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Fraser
2004-Sep-27, 05:00 PM
SUMMARY: Data accumulated by the ASPERA-3 instrument on board the European Space Agency's Mars Express spacecraft seems to indicate how Mars got so dry. Scientists believe that water used to cover Mars, but over the course of 3.8 billion years, it was stripped away from the planet by the Sun's solar wind. ASPERA-3 tracks the inflow of particles from the solar wind, and then tracks the outflow of particles escaping from the Martian atmosphere. It found that the solar wind penetrates deeply into the atmosphere to an altitude of 270 km, energizes particles, and causes about 1 kg (2.2 pounds) of material to trail away from Mars every second. Over the years it added up to make the planet bone dry.

What do you think about this story? Post your comments below.

om@umr.edu
2004-Sep-27, 05:38 PM
This is an interesting story, Fraser.

As I recall Harold Urey first discovered Deuterium, H-2, in residual water after successive losses by evaporation.

The H-2/H-1 ratio might provide a record of water loss from Mars.

The O-17/O-16 and O-18/O-16 ratios might also be enriched in the residual water.

Has anyone tried to extract and measure isotope ratios in traces of water extracted from Martian meteorites?

With kind regards,

Oliver
http://www.umr.edu/~om

GOURDHEAD
2004-Sep-27, 08:44 PM
Scientists believe that water used to cover Mars, but over the course of 3.8 billion years, it was stripped away from the planet by the Sun's solar wind.

No doubt much water has been stripped from the surface and the atosphere as stated. Since Mars has been volcanically quiet for a rather long time, the water that would have been recyled to the surface by that method must be trapped below the surface and there could be quite a bit of it. Has anyone guessed at how to estimate how much water might have been retained below the surface of Mars? One can easily imagine that as Mars cooled the vulcanism stopped and various cracking of its surface structures occurred. If so, quite a bit of water would have settled below the surface is various caverns (those minimally open to the surface), lava tubes, and acquifers, and any extant microbes (perhaps a few multicellulars)would have followed the water inside Mars and evolved into who knows what.

Guest
2004-Sep-27, 10:31 PM
bone dry is Mars :(

anaklinskywalkar1
2004-Sep-28, 03:12 AM
this gives a wonderful information.

mark mclellan
2004-Sep-28, 09:52 AM
If we could thicken the atmosphere to restrict the depths at which the solar winds reached, could we again see running water on the surface of Mars? :)

mark mclellan
2004-Sep-28, 09:54 AM
[QUOTE]bone dry is Mars ......is this guest Yoda ? :D :lol:

Eric Vaxxine
2004-Sep-28, 11:55 AM
When one can see Polar ice...how can it be bone dry? I like the idea of water trapped beneath. Standing water has been discovered in images in the public domain.

alfchemist
2004-Oct-01, 08:16 AM
Guess I'm at a loss here as far as comparative data for Earth and Mars are concerned. If solar wind is the culprit in drying up Mars, why is Earth not dried up as well, or stripped of its atmosphere? If the process spanned 3.8 billion years and the earth is 4.5 billion years old, then, earth must have been affected by the same process considering its proximity to the sun relative to mars. Was the martian atmosphere in the beginning not thick enough compared to Earth? The fact that liquid water existed long ago means the atmospheric pressure was strong enough to maintain water in that physical state and maybe comparable to atmospheric pressure here on Earth

GOURDHEAD
2004-Oct-01, 12:57 PM
If solar wind is the culprit in drying up Mars, why is Earth not dried up as well, or stripped of its atmosphere?

The earth is losing water continuously, but it also gains water by collecting comets some of which are quite small. The net effect is hard to assess; I haven't read whether it is a gain or a loss. There's a delicate balance between the disassociation of water in the upper atmosphere, the mean free speed of hydrogen comensurate with the temperature of the upper atmosphere, and the gravitational attraction of earth. As the sun expands and increases the temperature of the earth's upper atmosphere, one of the unpleasant effects will be the ultimate loss of earth's oceans to evaporation and subsequent disassociation of water.

