In response to my question of “How do you move Mars from its current orbit to one of the Earth-Sun Trojan points” :
If you can do that, why not just put a great BIG rocket motor on Mars itself? I seem to remember a Godzilla movie (or other low budget Japanese production from the 50’s or 60’s) where they did just that to the Earth.
Well, terraforming is surely a matter for long-term thinking. I’m not sure about the timescales implied by:
Well, they couldn’t even do it in Star Trek: The Next Generation (“Deja Q”) without resorting to ‘subspace warp fields’, but the consequences of a giant impact are generally disastrous. The leading model for the formation of the Earth’s moon is a Mars-sized impactor colliding with the early Earth. The impact ejected a significant part of the Earth’s mass into space, most of which ultimately either coalesced into the moon or fell back to Earth, over very long timescales. Io is about the same size, relative to Mars as Mars is to Earth, so one would expect a similarly destructive result. Of course, if you have the ability to pluck Io from Jupiter’s gravity well and taxi it around the solar system, you can make the collision gentle, but it doesn’t matter - putting two masses that large in contact with each other will result in disruption of the static spherical shape of each.
You’d basically disrupt Mars to a huge extent and create a big mess; most of the mass would ultimately coalesce into one or more bodies in Mars’ former orbit.
The suggestion of bombarding Mars with volatile-rich minor bodies is somewhat more reasonable. The masses are small enough that they might reasonably be displaced by a spacecraft with Newtonian propulsion, and they won’t risk disrupting Mars altogether. You’d make a lot of big holes in the ground, though, and you’d want to understand very well the mechanics of the transient ejection of material, so that you don’t end up blowing most of your volatiles into orbit.
This paper estimates the current rate of loss of CO[sub]2[/sub] at 6 grams per year, or roughly 200 tonnes/yr, based only on interaction with the solar wind (and not other effects that can result in atmospheric loss). The last paragraph of the article points out that this is almost certainly a significant underestimate of the total loss rate.
One can assume the loss rate would be even faster as the atmosphere got thicker and warmer. A key culprit is the lack of a protective magnetic field. But Venus has managed to hold onto a thick atmosphere without such a field, so maybe there’s something we still don’t understand.
Anyway, I wrote the above first post sitting in the atmospheric science room of Mars Science Laboratory Mission Control (I’m off shift now), but we were too busy for me to take time to ask the atmospheric modeling people about this stuff. I’ll see if I can get some answers from one of the people who know that aspect of Mars’ atmosphere better than I do.
Start with Mercury. It is pretty small, after all. Just tweak its orbit so that it goes into a shallow dive, bounces off the sun, slingshots around Venus and comes up behind Mars to run into it. The collision, if properly calculated, will pull Mars into a lower orbit while also adding to its mass (the slower the collision, the better). Might be enough to kick-start some good core action, get some magnetism and vulcanism running to beef up the atmosphere.
Thing is, we are looking at terraforming at a quick project. What kind of time frame is acceptable for this? Decades? Centuries? The faster we try to get this done, the more energy it will take. I am not entirely convinced that it could be up and running before humanity dies off completely.
This article on space.com says that the rate of atmospheric escape is pretty similar for Venus, Earth and Mars; it says that on Earth, the magnetic field just redirects the solar wind to the polar regions (hence auroras), leading to the stripping of the atmosphere in those areas:
Note that even for Mars, only about a foot of water equivalent (as hydrogen and oxygen ions, with a ratio of around 2:1) would have been lost over 3.5 billion years, which is to say, unnoticeable on a time scale of even millions of years.
Wait … they’re saying VENUS would have lost only 8 centimeters of water over the last 3.5 billion years?
Then why are there oceans on Earth, but not Venus? Did all the icy comets that hit the Earth during its formation miss Venus? Or is it the constant geological upwelling of subsurface material on Earth that keeps us all wet, like For You talked about in his post?
