Wouldn't it be (much) easier to cool down Venus than heat up Mars?

Question

Since Mars doesn't have enough gravity to hold a thick atmosphere, how about putting a giant 'sun shade' between Venus and the sun, so that it would cool down? After that, couldn't we transform Venus into Earth's 'twin'? Maybe smash a few (thousand) comets into it for water?

Answer 1

I think that adding some greenhouse gases to Mars might actually be a lot easier. It would be hard to maintain forever, because you'd have to replace what you're losing into space. However, making the chemical changes to the Martian atmosphere would probably be easier than building and maintaining a sun shade over Venus.

Considering the orbit that you'd need, you either have to encircle most of the planet with a series of shades, or place an enormous shade that's roughly the size of the planet at the L1 Lagrange point between Venus and the Sun. For comparison, fixing up Mars would just involve making a bunch of factories on the ground to spew greenhouse gases into the air, and we already know how to do that...

This is not to say that your idea could never work, but Mars will be an option far sooner than Venus.

Answer 2

OK - assuming you would want to do this so to make the planet habitable for humans at some point, I would say that it would still make more sense to try and terraform (to make earth-like) Mars.

Let's say you have a way to place a giant shade between Venus and the sun.....the atmosphere will eventually cool down, though by how much is uncertain. Also - there is the possibility that Venus is geologically active - its surface is young (as opposed to that of the moon, which has been cold and 'dead' for billions of years) as evidenced by relatively recent volcanic activity on the surface. As of yet an active volcano has never been observed on the planet, but the solidified lava flows are fresh. So therefore a percentage of the planet's boiling hot atmosphere is due to the heat from within.

Even if you could cool it, say, 50%, you still would be roasting at around 425 degrees Farenheight, thus requiring not only protection from the atmosphere and pressure (that's another huge problem!), you would still need heat shielding.

Then there's the pressure - even if you got Venus's surface atmosphere down to 75 F, the pressure is about 8 times that on the Earth's surface - requiring a pressure suit not unlike thosed used for deep diving.

Then there is the atmosphere itself - mostly carbon dioxide, but also containing some very corrosive gases - think aerosolized battery acid!

Even with reduced temps, a human visit (or habitation) would present some serious practical challenges to machinery and equipment, as well as dangers and severe limitations to the humans who would reside there.

BTW, adding water might make things worse - the atmosphere would be even more dense and suffocating - then you would have some serious acid rain to contend with when it stormed!

Now, while Mars does have a thin, dusty atmosphere also composed of mostly carbon dioxide, even the way it is now is much more hospitable than a 75 F Venus. There is water locked away in the ice caps and at other sites, and there is sunlight to power equipment and grow plants.

People have theorized ways to terraform Mars, some ideas include releasing huge amounts of CO2 to try and smog up the atmosphere, making it a bit thicker and warmer, thus melting the water ice on the planet, and then eventually growing plants on the surface which would convert the CO2 to oxygen, hopefully creating an earth-like atmosphere.

But even so, humans would still need support on the surface - the pressure is much less than the earth's surface and it may never be possible to get all the O2 a person would need from the atmosphere, even with a beefed up atmosphere. Then there are cosmic rays - humans will need shielding from them as well.

But despite the limitations in both scenarios, it's easy to see why Mars would be much simpler to attempt to make habitable for humans.

Answer 3

Mars' small size is not really an issue, it doesn't have much of an atmosphere because it has no magnetic field, and as a result the solar wind has stripped it away.

Titan, roughly the size of our moon, has an atmosphere about as thick as ours.

I've thought that an interesting concept for warming up Mars might be to build a fleet of spacecraft with huge inflatable balloons (say, the size of Texas fully inflated), and put them in a Venus-to-Mars roundtrip orbit. When they get to Venus, have them skim the atmosphere and fill up their balloons with Venusian CO2. When they get to Mars, just dump it out. A few thousand round trips, and Mars should have a decently-thick CO2 atmosphere that will warm the planet and should last for about 100,000 years before escaping to space again. The spacecraft would just need a nuclear reactor for power, they could use the captured atmosphere as propellant, and maybe a small robotic crew to patch up micrometeoroid holes in the balloon.

Cooling down Venus would be harder. A giant solar shade would always be battling against decomposition from hard radiation & micrometeoroids, and would also have a hard time staying in place due to pressure from the solar wind.

However, I once read about a plan where you could take a large asteroid, and in the right orbit have it continually sweep close to a planet. (In this case, Venus.) Over many millenia, you could gradually stretch out a planet's orbit to a more distant and cooler locale...of course, you'd also have to move Earth out of the way!

Answer 4

Excellent question
Relatively easy to answer logically.

Consider some facts:

Venus is 860+ degrees and is the same size (roughly) as Earth

Mars is 1/3 the size of Earth and about -60 degrees average temperature

Earth has an average temperature of 60 degrees

Simple deduction says that since Mars is both smaller AND closer to Earth's temperature, it would be easier to affect widespread change in its atmosphere.

Either way terraforming would be a collosal undertaking, greater than all the human engineering works of the last 2000 years combined in terms of energy and material outlay.

The fact that mars is small and may eventually lose its newfound atmosphere would not be our problem, as once in place, it would take millions of years to leak away into space.

However you do it with Venus, the residual heat has to go somewhere, and that would certainly take longer than heating up mars with some kind of Martian global warming.

Plus there is considerable evidence that Mars' climate has changed on its own (ice ages, etc) in the recent past, so it likely could be started again.

Smashing a planet temporarily would heat the surface, the cooling would only happen if the nuclear winter of increased cloud cover took affect. Venus already has 100% cloud cover. to cool it you would have to destroy the cloud cover to break its greenhouse effect.

Mars would heat up due to having a greater amount of atmosphere created, and having an increased greenhouse affect.

Answer 5

Not likely. Venus is still an active volcanic planet while Mars is geologically "dead". So what's the point of having an A/C with your windows open in Sahara desert. It's way easier to work and live in Mars than Venus. Not counting the crushing pressure and the acidic atmosphere in Venus.

Answer 6

There are a number of issues:
1. Venus day is longer than its year - making any sort of life as we know it problematic.
2. The only way to make Venus cooler would would be to remove most of its atmosphere - so much of it would have to go, there wouldn't be enough to sustain life. In addition to to that, having a thin atmosphere removes its protection against solar radiation - given (1) above, this would mean the sunny side would get baked by radiation, while the dark side would freeze (due to the lack of atmosphere).

Answer 7

We could probably do better to simply move Venus orbit (if we had the tech to do a sun shield then we would have the tech to change the orbit.) then do the same with Mars and move some of Venus excess gasses and moisture to mars. Also get some commets into it to add more mass and water and other elements onto mars.

Answer 8

The atmosphere of Venus is almost pure carbon dioxide. It is hot enough on the surface there to melt lead. Surely would take some solar energy to provide the air conditioning necessary to live in that environment. Maybe going to see how bad things are there up close would provide a lesson for all earthlings about what can happen on earth if we are not careful about our sources of energy.

Answer 9

That is very hard to answer. Think about it logically. Your question was something that would take extensive research. Plus, we would have to get people to Venus and Mars to check out the planet to see if it's even possible because of it's position in relation to the sun. I don't have much more to say, I'm curious to see what other people post.

Answer 10

I'll answer this one when I come back home this afternoon. Right now I don't have the time, but needless to say Mars is the much better proposition for quite a few reasons. Mainly to do with the Sun and their respective orbits. But I'll explain that later.