… for the air pressure to be the same as Earth sea level?
I’m thinking I might pop over in my spare time and set up a little biome.
… for the air pressure to be the same as Earth sea level?
I’m thinking I might pop over in my spare time and set up a little biome.
Good question. I’ve wondered about this myself; an artificial canyon on Mars might be a possible site for a colony. You could maybe dig it out using asteroid impacts or something.
Very roughly; the atmospheric pressure on Mars is 6 millibars, about the same as the pressure on Earth at a height of 20 kilometers. But the gravity on Mars is less, so the atmosphere is less compressed by its own weight; this has to be taken into consideration too.
The scale height of the Earth’s atmosphere is 8km; the scale height is the increase in altitude for which the atmospheric pressure decreases by a factor of e. (e is the base of natural logarithms, but we are looking for the ratio, so this will cancel out).
The scale height of Mars atmosphere is 11.1 km; divide this by Earth’s atmosphere scale height and you get 1.397. Multiply the original 20km by this factor and you get 27.7km; about 17 miles. Dig a canyon 17 miles deep and you might stand a chance. of a respectable pressure.
I thought that the bottom of the Valles Marineris might be a good place to start, since it is 11km deep in places; but unfortunately it is not that far below datum, since the surrounding land is quite high.
If anyone can work this out more accurately, feel free- it is a long time since I studied any of this stuff.
Like eburacum45 says you need to account for the exponential nature of atmospheric density.
P® = P[sub]0[/sub]e[sup]-(r/H)[/sup] where r is the distance from the reference level and H is the scale factor.
Mars has a scale factor of about 11000 m and a P[sub]0[/sub] of ~0.6 kPa and we’re shooting for a P® of 100 kPa
so 11000*ln(100/.6) = -z and z comes out as -56 km or so.
If you were going for a pressure like the summit of Everest (~40 kPa) z comes to 21 km.
As an added bonus, you’d expect Mars to be a lot warmer at 21 km deep. Now we just need to send Curiosity a couple of shovels.
56km is considerably deeper than my estimate, and a hole that deep would probably not be feasible. The rocks would tend to flow together under their own internal pressure and close the hole.
I agree. The number is so large it feels wrong but that’s what comes out of the math. I’m more than happy to be set straight if I’ve done it wrong.
Assuming I’m right, you’d be better off trying to get the CO[sub]2[/sub] to outgas and induce some sort of water cycle to thicken the atmosphere.
Possibly by bombardment with ice mined from the rings of Jupiter.
The core of Mars is believed to be solid, lacking a mantle similar to Earth’s.
NASA cite
I wonder if this means that the 56km deep canyon would be more durable on Mars than it would be on Earth, enough to make it worthwhile.
What is the potential to raise the surface pressure of Mars. If we can get it up just a bit, which by earth standards is a drop in the bucket, then the exponential effect should make that dept a lot less.
Sadly, within our solar system there appears to be a shortage of mining engineers with a thorough grasp of the finer points of asteriod-impact-based excavation. Or indeed the coarser ones.
Seems like it’s a wide open field then.
Thanks for the earworm, Saffer. :mad: I keep trying to sing the thread title to the tune of the Bee Gees’ “How Deep Is Your Love.”
And some time. That’s all you need really - pressure, and time. Ol’ Curiosity loves Areology.
Chapter 6 of Martyn Fogg’s Terraforming (1995 edition) has the constrained CO2 reservoirs on Mars to be:
Atmosphere ~7 mbar
Polar Caps < a few mbar
Regolith <190 (Zent et al) or <280 (Fanale et al)
Now both Zent and Fanale are papers from the 80s. I can only assume better models exist now.
The lower gravity should also make it possible to dig a deeper hole before its own weight collapses it.* How much* deeper is beyond me, though.
In due course this may change.
The idea has already been put forward by people such as Robert Zubrin and Paul Birch; because the asteroid approaches under the influence of Mar’s gravity, its momentum is multiplied considerably. For a comparatively small input of propulsive energy you could get a very large output of impact energy.
Hit the same spot over and over again and eventually you could have a 56 km deep crater; unfortunately I suspect it would be a crater filled with lava melted by the heat of impact.
The depth on earth at which a hole can’t be dug any deeper is due to mechanical strength of the rock versus the pressure from the overlying rock - which is in turn a function of the rock’s density and the earth’s gravitational attraction.
The Tautona Mine in South Africa is one of the deepest on earth, at 2.4 miles. At this depth, rock burst is a serious hazard, which means we probably can’t drill a habitable hole much deeper. Related question: how did the Russians manage to drill the Kola Superdeep Borehole, 8 miles down? Different rock maybe, or the stability provided by a tightly curved hole instead of a cavernous mine?
The gravity on mars is 0.376 times that of earth, so presumably we could create a habitable hole 1/0.376 times deeper, or 6.4 miles (10.2 km) deep. This is far short of the tens of km that has been suggested upthread.
If the 8-mile depth of the Kola borehole is taken as the earthly limit, then we should be able to hit 21.2 miles (34 km) on Mars. But I suspect you wouldn’t be able to make a habitable cavern at such depths, just a skinny borehole.
How deep you can dig a hole will surely depend on how much you slope the walls of it. For comparison, Olympus Mons is (probably) the solar system’s tallest mountain, but you could “climb” its slope without even noticing you were walking uphill.
The deepest crater on the Moon, the South Pole/Aitken Basin, is about 12km from the rim to the deepest part of the floor. I doubt that any Martian crater could be deeper, since the gravity there is twice as strong as on the Moon. To get deeper you’d have to dig wide, and without producing much waste heat. So the asteroid excavation technique would be useless at this depth.
Of all the solutions for building a sustainable colony on Mars, digging a hole ~30 miles deep to allow a human-friendly atmosphere seems like one of the less workable ones.
O2/CO2 cycle, to start with, anyone? If you can solve that for a pit, you can solve it for some kind of domed or near-surface underground city.