The custodians must intercede eventually.

Geology Student
2004-Oct-03, 03:45 AM
I have read the ESA article:
http://www.esa.int/esaCP/SEM75BADFZD_index_0.html
I have read the Science article (Richard Lundin):
http://web.utk.edu/~dteal/ (click on "Solar Wind-Induced"... or the others for a laugh :) )
I have read the abstract that the Lundin paper references:
http://www.agu.org.proxy.lib.utk.edu:90/pu...1JA000007.shtml (http://www.agu.org.proxy.lib.utk.edu:90/pubs/crossref/2001/2001JA000007.shtml)

NONE of these state that 1 kg of material is being lost a second. Where does it say this?
(I have not accessed the full pdf of the last paper, so that is my best guess of where this 1kg/s is stated.)
But at any rate, it is not stated in the Lundin paper or the ESA news release SO WHY IS IT IN THE SUMMARY on universetoday???

Thanks,
Geology Undergrad

P.S. please email me at cronodavid@hotmail.com to let me know and/or just post a reply to this.

Geology Student
2004-Oct-04, 04:30 AM
Originally posted by alfchemist@Oct 1 2004, 08:16 AM
Guess I'm at a loss here as far as comparative data for Earth and Mars are concerned. If solar wind is the culprit in drying up Mars, why is Earth not dried up as well, or stripped of its atmosphere? If the process spanned 3.8 billion years and the earth is 4.5 billion years old, then, earth must have been affected by the same process considering its proximity to the sun relative to mars. Was the martian atmosphere in the beginning not thick enough compared to Earth? The fact that liquid water existed long ago means the atmospheric pressure was strong enough to maintain water in that physical state and maybe comparable to atmospheric pressure here on Earth
Earth is not losing near as much atmosphere as Mars because of our magnetic field.
The Earth's magnetic field acts as a shield from the ionized solar wind by deflecting the solar wind (because charged particles are affected by magnetic fields.)

Mild mannered
2004-Oct-04, 11:02 AM
Originally posted by fraser@Sep 27 2004, 05:00 PM
It found that the solar wind penetrates deeply into the atmosphere to an altitude of 270 km, energizes particles, and causes about 1 kg (2.2 pounds) of material to trail away from Mars every second. Over the years it added up to make the planet bone dry.

What do you think about this story? Post your comments below.
Can this also be contributing to the cooling of the planet?

alfchemist
2004-Oct-05, 08:22 AM
Earth is losing water continuously (from the two replies) After 3.8billion years, even if the rate is small, the loss must be significant unless there's an equilibrium replenishing the loss or earth is not losing water at all

VanderL
2004-Oct-05, 07:20 PM
Geology student:
Earth is not losing near as much atmosphere as Mars because of our magnetic field.
The Earth's magnetic field acts as a shield from the ionized solar wind by deflecting the solar wind (because charged particles are affected by magnetic fields.)

Hi there, I believe this point was made earlier, but what about Venus? It has an atmosphere 90 times as dense as ours and, just like Mars, Venus also lacks a magnetic field. How come it hasn't lost it's atmosphere just like Mars? Venus would be subject to even more solar wind pressure (I'm not sure about this, but I assume the solar wind is densest close to the Sun).
I think the study is a nice example of our lack of understanding the history of the solar system. We can't just extrapolate back to the origin of the solar system; we don't know enough yet.
But by all means, keep the data flowing.

Cheers.

