Mars is a weird planet. It is cold and extremely dry today, but the geology and topography indicate it was much warmer and wetter in the past. That means its atmosphere must have been thicker a billion or two years ago. To sustain water, there must have been some sort of greenhouse gas to hold in the heat.
On Earth, we have carbon dioxide fulfilling that role (and methane, and water vapor). Scientists have assumed that the Martian atmosphere must have had quite a bit of CO2 back then to keep it mild, and in fact the thin air is mostly CO2 now.
But if that were true, where did it go? The total amount of CO2 must have dropped by a huge amount over the eons, and the most likely place it would be is trapped in carbonate rocks.
One teensy problem: those carbonates aren’t there, at least not in the amounts needed. You’d expect there to be limestone all over the planet’s surface, but there isn’t. Instead, the rovers found evidence of sulfur-rich rocks; jarosite is common on the surface, for example.
This has led scientists at MIT and Harvard to suppose something a bit radical: instead of CO2, maybe there was lots of SO2 — sulfur dioxide — in the early Martian air. This idea is a twofer: it explains the high sulfur content on the planet, and it also explains why there are few or no carbonates. Sulfur dioxide inhibits carbonate formation.
Mars clearly had lots of standing water on its surface long ago. If the air had SO2 in it, it would dissolve easily (much like CO2 does). The oceans would have become acidic, a solution of sulfuric acid. When the oceans dried up this sulfur rich water formed the jarosite.
In a sense, this mimics Earth’s carbon cycle, where CO2 in the air dissolves in the water and forms carbonates like limestone. But Mars… well, it’s different. It’s sometimes easy to forget that, which is why scientists have been thinking carbon all this time.
The primitive Mars much have looked very different. Before iron oxide tinted it red, and before the water all disappeared, what did it look like? Orange, or yellow, with its high sulfur content? One thing I can be fairly sure of: it would have smelled bad. Sulfur is the main ingredient in hydrogen sulfide, for one.
Ray Bradbury may have said that Mars is heaven, but I think, given the amount of brimstone that may have been there, he got his theology backwards.
December 21st, 2007 at 12:28 pm
Little correction: you won’t get sulfuric acid when you dissolve SO2 in water. You need SO3 to produce sulfuric acid and it can only be produced in lightings and in some volcanic processes.
What you’ll get is _sulfurous_ acid (see http://en.wikipedia.org/wiki/Sulfurous_acid)
Actually, sulfurous acid is not a very strong acid because it exists only in diluted solutions (it rapidly decomposes to SO2 and water if you try to concentrate it, just like carboxylic acid).
December 21st, 2007 at 12:38 pm
Wouldn’t this significantly hamper our efforts to live on the surface? Can we make such acidic water drinkable? Also, I can imagine that the ambient air would have that “rotten eggs” odor in spades. We’d better pack along a few air fresheners along with the purifiers. Had mission planners considered these possibilities earlier?
December 21st, 2007 at 12:40 pm
If I’m recalling that Bradbury story correctly, the explorers discover that Mars is definitly NOT heaven, but an illusion.
December 21st, 2007 at 12:49 pm
Well, of COURSE Mars is Hell. Anyone who’s ever played the Doom games knows THAT.
December 21st, 2007 at 1:04 pm
SO2 actually doesn’t smell of rotten eggs, it’s smell is more like the smell of burnt matches.
H2S (which smells bad) is a strong reducing agent and it reacts with _sulfurous_ _acid_ to produce water and elemental sulfur. So I don’t think the Martian air smelled that bad
Actually, to think of it, we have a possible cycle suitable for living organisms: some organisms can oxidize sulfur to sulfurous acid while the others can reduce it back to elemental sulfur. And it doesn’t even need free oxygen!
And if we ever get to Mars then purifying water polluted with SO2 is not going to be our main worry.
December 21st, 2007 at 2:31 pm
>> SO2 actually doesn’t smell of rotten eggs, it’s smell is more like the smell of burnt matches. <<
So the air might actually be of benefit if, say, a Mars base commode breaks down
I’m really curious to know, though, if mission planners consider such things as how our skin, eyes and sinuses would react to Mars dust. The thought of large, jagged dust grains, even the very few that somehow make it past the barriers and filters, is a bit disconcerting. I’ll reread Zubrin’s book and see if he brought this up.
December 21st, 2007 at 3:18 pm
It ain’t the kind of place to raise your kids, either.
December 21st, 2007 at 3:23 pm
It’s all very well saying ‘Mars is different’, but shouldn’t there be a reason? All the planets came from the same cloud of gas and dust. Maybe it’s that Earth has a bigger iron core which can sequester more sulphur, or something?
December 21st, 2007 at 5:05 pm
Forgive me for what may be a stupid question, but didn’t Earth have a sulfur based atmosphere originally? I’m sure I read that somewhere – that the first life forms died out as oxygen – a poison to them – began to predominate.
December 21st, 2007 at 6:55 pm
Fascinating. A nice reminder of how different the other “terrestrial” planets are from us. It’s all too easy to think of Venus and Mars as versions of Earth that are different in certain ways. But as we’re finding out, they are different in ways we never thought of.
December 21st, 2007 at 10:11 pm
gazza666,
If memory serves, Earth’s original atmospheres (there were multiple chemistries, in sequence) were reducing — hydrogen, carbon dioxide, methane, dash of ammonia. That sort of thing.
So yes, oxygen was poisonous to the first life on Earth. Biology as a whole, obviously, overcame this.
