes in North America. The river networks in those locations are similar in form to those on Titan, suggesting that geologic processes may have reshaped the moon’s icy surface in the recent past.

“It’s a weirdly Earth-like place, even with this exotic combination of materials and temperatures,” Perron says. “And so you can still say something definitive about the erosion. It’s the same physics.”

This research was supported by NASA’s Cassini Data Analysis Program.

Explore further: Computer model shows moon's core surrounded by liquid and it's caused by Earth's gravity

More information: 192.102.233.13/pubs/crossref/p… p/2012JE004085.shtml

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User comments : 12

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Pkunk_
3.8 / 5 (6) Jul 20, 2012
That map of Titan looks like something right out of Old Earth a.k.a Lord of the Rings.
Shootist
3 / 5 (4) Jul 20, 2012
That map of Titan looks like something right out of Old Earth a.k.a Lord of the Rings.


Middle Earth.
kevinrtrs
1.6 / 5 (13) Jul 20, 2012
rivers have created surprisingly little erosion. The researchers say there are two possible explanations: either erosion on Titan is extremely slow, or some other recent phenomena may have wiped out older riverbeds and landforms

They left out the OBVIOUS other, third possibility - the rivers on Titan are very young in a geologic sense. Certainly NOT billions of years old.
Torbjorn_Larsson_OM
4.1 / 5 (9) Jul 20, 2012
Creationists shouldn't comment on science, it is hilarious. It is known that the methane is photolysed on a scale of some 0.5 billion years. But most rivers on Earth are seldom that old due to the erosion they describe, so the models incorporate that naturally.

The oldest river on Earth (large and situated on persistent cratons obviously, is the Meuze @ ~ 0.38 billion years: "Paleozoic, dissects the Ardennes during the Hercynian". Yangtze is next @ 0.36 billion years: "Crosses Paleozoic and Mesozoic mountains[1]". And so on. [ http://en.wikiped...s_by_age ]

That is comparable with the age of Pangea @ 0.3 billion years, which seems obvious (colliding plates raised many mountain chains for rivers to cut down and be dated on).
Shelgeyr
2.1 / 5 (7) Jul 20, 2012
Radar images revealed an icy terrain...

That part, with the possible exception of the word "icy" (because we're not sure), is true.

...carved out over millions of years by rivers of liquid methane, similar to how rivers of water have etched into Earths rocky continents.

That part is pure speculation. Even if it turns out to be ultimately true, they don't currently have an evidentiary basis for making such a claim.
kevinrtrs
1.4 / 5 (11) Jul 21, 2012
Its a surface that should have eroded much more than what were seeing, if the river networks have been active for a long time, says Taylor Perron, the Cecil and Ida Green Assistant Professor of Geology at MIT

The actual observation clearly looks like the rivers have not been eroding for billions of years, i.e. the rivers are YOUNG.
Further more the craters show that the surface itself is also YOUNG.
The only reasonable statements that can be made is that according to what they are currently observing, Titan defies the notion that it has existed for billions of years. Anything else is speculation about UNobserved events either in the present or UNobservable events from the past. Any statement regarding what may or may not have happened is not scientifically justifiable since there is a distinct lack of information in that regard.
kevinrtrs
1.7 / 5 (11) Jul 21, 2012
@Torbjorn_Larsson_OM. Perhaps you should focus on the facts instead of raising speculation about what may or may not have happened. Science is like that - face the facts and then follow where it leads. Your comments regarding creationists show that you are letting your emotions get in the way of what has been presented and you are now simply running on a religious belief.
The facts speak for themselves.
If you adhere to the idea of billions of years you begin to have to appeal to adhoc assumptions[which are not scientifically represented right here] to bring the actual observed/observable evidence in line with your belief in giga-years.
Anda
5 / 5 (4) Jul 21, 2012
It's sad to see people that already know the truth about everything.
Our knowledge grows day by day as astonishing and marvelous discoveries are made.

Kevin, your arguments are bullshit, so are you. You are a pathetic individual, but I don't care.

I'm fascinated by Titan and can't wait to know more. ;)
kevinrtrs
1 / 5 (8) Jul 21, 2012
@Anda
It's sad to see people that already know the truth about everything.

Yes, I agree. Just as people know the truth about billions of years yet they weren't there to witness it. Nor do they have any documented records by other who were there to witness it over the supposed billions of years. All they have are theoretical models which are now touted as the truth, even though it cannot be verified. Please Get real.
roboferret
5 / 5 (4) Jul 23, 2012
As you've been told before, Kev, eyewitness evidence isn't particularly reliable because:

1) Eyewitnesses forget/conflate details
2) Eyewitnesses can be mistaken.
3) Eyewitnesses can lie.

The best forms of evidence are forensic. The forensic evidence for the age of the solar system is overwhelming.
Also, scriptures are not eyewitness testimonies. They are an attempt by bronze age people to understand the world, and are consistent with the knowledge they had at the time.
Torbjorn_Larsson_OM
3 / 5 (2) Jul 23, 2012
Creationists shouldn't comment on science, it is hilarious.

As noted we observe many old rivers and we can tell how they are dated. We observe billions of years old events daily, when astronomers look at the sky on distant galaxies or the cosmic background radiation.

Repeating that they can look young isn't answering that, nor the insistence that accepted ages out of many independent methods should be rejected on no basis whatsoever. That would be funny, like throwing out a car that runs well and not even have a fantasy dragon to ride.

@ Shelgeyr:

I gave a link to similar observations here on Earth. Their river networks reproduce the observed patterns, on Earth as well as on Titan. It tests well for "pure speculation".
Shelgeyr
1 / 5 (1) Aug 17, 2012
@Torbjorn_Larsson_OM said:
I gave a link to similar observations here on Earth. [snip] It tests well for "pure speculation".


I disagree. There is bountiful evidence that countless terrestrial rivers follow preexisting contours, most of which continue far underground as part of formation features or boundaries. To assume that rivers initially carved their beds is rash, and in many cases provably untrue.

Also, to infer the genesis of Titan's landscape from an incomplete and erroneous understanding of how Earth rivers form strikes me as untenable. I could just as easily stress that the Lichtenberg figures in Titan's topology indicate an "electric discharge machining" (EDM) origin, and produce similar scalable examples in the lab. But it would be just as wrong for me to say "this is the way it had to be" given that all the evidence we have A) is sparse, B) was gathered from a distance, and C) was not acquired through instruments designed to investigate such an hypothesis.