Atmosphere on the moon?

A bit bored on lunch break and began idly wondering whether it would be possible to terra-form the moon.

Now I realise that the Moon wouldn't be able to hold onto an atmosphere for very long but as a mental exercise I was trying to think of ways that would allow humans to give it one at least for a short while.

My initial thought was to crash an asteroid on its surface with enough water/frozen gas to accomplish this task but I think that any gas release would probably leak off into space or be captured by Earth's gravity. Also this has probably happened in the past and since there is no atmosphere to speak of I assumed that this is true.

However I recently read that there might me some form of water cycle operating on the moon where ice is moved to the coldest regions as water vapour, if this were true then it might be possible to create at least a thin atmosphere.

So some questions to chew over:

How many tons of ice would be needed to achieve a brethable atmosphere?

How long would the moon hang on to it?

Would you need to continually add to the ice supply to replenish the atmosphere or could you keep it there with the use of an artificial shield (made from Ozone or CFCs perhaps)?

And finally if the loss was relatively slow and the atmosphere took hundreds of years to dissipate would it be worth it to set up a large moon colony?

Anyone got any thoughts?

Just saw the "Exploring Space - The Quest for Life" documentary, and some of the people interviewed argue that even Mars wouldn't be able to hold anything similar to an earth atmosphere.

However, one of the pro-martian-terraforming plans was to add some of the worst greenhouse gasses here on Earth to the Martian atmosphere, to increase the temperature and release frozen CO2, which in turn would heat it even more until watery ice would start to thaw.

In the unlikely chance that this is possible on the moon, I guess the question if you have to replenish the atmosphere from external sources depends on how much water you find, and what the O2 vs. CO2 breathing creatures populate the moon. How much tonnes of ice you'd need, along with other things, depends on the volume you'd get with breathable atmosphere.

Like a lot of places (Ceres, Mercury, and Vesta, among other), I wouldn't give it a full atmosphere, but rather a 50mb one. This would be enough for plant life, maybe some engineered insects, as well as water dwelling creatures, and make life support easier.

At 50 mbar, water boils at 32.5C. It will still be possible to have some kind of ecosystem, but the temperature will have to be controlled very carefully. Most warm blooded animals have a body temperature of about 35-40C. They would have to be segregated from the low pressure ecosystem.

johno

I know, but they require a minum of 100mb partial pressure oxygen to breathe anyway. I have no issue with farming animals inside, and growing crops outside.

Lakes would tend to pool at the bottom of craters, where they'll be shaded.

With an atmosphere of 50mbar, growing crops outdoors will require carefully controlled temperatures, ie it'll have to be done indoors. Sunlight currently heats the surface of the moon to over 200C. Even with a 1/20th atmosphere to protect it, it's going to get hotter than 32.5C.

Lifeforms at hydrothermal vents can survive temperatures of well over 200C because the water isn't actually boiling due to the high pressure. Strictly speaking it's not pure heat that kills living organisms, it's the water in their cells turning to gas and rupturing the cell walls. Heat can destroy other molecules essential for life as well though. 32.5C will kill your moon grass as surely as 100C air will kill your earth grass.

If you grow in shaded areas like deep craters you will have to compensate for the lack of light, and it still doesn't remove the heat problems. Heat on the moon currently only travels via conduction and radiation. A shaded spot will help with the radiation, but an atmosphere will introduce heat transfer via convection. ie hot gases moving into colder areas.

It's not easy.

johno

Meh, perhaps if you had a less volatile atmosphere, then you could get some decent ambient pressure. Meanwhile, you could then live inside domes with breathable atmosphere. The atmosphere outside the domes might support an engineered ecosystem, buffer against temperature swings, as well as act as a barrier against meteor strikes.

If the Moon's temperature swings were suitably buffered by an atmosphere, thus evening out the hot and cold extremes, then what would the ambient temperature be? I suppose it would depend upon the gas you chose, in order to regulate the internal reflection or greenhouse effect.

The problem is actually the solar wind and the lack of a magnetosphere. Which is also the reason you can't terraform Mars. The solar wind runs about a million miles/hr and strips away any atmosphere not protected by a magnetosphere. Neither Earth's Moon nor Mars have a magnetosphere (neither does Mercury but I don't think anybody's considering terraforming Mercury ).

Yeah, but that stripping process occurs over a very long timescale, and not one that would concern us.

Maybe you could create an expanding solar wake by positioning a huge solar sail between the Sun and the body you're trying to protect. A large magnetic solar sail could deflect the proton wind outward, like a mini-bowshock, but one positioned much ahead of your planet/moon/etc.

is there research going on into generating artifical magnetospheres for the purposes of interplanetary vessels or surface stations?

I think there are papers that have been published about creating large magnetic plasma bubbles as solar sails. Theoretical research has been done. I don't know that anybody's built any kind of experimental apparatus, though.

I have never done the math but I have often wondered if it would be possible to slowly build up a magnetosphere on Mars. If everyone that settled was required to bury a certain number of strong permanent magnets in a north south direction, would it eventually be strong enough to deflect solar wind?

It seems that if the extremely weak field at the surface of earth was duplicated at the surface of another planet then it should in theory appear identical from space.

Since Mars is a bit smaller, I would assume that the local field would have to be a bit stronger than earth's in order to extend out far enough though. Any EM guys on here?

~Daniel

just a guess, but i'm pretty sure that the atmosphere would actually be extremely transient. the moon does naturally have an exosphere, though a surprisingly significant portion of it is due to human activity. what that means, however, is that the density is still lower than even the earth's atmosphere in LEO near the ISS. you have to go above that before you reach the natural density of the moon's atmosphere. now, while the solar wind is a problem for holding an atmosphere on the moon, simple statistical physics is an even bigger problem. the reason that venus has no water is because the fraction of hydrogen molecules/atoms (stripped off of the water by ionizing radiation in the upper atmosphere) that have a velocity greater than escape velocity in the maxwell distribution is somewhere on the order of 10^-6, which means that all the hydrogen leaves relatively quickly on geologic scales. comparably, on earth this number is somewhere closer to 10^-9 (temperature also matters). on the moon, with a FAR lower escape velocity and comparable temperature to earth, hydrogen will be lost extremely fast due to the low gravity and high amount of ionization. there's simply no way to keep it there, and probably not enough easily accessible to replenish it.

my EM is a bit weak, but I don;t think it works quite like that

on the same note, I wonder if it would be possible to build a small scale version of the earth's core (i.e. circulating molten) and see if that would produce any results

Heh, well, living under giant inflated tent domes might be an option, but I think even the strongest material (eg. graphene) would be susceptible to penetration by meteor/micro-meteor strikes. Maybe you could have a laser protection system to intercept those.