Guest
2004-Oct-06, 05:08 AM
Sounds like there's insufficient data to jump into conclusion that the loss or deterioration of the martian atmosphere is due to solar wind. Isn't there a much more extensive study on how/why Mars lost its water and atmosphere? What could possibly cause such event or process? An impact? planetary influence? I find it hard to accept solar influence singling out the "fourth rock" from the sun

Guest
2004-Oct-06, 05:10 AM
Sorry, could not register. I tried four times but i can't log in

Alfchemist

GOURDHEAD
2004-Oct-06, 02:42 PM
Venus also lacks a magnetic field. How come it hasn't lost it's atmosphere just like Mars? Venus would be subject to even more solar wind pressure (I'm not sure about this, but I assume the solar wind is densest close to the Sun).



What could possibly cause such event or process [on Mars] ?

I too believe you're right in assuming that Venus orbits in a more dense solar wind. I think the answer lies in the binding energy of various molecules versus the mean velocity of the molecules and their constituent atoms due to their kinetic energy from the atmosphere's temperature. Due to hydrogen's low mass, it must have an appreciably higher velocity when in kinetic energy equilibrium with the other atoms/molecules in the same thermal environment. The higher velocity of the hydrogen atoms allows them to escape Venus' gravity while the heavier objects are retained due to their slower velocities. Once hydrogen is separated from the oxygen in water molecules, it escapes leaving the oxygen free to combine with other atoms such as carbon at a different binding energy; although neither carbon nor oxygen are likely to achieve escape velocity in appreciable quantities. Since there is no magnetic field to deflect the charged particles, mostly protons, incoming from the sun, one would expect them to slam into the CO2 in the upper atmosphere dislodging the oxygen from the carbon and produce more water. Since each of these processes is highly stochastic, its difficult to guess where the equilibrium point lies and what the net effects are. From observation of the current constituents of Venus' atmosphere, water production is losing to hydrogen escaping.

Note that the upper atmosphere of Venus is rich in H2SO4 which may act as a protective blanket for the portion of the atmosphere lying below the H2SO4. I assume the binding energy holding the hydrogen to the SO4 is stronger than that holding the hydrogen to oxygen in water. Since H2SO4 obviously weighs more than CO2, the volume occupied by a molecule of H2SO4 must be sufficiently larger than that occupied by one of CO2 to enable the floating of the H2SO4 on top of the CO2.


On Mars, with much lower escape velocity for the hydroen due to its gravitational attraction being smaller, the net escape of hydrogen is larger and the remaining oxygen seems to have combined with iron and silicon to a greater extent than with carbon which must not have been proportionally as plentiful.

A first step in making Venus less inhospitable is to infect it with carefully chosen extremophylic microbes, genetically modified as required. Part of the region occupied by the H2SO4 clouds is near one atmosphere of pressure and at temperatures near the freezing point of water at that pressure. There are microbes currently extant on earth that are acid loving and efficiently functioning in these conditions (euplotes antarcticus, polaromonas vacuolata). There are others that function well at and slightly above the boiling point of water (methanopyrus kandleri) and don't require free oxygen to do so. These types of microbes in the presence of all that energy on Venus with perhaps some attention from our genetic engineers can drastically transform Venus' atmosphere to be less greenhouse effect supporting. These engines are self replicating so an initial few will go a long way without further support from us. This will result in cooling the atmosphere; although I'm not sure of the rate of cooling. If we are careful about selecting the microbes and their modifications, the main byproduct of this process will be water from the H2SO4 and to a lesser extent from solar protons disassociation of CO2 and combining with the O2. The subsequent combining of the excess oxygen and sulfur with surface minerals with the newly formed ocean acting as a catalyst will reduce the atmopheric pressure to tolerant levels. What is not accounted for is a buffering agent performed by nitrogen on earth to keep the atmosphere from being too oxygen rich.

VanderL
2004-Oct-10, 12:01 AM
Thanks Gourdhead for this long explanation,
but is there really such a big difference between the mass of Mars compared to Venus? I always thought Mars was just a little bit smaller than Venus and both are smaller than Earth.
If this solar wind idea is correct than only Earth should have an appreciable atmosphere and both Mars and venus should have thin atmospheres, no?
Is there any information about the mass-loss of Venus or Earth using the same method as was used on Mars?

