13 November 2008
Tectonics on Mars
Posted by Ryan Anderson
Mars is often touted as the “most earth-like” planet, but if you take a look at its surface there are some aspects that are decidedly alien. Sure, there are dry river beds and canyons and volcanoes. But there are also craters. Everywhere. So many that, when Mariner 9 sent back the first spacecraft images of Mars, people were dismayed to see a surface that looked just like the moon!
Is Mars just astronomically unlucky? Nah, we get hit with just as much stuff as Mars does, only Mars is old. More specifically, its surface is old. The planet itself is about the same age as earth. However because Mars is smaller, it cooled faster and that means that it is much less geologically active.
Take a look at this image of Earth’s topography:
What do you notice? Yes, state the obvious. (if there’s one thing that I’ve learned from years of professors asking questions in class it’s that often they are looking for a really obvious statement) In this case we have a lot of obvious statements to choose from, such as: “The oceans are lower than the continents!” and “There are no craters” and “Mountains form in long ridges!”
All of this is because earth’s crust slides around as plates “floating” atop layer of softer rock. The plates pull apart in places like the middle of the Atlantic, and new crust is formed as the hot rock from underneath is extruded upward. The plates crash together in places like the Himalayas and western South America, forming huge mountain ranges as the crust buckles and folds.
Plate tectonics is a tremendously important process on the Earth. It recycles our crust, processes the rocks, and even moderates our atmosphere. There are some scientists who think that plate tectonics may be a requirement for a planet with thriving life!
Anyway, now let’s take a look at the topography of Mars instead:
What observations can we make here? The northern hemisphere is lower and smoother. There is a giant canyon and giant volcanoes! There are lots of craters! Also note what mars lacks. There are no long linear mountain ranges and no mid-ocean-ridges. There is not a really sharp distinction between “low” and “high” like there is on the Earth. It just sort of slopes gradually from the southern highlands to the northern lowlands.
All of this is because Mars lacks plate tectonics. Its crust is, as far as we can tell, one big slab of rock. The only hint that there was ever plate tectonics on Mars comes from its magnetic field, shown below.
Red on this map is magnetic “north” and blue is magnetic “south”. Clearly astronauts can leave their compasses at home. Notice that the magnetic field forms stripes. On earth this happens at a very much smaller scale at the mid-ocean ridges: as the magma wells up between the spreading plates, it freezes and traps the current magnetic field of the planet. As the magnetic pole switches (which it does occasionally) the changes get trapped in the rocks. Some scientists have looked at the map of Mars’s magnetic field and said “aha! stripes! there must have been plate tectonics!” I’m a bit skeptical of that though. Where are the spreading centers and mountain ranges you would expect?
It’s possible that the magnetic field we’re seeing is the remnant of such ancient plate tectonics that there are no surface features left, but I don’t think we can definitively say “yes, Mars had active plate tectonics. It is interesting to note that the presence of water in the crust and mantle seem to make plate tectonics much easier to maintain. It turns out that water makes rocks melt at lower temperatures, effectively “lubricating” the undersides of the plates on earth. Could Mars have lost its plate tectonics because it lost it’s water? Maybe, but nobody really knows for sure.
Mars is/was certainly tectonically active though. One of the biggest events in Mars history was the formation of the Tharsis rise (the huge area of high topograpphy, capped by four giant volcanoes). Notice what is directly to the east of Tharsis? A giant crack in the crust, otherwise known as Valles Marineris. It’s likely that Valles Marineris formed when the stress of the growing Tharsis rise of the crust became too great and the martian crust just ripped like the seam on a pair of too-tight pants. In fact, there are faults and cracks encircling Tharsis. Here’s a map of one type of fault, marked with the black lines:
An even closer look shows that there are places on Mars where the surface is pretty much all faults! For example, check out this view of the volcano Alba Patera, north of the main Tharsis rise. It is shot through with cracks!
