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>That's the reason Earth has kept its atmosphere while Mars did not How would you explain Venus having an atmosphere while not generating a magnetic field?

mbell 7y ago
Venus has a very thick, hot and high pressure atmosphere. This both makes it hard to blow off and gives it a strong ionosphere which acts as a stand in for a magnetosphere.
logfromblammo 7y ago
Mars is also much lighter than Earth. Venus is less massive than Earth, but not by much. Even so, Venus has had most of its hydrogen stripped away over time. Thanks to its high temperature, that also includes hydrogens formerly bound in heavier molecules, like water. The process continues, very slowly. Venus is still losing its hydrogen and helium, more quickly than Earth. One terraforming plan for Venus involves shipping magnesium hydride there, decomposing it, and using both the H2 and the Mg to react with all the CO2 in the atmosphere to make soot, chalk, and water, reducing the surface pressure to about 3 atm of mostly N2. Nothing works without shipping hydrogen to Venus. But once it's there, it will take many millions of years to get stripped away again, because that happens so slowly, over geologic time scales.
- whatshisface 7y ago
  How long could a constant supply from the asteroid belt be kept up?
  - jandrese 7y ago
    I guess it depends how much magnesium hydride you find or can make there. It's a very long trip from the belt to Venus though. And honestly, if you have the resources to mine global amounts of magnesium hydride from the belt and ship them all the way to Venus you have the technology to build a nearly unlimited number of space colonies that would be much much nicer to live on than even a terraformed Venus.
    - magduf 7y ago
      Yep, that's the problem with these ideas about terraforming. If you have the technology and energy to change the environment on a planet that much, it's really easier to just build O'Neill cylinders or some other large stations and rotate them so that you get perfect 1g gravity, and you can stick them in whatever orbit you want (i.e., close to Earth) so that they aren't far away and they're at just the right distance from the Sun so that they aren't too hot or cold.
      - eloff 7y ago
        That's the problem with Elon Musk's mars colony plan. There seem to be better alternatives closer to home. Even the moon would be better in many respects, but space stations make more sense.
        magduf 7y ago
        Well to be fair, building an O'Neill cylinder is well beyond our current capabilities, and simply flying a craft to Mars and blowing up an inflatable dome is much easier and more practical given our current technology. However, I do agree that this colonize-Mars idea seems a little silly. We have a large body (the Moon) that's only a few days away, instead of 6-18 months; why not start there? Once we get pretty good at mining on the Moon and nearby asteroids, we should get better at building some rotating space stations.
      - hereonbusiness 7y ago
        I wonder if maybe future space dwelling people will look at living on planets like we do at living in caves. What I feel would be missing for me is the scale and freedom of living on an earth like planet. It might be different if one is born and raised on a space station.
        magduf 7y ago
        For "scale" and "freedom", theoretically, you could build as many O'Neill cylinders as you want (there's lots of resources in a star system), and make them quite large. What's easier about planets is that you don't have to have this technology or go to this trouble, but the problem is that in reality, there just aren't any habitable planets out there within a reasonable distance, except the one we're standing on right now. If we discovered warp drive or some alien stargates or something and could easily transport ourselves to countless distant star systems, that might be different, but right now it isn't.
  - logfromblammo 7y ago
    It's the initial bolus of hydrogen to re-wet the Venus atmosphere and cool it off that's the megaproject. After that, the replacement rate is ridiculously low. And if the lost hydrogen is never replaced, the terraforming-added hydrogen will still likely last longer than human civilization. Venus has been losing H2 and He for billions of years, and still has some left to lose. If we add enough H2 to precipitate all the CO2 out as mountains of C and oceans of H2O, and cool off the planet enough that the hydrogen stays in the water, the atmosphere will be fine for the foreseeable future. One basic Venus atmospheric-terraforming equation is "2 CO2 + MgH2 -> C + MgCO3 + H2O", by multiple reactions at different temperatures and pressures. By mass, 4.6e23 g CO2(g) + 1.4e23 g MgH2(s) -> 6.3e22 C(s) + 4.4e23 g MgCO3(s) + 9.4e22 g H2O(l). That produces an ocean about 12% the mass of Earth's, but requires roughly 4% the mass of the asteroid belt in MgH2, or a sphere of solid MgH2 with diameter 570 km--about the same volume as Pallas, Vesta, or Hygeia (but half the mass). Magnesium is the 12th-most abundant element in the solar system, and could be mined from olivine-plagioclase asteroids. (Calcium can also be used to transport H2.) About 17% of asteroids are S-type. Seems doable. Alternatively, decompose the MgH2 to Mg and H2 in Venus orbit, and only send down the H2, sending the Mg back out to store more hydrogen. That's "CO2 + 2 H2 -> C + 2 H2O". By mass, that's 4.6e23 g CO2(g) + 4.2e22 g H2(g) -> 1.3e23 C(s) + 3.8e23 g H2O(l), which would make an ocean about 28% as massive as Earth's, but requires that some magnesium (or calcium) make several round trips just to carry H2, which is relatively light. If you're going to do that, you could also just ship H2O to Venus, electrolyze it in orbit with solar power, drop the H2 down the gravity well, and ship the O2 back out to the comet wranglers for breathing gas. You'd need to move exactly as much water into orbit as you're eventually creating on the surface, so 3.8e23 g H2O. That's more mass to ship than the MgH2 answer, but at least we know that the water is easily found in comets, and on Europa and Callisto, and easily processed. There's no reason why any of these should be mutually exclusive.
    - api 7y ago
      Crash Ceres into it? You just have to... uhh... adjust the orbit of Ceres by quite a lot.
      - logfromblammo 7y ago

mbell 7y ago

Venus has a very thick, hot and high pressure atmosphere. This both makes it hard to blow off and gives it a strong ionosphere which acts as a stand in for a magnetosphere.