Cheers.

damienpaul
2004-Oct-10, 12:18 AM
but Mars is significantly smaller than the earth and Venus, about half to a third of the size.

VanderL
2004-Oct-10, 09:13 AM
Yep, you're right of course,Mars is only one third of the mass of Venus.

Still, the current value of the mass-loss of the atmosphere of Mars is too small to account for Mars losing almost all of it's atmosphere in it's presumed history. Venus has an atmosphere 90 times as dense as Earth's, if the story of Mars is true, then Venus should have even less of an atmosphere than Mars.
The explanation of the magnetic field protecting Earth doesn't work for Venus (it seems Mars used to have a magnetic field in the past, so that also argues against the simple solar radiation idea), so I don't think this model is valid.

If anything, the data show that our solar system must have had a chaotic, complex history. It seems every planet has a unique history, no two planets are even remotely alike. If they all formed in a similar way I would expect some of them to resemble each other, no such thing in reality.
I think the mistake we make is in assuming planets formed in their current positions and have been circling and orbiting like a clockwork ever since.
It makes it all extremely difficult to piece together the history of the solar sytem, on top of that there is also a lesson to be learned from the exoplanets that have been found thusfar, our solar system seems to be in a class of it's own (this is after correction for the bias in the detection method).

Cheers.

alfchemist
2004-Oct-11, 07:55 AM
Sounds like the solar wind thing is hard to sell! and my friend VanderL is challenging the current model of planet/solar system formation. Before we go that far VanderL, i guess it's prudent to look at all plausible simple explanations why/how Mars lost its water, atmosphere, and magnetic field. Solar wind influence seems unlikely at this point. What about an impact or planetary influence? Could it be that Mars was at some point near enough to Jupiter that the gas giant influenced Martian features? Or there could be one powerful event or process on Jupiter long ago that influenced Mars even at the present distance separation! Could there be one possible cause to explain all of Martian features? Bottomline is, Mars used to be a viable planet with surface water but is now practically a dead planet. There must be one powerful event or process that caused that.

Guest
2004-Oct-11, 09:41 PM
Hi Alfchemist,

First off, I think the history of the solar system is very difficult to unravel (and that it an understatement).
So many things could have happened (and apparently did happen) between the formation and now, that almost every planet is completely different from any of the other planets. Best example for me is Uranus, try to imagine how that planet formed wheb we find it in an orbit with an inclination of 90 degrees and moving with its pole in the direction of it's orbit while all of Uranus' moons happily orbit about it's axis of rotation around it's equator!

Any model that describes the history of the solar sytem has to include the catastrophic events that apparently happened. My contention is that no planet formed where it is now. Having said that , we also need to look at the exoplanets and what they tell us. Apparently most sytems have close-orbiting giant planets, and the idea is that they couldn't have formed where they are, so they must have formed further out and spiralled inwards.

There is another option that we need to consider, imo. Why can't planets be ejected from their host star, it would explain why there are many large planets in close orbit, and moons can form from the debris of such an event. These events are violent and maybe we see these events as novae, suppose these events do not signal a dying star, but the birth of new planets, it would be nice to find out if planets are formed in such an event. (I realise that maybe this belongs in the alternative section).


Alfchemist: What about an impact or planetary influence? Could it be that Mars was at some point near enough to Jupiter that the gas giant influenced Martian features? Or there could be one powerful event or process on Jupiter long ago that influenced Mars even at the present distance separation! Could there be one possible cause to explain all of Martian features?

Maybe all the inner planets were once moons of Jupiter (or Saturn) and something (perhaps Saturn or Uranus were later additions to the solar system pushing every moon into different orbits) destroyed the configuration, leading to formation of the inner planets (notice how closely Titan resembles the inner planets?). The following chaos ended in planets in their new orbits, heavily scarred in the process. Maybe the only thing that kept Earth a habitable world was sheer luck!


