I really like the maintenance free solution we have here on Earth. 
-
-
You would need a helluva snow machine to make 18,000 tons of snow an hour. I think you should just crash the comets, after all the chances of anyone being hurt are pretty minimal.
Ski resort snow machines consume 107 gallons per minute. So, 18,000 tons would be 750 times that. It is not an unthinkable amount of equipment. More to the point, you have to filter and distill the water anyway. I think comets have a lot of toxic stuff in them that you do not want to drop on Mars. It forms gas and blows out when comets approach the sun.
One comet dropped on Mars with some toxic gases and elements would cause no harm. If you needed this for a starting water supply, it would probably be no worse than Martian polar ice. Millions of comets, enough to fill one-tenth of an ancient ocean (3% of the planet surface), would cause harm. It is a matter of scale.
This project would continue for about a century, with dozens or hundreds of small comets dropping every day. * If they were large chunks of ice that reached the ground in one piece, I am sure that over the course of a century many of them would cause harm and kill people. If the method required robot action to avoid harm, such as breaking up the ice before it reaches Mars, or going into orbit, I expect it would fail often enough to threaten harm. It has to be fail-safe.
(You need 14 million tons per day, which I suppose would be 14 small comets. Most are a lot bigger. The average is reportedly ~1 km and 4*10^14 g = 4.2 billion tons. (Right?) I do not think you want to drop 4 billion ton objects on Mars. There are roughly a trillion comets in all.)
-
I really like the maintenance free solution we have here on Earth. [Photos of clouds]
That's what you end up with, after a century or two. That's the whole point! Bring in enough water to cover 3% of the planet surface, heat up the atmosphere with giant mirrors, develop plants that survive the conditions, and eventually you have oxygen and a closed system with clouds and rain.
No doubt it would take many other steps I am unaware of. I do not know much about terraforming. No one does. It hasn't been done yet. Mostly we have been un-terraforming earth, making it unlivable, for example, by paving over 6.3 million square kilometers (an area the size of Delaware).
The planetary-scale damage we are causing now on Earth is on a far greater scale than the project to bring water to Mars, or the other terraforming projects that have been suggested.
-
Here is a dystopian movie about the future that we are preparing for ourselves: http://climatestate.com/2013/0…he-day-the-oceans-boiled/
After this Terra may need some reformatting.
For those who are not afraid of the dark I can recommend the movie The Road.
Caveat: I may have exaggerated a bit.
-
'The Road' is really for the tough. Be warned.
