UCLA scientist discovers plate tectonics on Mars

[bystander]

UCLA scientist discovers plate tectonics on Mars
University of California, Los Angeles | Stuart Wolpert | 2012 Aug 09

View of central segment of Mars' Valles Marineris, in which an older circular basin created by an impact is offset for about 93 miles (150 kilometers) by a fault.
(Credit: Image from Google Mars created by MOLA Science Team)

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For years, many scientists had thought that plate tectonics existed nowhere in our solar system but on Earth. Now, a UCLA scientist has discovered that the geological phenomenon, which involves the movement of huge crustal plates beneath a planet's surface, also exists on Mars.

"Mars is at a primitive stage of plate tectonics. It gives us a glimpse of how the early Earth may have looked and may help us understand how plate tectonics began on Earth," said An Yin, a UCLA professor of Earth and space sciences and the sole author of the new research.

Yin made the discovery during his analysis of satellite images from THEMIS (Thermal Emission Imaging System), an instrument on board the Mars Odyssey spacecraft, and from the HIRISE (High Resolution Imaging Science Experiment) camera on NASA's Mars Reconnaissance Orbiter. He analyzed about 100 satellite images — approximately a dozen were revealing of plate tectonics.

Yin has conducted geologic research in the Himalayas and Tibet, where two of the Earth's seven major plates divide.

"When I studied the satellite images from Mars, many of the features looked very much like fault systems I have seen in the Himalayas and Tibet, and in California as well, including the geomorphology," said Yin, a planetary geologist.

For example, he saw a very smooth, flat side of a canyon wall, which can be generated only by a fault, and a steep cliff, comparable to cliffs in California's Death Valley, which also are generated by a fault. Mars has a linear volcanic zone, which Yin said is a typical product of plate tectonics.

"You don't see these features anywhere else on other planets in our solar system, other than Earth and Mars," said Yin, whose research is featured as the cover story in the August issue of the journal Lithosphere.

The surface of Mars contains the longest and deepest system of canyons in our solar system, known as Valles Marineris (Latin for Mariner Valleys and named for the Mariner 9 Mars orbiter of 1971–72, which discovered it). It is nearly 2,500 miles long — about nine times longer than the Earth's Grand Canyon. Scientists have wondered for four decades how it formed. Was it a big crack in Mars' shell that opened up?

"In the beginning, I did not expect plate tectonics, but the more I studied it, the more I realized Mars is so different from what other scientists anticipated," Yin said. "I saw that the idea that it is just a big crack that opened up is incorrect. It is really a plate boundary, with horizontal motion. That is kind of shocking, but the evidence is quite clear.

"The shell is broken and is moving horizontally over a long distance. It is very similar to the Earth's Dead Sea fault system, which has also opened up and is moving horizontally."

The two plates divided by Mars' Valles Marineris have moved approximately 93 miles horizontally relative to each other, Yin said. California's San Andreas Fault, which is over the intersection of two plates, has moved about twice as much — but the Earth is about twice the size of Mars, so Yin said they are comparable.

Yin, whose research is partly funded by the National Science Foundation, calls the two plates on Mars the Valles Marineris North and the Valles Marineris South.

"Earth has a very broken 'egg shell,' so its surface has many plates; Mars' is slightly broken and may be on the way to becoming very broken, except its pace is very slow due to its small size and, thus, less thermal energy to drive it," Yin said. "This may be the reason Mars has fewer plates than on Earth."

Mars has landslides, and Yin said a fault is shifting the landslides, moving them from their source.

Does Yin think there are Mars-quakes?

"I think so," he said. "I think the fault is probably still active, but not every day. It wakes up every once in a while, over a very long duration — perhaps every million years or more."

Yin is very confident in his findings, but mysteries remain, he said, including how far beneath the surface the plates are located.

"I don't quite understand why the plates are moving with such a large magnitude or what the rate of movement is; maybe Mars has a different form of plate tectonics," Yin said. "The rate is much slower than on Earth."

The Earth has a broken shell with seven major plates; pieces of the shell move, and one plate may move over another. Yin is doubtful that Mars has more than two plates.

"We have been able to identify only the two plates," he said. "For the other areas on Mars, I think the chances are very, very small. I don't see any other major crack."

Did the movement of Valles Marineris North and Valles Marineris South create the enormous canyons on Mars? What led to the creation of plate tectonics on Earth?

Yin, who will continue to study plate tectonics on Mars, will answer those questions in a follow-up paper that he also plans to publish in the journal Lithosphere.

Structural analysis of the Valles Marineris fault zone: Possible evidence for large-scale strike-slip faulting on Mars - An Yin

Lithosphere 4(4) 286 (Aug 2012) DOI: 10.1130/L192.1

[Ann]

This is interesting, but also strange. The problem as I see it is why Mars would begin to have plate tectonics now, four billion years ago or so after this rather small planet formed. Doesn't it take a churning interior to cause plate tectonics? Isn't Mars relatively cool and stiff inside?

The Valles Marineris is a strange formation, and I don't see why early plate tectonics on Mars, when the planet retained a lot more heat than today from its formation, may have played a part in forming this magnificent crack. Perhaps something "rattled" Mars (pure speculation on my part) and caused an instability, contributing to the amazing canyon. It does not seem entirely far-fetched to imagine that if plate tectonics had somehow got going around Valles Marineris, further development might have led to horizontal shifts along the crack.

