[Sally Edwards]

Sally Edwards  asked the Naked Scientists:
   
My name is Sally Edwards (19) and I've been trying to find an answer to a rather strange question and I was wondering if you could help me?
 
If Mars was to have the same atmosphere as Earth, what would the temperature and climate be like? Also, why would, or would not, this theory be possible?
 
Thanks very much

What do you think?

[graham.d]

I think it is theoretically possible to produce an atmosphere on Mars that may be livable within, but it would not be the same atmosphere as the earth. The lower gravity on Mars (about 38% of eath's) means that the atmosphere, to have a similar atmosheric pressure, would have to be much thicker than on earth. I am not sure anyone has worked out how this would behave in terms of the weather, but I think it would have to have significant effects. Mars is further away from the sun than the earth. This does not necessarily mean that it would be colder overall, but certainly it may require a fair bit of engineering of the atmoshere to make the most of the lower solar power. I expect this, and other factors, make it unlikely to be similar to that on earth.

[syhprum]

The problem would be to maintain a reasonable temperature that would require a great deal of CO2 and of course a lot of biological activity if you wanted Oxygen.
I do not think this could be maintained due to the relativity low gravity for any length of time 

[LeeE]

Hmm... funny how we sometimes get related posts from seemingly unrelated people, but as I've only just pointed out in another Terraforming Mars thread, Mars has no magnetosphere and would not be able to hold on to any significant atmosphere due to the solar wind 'blowing' it away, as seems to have happened with Mar's original atmosphere.

[flr]

Few things I would add:
1. Mars is too far away from Sun to have a reasonable temperature even if an Earth-like atmosphere is "seeded"
2. Eventually Mars will loose its "seeded" atmosphere due to lower gravity of the planet.
3. Mars have no molten core to generate a magnetic field, having a reach Earth-like atmosphere will result inn spectacular auroras? which will eventually blow away the atmosphere...
4. Mars have no Moon to stabilize it, hence its weather is more violent than Earth weather. If it will have a much denser atmosphere I guess the storms will be spectacular.

[graham.d]

I think it's quite a hard thing to do (not without a few difficulties) but let's be optimistic. The atmosphere will disappear but we are talking a long timescale here. If we can terraform the place we can replace atmosphere that gets lost. The thick atmosphere gives more protection to radiation. The atmoshere will not be denser, just that there will be more of it (higher before getting into space) to get the pressure up.

Lets start next week.

Anyone got a spaceship?

[LeeE]

Without a magnetosphere there'll also be radiation problems...

[graham.d]

The much greater depth of atmosphere will reduce radiation (as I already said) so I'm not sure what the net resulting radiation levels would be - it maybe less. The magnetosphere only affects charged particles too.

[LeeE]

The magnetosphere is responsible for the formation of the Van Allen radiation belts where a lot of dangerous solar radiation is channeled and trapped.  From the wikipedia article on Radiation Belts:

Solar cells, integrated circuits, and sensors can be damaged by radiation. Geomagnetic storms occasionally damage electronic components on spacecraft. Miniaturization and digitization of electronics and logic circuits have made satellites more vulnerable to radiation, as incoming ions may be as large as the circuit's charge. Electronics on satellites must be hardened against radiation to operate reliably. The Hubble Space Telescope, among other satellites, often has its sensors turned off when passing through regions of intense radiation.

Missions beyond low earth orbit leave the protection of the geomagnetic field, and transit the Van Allen belts. Thus they may need to be shielded against exposure to cosmic rays, Van Allen radiation, or solar flares. The region between two to three earth radii lies between the two radiation belts and is sometimes referred to as the "safe zone".

A satellite shielded by 3 mm of aluminium in an elliptic orbit (200 by 20,000 miles) passing through the radiation belts will receive about 2,500 rem (25 Sv) per year. Almost all radiation will be received while passing the inner belt.

http://en.wikipedia.org/wiki/Van_Allen_radiation_belt#Impact_on_space_travel

Thus it seems to me that without a magnetosphere there'd be no Van Allen radiation belts and that the radiation that would otherwise be trapped there would reach the surface of the planet.  Quite a bit of shielding would be required for long term stays.

Although a thicker atmosphere might slow the passage of radiation, that radiation doesn't just go away: it has to end up somewhere.

[graham.d]

Lee, the protection afforded by the earth's magnetosphere is highly significant but so is the atmosphere itself. Hardly any primary cosmic radiation can penetrate the atmosphere (being mostly protons and alpha particles) but these have impacts high in the atmosphere and produce an array of secondary radiation (muons, gamma rays etc) which is what reaches the earth's surface. Most of the primary radiation is from the solar wind. I don't know what the balance is in protection by the magnetosphere compared with the atmosphere, but both do a job here. Mars is further away from the sun which reduces the flux density of the solar wind and an terraformed atmosphere would have to be much deeper on Mars to retain a reasonable pressure - perhaps 3x. I would not overrate the importance of the magnetosphere in this scenario. I would be interested to know some quatitative data on this though.

The concept of atmoshere "slowing down" radiation but "having to end up somewhere" is a bit misleading - I'm sure you didn't mean this. Secondary gamma rays don't get slowed (obviously) but they do get scattered. Muons can reach earth but only a percentage because some don't have a long half-life (even though famously extended by time dilation) and then their radiation effect depends on their collision cross section.

[LeeE]

Yeah - re the atmosphere slowing stuff: I was only thinking about alpha.  With hindsight it was a rather bad/flawed comment.

Actually, I'll demur to your assertions re atmospheric shielding.  It's just not something I've come across before, whereas I've seen quite a few articles that mention the radiation risk on Mars, but then I think they're all in the context of its current atmosphere.

It would be interesting to actually see the figures for an estimated rate of atmosphere loss due to the lack of a magnetosphere, just to see how much 'new' atmosphere would need to be produced to balance the loss.

[graham.d]

I think the rate of atmospheric loss would be actually quite low - millions of years to significant depletion, but I have no hard references. It is reckoned Mars did have a substantial atmosphere for a long time and it's only because it's been around a while that it's lost it; so if humans can put a new one there I reckon they could maintain it.

[LeeE]

Yes, I believe that the ancient Martian atmosphere was substantial.  Dunno how long it took to lose it though: for some unremembered reason I tend to think of it happening quite (relatively) quickly.

How quickly could a new atmosphere be created though: that's the real issue, methinks.