Alfchemist: Bottomline is, Mars used to be a viable planet with surface water but is now practically a dead planet. There must be one powerful event or process that caused that.

I agree with this picture, and to add to this picture: maybe some of these events were witnessed by people in antiquity and recorded in the ancient myths of the world.

Maybe part of what Velikovsky proposed decades ago wasn't far besides the truth, although I think his chronology is way off (he trusted the Biblical timeline, while he should have researched older documents). I saw a thread about him somewhere recently, but imo it can't hurt to see what happens if we consider other ways of planet formation.

I know I'm out on a limb here, but I also think it is worthwile to look at any available record we possess.

Cheers.

VanderL
2004-Oct-11, 09:44 PM
Darn,

Forgot to login again (happens when I come home late), that post was me.

Cheers,

Louis.

GOURDHEAD
2004-Oct-12, 02:15 PM
I think the mistake we make is in assuming planets formed in their current positions and have been circling and orbiting like a clockwork ever since.

This could be; however, that they formed in essentially their current orbits give or take a few million miles for the semi-major axis of the orbit for each is a reasonable assumption and invokes the least number of highly improbable events. My guess is that the major influence in shaping the atmospheres of Venus, Earth, and Mars is the interplay between the escape velocity for each planet and the atmospheric and ground/water chemistry including the sequence of occurrence of various catylists especially temperature and the amount of water.

The controlling force for Mars was probably its low gravity. On Venus the nature of the catalyzing effect of its probable early ocean somehow allowed much more sulfur, carbon, and oxygen to remain unicorporated in the soil and rocks thus leaving them free to form H2SO4 and CO2. CO2 has the physical properties to collect in the atmosphere and also avoid disassociation or, if disassociated, avoided escape velocity from Venus in significant numbers. Somehow hydrogen has managed to stay stuck to SO4 or has achieved some balance beween gain and loss. Also, hydrogen is the most volatile of the elements and may have been in relative short supply at the orbit of Venus compared to that of the others causing Venus to be assembled with proportionately less of it. With less hydrogen there would be no ocean or a very small one of short duration unable to provide the catalyzing function required to fix the S and C in the soil and rocks.

VanderL
2004-Oct-12, 04:23 PM
Hi Gourdhead,

Thanks for the detailed description of how the differences might be explained if the orbits are assumed to be essentially unchanged.
I'm sorry but I think there is enough evidence to show this assumption could be wrong.
Let me make a list:

1. No two planets are the same.
2. Even a stronger argument, the 4 inner planets (Mercury, Venus, Earth and Mars) are completely different.
3. Saturn's rings are a short-lived phenomenon.
4. Uranus (including it's moons) orbits in the direction of it's axis.
5. Exoplanets show us that our system is the "odd one out" (making it necessary to review our assumptions)
6. Close-orbiting "hot Jupiters" are very common.

There are similarities between the planets, they all roughly orbit in the plane of the Sun.
Apparently there is a stabilizing mechanism that ensures that planets aren't "kicked out" of the system even though some disruptions must have occured (assuming we didn't start out with hundreds of planets to begin with).
I think bold new models are needed, I saw mention of planets forming by close encounters of two stars. I mentioned the ejection model. Any model that can explain a close-orbiting giant and how planets can survive disruptive events are favoured imo.

Cheers.

wstevenbrown
2004-Oct-12, 08:20 PM
Our method of discovery favors high-mass, close-in planets, just as you don't see many fireflies in Times square. We are on the threshhold of improving our methods to give a more balanced picture of the "normalcy " of low- mass planets. I stipulate that hot Jupiters swept their particular systems clean, and something very odd happened to Uranus, the more peculiar because whatever it was didn't raise its temperature much. An interloper, perhaps. Regards, Steve

VanderL
2004-Oct-12, 09:39 PM
Thanks Steve,

The bias in detecting exoplanets was taken into account and still our system came out highly unusual. I'm not saying it is unique, merely that we shouldn't base our models just on our own solar system, we should model the more common system, meaning the "hot Jupiter" version.

