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https://www.livescience.com/65470-strange-martian-water-cycle.html
There's a hole in the Martian atmosphere that opens once every two years, venting the planet's limited water supply into space — and dumping the rest of the water at the planet's poles.
[...]On Earth, summer in the Northern Hemisphere and summer in the Southern Hemispheres are pretty similar. But that's not the case on Mars: Because the planet's orbit is much more eccentric than Earth's, it's significantly closer to the sun during its southern hemisphere summer (which happens once every two Earth years). So summers on that part of the planet are much warmer than summers in the Northern Hemisphere.
When that happens, according to the researchers' simulations, a window opens in Mars' middle atmosphere between 37 and 56 miles (60 and 90 kilometers) in altitude, allowing water vapor to pass through and escape into the upper atmosphere. At other times, the lack of sunlight shuts down Martian water cycles almost entirely.
https://doi.org/10.1029/2019GL082839 Dmitry S. Shaposhnikov, Alexander S. Medvedev, Alexander V. Rodin, Paul Hartogh. Seasonal Water “Pump” in the Atmosphere of Mars: Vertical Transport to the Thermosphere (pdf; paywalled)
(Score: 2) by The Shire on Monday May 20 2019, @03:00PM (6 children)
The problem here is that the energy required to shift something from one orbit to another is significant and directly related to both the mass you're trying to move and the relative distances between orbits. And if you are moving "heroic quantities" down towards Venus, you must also move "heroic quantities" of something else in the opposite direction. And in addition to having to overcome the orbital energy differences (there is a 50,000mph difference in orbital speeds between Jupiter and Venus), you must also escape Jupiter's intense gravitational field - no easy trick. Jupiter does not willingly let go of what it holds.
The solar wind travels in the opposite direction - you can't sail directly into the wind. And if you chose to go the ion engine route you would quickly realize there isn't enough xeon or krypton available to even approach the fuel requirements for such a venture.
In any event, you're still left with the same problem we have on Mars. Venus does not have a magnetic field to prevent the solar winds from whisking away the lighter elements like hydrogen, which is why there is essentially none in it's atmosphere. So even if you could get all that hydrogen to Venus and even if you could split the co2 and form h2o, it would still ionize in the upper atmosphere and get carried away again. The only reason Venus has a thick atmosphere at all is because it has a gravitational field close to that of earth to hold the heavier gases down. And even if you achieved all that you wanted, all you would have gained is sky city in a cloud of acid. Nothing can exist on the surface, water or not. The pressures are so great you may as well be living on the floor of the ocean sitting on top of a magma vent.
Considering the raw power and massive materials needed for such an undertaking, you would be far better off simply building an enormous space station, perhaps using a large iron asteroid as it's core.
(Score: 2) by deimtee on Monday May 20 2019, @10:28PM (5 children)
Provided you can adjust the sail faster than your orbit you can use it to break orbit. Adjust for maximum thrust when it will increase orbital speed, minimum on the other half. Regarding sailing 'into the wind', the solar wind is a minuscule effect on the sail, photon pressure is much greater [nasa.gov]. You are not going to go in a straight line line Jupiter to Venus, and by angling the reflection from the sail, you can adjust the thrust vector by up to 45 degrees. It might take a while, but if you plan far enough ahead you can use a solar sail to go anywhere in the solar system.
Obviously, if you go the ion drive route you will need to develop one that throws H+ or He+. Jupiter has plenty of both.
If you use the H2 to convert >95% of the CO2 to C and H2O, you will have enough water for small seas and a livable gas pressure at the surface. Lots of C to build with too. Did I mention long term and large quantities of H2? Actual mass quantities moved would be similar to the water to terraform Mars, but you would get a bigger, brighter planet with near normal gravity. The rate of H loss isn't really that high, if this was done it would remain habitable for millions of years.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by The Shire on Tuesday May 21 2019, @02:41AM (4 children)
It would literally take tens of thousands of years to deliver any hydrogen from Jupiter to Venus using solar sails that relied on 'tacking' against the wind. And you would first have to get it far away from Jupiter's gravity well or you won't be going anywhere at all.
