Anomalous swelling of Martian Tharsis plateau

[dougettinger]

There was much previous discussion about an APOD dealing with the very striking Martian feature, Valles Marineris, and its origins. Numerous ideas were presented that became linked with other nearby geological features: the unusually elevated Tharsis plateau, the Tharsis volcanoes, and the Hellas impact basin which is almost one the opposite side of the planet from the Tharsis plateau. A central question which was not conclusively answered is why the Tharsis plateau was bulged well above the all the other surface elevations on Mars. Such a condition has no relative comparison in the solar system.

I believe the answer can be found by studying the Mars MOLA map. Obviously, a large impactor struck Mars creating one of the largest impact basins, Hellas, in the solar system. The impactor was much harder than the mostly molten young Mars. The impactor penetrated the already differentiated crust and the molten interior. A combination of ejecta returning to the surface from the impact and the displacement and expulsion of molten mantle material created the highlands of the southern hemisphere. The smooth Borealis basin in the northern hemisphere is the original differentiated crust, although it is postulated to be even a larger impact basin. Any impactor that could have created such a basin would have destroyed the planet. Most of the ejecta did not reach escape velocity and over a period of time fell back creating the other numerous, but smaller impact craters seen in the southern hemisphere.

The impactor was an ice ball composed mostly of CO₂ and water with a small rocky/iron core. This composition is very likely after considering the power law of comparative compositions and sizes of solar system bodies. As already postulated a substantial amount of the impactor due to the restitution coefficient penetrated the mantle and traveled almost 1/2 to 2/3 of the distance through most of the very liquid mantle and core. The ices would of course gasify and almost immediately begin to differentiate and rise to the surface of the planet on the opposite side. These gases mixed with its small core of iron and sufides and partially some of the stripped Martian core and then became trapped under the existing crust on the opposite side of the planet from the impact location. This entrapment of the lighter volatiles bulged the crust to create the Tharsis plateau.

Fissures in the crust created volcanic activity that released the CO₂ and water into the atmosphere along with iron and sulfides to produce the atmosphere and the orange color of the Martian surface. The volcanic action efficiently released the volatiles from underneath the crust thereby causing the collapse of the crust that created the largest canyon in the solar system. I know of no other way to explain all the Martian surface features except in this way. You now have the reason for the swelling of the Tharsis plateau.

I am hoping to receive some worthy commentary on this topic. Other reasons for the Martian bulge may erupt. Please, no flamingoes

April 19, 2011

[BMAONE23]

It would seem to me to be unlikely that a cometary impactor consisting mostly of water ice and dry ice with a small iron core would have the potential to reach the core of Mars. If it were traveling fast enough, the friction heat from the initial impace would likely cause most of the volatile material to flash to a vaporous/gaseous state. For much the impactor to remain intact upon impact and reach the core, it would need to be quite large and dense ( like roughly the size of Hyperion ). If it did reach the core the heat there would cause the remaining water ice and CO2 ice to instantly vaporize and explosively fracture the planet, much like a hand wrapped closed around a firecraacker when it explodes will remove fingers. I don't think it likely that an impactor would have reached the planet's core.

[dougettinger]

I should know the size of the Hellas impact basin but do not. The diameter of the impactor should be 1 1/2 to 2 times the diameter of the basin. Smaller pieces would break-off prior to impact similar to the comet that hit Jupiter. And the perimeter wall of the impact basin would fall inward causing the basin to become or appear much smaller.

Do you know the diameter of the Hellas impact basin ?

A very rough comparative collision would be a snowball with a rock in the center being thrown into some thick soup that has been boiled away enough to create a thick crust on top. Perhaps you can think of a better analogy.

4/19/2011

[BMAONE23]

According to this calculator the impact of something the size of Hyperion 286k or 286000 meters dia. (presuming porous rocky material covered by mostly water ice) will produce a crater that is 4.49X10(6) 4,490k or 4490000.00 meters in diameter.

To get a Hellas size basin with an impactor made of porous rock and ice, it would need to be roughly 71km diameter & strike Mars at an approx 45deg angle

[dougettinger]

Hello Bmaone23,

My thoughts are that the impactor should be about the size of Pluto, 2300 km, or larger and about Pluto's density of 2 g/cm3. I also assumed a 75 degree angle of impact due to its assumed penetration. The "calculator" only gives me a rim to rim diameter of 96 meters. How could this result be anywhere near correct ? Thanks for showing me the calculator; I am not sure it works for the scale of impact that I am envisioning. Per Wikepedia - the Hellas impact basin is about 2300 km in diameter and 7 km deep.

4/20/2011

[BMAONE23]

Just ran it myself for an impactor that is 2400km or 2,400,000m comprising porous rock and came up with an impact crater that would be (1.15k x 10(7))11,500k or 11,500,000m and Mars is 6800k diameter. Something the size of Pluto would very likely obliterate Mars

[dougettinger]

Hello Bmaone23,

This is my second reply. You referenced the calculator. I would be very interested in knowing how they calculate the heat energy output of impacts. Do you know how the series of calculations that are used can be accessed. Thank you.

4/21/2011

[BMAONE23]

Of that, I am uncertain myself. So I couldn't speak to the accuracy of the end product or the formulae utilized for the results stated.

