Why isn't Mercury as red as Mars, even though it has more iron?

[bbbl67]

Mars' red surface is said to be FeO rust. Rust requires Oxygen to exist. Are there any theories about where that original oxygen came from? I'm obviously trying to fish for possibilities of life in the past.

 

[Bandersnatch]

Oxygen, as one of the main products of stellar fusion, is among the most abundant elements in the solar system, after hydrogen and helium. It's been like that even when the solar system was but a wee lil' cloud of gas.
So it doesn't need life to be produced. And in fact, life can't produce it, because it's not running on nuclear reactions. What life can do, is separate oxygen from molecules that the primordial oxygen bounded into. Hence it's considered that life is needed to maintain an oxygen-rich atmosphere, because without life it'd just stay bound in silicates, rust, and the entire remaining zoo of oxides and whatnot.

 

[bbbl67]

I'm not talking about atomic oxygen but molecular oxygen. That does require life to produce.

 

[snorkack]

Mars' red surface is said to be FeO rust. Rust requires Oxygen to exist. Are there any theories about where that original oxygen came from? I'm obviously trying to fish for possibilities of life in the past.

Wrong. Not FeO. That´s the point.
Only Fe₂O₃ is red. The reduced iron oxides such as FeO and Fe₃O₄ are not red - they are colours like black, blue, green.
Where did the excess oxygen come from, to allow Mars to be red?

 

[Dr-Flay]

Before life on Earth there was a small amount of oxygen in the atmosphere. Life did not put it there. Chemistry and Physics put it there.
In water oxygen is bound to Hydrogen, and we know Mars had water and still has iced water.
Oxygen is not "produced" as such, it is unlocked from other compounds.
There are no molecules of oxygen, it is an element that can bond with other elements, some easier than others.

"Oxidisation" of a material does not require free-roaming oxygen gas, or trapped in water, it just needs for oxygen in whatever state or compound it is, to prefer bonding to another material.
Oxygen likes Iron a lot so the process is relatively fast.

...so no. Mars is not covered in rust due to the massive amount of life it must have had.
It just happens to be very rich in Iron compared to Earth.

 

[bbbl67]

...so no. Mars is not covered in rust due to the massive amount of life it must have had.
It just happens to be very rich in Iron compared to Earth.

If that's the case, then wouldn't Mercury be even redder, as it is even richer in iron?

 

[Vanadium 50]

If that's the case, then wouldn't Mercury be even redder, as it is even richer in iron?

Why should all the iron in the core make Mercury's surface red?

 

[Dr-Flay]

Not a bad question, better than the first actually, but as mentioned above, where the iron is makes a big difference.
Mars has a lot of iron-rich Basalt at the surface.
There is also still a very thin atmosphere which will move any remaining Oxygen around with wind-blown particles of Basalt encouraging a faster reaction.

The asteroid that Japan and NASA are doing experiments with has been found to have iced water on it.
If this asteroid also contains any iron, there is a good chance that if the 2 have been in contact you will find some rust there.

It turns out that H2O is not such a rare thing in the Universe (apparently the 3rd most common molecule), meaning that neither is Oxygen, but as noted earlier Hydrogen and Oxygen, like most of the periodic table are produced by stars.
Some elements come from the birth of stars, and some from the death of them.
Black holes pulse jets of freshly ground and recycled elements from their poles when they hit bursting point, like giant galactic farts of galaxy food.

Oxygen is 1 reason why biological life on this planet exists, not the other way round. Oxygen was here before any respiration or conversion by living things.
Plants do not make Oxygen, they unlock it.
H2O: 1 third of the water on this planet is Oxygen, 2 thirds Hydrogen. Put any Iron in it, and it will rust. However it will be slow depending on how much extra Oxygen is mixed in but not bonded.
In water with no extra Oxygen the process is very slow as Oxygen also very much likes to bond with Hydrogen. In fact it does it very easily, so it is a wrestling match between Hydrogen and Iron. This is why deep sea wrecks last so long.
However it will still Oxidise and go rusty.

There are many other Oxides and compounds with Oxygen that can be found here and off-planet.
Rust was on this planet long before the first life.

 

[Ophiolite]

Archean banded iron formations have been proposed as terrestrial analogue for Mars. (See Fallacaro, A. & Calvin W.M. Lake Superior Type Banded Iron Formations as an Analog to Mars 2002). The consensus is that these formed by precipitation from iron saturated sea water as a consequence of the Great Oxygenation Catastrophe, caused (probably) by the photosynthetic activity of cyanobacteria. Thus the presence of 'rust' on Mars is consistent with the presence of abundant life in the shallow seas of Noachian Mars. However, as noted by others, it is not the only way the iron oxides may have formed.

Side note: Expanding on Bandersnatch's comment re-the abundance of oxygen, it makes up almost 1/3 of the mass of the Earth and just under 1/2 of the mass of the crust. Most of it is bound up in silicates. The figures for Mars would be broadly similar.

 

[stefan r]

If that's the case, then wouldn't Mercury be even redder, as it is even richer in iron?

The atmosphere on Mercury is measured in nanopascals. So the partial pressure of oxygen is 14 orders of magnitude lower than Earth. Here is a chart with mineral redox buffers for iron. At equator temperatures there is not enough oxygen to drive the reaction magnetite to hematite. On Mars the partial pressure of oxygen is much higher and there will be less solar radiation stripping ions off of minerals.

...
...so no. Mars is not covered in rust due to the massive amount of life it must have had.
It just happens to be very rich in Iron compared to Earth.

Are you sure? I thought rust makes its way to the oceans and sinks. It is water solubility combined with gravity. Then the oceanic plates sink too. Some parts of Earth's mountains are very red. Especially some of the old parts like Australia.