This is discounting the low-mass planets, they could also be present in the already "known" exoplanetary systems.

Cheers.

wstevenbrown
2004-Oct-13, 06:57 PM
Your point is well taken, VanDerL. I read that study also. The problem is lack of data to discriminate amongst the various models of planetary formation/capture. I favor an iterative model which keeps it simple-- that what forms next depends on what was formed previously. For instance, close binary stars won't have close-in planets of any sort. Single stars will probably follow a power law similar to that for stars: very few W, O, and B, many more A,F, G, and K, MANY more M, L, and T. In this analogy, the hot Jupiters correspond to the AFGK class, and terrestroid worlds like us the MLT class. Nature doesn't always choose simplicity (William of Occam is a guide, not a high priest), but I would find a fractal model, self-similar at all scales, mildly comforting. I hope to live long enough to find out how common the L's, T's, rogue superJupiters and bound superJupiters are. At the present moment, though our detection methods favor bright objects. The study did not seem to me to take into account precursor objects: e.g., local conditions within the protoplanetary nebula, which influence the distribution of nearby massive objects. Thanks for your thoughts--Steve

alfchemist
2004-Oct-14, 04:33 AM
Hey VanderL, that was a very nice picture of how the solar system was formed assuming the "hot Jupiter" model is correct or applicable to our system. This picture (terrestial planet formation) can easily be verified. You know that putting an object near a heat source like our star would definitely change the object's properties. If indeed, the terrestial planets were once moons of jupiter, then we can make a comparizon between its present moons and the terrestial planets minus the Sun's effect at their(terrestial planets) present distance. But let me just bring the attention to the topic at hand : Mars losing/lost water and atmosphere. Assuming Mars lost it's water and atmosphere due to one cataclismic event that removed it from an orbit around jupiter, it follows that Mars, as one of jupiter's moons, had already its atmosphere at that time. Dating can easily verify such picture. Let me introduce another possibility out of the picture you have drawn using the "hot jupiter" model. Mars was once one of the moons of jupiter but did not have the characteristics such as viable atmosphere we were able to establish (that it existed, including surface water) but later evolved into a viable planet because of its proximity to the sun. Or, Mars was formed out of the moons and other materials from jupiter and ejected to be a terrestial planet, evolving as a viable planet when it got near our sun. These two pictures seem to be more plausible than Mars having a viable atmosphere, orbiting jupiter. In these two cases however, the question remained: How/why Mars lost it's water and atmosphere? Is it not possible that Mars didn't come from jupiter but was heavily affected by some cataclismic event that happened on jupiter during the time when it had a viable atmosphere?

VanderL
2004-Oct-15, 10:44 PM
Hi Alfchemist,

Now that was a post with lots of things to ponder. The puzzle still remains why Mars is so different from it's neighbours. Cataclysmic events are, imo, a certainty. You can't expect planets to change their orbits, speeds, or rotation axis by themselves. External factors are needed and there are plenty possibilities to choose from.
I'm certain the history of the solar system is very complex (imagine planetary pinball), because there are just too many differences between the planets. My guess is that Mars, Venus and Earth were all displaced from their initial orbit around either Jupiter or Saturn, affecting each planet in a different way, Earth was just lucky and Venus and Mars weren't. Apparently Mars lost much of it's atmosphere and surface, (maybe to Venus?) in the process.
The event that pushed out the inner planets (maybe including Mercury) created the rings of Saturn as well, so that would place the inner planets as having been satellites to Saturn, and since the ring are unstable and thought to last only several hundred thousand years, this event was quite recent. What about an interloper caught by the gravity of our Sun?
Sorry, I'm starting to ramble, I'll ponder some more and try to post a more coherent story. :rolleyes:


wstevenbrown:

I favor an iterative model which keeps it simple-- that what forms next depends on what was formed previously. For instance, close binary stars won't have close-in planets of any sort. Single stars will probably follow a power law similar to that for stars: very few W, O, and B, many more A,F, G, and K, MANY more M, L, and T. In this analogy, the hot Jupiters correspond to the AFGK class, and terrestroid worlds like us the MLT class. Nature doesn't always choose simplicity (William of Occam is a guide, not a high priest), but I would find a fractal model, self-similar at all scales, mildly comforting.