Venus is too hot for liquid water to exist on its surface - the surface temperature is around 730 K. Which brings us back to the thick atmosphere and its greenhouse effect. It’s not entirely clear why Mars, Earth, and Venus diverged so much in that respect.
So I polled the guys working in the atmospheric science room here at MSL ops, and the consensus seems to be:
Thank you wolfstu!
I forgot to think about the impact as being something that would MOVE Mars, and I had hoped that the “slow impact” idea would keep it from turning both objects into so much orbital debris that would take millions of years to re-accrete. I guess just a constant bombarding of asteroids and cometary bodies would do it.
Venus has lost a significant portion of its hydrogen. Presumably a similar amount of water was delivered to that planet as came to Earth, but the bright sunlight split the water into hydrogen and oxygen. hydrogen, being very light, has mostly escaped over time. while the oxygen remains in the rocks and in the CO2 of the atmosphere.
Interesting!
I remember reading that the Sun was only about 70% as bright as it is today, back when it first settled onto the Main Sequence. Over time, the sun slowly brightened as all stars do over their main sequence lifetime. Why would the sun have emitted MORE ultraviolet back when it was less bright overall?
According to Wikipedia, you wouldn’t need any extra CO2. We would just have to melt what is already there. This would rise atmospheric pressure to about 30 KPa, which in turn would rise temperature enough that the CO2 does not freeze again. If plants would then turn 95% of CO2 into oxygen, the resulting atmosphere would be breathable.
That was exactly my response – what about the ‘faint young sun paradox’? The agreement among the guys in the science room was that the sun is thought to have been fainter back then, but that it appears to have been more active in the UV – probably in transient events, if not in steady-state.
They’re planetary atmosphere specialists (and I’m a robotics engineer), not stellar astronomers, so they didn’t have an immediate detailed explanation on the reason for the UV activity. And we were busy with other work 
This article probably explains why; younger stars rotate faster and have stronger magnetic fields, which in turn leads to stronger flares, far stronger than anything measured on the Sun today:
As I read this, if the Sun lasts long enough, it will eventually stop producing flares and no longer have solar cycles, just a nearly constant output (currently brightness varies by about 0.1%; the article talks about variations 100 times larger, and UV increases of 200 times above normal levels).
If anyone is interested “Terraforming - Engineering Planetary Environments” by Martyn J. Fogg has two chapters (5 - The Ecopoiesis of Mars, 6 - The Terraforming of Mars) which go into detail on altering the Martian atmosphere and temperature profile.
Would just painting the poles black be enough to start the process?
The end result of Zubrin and Mckay’s terraformation process, and that of Martyn Fogg, all include a high proportion of CO2, more than is toxic to unaltered humans. You can have a warm planet, or a breathable atmosphere, but not both.
It would be necessary to modify humans to tolerate high levels of carbon dioxide if they want to live on the surface; otherwise they could live in domes and greenhouses, and use breathing equipment to go outside.
If the domes are big enough you might not need to go outside often; on the other hand future-tech breathing gear might be very comfortable and easy to use.
CO2 is not actually toxic to humans, any more than helium or nitrogen, it just crowds out the oxygen we need. Unaltered humans can tolerate as much as 4% CO2 at STP, as fragile as we are, we can be remarkably adaptable. Not to mention there are people happily living at ten thousand feet and higher, where the air pressure is much lower. Establishing an atmosphere that humans can use is not a matter of simply replicating that of earth but working out what Mars could sustain in order to support us.
I think CO2 levels on a terraformed Mars would exceed the 10% level which causes asphyxia, so we wouldn’t be able to adapt to the atmosphere naturally.
Nitrogen levels in the atmosphere exceed 78%, but is not toxic at that level- so I can’t see why we shouldn’t be able adapt to high CO2 levels with a little help from biotechnology. Or maybe with a lot of help…
Ha, the “fusion candle” idea from A World Out of Time (just so you know someone got the reference).