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?

[[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.

Let’s get started on that soon, ok?

Gary 7

[[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.

[[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).

In fact, it’s cold as hell.

(Assuming that was a hat-tip to the song “Rocket Man”)

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 …

The two Martian moons Phobos and Deimos actually NOT Mars werehell or portals thereto I think!

[[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).

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.

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.

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.