I like your comment on the fractal model, I think one mechanism that can explain all the features we see is preferred. What I think is that planets slowly condensing from a nebula cannot explain the "hot Jupiters" and is therefore not the way forward. Why do you think binary stars won't have close-in planets?

Cheers.

wstevenbrown
2004-Oct-18, 01:39 PM
Extremely close, few-hour orbiting binaries could have planets from the same accretion event, but they would be further out than usual, due to mass depletion by the twin primaries, and probably less massive for the same reason. Month-to-years-period systems, such as Alpha-Beta Centauri wouldn't allow planets to form, other than in the frigid zone-- anything closer is either absorbed or ejected. I didn't mean never-- any system can capture rogue bodies, whether into stable orbits or not. Thanks-- my vague generalities need checking. Regards, Steve.

Geology Student
2004-Nov-05, 03:21 AM
Hi there, I believe this point was made earlier, but what about Venus? It has an atmosphere 90 times as dense as ours and, just like Mars, Venus also lacks a magnetic field. How come it hasn't lost it's atmosphere just like Mars? Venus would be subject to even more solar wind pressure (I'm not sure about this, but I assume the solar wind is densest close to the Sun).
I think the study is a nice example of our lack of understanding the history of the solar system. We can't just extrapolate back to the origin of the solar system; we don't know enough yet.
But by all means, keep the data flowing.


You make a very good point, but here are a few things to consider:
1.) Venus is much larger than Mars and has a much higer gravity
2.) Venus's amtmosphere is composed of mainly CO2 like Mars with some N2 and SO2
3.) Venus has been geologically active much more recently than Mars and has also been able to replenish any lost atmosphere through its volcanic eruptions (theoretically)

At any rate, I think that ONLY the lightest of the elements are swept away by the solar wind, i.e., Hydrogen and Helium, but heavier compounds like O2 and CO2 remain.

I hope that clears some things up.

VanderL
2004-Nov-06, 11:59 AM
Hi Geology Student,

Do they clear up the issue? Yes and no.
The mechanism of depletion can be straightforward and logical. but there is a whole lot we don't know about the history of the solar system that can overrule the proposed mechanism.
The idea that Venus was geologically much more active than Mars recently could be very wrong.
I said it in other threads, I think crater counts are not a reliable way to date geologic events. And there is the notion that Venus and Mars both suffered some cataclysmic event(s) when they are compared to Earth.
Thanks for the response,

Cheers.

om@umr.edu
2004-Nov-06, 03:16 PM
Hi, Geology Student.

Atmospheres of terrestrial planets likely formed by degassing the solid, meteorite-like material that accreted to form these planets.

The amounts of radiogenic gases, like Ar-40, Xe-129, etc., in the atmosphere depends on the amount of radioactive parent, like K-40, I-129, etc., initially trapped in the planet and on the fraction of the planetary body that degassed (released its volatiles).

Dr. Dwarka Das Sabu and I used the inventory of radiogenic gases in the atmospheres of Mars, Earth and Venus to estimate the fraction of material that released volatiles to their atmospheres.

Mars = 1-2% degassed
Earth = 17% degassed
Venus = 100% degassed

That paper is available as a pdf document.

http://web.umr.edu/~om/archive/NobleGas.pdf

With kind regards,

Oliver
http:://www.umr.edu/~om