Mountains of Mars
Posted 12 June 2013 - 12:21 AM
Mars seems to be pretty universally considered to have lacked plate tectonics right from the get-go, and all the mountains on Mars are actually the rings of impact structures. This idea is repeated in the article in this month's S&T article "Is Plate Tectonics Necessary For Sentient Life?", where, in the picture caption on page 22, the author says "Laser Altimetry mapped Mars's topography at high resolution but yielded no evidence of plate tectonics."
This isn't completely accurate, however; the left-hand topo image of Mars clearly shows the "Thaumasia Mountains" describing an L-shaped arc toward the bottom of the image, making an almost square figure with Vallis Mareneris cutting catty-corner across the upper right corner.
Almost the only place I've seen any mention of this is in William Hartmann's "A Traveller's Guide to Mars", where he discusses the matter on pages 217-218 and concludes that there is a good possibility that these were formed by early tectonics, as there's no sign of an impact structure that might be responsible.
It seems like I've seen another reference to the mountains somewhere, in particular the unprecedented square shape; but I can't remember where it was. In any event, they are the only bona-fide mountain range on Mars, and they came from somewhere. Crustal stresses from the formation of Vallis Marineris is another possibility.
But, if there were tectonics, running fresh water, and a more clement atmosphere and climate, it seems as though life could have had a really good chance of at least starting out, and possible spreading a goodly distance, before the ax fell.
Interestingly, the mountain range constitutes the southern eyelid of the "Eye of Mars", while Vallis Marineris constitutes the northern one. The Eye is one place where topographic and albedo features come together to form the same structure.
I don't know; Does this topic merit any discussion? I'd love to hear opinions and speculations from other students of Mars.
Posted 12 June 2013 - 01:40 AM
Posted 12 June 2013 - 11:52 AM
My Mars reading is about 10 years out of date but here goes: Mars has a general gradient from south to north from higher and older terrain to younger, lower terrain. The southern highlands of Mars are the most ancient, heavily cratered surfaces on the red planet. They are 4 Billion + years old and cover a big fraction of Mars’ surface – compare that to the tiny vestiges of rock with similar age on Earth. The ancient southern highlands also show the most earth-like gully systems seen on Mars, so dendritic or branching they are suggestive of rainfall runoff.
The southern highlands also have relict magnetism, maybe with hints of the striping like on earth but at different scales. I don't know what the latest take is on this magnetism, there was excitement about it > 10 years ago. Mars’ magnetism may have been at least as intense as Earths -- but it didn’t last very long. When the rocks cooled after the immense Hellas Basin impact into the ancient highlands and the smaller Argyre Basin, they kept no magnetism, so the planetary field was gone very early in Mars history, perhaps by 4 billion years ago.
Mars may have had up to twice the impact rate of the moon so early impact heating had a greater additive effect with radiogenic heat and accelerated the differentiation of an iron core to generate a Martian magentic field. If that core formation was a slower process it would have provided more internal heat later in Mars history. Maybe the rapid core differentiation and early spike in heating led to more rapid cooling and shutdown of magnetism and any nascent plate tectonics even as impact basins were still forming.
The vast northern lowlands of Mars include other basins beside Hellas and Argyre to the south: Isidis at the edge of the southern highlands (reminds me of Sinus Iridium on the Moon), and Utopia as a possible impact basin; and the topography suggests an even larger ancient ‘north pole basin’ on Mars. I don’t think any basin-scale impact features are still present on Earth. From this standpoint, a lot of Mars resembles the moon: turn your topographic Mars globe so Tharsis faces away and I expect it looks a lot like a Moon globe.
But look at Tharsis, Valles Marineris and the vast northern lowland plains and the canyons or rivers flowing in from the highland edge, and Mars isn’t as moon-like. The vast northern lowland could have held 100’s of meters to a kilometer of water within a possible shoreline of smooth, constant elevation terrain. An ancient river seems to have flowed into Hellas, maybe it held a lake. Mars had a fair amount of water early on, but it’s hard to say if it was recycled to any extent by plate tectonics, like on Earth.
The giant volcanic mountains crowned by Olympus Mons are piled on a static thick crust. The area southeast of the Tharsis volcanoes looks a little like the edge of a plateau and the Fossae fractures running north to the less lofty Alba Patera volcano, along with the Valles Marineris running east from Tharis, look like rifts. Maybe these mark the last chance for Mars, had there been more water deeper in the crust, more internal heat, or a thinner crust, to exhibit something more like plate tectonics we see on earth.