Mars may have had plate tectonics, but if it did, all evidence was erased except for the magnetic stripes preserved in the ancient southern crust. Mars did have lots of other tectonics though. All over the planet there are cracks and faults indicating that once, long ago, the surface quaked and split. We don’t know how active Mars is today. Someday, we may send a lander, or even better a network of landers, carrying seismometers that could listen to the tremors of the red planet’s crust and tell us what is going on deep inside. Until then all we can do is look at the surface, trace the faults and imagine what must have caused them, billions of years ago.
Thanks – On Earth, the oceanic floor is basaltic, and the continental areas are granitic (well, to first order, but please correct me if I am wrong). Could a similar reasoning apply to Mars’ two distinct hemispheres?
The difference in composition between the continents and the sea floor on earth is due to plate tectonics. Granite tends to “float” a little more than basalt, so as the crust gets recycled the granite stays on top and forms continents. On mars the whole planet is basaltic, which is more evidence that if there was plate tectonics, it didn’t last long, since it never managed to separate out granitic rocks from basaltic.
Until I read this article I thought the the late bombardment of bodies in the inner solar system at around 4 billion years ago was just the last of a series of bombardments that were almost continuous from when the solar system formed 4.5 billion years ago. I had thought that between 4.5 and 4 billion years ago the Earth had a mantle and a core but effectively no crust. I thought that at this time the surface of the Earth had the same composition as the mantle and that the only discernable feature on the surface of the Earth was meteor craters and lava flows.
Now this evidence of ocean crust on Mars predating the late bombardment reveals a time, perhaps between 4.2 and 4.0 billion years ago when Mars and possibly also the Earth had ocean crust, plate tectonics and possibly even oceans, much as is theorised for the Archean period on Earth a few hundred million years later.
Is it possible that the colision between a large body and the Northern hemisphere of Mars at the time of the late bombardment disrupted Mars’ core, killed off Mars’ magnetic field and put a stop to plate tectonics all at the same time?
What is known about the late bombardment? I read a theory that the meteors and comets of the late bombardment entered the inner solar system as a result of collisions between bodies beyond the orbit of Pluto? Is this a recognised theory?
Is it possible that the acretion of the planets was effectively complete by 4.2 billion years ago and the late bombardment was a brief but intense anomoly 200 million years later?
I have read about individual Zircon crystals on earth and even a recently discovered rock formation predating the late bombardment. To what depth would the late bombardment have obliterated the Earth’s surface?
There is no evidence of ocean crust on Mars. There are magnetic fields that appear in vague stripes, in the ancient crust but that doesn’t mean it’s oceanic, or even that the stripes are due to plate tectonics.
The best theory for the late heavy bombardment is that it was a brief and intense event that occurred after the planets had mostly formed. In the “Nice Model” (named for the city in France) Jupiter and Saturn enter a resonance where Jupiter goes around the sun twice for every one time that Saturn goes around. This causes all hell to break loose in the outer solar system. Saturn moves out farther from the sun, causing Uranus and Neptune to move outward and *switch orbits* and in the process scattering millions of planetesimals into the inner solar system.
I don’t think a large impact is needed to stop the magnetic field and any plate tectonics on mars. It would take a nearly planet-destroying impact to have much of an effect on the core. I think it’s much more likely that Mars just cooled down to the point where the core couldn’t maintain convection, causing the magnetic field to die. The cooling would also halt any plate tectonics. The loss of the magnetosphere would allow the solar wind to hit the atmosphere and strip most of it away.
Determining if Mars had plate tectonics in its past will, I believe, indicate the likeliness of “Earth-like” planets in the galaxy. Many believe that plate tectonics is essential for the formation of a stable biosphere. It is also believed by some that the “giant impact” that created the Earth-moon double planet is necessary to initiate plate tectonics and the additional tidal stresses from a large moon necessary to sustain them. If Mars indeed had plate tectonics in its past, this suggests that a large moon is not necessary for the initiation of plate tectonics. Thus, Earth-like planets may be common in the galaxy.
