Hacker News Reader

Comment by jqpabc123 | Hacker News Reader

Next question --- what's the plan to keep an atmosphere in place?

It's my understanding that evidence suggests that Mars once had an atmosphere that has since been lost.

Mars loses atmosphere due to solar winds over the course of billions of years. It's not hard to outrun that.

If you could give mars an atmosphere tomorrow the loss of atmosphere won't be a problem on human civilization timescales.

Isn’t it a little wasteful though? The materials for the atmosphere need to come from somewhere, otherwise you’re just throwing out Mars materials. If you import atmospheric material from somewhere else, it feels like other worlds like Jupyter/Saturn moons might be a better call for settlement?

Also, Mars doesn’t have a (strong) magnetic field so going outside would be dangerous because you will be bombarded by radiation.

If solar energy is powering the devices, the lower amount of sunlight reaching the outer moons might be a big problem.

Atmosphere blocks radiation, and atmosphere can be made from the rocks themselves. There is an effectively endless supply.

> atmosphere can be made from the rocks themselves. There is an effectively endless supply.

Do Martian rocks have significant amounts of nitrogen?

Why would you need nitrogen in your atmosphere?

Presumably for whatever reason it worked well for us to develop as we did down here? Stops everything from exploding, dissolves all the other gases quite nicely? What other gas would you use?

Nitrogen does absolutely nothing on Earth. It is inert.

Like, without that inert gas there would have to be something else. Being in a pure oxygen environment for a prolonged period has health impacts to many animals including us. Anything even remotely flammable, like paper, wood, sugar, would burn uncontrollably with the slightest spark.

If you didn't have nitrogen you would need another inert gas to make up 80% (or whatever) of the atmosphere you were going to make.

For the most part, partial pressure is what matters, not absolute pressures. The only contribution inert nitrogen has to life is raising the boiling point of water. But on a frigid planet like Mars that’s not going to be an issue.

Being in a pure oxygen environment does not have a long term impact on animals… if the pure O2 environment is 0.21 atm oxygen. There’s a long history of biological experimentation done by space agencies on this, and the Apollo missions operated on a 0.2 atm pressure for the duration of their missions. Apollo 1 famously had trouble not because it was pure O2, but because it was 1.2atm O2.

There is no reason you need backfill inert gasses to have 1.0 atmospheres.

The Nitrogen cycle [1] is a critical component of many ecological systems. Critical compounds in plants have nitrogen, and the nitrogen for these is absorbed from the soil, where it is fixed by bacteria.

[1] https://en.wikipedia.org/wiki/Nitrogen_cycle

The nitrogen cycle almost entirely involves fixed nitrogen, not inert N2. Nitrogen is fixed from the atmosphere slowly over time through lightning strikes and a very small number of nitrogen fixing bacteria that live symbiotically on the roots of very few plants.

The vast majority of the biomass on earth, including about half of the fixed nitrogen in your body was synthesized industrially via the Haber-Bosch process over the last 100 years.

Aside from those nitrogen fixing bacteria whose output we have already surpassed with industrial processes (artificial fertilizer), inert nitrogen plays no role in biological metabolism. It is not needed, at all.

Mars colonists can import nitrogen, or mine fixed nitrogen from the few deposits that are known to exist. It doesn’t need a massive atmospheric reservoir.

A pure oxygen atmosphere would completely ignite itself in contact with a spark. So you need to have another gas to dilute the oxygen.

Mars' (almost non-existant) atmosphere is mostly CO2, and you could use that, except that a CO2 level above 10% is lethal for humans and at 10%, it's still too oxygen rich.

Nitrogen has the advantage that it's inert and non-lethal.

There's no reason Mars' atmosphere needs to be a 1 atm pressure. For biological processes, it is partial pressure that matters, and nitrogen gas is inert. Mars' atmosphere could be 0.2 atm oxygen + trace gases and that would be perfectly acceptable for human beings.

However people can wear breathing masks when outside of buildings. Plants cannot. Most terraforming proposals focus on supporting surface plant life, and plants thrive in high-CO2 environments. These proposals involve toxically high (for humans) level of CO2 in order to support lush plant life. Once the O2 and temp gets high enough, people can survive on the surface without space suits, so long as they carry a bottle of oxygen and a breathing mask.

Longer-term, atmospheric pressure could be supplanted with a couple of Kuiper Belt objects consisting of frozen nitrogen and organics. Let it burn up in the thickening atmosphere and contribute to the developing pool of gases.

Plants also need nitrogen. Even if you chose plants that can get it just from soil and not worry about any fixing from the air, you need to get a lot to Mars for a terraform.

Not N2, no. There is not plant anywhere in the world that uses atmospheric N2. Plants used fixed nitrogen from the soil. In Martian greenhouses, that would be provided in the form of artificial fertilizer and/or organic waste.

> In Martian greenhouses, that would be provided in the form of artificial fertilizer and/or organic waste.

Which requires supply from somewhere. How far you can go with ISRU depends on how big the colonisation development gets.

