<p><strong>tl;dr</strong>: Compared to Earth, the atmosphere on Mars is very thin; in addition, it contains much less of oxygen and water (i.e., is very dry). It is much colder there. These conditions may slow down oxidation to an irrelevant rate.</p>

<p>For an object of pure iron, note that according to the English Wikipedia about <a href="https://en.wikipedia.org/wiki/Mars#Atmosphere" rel="noreferrer">Mars</a>:</p>

<blockquote>
  <p>"The atmosphere of Mars consists of about 96% carbon dioxide, 1.93%
  argon and 1.89% nitrogen along with traces of oxygen and water."</p>
</blockquote>

<p>This contributes as <em>plausible contribution</em> for a lesser rate of oxidation than on earth because the concentration of an oxidizer (i.e., oxygen) is much lower (0.146 vol%, according to the side table, <em>ibid.</em>)  if one assumes absence of processes splitting the <span class="math-container">$\ce{CO2}$</span> to yield oxygen.  To set these values into context (entry <a href="https://en.wikipedia.org/wiki/Earth#Atmosphere" rel="noreferrer">Earth</a>):</p>

<blockquote>
  <p>"A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen,
  0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules. [...] Water vapor content varies between 0.01% and 4% but averages about 1%."</p>
</blockquote>

<p>Equally note that the reported surface temperatures on Mars (min 130 K, mean 210 K, max 308 K) are substantially lower, than on Earth (min 184 K, mean 287.16 K, max 330 K) -- <em>equally</em> slowing oxidation.</p>

<p>About water and atmosphere humidity:  Provided the meteorites get water wetted, said perchlorates could start to work as oxidizer of iron.  In comparison to this, <em>dry</em> perchlorate will remain inactive.  Again, Mars' atmosphere (0.0210 vol% of water vapour, <em>ibid.</em>) seems to be considerably more conservative than Earth's.</p>

<p>You can't have oxidation alone, it is a electrochemical process where some other material in contact with the one oxidized has to be reduced. Corrosion of the meteorites equally could occur if these simultaneously contain grains of metals / alloys differing in the their <a href="https://en.wikipedia.org/wiki/Standard_electrode_potential" rel="noreferrer">electrode potential</a> provided</p>

<ul>
<li><p>these grains  were in close contact with each other, especially if their grain boundary were water wetted, <em>and</em> </p></li>
<li><p>if one of the metals / alloys -- relatively speaking -- would be «less noble», i.e. a material with a more negative reduction potential, than any other grain / material in contact.  The less noble grain than would become a <a href="https://en.wikipedia.org/wiki/Galvanic_anode" rel="noreferrer">galvanic anode</a> and eventually be "eaten away", protecting the other, more noble one, to be oxidized.(<a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/electpot.html" rel="noreferrer">table</a>)  The formation of these little, local <a href="https://en.wikipedia.org/wiki/Electrochemical_cell" rel="noreferrer">electrochemical cells</a> could be even more important if there were <em>salty water</em> droplets on the surface at room temperature and above accelerating corrosion.  (This, by the way, a reason why steel bridges and copper house roofs exposed to the climate and atmosphere of salty seas are more prone to <a href="https://en.wikipedia.org/wiki/Galvanic_corrosion" rel="noreferrer">galvanic corrosion</a> than similar constructions only exposed to fresh water.)  Presence of phosphates in said meteorites however could slow down the oxidation of the meteorites (<a href="https://en.wikipedia.org/wiki/Passivation_(chemistry)" rel="noreferrer">passivation</a>, as assumed for the <a href="https://en.wikipedia.org/wiki/Iron_pillar_of_Delhi" rel="noreferrer">Iron pillar in Dehli</a>).</p></li>
</ul>

<p><em>Note:</em> The initial answer assumed iron meteorites to contain discrete grains, occasionally altogether with grains of other metals.  A comment by<code>@KenFabian</code> pointed out <a href="https://en.wikipedia.org/wiki/Iron_meteorite" rel="noreferrer">iron meteorites</a> however mainly consist of (Fe,Ni) <em>alloys</em>.  Their electrochemical properties may be different to their components (e.g, <a href="https://web.archive.org/web/20150516030826/http://www.corrosionist.com/Galvanic_Series_of_Metal_in_Seawater.htm" rel="noreferrer">table</a>), which the edit aims to include.</p>