While there may be hints of tectonics in Mars' past, it's not the predominant crustal process as we see on Earth.
Posted 12 June 2013 - 01:18 PM
No tectonic ok, but the european Mars Probe had a deep penetrating radar that showed ice buried miles deep, almost like ice 'plates' that could slide perhaps.
I don't think the probe has shown how deep these ice plates go. Perhaps Mars crust is more like a swiss cheese, with hole filled by ice, although i assume this would be detectable by 'gravitational variation detectors'.
Posted 12 June 2013 - 02:04 PM
For plate tectonics on Mars, I think the story is not much happened. If anything, the extent of Tharsis volcanism seems closer to a Venus style ‘overturning’ or ‘resurfacing’, when internal heat builds up until lava floods out a scale that makes even the largest ‘traps’ eruption on Earth look small, and covers the former surface.
The ice on Mars is within the uppermost solid or ‘cold’ thick crust of Mars, and not likely a means for plate motion. On a smaller scale unrelated to plate tectonics, ice might have a big role helping to lubricate mass movements, like the big landslides off the flanks of Olympus Mons seem to have created the escarpment that rings much of the mountain.
The deep ice on Mars is great evidence for a global scale aquifer. Swiss cheese is probably a good analogy: some think that Mars has a ‘mega regolith’ shattered by countless impacts into being fairly porous, even a few kilometers deep. While this concept is similar to parts of the lunar surface, on Mars it would provide a big subsurface sponge to store some of the water of a wet very young Mars, instead of all the water being lost to space. It could have been a subsurface path for water to flow as the source of some of the larger channels draining to the north, features that post-date the possible rainfall gully networks of the ancient highlands. Locally it may still provide a path for Martian groundwater flow – as seen in small scale changes to gullies that seem to emerge from steep slopes like crater walls or escarpments.
Is the mega regolith thought to extend under the northern lowlands and their sedimentary (?) veneer? I'd think that it must, if that lowland surface was bombarded after the basin-size impacts that created the lowlands.
There’s a lot of evidence for subsurface ice or water on Mars at various latitudes, from landform indications like the outflow channels, pedestal or splash craters, and patterned ground, to direct detection of ice. Mars seems to have made a transition from a hydrologic cycle in extreme youth even with rainfall (?) 4 Billion years ago, to slow groundwater movement, until the remaining stored water may have frozen sometime after the big floods of the outflow channels.
Posted 12 June 2013 - 04:03 PM
The deep ice on Mars is great evidence for a global scale aquifer
Assuming it was a global phenomena and an entire primordial ocean trickled down the faults in the crust, the water was liquid when it sunk and solidified once inside. Shouldn't we expect to see the global scale fractures associated with the volume expansion?
Posted 12 June 2013 - 06:16 PM
I would also have expected some shrinkage of the planet overall as the core cooled and crystallized. I would think that would show up in the crust as compressional features as well, either folds or thrust faults. I'm a little puzzled by their absence.
Posted 12 June 2013 - 07:39 PM
As for why there aren't widespread features visible from subsurface ice:
Not seen in many areas; maybe these are where the available 'sponge' volume of subsurface porosity was a lot bigger than the volume of primordial water left underground; or higher elevations left 'high and dry' as the young Mars water cycle dried up.
But signs of subsruface water or ice are seen in lots of places concentrated toward the northern lowlands, such as:
+ patterned ground that looks like permafrost polygons on earth, but is at a much larger scale on Mars
+ glaciers or rock glacier like features suggesting ice flow or at least a lot of interstitial ice between rocks.
+ "splat" craters with liquified-appearing ejecta lobes
+ chaotic terrain, often above channels, this looks like a subsurface water emergence similar to earthquake liquifaction of saturated soil on earth.
Posted 12 June 2013 - 09:18 PM
Posted 13 June 2013 - 04:54 PM
Sometimes even features at depth are expressed through a mantling of younger material on Earth because crustal motions propogate up through the covering material, but Mars is less dynamic than Earth.
Tectonic features like faults, folds, from compression or tension could be hidden under Mar's "Vastitis Borealis" northern plains which may be a mix of water lain and wind lain sediments. Some other areas of Mars are mantled by lava flows.
Gravity measurements, maybe penetrating radar, or magnetic surveys might all see through the overburden to give some information about buried structures.
It would take a lot to cover other fractures and valleys as big as those visible around Tharsis. Maybe some features that big are present under the northern lowland plains.
Posted 13 June 2013 - 07:23 PM
Posted 21 June 2013 - 09:16 PM