If Mars never had plate tectonics, it suggests, but does not prove, that a large moon is necessary for them. However, if a large moon is necessary, given the improbability of the giant impact to make the large moon, Earth-like planets could indeed be very rare in the galaxy. This, of course, would certainly explain Fermi’s Paradox.
Regarding the late-heavy-bombardment, it has been argued that this point in time -3.8 Ga – makes a ‘nice’ (no pun intended) dividing line between the Hadean and the Archean eons (Earth eons, that is).
awesome post! thanks!
the mag field map is really interesting! quite intriguing…
how big is the core of mars, compared to earth’s? and does the density contrast matter? mercury has quite a large and active core and thus a large and active mag field (it too is interesting) and is super dense!
in a different direction – since there is no subduction, the volcanism is only accommodated through isostasy and faulting, which means to me extremely awesome faults! because the volcanos are quite extensive! because of my “earth mind” i am pretty impressed! (mapping on mars would be something else!)
Question: do we know what creates or initiates active plate tectonics?
thank you again!!
-danielle
ps how is the novel? I met some women at school who are doing it and they are not getting much else done…
another question i forgot!
is mars cooling as we speak? is earth cooling? is the universe cooling post big-bang (or whatever you want to call the beginning of the universe)?
“…s the universe cooling post big-bang (or whatever you want to call the beginning of the universe)?”
Yes
1. What ’caused’ plate tectonics to stop on mars – or at least the inner core to freeze up? Did it just cool?
2. Was mons olympus a ‘hot spot’ like Hawaii?
I’ve always resisted expansion theories because I can’t imagine any mechanism that would make such a thing possible, but Mars now has me rethinking everything.
I was so blown away by this that I started playing with Mars topography images. I put in an “ocean” where one would be if tons of water was on Mars, and the temps were right. NOT that I believe Mars had oceans. I just wanted to see what the “shorelines” looked like, based on upper and lower topography.
Don’t know if links work or not here, but my name should link to the Google Earth file I just made/modified in Photoshop.
http://orderjet.com/kml/mars_ocean.kmz
Look at the gradually thinning regions as they lead up to the “shorelines”. The nortnern “oceanic” area, with the Martian north pole turned face on, is just like our massive Pacific in terms of size.
The entire old, pitted southern hemispheric crust looks like it’s “clinging” with “claws” to a much smoother, younger emerging shell — like Mars has been “inflating” itself right out of its own skin.
Think of blowing a balloon, or bubble with chewing gum, that has one weakened, thinner side to it. It gets all the expansion, all the attention. The stronger thicker areas can only cling, and catch up later.
Off my rocker and seeing things? Maybe. But that’s the first impression that struck me when I read this page, and then look Mars with a fake ocean area added.
OK, it works. Just right click and save the .kmz file (a little over 2MB) and open it in Google Earth. It’s false color topography from NASA that I modified in Photoshop (color range selection for lower altitudes, then a new layer to make the “ocean”, slightly transparent so you can see the underlying features).
[…] ranges like this, it may not be the case on some planets which are less geologically active. See This article about Mars for more details on planets that have less tectonic […]
I made this comment on the old blog before I realized you had moved – so I will repost here:
Interesting post. But a curious problem – if the Tharsis volcanoes emitted lava (as we can logically conclude), where did the lava come from? Logically, wouldn’t another part of Mars have to be subducting or sinking in some fashion in order to generate magma that came out of the Tharsis volcanoes? I’m not saying plate tectonics, but there has to be some mechanism by which some of Mars’s crust was drawn inward so that lava could erupt somewhere else. Unless – Mars is magically creating new material in its interior and expanding… 😀
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Plate tectonics stop 4.2 billion years ago then no life could form on Mars period. The oceans on Mars dried up to fast for life to form as well. Even if Demos was there 4.2 billion years ago it is not big enough to stabilize the climate on Mars. Everyone knows Earth’s moon is critical to stabilize climate So can someone explain to me why everyone wants to spend so much money Studying mars and going to mars?