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Thread: Mars vs Titan - Atmosphere

  1. #1
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    Mars vs Titan - Atmosphere

    Hi Everyone,
    I read this forum all the time but rarely post anything since you seem to cover most of the stuff I'm interested in anyway.... I have a question which has been bugging me for a while and I had to ask.... I'm sure there's something simple I'm missing here and I know you guys have the answers!!!

    This has to do with the atmospheres of planets and moons in our solar system!! Since it seems to me that a planet/moon's ability to hang onto it's atmosphere must be based largely on it's mass/surface gravity I have a hard time understanding why some planet's have such thick atmosphere's and others have barely any..... A good example of my question could be Mar's and Titan... Mars is signifigantly more massive than Titan and yet Titan has a much larger Atmosphere.... I'm guessing that local Temps and Planetary Evolution must play a role here but I just don't get this relationship....

    Mars ~6.42e23kg ~0.0071 atms
    Titan ~1.35e23kg ~1.63 atms

    The differences between Venus and Earth seem even more wacked out...

    Earth ~5.97e24 kg ~1 atms
    Venus ~4.86e24 kg ~91.7atms

    Anyway, I'm hoping someone can set me straight on why this might be!! I just like to read space news sooo please excuse me if I'm being dumb!!

    THANKS!!!!

  2. 2006-Mar-13, 04:30 PM

    Reason
    Duplicate post.

  3. #2
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    oooppsss.... Hehehe... My Name is computer Dude and I posted the same question twice..... anybody want me to do some IT work for you!!?? Hopefully an Administrator can clean up my mess here?? Sorry!

  4. #3
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    I've heard that Mars' atmosphere was blown away by solar winds when Mars' liquid iron core "froze" and it's magnetic field died out. Regarding Titan's atmosphere I'm guessing that the solar wind is weaker at Saturn's distance and Saturn's magnetosphere protects Titan somewhat.

  5. #4
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    One thing you can do is edit your original post above, and replace it with something like "Duplicate post deleted. Nothing to see here. Move along." and it will gradually gravitate down to the sump of the topic list.

    Another trick is, if no one has responded to your post, you can delete it yourself. Not sure what will happen if the post is the start of a thread.

    Finally, you can PM a moderator, asking them to kill a thread. I know they can do it; spam threads have been disappeared in the past.

    Fred
    Hey, you! "It's" with an apostrophe means "it is" or "it has." "Its" without an apostrophe means "belongs to it."

    "For shame, gentlemen, pack your evidence a little better against another time."
    -- John Dryden, "The Vindication of The Duke of Guise" 1684

    Earth's sole legacy will be a very slight increase (0.01%) of the solar metallicity.

  6. #5
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    There are seveal factors involved, but I think in the case of Titan it has to do with the planet's (moon's) abiltiy to replenish its atmosphere. Titan appears to have a methane cycle much like earth has a water cycle.

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    This is a question of considerable intrigue., Mars is smaller than Venus. Is it that simple,? No. The formation of this planetary disk which has become this solar system has at times been traumatic and massive collisions may be why some planets or moons have a depth of atmosphere that other bodies seem to have lost. The explanations are going to get complicated. As is the universe. Does the answer lie in the expulsion of or venting of gasses or is it more complicated,?

  8. #7
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    I think I read somewhere that the reason a planet/moon loses it's atmosphere is when the individual atmospheric moleclues reach escape velocity, which relates to a certain temparature. This is why Titan retains it's atmosphere, the gas is slow cold it cannot reach escape velocity for the small gravity of the moon. (I know it also has to do with the magnetic field, which is why I believe Mars lost it's atmosphere, being closer to the sun) But this dosn't answer why 'Hot' Venus has such a thick atmosphere.