The very strange thing is the suggestion that plate tectonics on Mars are getting going now, or so I think anyway. What do other scientists say about Yin's conclusions?

Ann

[rstevenson]

I don't see anything in that article which suggests the plate techtonics are "getting going now". He says he sees evidence that it has happened, and presumably is continuing "now," but not that it started recently.

Rob

[Ann]

I don't see anything in that article which suggests the plate techtonics are "getting going now". He says he sees evidence that it has happened, and presumably is continuing "now," but not that it started recently.

Rob

You may well be right, Rob. However, Stuart Wolpert at University of California, Los Angeles wrote on Aug 9, 2012:

"Mars is at a primitive stage of plate tectonics. It gives us a glimpse of how the early Earth may have looked and may help us understand how plate tectonics began on Earth," said An Yin, a UCLA professor of Earth and space sciences and the sole author of the new research.

...

"Earth has a very broken 'egg shell,' so its surface has many plates; Mars' is slightly broken and may be on the way to becoming very broken, except its pace is very slow due to its small size and, thus, less thermal energy to drive it," Yin said.

The way I read this, the scientist is suggesting that Mars may be on its way to getting more plate tectonics, even though plate tectonics should be "dying down" as the interior of Mars cools and stiffens. At least it seems that way to me.

Ann

[Chris Peterson]

This is interesting, but also strange. The problem as I see it is why Mars would begin to have plate tectonics now, four billion years ago or so after this rather small planet formed. Doesn't it take a churning interior to cause plate tectonics? Isn't Mars relatively cool and stiff inside?

Mars is presumed to be tectonically active to some uncertain degree. We have samples of Martian basalts that flowed as recently as a couple hundred million years ago (the shergottite meteorite family). Models of the Martian interior exist for both solid and liquid iron cores, and combinations of both, but all models suggest that the interior is dominated by a very thick mantle. Given the residual heat in the interior of Mars, the expected mantle (olivine-pyroxene, spinel?) would be fluid, like Earth's. That means convection is likely, which means one of the presumed mechanisms for plate tectonics is present.

Because Mars is much cooler inside than Earth, its mantle is more viscous, and there is also less energy to drive convection. I think what Yin is suggesting is that this means Martian plate tectonics are operating much slower than Earth's, and we're now seeing Mars in a "primitive" state, meaning its crust is like Earth's was a few billion years ago. If Yin is correct, plate tectonics continues to operate on Mars, just very slowly, so over another few billion years, the Martian crust may evolve to be more like Earth's in some respects.

[Ann]

How long can plate tectonics realistically go on on Mars? Doesn't it take a moderately active interior? Mars, for example, doesn't have a global magnetic field. Is it true, or likely, that it used to have one? If it had a global magnetic field before but doesn't have one any more, then that suggests to me that Mars might be running out of whatever it takes to drive plate tectonics.

I think the claim that surprises me most is the suggestion that Mars might become as "cracked" as the Earth is in the future, suggesting that Mars might be "catching up" with the Earth. This is turn suggests, at least to me, that plate tectonics on the Earth may sort of "cease"or at least "settle down", but they will go on on Mars, so that the red planet will "catch up with us" and be like us.

Or maybe I should read this as a prophecy that the Earth will become ever more broken, so that it will not have seven major tectonic plates in the future, but maybe seventy? Or seven hundred?

What does it realistically take to drive "slow" but "persistent" plate tectonics?

Ann

[Chris Peterson]

How long can plate tectonics realistically go on on Mars? Doesn't it take a moderately active interior?

It can go on a very long time. Mars is still hot inside... not as hot as Earth, but plenty hot enough to support convection in the mantle. When we talk about a "fluid" mantle, imagine something like plastic, not water. All you need is a temperature gradient, and Mars will require many billions of years before it's essentially a uniform temperature throughout. Very slow convection might reasonably lead to very slow plate tectonics.

Mars, for example, doesn't have a global magnetic field. Is it true, or likely, that it used to have one? If it had a global magnetic field before but doesn't have one any more, then that suggests to me that Mars might be running out of whatever it takes to drive plate tectonics.

Mars is cooling down. But that doesn't mean it can't continue to drive plate tectonics for a long time.

I think the claim that surprises me most is the suggestion that Mars might become as "cracked" as the Earth is in the future, suggesting that Mars might be "catching up" with the Earth. This is turn suggests, at least to me, that plate tectonics on the Earth may sort of "cease"or at least "settle down", but they will go on on Mars, so that the red planet will "catch up with us" and be like us.

Mars won't "catch up" until both planets are frozen through... and that won't happen until the Sun has become a dwarf and the terrestrial planets may not even be here. I think all that's being suggested is that Mars is lagging the Earth in terms of the results of plate tectonics; the same sort of crustal behavior may occur, simply much, much slower. Over time (billions of years) its crust may become more like the way Earth's is today.

Or maybe I should read this as a prophecy that the Earth will become ever more broken, so that it will not have seven major tectonic plates in the future, but maybe seventy? Or seven hundred?

Probably not, but how major plates form and rejoin is not well understood.

What does it realistically take to drive "slow" but "persistent" plate tectonics?

A temperature gradient and a fluid mantle... both present in Mars.