December 22nd, 2007 at 5:05 am
Sam Wise writes:
[[If memory serves, Earth’s original atmospheres (there were multiple chemistries, in sequence) were reducing — hydrogen, carbon dioxide, methane, dash of ammonia. That sort of thing. ]]
That was the consensus at least through the 1970s, but the consensus now seems to be switching to a neutral atmosphere for the early Earth, largely CO2 and nitrogen (and with a big side order of steam in the very early period –the early Hadean — when the magma ocean was still around).
December 22nd, 2007 at 5:26 am
So, this explains Mars’s CO2 deficit how?
December 22nd, 2007 at 1:11 pm
Thanks for clearing up one of the big theological mysteries: namely the location of Hell. Now, I wonder, are any of those Mars landers equipped with microphones? Are they picking up the screams of the hordes that have been cast into hell/Mars? Is NASA engaged in a cover-up, hiding the existence of the location of Hell from us?
December 22nd, 2007 at 8:23 pm
# Technogeekon 21 Dec 2007 at 12:49 pm
Well, of COURSE Mars is Hell. Anyone who’s ever played the Doom games knows THAT.
The two Martian moons Phobos and Deimos actually NOT Mars werehell or portals thereto I think!
December 22nd, 2007 at 8:27 pm
# Technogeekon 21 Dec 2007 at 12:49 pm
Well, of COURSE Mars is Hell. Anyone who’s ever played the Doom games knows THAT.
The two Martian moons Phobos and Deimos actually NOT Mars were hell or portals thereto I think!
Come to think of it if high sulphur = hell then Io (Jupiter’s volcanic moon) comes closest …
… Or perhpas Venus best qualifies for the conditions there …
.. maybe Hell is the eponymous crater on the Moon near Mare Nubium & named for a Jesuit preist Maximillan Hell …
December 22nd, 2007 at 8:27 pm
D’oh! Double post. Mea culpa.
December 23rd, 2007 at 5:20 am
Zorak said:
“It ain’t the kind of place to raise your kids, either.”
In fact, it’s cold as hell.
(Assuming that was a hat-tip to the song “Rocket Man”)
December 23rd, 2007 at 5:36 am
Lab Lemming writes:
[[So, this explains Mars’s CO2 deficit how?]]
Carbonate deficit. I guess the idea is that for some reason, Mars was deficient in carbon and enriched in sulfur to begin with. I, personally, would like to wait until more evidence is in before drawing that conclusion. I can think of other possible reasons for a carbonate deficit, e.g., if early CO2 was blasted away by early impacts (”atmospheric impact cratering,” a process important for relatively low-gravity planets like Mars).
December 23rd, 2007 at 1:27 pm
Well, you know, for a planet that REALLY turned out to be the opposite of what a prominent SF writer said, consider C.S. Lewis’ Perelandra — which was, literally, the Earthly Paradise — and then consider what Venus REALLY turned out to be (sulfur and all).
December 23rd, 2007 at 8:05 pm
Where did the nitrogen go? Or why is Earth’s atmosphere mostly nitrogen and Mars and Venus mostly CO2 with little or no nitrogen. This would be (another) problem for terraforming.
December 24th, 2007 at 4:28 pm
Lyle Gaulding writes:
[[Where did the nitrogen go? Or why is Earth’s atmosphere mostly nitrogen and Mars and Venus mostly CO2 with little or no nitrogen. This would be (another) problem for terraforming.]]
Like the oxygen in Earth’s atmosphere, the nitrogen is largely a by-product of the biosphere. I don’t know the chemical details offhand, but I remember reading that.
Venus’s atmosphere is indeed only 3.5% nitrogen, but consider that that’s out of 92.1 bars atmospheric pressure, and you’ll see that Venus actually has more nitrogen in its air than Earth does.
December 24th, 2007 at 7:06 pm
So, if we impact a large water ice comet into Venus, it should allow the sequestration of Co2 into H2O oceans and a reduction of temp???
Let’s get started on that soon, ok?
Gary 7
December 26th, 2007 at 7:03 am
Didn’t the water on Mars come from the same place, and arrive at the same time ours did, namely ice impactors? It’s just that Mars didn’t have enough gravity and other atmosphere to hold it. An interesting thing to do is figure out how long it stayed around and the effects it had while it was flowing on the surface.
December 26th, 2007 at 2:11 pm
Gary writes:
[[So, if we impact a large water ice comet into Venus, it should allow the sequestration of Co2 into H2O oceans and a reduction of temp???
Let’s get started on that soon, ok?]]
The same sequence would take place as before — the heating from sunlight would evaporate some water, which would cause greenhouse heating, which would evaporate more water, and so on until the system ran away and the oceans evaporated entirely. Photodissociation would then remove the hydrogen and the oxygen would combine with the rocks.
There’s a reason astronomers put the inner edge of the sun’s continuously habitable zone at 0.95 AUs.
January 20th, 2009 at 9:44 pm
[...] Maybe. Mars is different than Earth. The laws of chemistry are the same there as here, but the chemistry going on is different. The air [...]
February 5th, 2009 at 11:20 am
If there were sulfur-based life-forms on Mars, we would know. In fact, we’d probably find evidence of sulfur-based life-forms on Venus, and maybe even on Io, but nothing / nadda / nope.
Actually I find it particularly interesting that both Mars and Venus have prevalent sulfur, mass within a power of ten of each other, relatively similar magnetosphere, and historically similar atmosphere assuming Mars’ atmosphere was predominantly SO2, and the planets formed at relatively the same time. But Venus has roughly ten-thousand times the surface pressure that Mars does (90 bar compared to 0.007 bar). That’s strong evidence that the Martian atmosphere did have a thicker and thus warmer climate. The question is, what happened to it?