logfromblammo 7y ago

Mars is also much lighter than Earth. Venus is less massive than Earth, but not by much. Even so, Venus has had most of its hydrogen stripped away over time. Thanks to its high temperature, that also includes hydrogens formerly bound in heavier molecules, like water. The process continues, very slowly. Venus is still losing its hydrogen and helium, more quickly than Earth. One terraforming plan for Venus involves shipping magnesium hydride there, decomposing it, and using both the H2 and the Mg to react with all the CO2 in the atmosphere to make soot, chalk, and water, reducing the surface pressure to about 3 atm of mostly N2. Nothing works without shipping hydrogen to Venus. But once it's there, it will take many millions of years to get stripped away again, because that happens so slowly, over geologic time scales.

whatshisface 7y ago
How long could a constant supply from the asteroid belt be kept up?
- jandrese 7y ago
  I guess it depends how much magnesium hydride you find or can make there. It's a very long trip from the belt to Venus though. And honestly, if you have the resources to mine global amounts of magnesium hydride from the belt and ship them all the way to Venus you have the technology to build a nearly unlimited number of space colonies that would be much much nicer to live on than even a terraformed Venus.
  - magduf 7y ago
    Yep, that's the problem with these ideas about terraforming. If you have the technology and energy to change the environment on a planet that much, it's really easier to just build O'Neill cylinders or some other large stations and rotate them so that you get perfect 1g gravity, and you can stick them in whatever orbit you want (i.e., close to Earth) so that they aren't far away and they're at just the right distance from the Sun so that they aren't too hot or cold.
    - eloff 7y ago
      That's the problem with Elon Musk's mars colony plan. There seem to be better alternatives closer to home. Even the moon would be better in many respects, but space stations make more sense.
      - magduf 7y ago
        Well to be fair, building an O'Neill cylinder is well beyond our current capabilities, and simply flying a craft to Mars and blowing up an inflatable dome is much easier and more practical given our current technology. However, I do agree that this colonize-Mars idea seems a little silly. We have a large body (the Moon) that's only a few days away, instead of 6-18 months; why not start there? Once we get pretty good at mining on the Moon and nearby asteroids, we should get better at building some rotating space stations.
    - hereonbusiness 7y ago
      I wonder if maybe future space dwelling people will look at living on planets like we do at living in caves. What I feel would be missing for me is the scale and freedom of living on an earth like planet. It might be different if one is born and raised on a space station.
      - magduf 7y ago
        For "scale" and "freedom", theoretically, you could build as many O'Neill cylinders as you want (there's lots of resources in a star system), and make them quite large. What's easier about planets is that you don't have to have this technology or go to this trouble, but the problem is that in reality, there just aren't any habitable planets out there within a reasonable distance, except the one we're standing on right now. If we discovered warp drive or some alien stargates or something and could easily transport ourselves to countless distant star systems, that might be different, but right now it isn't.
- logfromblammo 7y ago
  It's the initial bolus of hydrogen to re-wet the Venus atmosphere and cool it off that's the megaproject. After that, the replacement rate is ridiculously low. And if the lost hydrogen is never replaced, the terraforming-added hydrogen will still likely last longer than human civilization. Venus has been losing H2 and He for billions of years, and still has some left to lose. If we add enough H2 to precipitate all the CO2 out as mountains of C and oceans of H2O, and cool off the planet enough that the hydrogen stays in the water, the atmosphere will be fine for the foreseeable future. One basic Venus atmospheric-terraforming equation is "2 CO2 + MgH2 -> C + MgCO3 + H2O", by multiple reactions at different temperatures and pressures. By mass, 4.6e23 g CO2(g) + 1.4e23 g MgH2(s) -> 6.3e22 C(s) + 4.4e23 g MgCO3(s) + 9.4e22 g H2O(l). That produces an ocean about 12% the mass of Earth's, but requires roughly 4% the mass of the asteroid belt in MgH2, or a sphere of solid MgH2 with diameter 570 km--about the same volume as Pallas, Vesta, or Hygeia (but half the mass). Magnesium is the 12th-most abundant element in the solar system, and could be mined from olivine-plagioclase asteroids. (Calcium can also be used to transport H2.) About 17% of asteroids are S-type. Seems doable. Alternatively, decompose the MgH2 to Mg and H2 in Venus orbit, and only send down the H2, sending the Mg back out to store more hydrogen. That's "CO2 + 2 H2 -> C + 2 H2O". By mass, that's 4.6e23 g CO2(g) + 4.2e22 g H2(g) -> 1.3e23 C(s) + 3.8e23 g H2O(l), which would make an ocean about 28% as massive as Earth's, but requires that some magnesium (or calcium) make several round trips just to carry H2, which is relatively light. If you're going to do that, you could also just ship H2O to Venus, electrolyze it in orbit with solar power, drop the H2 down the gravity well, and ship the O2 back out to the comet wranglers for breathing gas. You'd need to move exactly as much water into orbit as you're eventually creating on the surface, so 3.8e23 g H2O. That's more mass to ship than the MgH2 answer, but at least we know that the water is easily found in comets, and on Europa and Callisto, and easily processed. There's no reason why any of these should be mutually exclusive.
  - api 7y ago
    Crash Ceres into it? You just have to... uhh... adjust the orbit of Ceres by quite a lot.
    - logfromblammo 7y ago