Effect of pouring a vast quantity of water onto Mars

Suppose someone took a large volume of water - equivalent to, say, all the Great Lakes combined, or the Atlantic - and poured it onto Mars. What effect would it have on Mars’ climate and would the water just all freeze up or partially evaporate and give Mars a wet atmosphere?

I’m not sure about atmosphere, but this what if- xkcd suggests all the ocean water from earth would freeze up and get covered in dust.


Ah, perfect

Mars is, mostly, freezing cold. It has its moments where it can be warm but mostly pretty cold. So, water we put there would just freeze.

The trick to terraforming Mars would be to warm it up. And to do that it needs a thicker (more dense) atmosphere with a lot of CO2 in it to trap heat.

Problem is, IIRC, Mars gravity is just a little too low to hang on to a dense(ish) atmosphere.

Honestly, as an engineering problem, terrforming Mars is totally doable. But the effort would be massive so don’t expect it any time soon (if ever).

Don’t expect it till we can easily fling ice rocks into Mars (with precision…do not want to hit Earth) from the Oort cloud.

At last, something to do with all that water we can drain from Lake Erie!

Do I remember correctly that the theory is that Mars could have been bigger if it wasn’t so close to Jupiter?

Water we put on mars would not just freeze, it would boil until it froze.
Mars pressure varies a lot but 6mBar is a reasonable average.
Water boils at that pressure, releasing gas and heat. I doubt the Atlantic would put out enough heat and pressure, water gas, to stop itself from mostly freezing, and then nearly entirely freezing as the gas snows out. The process would be pretty spectacular to watch, but probably would not do us, or mars a speck of good.

Mars also lacks a magnetic field to shield it from solar flares and storms, which would gradually help strip away the atmosphere.

Interestingly, Mars has pretty close to the same dry land area that Earth does. So in the event of terraforming, future settlers would have a lot less area to chose from.

You would need to add a whole bunch of nitrogen as well, to act as a buffer, and a load of CO2 to warm the atmosphere. The nitrogen and water could both come from Titan (at a very high price of course). If we added enough CO2 to Mars atmosphere to make it as warm as Earth, the carbon dioxide would exceed toxic levels for humans. You’d have to get the CO2 from Venus, and maybe genetically tweak humans so they can tolerate higher levels. There are other toxic chemicals in the soil too.

I wouldn’t worry too much about the loss of volatiles in the short term, as Mars could probably hang onto a thick atmosphere for tens of thousands of years, and a thinner one much longer. But if you went to all the trouble of tweaking humans to live on this toxic planet, then found that the world was doomed in less than a million years, the whole enterprise might seem pointless.

I once experienced an interactive documentary on this very topic. Apparently the “canali” identified by Giovanni Schiaparelli in the 19th century really are giant, dried-out canals, and could in theory be refilled by melting the polar icecaps. Unfortunately, our plans to do so have been thwarted by an ancient Martian spirit inhabiting the body of Grigori Rasputin, who was shot to Mars with a giant space cannon in 1893.

OMG spoilers