There are fixed nitrogen deposits on Mars (which are also of scientific interest because they might contain fossil remains).

But even without access to such deposits, fixed nitrogen in the form of ammonia could be brought from earth in sufficient quantities to support each settler. Organic waste would be composted and thus the nitrogen recycled with very little loss. N2 waste produced by decomposition would be recaptured by the atmospheric regulators, and either fixed by certain plants brought for that purpose, or industrially fixed by an arc or Haver-Bosch process in the bigger cities.

A synthetic magnetic field is easy compared to adding an atmosphere. Big wire with current, very big by wire standards (one square meter cross section isn't close to enough for reasonable input values if it's on or close to the ground, but it doesn't really need to be) but still small compared to the mass involved in making a dent even compared to the thin Martian atmosphere.

Compared to Mars the moons of the gas giants have at least three major hurdles for long-term human habitation: their distance, with the trip there being around 6 years, the incredibly harsh planetary radiation belts the moons weave through, and ineffectiveness of solar energy that far away from the sun.

I think we should try to overcome these hurdles, but getting humans out there is a much taller order than establishing a human presence on Mars.

The short answer is that it would be underground or in domes for the foreseeable future. The long answer is that people have lots of clever thoughts about how they might achieve it, although none of them are yet practical: https://en.m.wikipedia.org/wiki/Terraforming_of_Mars

Musk had the idea of nuking the polar ice caps on Mars, which we could probably technically do today...

And accomplish nothing. It was a terrible idea that wouldn’t work, rightly ridiculed by people who have been studying this for decades before Musk arrived.

Yeah, to offer an analogy:

"CelebrityDude had the amazing idea of flying around by building a set of robot arms that would reach down and pull really hard on your own shoelaces, which is something we could do today..."

It's not clear why we would care about that except as a reason to point and laugh at CelebrityDude.

I'm not Musk's biggest fan by any means, but after decades in existance he made electric cars "a thing", and he drove the costs of getting to space down by so much that it makes the existing players look like idiots. He's clearly not the dummy your portraying him as. I'd definitely listen to his ideas, even if some of them aren't good.

He also wanted to run air levitated trains in a partial vacuum and that was a nonstarter. Not every idea can be a winner.

(For the record, I wouldn't apply this to Elon specifically, but I think this is a good moment to plug a book-quote.)

> You think he's a genius?" she said, raising her eyebrows. The high-[noble] twit?

> "I don't know him quite well enough, yet. But I suspect so, a part of the time."

> "Can you be a genius part of the time?"

> "All the geniuses I ever met were so just part of the time. To qualify, you only have to be great once, you know. Once when it matters."

-- Komarr by Lois McMaster Bujold

I disagree with the implied-worldview behind that: Such progress is fundamentally incremental and stochastic, rather than hinging on "Great Men" (or women).

For a great many discoveries or inventions or ideas, digging a little further into the history shows the famous-people often aren't the first to say/try something, but the ones who attempted it again at a more favorable time or place, were more powerful or influential, or just plain got lucky.

We're talking about SpaceX specifically, not Tesla or any of his other companies. In the context of SpaceX, what GP said is absolutely true. The rocket industry has not been getting incrementally better over time. If anything, costs have incrementally gone up over time. Until SpaceX, nobody was able to significantly lower launch costs. Then SpaceX came along and succeeded where dozens of previous startups had failed, and the price floor drops out. In this particular case, "revolutionary" is the right descriptor to use.

I mean, my world view is that you should listen to people's ideas when they've had some good ones in the past. I'm not saying we have to believe they're always right.

I don't believe in great men, but I don't believe innovation just stochastically appears either. Behind all those little steps upwards is someone who's stumbled on some kind of insight and did something about it. Sometimes an idiot can get lucky and have it work out once, but Musk has done it several times.

The problem really is a lot of people seem to think he's an engineering genius, which he isn't. What he is is a marketing genius.

I don't know about Tesla, but at SpaceX he is actually the Chief Engineer, and in more than just title. A lot of the innovative stuff SpaceX has done were the result of engineering decisions he made. According to Eric Berger's book on the beginning of SpaceX, he is a quite capable self-taught engineer respected by the people who work for him, including those who moved on to other things and had no incentive to lie.

I don't hold him on any pedestal. But saying he's just a marketing guy isn't correct either.

The best thing you can do when you have the resources is to outsource your thinking to other people. Don’t want to figure out your own taxes? Pay someone to figure it out. Don’t want to figure out the law? Pay someone to figure it out. Don’t want to figure out your schedule? Pay someone to figure it out.

My point is, you’d probably get a lot farther by talking to the experts he pays to be close to rather than listening to him.

There are many, many questions between how to produce oxygen to breathe in a settlement, and terraforming the entire planet.

This isn't about putting a whole new atmosphere on Mars.

But if we did, it would have to be replenished but it would be lost on geological not human timescales. Think significant amounts of atmosphere lost after 100,000 years.

You could do the same with the moon.

Reply on news.ycombinator.com