After that, it would tack several more millennia to generate the power needed to pyrolize the co2 with the hydrogen in order to produce water and carbon. This also requires molten metals and a constant temperature of somewhere around 1,000 C for the reaction to occur at all.
And lets assume that tens of thousands of years in the future you have accomplished this incredible feat and now Venus is covered with water. Now you find yourself trying to prevent the water that faces the sun from boiling off while the water on the other side freezes since a Venutian day is around 4 Earth months long. Additionally, you still have no magnetic field so the surface is being constantly bombarded by hard radiation from the sun, much worse than standing naked in the Sahara desert in the middle of summer. It would be bad. And that's under ideal conditions.
Nah, the giganto space station is the way to go. Build your own pressurized habitable world from scratch rather than trying to fight an entire planet to be how you need it to be.
(Score: 2) by deimtee on Tuesday May 21 2019, @06:42AM (3 children)
Delta V Jupiter to Venus is somewhere around 80 - 90 km/s with no gravity assists. At 1/100,000 of a G (0.0001 m/s2) that takes 25 years. This is obviously a long term project. I am also pretty certain that by the time anyone undertook this as a project we would have ion engines that can throw any element you like. If you are in a hurry, run solar powered ion engines instead and throw away 1% at 9,000 km/s.
You don't do it that way. You seed the atmosphere with algae and let it eat the CO2 to produce O2. Then you just burn the H2.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by The Shire on Tuesday May 21 2019, @07:31PM (2 children)
Escape velocity from Jupiter is around 60 km/s - how exactly do you plan to get your enormous tanks of hydrogen moving at that speed? You can't just apply .0001m/s2 over extended periods of time - you won't go anywhere ever. You have to hit that 60km/s speed or you'll never leave Jupiter at all. Ion engines can never provide sufficient thrust. Ion engines aren't even capable of lifiting a 1kg mass off the moon let alone reach escape velocity on Jupiter. Your trip to Venus won't even get started if you can't escape Jupiters gravity well.
There is no such organism that could survive those conditions, with or without water. There is also no such organism that can subsist soley on sunlight and co2 and the Venutian atmosphere has none of the other things such life might require. Algae certainly does require sunlight but sunlight without a magnetic field would sterilize any organics. There is no shielding at all from the suns hard radiation.
Such fantasy is fun and makes for good books and movies. But the universe is a lot harder to tame than that.
(Score: 2) by deimtee on Friday May 24 2019, @11:28PM (1 child)
That is not how escape velocities work unless you are firing unpowered projectiles out of a gun.
Provided you start in an orbit that is high enough that your available thrust exceeds atmospheric drag, you can simply point the thust vector along your orbit and start your engine. You won't go faster, in fact you will slow down and climb into a higher orbit. That bold part is the important bit. You keep applying thrust and eventually you climb out of the gravity well. At no point do you ever need a sudden velocity change of 60km/s, that is just the sum over time of the acceleration your engine will need to apply.
Yes, you might need to supply some other trace elements. One of the main ones is going to be nitrogen compounds.
Earth's magnetic field only blocks charged particle radiation. It does absolutely nothing for UV / X-ray / gamma radiation. Yes, it's important here, but all that extra atmosphere provides shielding at least as good.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by The Shire on Saturday May 25 2019, @05:33PM
It absolutely IS the way escape velocities work. While it's true that a projectile with an instantaneous speed exceeding 60km/s will break free of Jupiter's influence, the fact is that no matter how slowly you accelerate, at some point you MUST reach escape velocity or all you will have achieved is an orbit.
And an ion engine can never escape Jupiter's gravity, I don't care how long it burns - duration of thrust is not the key - the power of the thruster to overcome "g" and any atmospheric resistance is the key. If you can't push forward faster than the planet is pulling you back, you're not going anywhere. You have to overcome that gravity well otherwise all you will be doing is falling at a slightly reduced speed. And that thrust has to increase proportional to the mass you're trying to move - in this case a truly enormous amount of mass indeed. Basically the only accelerating an ion engine can do in Jupiter's atmosphere is accelerating downward.
It's simply not possible with any known or even conjectured technology to do what it is you're suggesting. This kind of thinking is pure fantasy.