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    Potted summaries, as I understand it:
    Titan: very cold, so gas molecules move slowly, and therefore leak into space very slow.
    Mars: warmer than Titan, so gas molecules escape more readily; also subject to a more intense solar wind, which strips gas from the upper atmosphere; also subjected to bombardment early in its history which was energetic enough to blow away big chunks of atmosphere from such a low-gravity world.
    Venus: close enough to the Sun to lose its water in a "runaway greenhouse": Earth has about the same amount of CO2 as Venus, but on Earth it dissolved in the oceans and formed carbonate rocks; on Venus it ended up in the atmosphere.

    Grant Hutchison

  10. #9
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    Titan and Venus are probably geologically active, with some sort of activity that replaces the atmosphere lost to the solar winds.

    Mars appears to be volcanically dead (or nearly so, there may have been some limited eruptions in the last million years).

  11. #10
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    Hi Everyone!! Thanks for the Answers!!!

    I guess there is quite a bit more involved than just the mass of the planet/moon/body..... On the surface of things it seems that's the case (I bet Saturn and Jupiter don't lose too many gases into space.. maybe some hydrogen, helium??)... But I guess you also have to factor in the history of the object, the local conditions, and if the object is actually replenishing it's atmosphere.... Any other factors??

    Too Bad we couldn't somehow reconstitute the atmosphere on Mars with some heavier molecules (and warm it up) and or blow away/absorb some of Venus' CO2 (to cool it down).

  12. #11
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    Quote Originally Posted by ComputerDude
    Too Bad we couldn't somehow reconstitute the atmosphere on Mars with some heavier molecules (and warm it up) and or blow away/absorb some of Venus' CO2 (to cool it down).
    I'd add nitrogen to Mars if we could.

    And remove most of Venus' CO2 and replace it with a little H2O.

  13. #12
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    The ability of a planet to retain an atmosphere is related to the planet's escape velocity, the molecular mass of the element or compound, and the planet's temperature.

    In short, if a gas is heavy, a planet of a given mass will be able to hold onto it. If a gas is cold--and thus, if its atoms/molecules are moving slowly--a planet of a given mass will be able to hold onto it. Best of all is if the atmospheric components are cold and heavy gas, which is the case for Titan. "Cold" here is a relative term; it only means that enough of the components are moving below a planet's escape velocity to retain them for a long time. The atoms/molecules must have an *average* velocity that is *well below* escape velocity; if the mean velocity is only somewhat less, the atmosphere will still dissipate, because enough will dribble away over time to eliminate the atmosphere.

    There is actually a mathematical formula used to determine whether or not a given gas can be retained by a planet, which I'm sure is floating around the 'Net, somewhere. You'd be surprised at the answers you can get; for instance, I once was able to calculate that Mercury could indeed hold onto a atmosphere of gaseous mercury for the lifetime of the Solar System, in spite of its temperature and low mass.

  14. #13
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    Not dumb! Good question.

    Mars and Titan - Big differences:
    1) Temperature. Titan is much colder. Molecules in a colder gas move much slower and therefore have much less kinetic energy. Therefore, they have much less chance of reaching escape velocity.
    2) Solar radiation. Titan is over six times as far from the Sun as Mars. Therfore it is much less likely that molecules will be broken down to atoms (or ions) that, having lower mass, will be able to reach escape velocity.

    Earth and Venus - Big difference:
    Molecular weight of atmospheric gases. Earth's atmosphere is mostly nitrgen (molecular weight N2 = 28). Venus' atmosphere is mostly carbon dioxide molecular CO2 = 44). The heavier molecules are much harder to accelerate to escape velocity.

  15. #14
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    Dang! I posted my answer in the other thread.

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    Haha!!! You fell into my trap!!! I read the other post just now and like your explanation.... Molecular weight!!! Of course!!! I can feel my Highschool and Uni chemistry courses coming back to haunt me now!!

  17. #16
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    Quote Originally Posted by ComputerDude
    oooppsss.... Hehehe... My Name is computer Dude and I posted the same question twice..... anybody want me to do some IT work for you!!?? Hopefully an Administrator can clean up my mess here?? Sorry!
    No worries, ComputerDude -- I merged the two topics. Welcome to the forum.

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