Add "running out of CO2" and "the atmosphere thins too much" to the list. I don't know when those could happen, but they've been happening slowly for billions of years, and they will finish happening eventually, most likely well before the Sun's output gets too high.
Atmospheric loss is an interesting and not-entirely-understood subject [1].
But here's one aspect we do know that puts the scale in context. Any gas has a Boltzmann distribution of kinetic energies. You can calculate that a certain portion of that will have a kinetic energy high enough to escape gravity. This is called the Jeans escape energy [2].
For Earth this amounts to losing 60-100,000 tons of atmosphere every year, which is actually a complete non-issue.
I mention this because the idea of terraforming Mars is a popular sci-fi trope but really makes absolutely zero sense. Mars has lower gravity (and no magnetic field, although part this is fixable) so the atmospheric loss would be significantly higher if we wanted to produce 1 atmosphere of pressure at the surface.
So however we produced that atmosphere would have to be able to sustain a loss of 100,000+ tons of atmosphere every year as a rounding error. That's the scale of just one of the many problems in terraforming Mars. You also have to produce (or ship in) that atmosphere without boiling the planet. The scale combined with thermodynamics makes this a nontrivial problem.
And where is all this energy coming from? We return back to the Dyson Swarm.
Jeans escape is not the only way an atmosphere can be lost.
If a planet doesn't have a magnetic field, the solar wind can directly erode the atmosphere (ionizing molecules and carrying away the ions and electrons in the magnetic fields of the wind.)
I got a lot out of your comment, but I don't know that Mars and Earth are directly comparable.
- Earth has nearly 10x the surface area of Mars. This decreases the rate of escape.
- Mars has lower gravity meaning escape velocity is roughly 1/3 Earth's, or escape energy is 1/10. This increases the rate of escape.
- Mars has lower temperatures, which reduces what fraction of the atmosphere is at an escape velocity. This reduces the rate of escape. Though if we terraform it, maybe it warms up as well?
So Mars and Earth are not easily compared, and are likely off by an order of magnitude.
Still, it is worth thinking about what general scale we are talking about. Terraforming requires a civilization with access to resources many times our own.
This [1] may interest you. It estimated Mars's atmospheric loss at 0.1-0.5kg/s, which amounts to about 3-16k tons/year but that's also with Mars's current almost nonexistent atmosphere. Losses would be higher with a thicker stmosphere that would be ~1 atmosphere of pressure at ground level.
Mars currently has less than 1% of Earth's sea level atmospheric pressure.
Cusco is roughly 0.6atm of pressure.
So Cusco is a lot closer to use. Mars is essentially the Moon. Actually, it's worse than the Moon. Because all Mars's atmosphere dos is blow really annoying dust all over your equipment. Everything about Mars is the worst [1] eg specifically about the problems of landing on Mars:
> “It’s like this annoyingly middle value,” he said. “The atmosphere is thick enough to cause you all the problems you have on Earth, but too thin to really stop you like on Earth.”
Right, but the idea is that if you had an atmosphere with a higher partial percentage of O2 you could get by with far less inert gas filler, which makes terraforming a bit less daunting. You could imagine an atmosphere with 35% O2 at 0.3 atm being possibly habitable and requiring many trillion less tons of material added to Mars.
Cody's Lab has a few interestig videos about burning things in pure oxygen. For example https://www.youtube.com/watch?v=JlSeHSDc-Do So it's no so simple becuae you can't just ignore the 80% of nitrogen and use only the 20% of oxygen.
(IIR/UC the problem is that the nitrogen absorbs heat, so the pure 20% of oxygens burn things too easily.)
I'm not arguing that Mars atmosphere is close to Cusco. I'm responding to the parent comment implying that 1 atmosphere off pressure would be lost very quickly on Mars. Would this be the same for 0.6 or 0.5 atmospheres? If we could create such an atmosphere is a whole different discussion
I believe that the issue is the loss rate exceeds the creation rate, making a viable atmosphere a nonstarter - not that "an atmosphere suddenly appears and lasts 100,000 years"
The "plans" for Mars terraforming will probably include slamming comets into it (at low relative speeds), on the scale of 1000-10000 years. It's unlikely to involve slow-and-steady air production.
I looked into this a while ago, and a major problem with Mars terraforming is that if you add a bit of additional carbon dioxide (or water vapor), it'll mostly just get frozen and deposited onto the ice caps.
So you need to add something like nitrogen to "bulk up" the atmosphere to prevent it from freezing out. And there's just no nitrogen on Mars.