[dougettinger]

Just ran it myself for an impactor that is 2400km or 2,400,000m comprising porous rock and came up with an impact crater that would be (1.15k x 10(7))11,500k or 11,500,000m and Mars is 6800k diameter. Something the size of Pluto would very likely obliterate Mars

Maybe I used the wrong units. I am now getting better results with the calculator. I used 950,000 m for the size of the impactor which is as big as Ceres. I used 1200 kg/m3 which is the density between porous rock and ice, 45 km/s for the impactor velocity estimating cometary orbital characteristics, 75 degree impact angle assuming the impactor penetrated 50 % or more of the Martian mantle, 1500 kg/m3 for the target density, an acceleration of 3.7 m/sec2 due to Martian gravity, and liquid water for the target assuming the young Martian crust is thin and the underlying mantle is still liquid. The new result was 2310 km rim to rim crater which matches the size of the Hellas impact basin.

I do assume that much of the energy transfer of the impactor's kinetic energy is transfered to other kinetic energies and not so much heat energy. Do you have comments about my chosen parameters ?

4/21/2011

[dougettinger]

Hello Chris, Since you are the asteroid expert you may have some ideas about collisions occurring on Mar. I am begging for a response from this unfinished thread of thought. The "calculator" given me by Bmaone actually aided my ideas but may have led me off the track. Not sure.

[Chris Peterson]

Hello Chris, Since you are the asteroid expert you may have some ideas about collisions occurring on Mar. I am begging for a response from this unfinished thread of thought. The "calculator" given me by Bmaone actually aided my ideas but may have led me off the track. Not sure.

Certainly, asteroids can collide with Mars, and must certainly have done so. I have no confidence that any of the available "simple" impact calculators are capable of producing reliable analyses for objects larger than a few hundred meters across. This is the point where the collision dynamics go from fairly simple energy dominated events ("explosions") to complex systems that have to consider energy transfer inside the planet. The latter can only be considered using complex numerical simulations.

My view remains that Tharsis plateau is most easily explained as the product of tectonics, just as we see on Earth (the Tibetan plateau, numerous cratons, etc.) Tharsis is somewhat higher than similar structures on Earth, but that makes sense given Mars's considerably lower gravity.

[dougettinger]

Chris, thanks for your input, especially about the "calculator". I was somewhat sure that it did not account for energy transfer inside the planet.

I am not in total agreement with your view of tectonics on Mars. The Valles Marineris indicates to me that the crust cracked and collapsed. It does not appear to be a subduction zone where one plate pushes under another creating a trench and a parallel uplift or mountainous region with some volcanoes.

[dougettinger]

It would seem to me to be unlikely that a cometary impactor consisting mostly of water ice and dry ice with a small iron core would have the potential to reach the core of Mars. If it were traveling fast enough, the friction heat from the initial impace would likely cause most of the volatile material to flash to a vaporous/gaseous state. For much the impactor to remain intact upon impact and reach the core, it would need to be quite large and dense ( like roughly the size of Hyperion ). If it did reach the core the heat there would cause the remaining water ice and CO2 ice to instantly vaporize and explosively fracture the planet, much like a hand wrapped closed around a firecraacker when it explodes will remove fingers. I don't think it likely that an impactor would have reached the planet's core.

Hello to BMAONE23 and other explosive/celestial collision experts:

Let's assume a body the size of Ceres but with much more frozen ices like a comet instead of a typical asteroid struck Mars where the Hellas impact basin is located. Pieces of this impactor would break off like a body being heated up by the friction of the planet's atmosphere. However, in the very young solar system of about 3.9 billions years ago, the atmosphere around Mars was still developing due to differentiation or still non-existent. Also, the resulting tidal forces of such a small planet like Mars would not likely break it into pieces comparable to our experience with the comet that struck Jupiter. Hence, the impactor is almost whole as it strikes the thin, halfway friable, but still flexible forming crust. The impactor easily penetrates the crust and the liquid mantle underneath.

In fact, the momentum of the impactor easily causes much movement through the liquid mantle toward the hotter and more pressurized core of the planet. Because of the size of the planet Mars, the core is probably are liquid wthout any solid portion. The anology is similar to punching a hole into a raw egg with a pointed pencil; this anology is in contrast to punching a hole into a boiled egg. I am assuming the very young planet has not cooled sufficiently to create any solid mantle. And the impactor is small enough that it has already become very dense, frozen, and hard due to its orbiting the cooler regions of the solar system near Mars. This combination of hardnesses of the impactor and the planet almost guarantees the restitution coefficient is very close to zero meaning that a very small percentage of its material is ejected in the collision.

It was proposed by BMAONE23 that the highly volatile materials would quickly expand and blow apart the planet like a firecracker held in someone's hand would blow apart their hand. The difference is a thick silicate soup is encasing and at considerable depth pressurizing the volatiles so that its expansion into a gas is controlled. The denseness and hardness of the impactor also helps to slow the phase change and control expansion. Then the globules of volatile gases; more than likely CO2, H2O, mixed with particles of iron and and sulfur under pressure may resemble a lava lamp. With the aid of gravity, the globules' interface surface friction with the silicates of the mantle, and convection the volatiles rise slowly to the surface of the planet and are trapped under the thin crust away from the original penetration. The pressure of the volatiles underneath the crust creates a bulge. The release of gases is finally accomplished by volcanoes over a period of time. Then some the raised crust collapses after the evacuation of the gases; this collapse creates the huge Valles Marineris.

I am only employing inductive reasoning at this point having knowledge of the conditions at the beginning and at the end. Laboratory experiments could possibly test the conditions that I am proposing. These thoughts are not mere musings; this reasoning is trying to connect the dots with aid of the various academic disciplines. You are welcomed and encouraged to dismantle any of these thoughts.