New Mars Forums

I think I can see what nickname is trying to say, and perhaps I can give him (or her) a missing piece of the puzzle.

Let's say that earth was cold and bone dry at the surface, with permafrost near the surface, and frequent powerful meteor impacts, each generating large amounts of heat on impact. The heat would generate steam, which would rise up out of the impact crater, cool and condense back as snow or frost on the surface. Why, then, wouldn't we see similar frost on the surface of a Mars with ice under the surface?

Because Mars, unlike Earth, lacks an ozone layer, and ultraviolet light reaches the Martian surface at almost the full strength one would find it at in space. UV photons are energetic enough to break the bonds in water molecules, so illuminating water ice under martian conditions with the high UV levels found there will result in the liberation of elemental hydrogen, which Mars hasn't a deep enough gravitational well to hold onto, and which won't find much of anything to react with on the way out. A little free oxygen is liberated in the process, which then is removed from the atmosphere through the weathering of rocks on the surface which, on Mars, is not counterbalanced through volcanic outgassing, as it is on Earth. The hydrogen ends up gone and the oxygen ends up bound.

That's where your surface frost went.

Yes, I'm creating a second thread when the first one is still active, kind of. I'm a bad, bad man who must be punished most severely. Be that as it may, brief notes written in reply to lengthy queries have a way of being lost in the shuffle when the threads go off on extended tangents, like the one about planetary migration.

Let's focus this one a little more narrowly. We've presented with the almost poetic image of cities floating in the Venusian atmosphere, I guess slowly drifting downward as centuries or millenia of terraformation convert a Carbon Dioxide atmosphere into a Nitrogen-Oxygen one, the cities coming down to a new earth out of a new heaven (and don't ask me where the Nitrogen is coming from, because I have no idea). A few Christian fundamentalists might be absolutely intrigued by the parallel with the image of the new Jerusalem in Revelations, but as much fun as we could probably all have with the subject of the cultural implications of all of this, one can possibly shoot the idea down in one word.

Convection.

The heat engine on Venus is going to be a lot more powerful than the one on earth, and I have to wonder what is going to happen to one of those floating cities when it floats into a downdraft. Yes, it has bouyancy pushing it back up, but one can say the same of any unfortunate swimmer who gets himself caught in an undertow. He still goes down. Any reputable studies done of how much force our meterological undertow (convection powered downdrafts) would place on those bobbing cities, and how far down one of those cities might drop?

In the Mars vs. Venus vs. Titan competition, this strikes me as being a good reason to favor Mars. Yes, Mars can get very, very cold, BUT one can build underground. In fact, given the reality of radiation levels on the surface pre-terraformation, one would probably have to do so. Rock makes an excellent thermal insulator, so even if the surface is frigid, it doesn't follow that a great amount of energy will be needed to keep a subsurface habitat warm, or that a power failure would rapidly throw everybody into the deep freeze. There would be the difficulty of getting sunlight down to any gardens beneath the surface, but if one is willing to build parasols the size of planets, building a series of reflectors to concentrate and collimate sunlight and then bounce a few ferocious sunbeams underground would seem to be a trivial enterprise by comparison.

One which, by the way, might very well be practical with present-day technology, or something very close to it, unlike that planetary parasol. The beauty of one's Martian burrow is that one doesn't have to worry about where it's going to go. Out of these three choices, my vote would definitely be for Mars.