CC BY-SA 4.0
2020-03-26T04:44:56.013Z
This pretty much sums it up. There is very little oxygen in the Martian atmosphere. Whatever "trace oxygen" is in the atmosphere, it's at an even lower total pressure, so the partial pressure of oxygen is negligible.
Gimelist
CC BY-SA 4.0
2020-03-26T05:39:56.910Z
Note that metallic meteorites have never been found as pure iron; they are all Nickel-Iron alloys - mostly taenite or kamecite.
Ken Fabian
CC BY-SA 4.0
2020-03-26T09:08:02.910Z
@KenFabian Thank you for pointing out iron meteorites are an alloy.  My edit now aims to include this perspective.
Buttonwood
CC BY-SA 4.0
2020-03-26T10:40:10.930Z
Can you address the two linked items (the "Stirs Controversy" and "Triggers Questions" and see how well this agrees with [Evidence for mechanical and chemical alteration of iron‐nickel meteorites on Mars: Process insights for Meridiani Planum](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JE003672) mentioned in my first comment? I think this answer states some general principles but I don't know how well it matches what's actually known. Also I can't figure out what the answer to "Why don't...?" is exactly. Is it "because Mars is dry" or ""They do after a while"?
uhoh
CC BY-SA 4.0
2020-03-26T10:40:41.167Z
a **tl;dr** would be helpful for me if possible, *Thanks!*
uhoh
CC BY-SA 4.0
2020-03-26T11:14:11.770Z
@uhoh Your first quote (WikiNews' 2005 article) allows: a) metorites found are shiny, because they are young. b) They are old, but because they are sand blasted traces of oxidation are insignificant (Mars' dust storms). c) They are old, but low concentration of oxygen and water (wikipedia's entry about the Martian atmosphere reads almost like a low-pressure inert gas here) slow down oxidation to a minimal rate / there is no significant oxidation.  Source accessed by mine do not indicate if the time since the impact of these meteroites on Mars was determined to exclude either a), b), or c).
Buttonwood
CC BY-SA 4.0
2020-03-26T11:38:28.637Z
@Buttonwood I see, so would the following be at least a rough paraphrase of your answer? "For these particular meteorites we don't know because we don't know how long they've been there. In fact, *even if we did know that*, we still wouldn't know the answer because none of these can be ruled out. However, here are the underlying factors that are at play..."
uhoh
CC BY-SA 4.0
2020-03-26T11:40:11.563Z
I'm perfectly happy finding out that my question can't have a definitive answer. I just want to make sure I understand. *Thanks!*
uhoh
CC BY-SA 4.0
2020-03-26T12:29:11.607Z
@uhoh Re ruling out one in (a,b,c) / narrowing range of age of these metorites: according to http://www.meteoritestudies.com/protected_dating.htm, it is possible to date them.  While the principle is similar to the carbon clock, isotopes determined here by mass spectroscopy were Sr/Rb ratios, a technique dominant till about the 1980s. Maybe the mars rovers (will) use such an analyzer.
Buttonwood
CC BY-SA 4.0
2020-03-26T15:08:33.527Z
$\ce{CO_2}$ can reduce to the monoxide and by doing that, oxidize iron. It is way less oxidizing than oxygen though. But the important key is the low total pressure.
Stian
CC BY-SA 4.0
2020-03-26T02:00:08.477Z
2020-03-26T11:58:35.123Z
2020-03-26T11:58:35.123Z
Buttonwood
<p>Wikipedia's WikiNews' 2005 article <a href="https://en.wikinews.org/wiki/Mars_Rover%E2%80%99s_Basketball-Shaped_Discovery_Stirs_Controversy" rel="noreferrer">Mars Rover’s Basketball-Shaped Discovery Stirs Controversy</a> says:</p>

<blockquote>
  <p>The surface of the meteorite was found to be remarkably free of corrosion. Researchers are as yet unsure whether this means it arrived recently or that it has possibly been sandblasted thoroughly.</p>
</blockquote>

<p>and links to Space.com's <a href="https://www.space.com/707-mars-rover-meteorite-discovery-triggers-questions.html" rel="noreferrer">Mars Rover's Meteorite Discovery Triggers Questions</a></p>

<p>On earth we don't normally see clean, shiny iron surfaces because iron is easily oxidized in a short time even at room temperature by several oxidizing components of air. Some of these are present on Mars but of course at far lower in concentration, but there are other oxidizers including <a href="https://en.wikipedia.org/wiki/Perchlorate" rel="noreferrer">perchlorate</a>. Yet both iron meteorites discovered on Mars that I'm aware of (<a href="https://en.wikipedia.org/wiki/Heat_Shield_Rock" rel="noreferrer">Heat Shield Rock</a> and <a href="https://skyandtelescope.org/astronomy-blogs/astronomy-space-david-dickinson/curiosity-examines-iron-meteorite-egg-rock/" rel="noreferrer">Egg Rock</a>) look clean as do others shown in that Sky &amp; Telescope article.</p>

<p>Is it known why? Have they landed so recently that oxidation hasn't had the time to make much change, or are they <em>sandblasted clean</em> as <a href="https://en.wikipedia.org/wiki/Karen_Steele" rel="noreferrer">Karen Steele</a>'s character Eve McHuron told <s>Kirk</s> one of the miners to do with a dirty cast-iron skillet<sup>†</sup> on the storm-plagued planet Rigel XII.</p>

<p>Photos of these two meteorites taken by Curiosity can be seen in </p>

<ul>
<li><a href="https://astronomy.stackexchange.com/a/31815/7982">this answer</a> to <em>What is the name of meteoroids which hit Moon, Mars, or pretty much anything that isn’t the Earth?</em></li>
<li><a href="https://space.stackexchange.com/a/24660/12102">this answer</a> to <em>Who discovered “Egg Rock”? The Curiosity rover or people?</em></li>
</ul>

<p>Also see <a href="https://mars.nasa.gov/resources/6433/curiosity-finds-iron-meteorite-on-mars/" rel="noreferrer">Curiosity Finds Iron Meteorite on Mars</a></p>

<hr>

<p><sup>†</sup>from <a href="https://scifi.stackexchange.com/a/229030/51174">this answer</a></p>

<p><a href="https://i.sstatic.net/LT9h0.jpg" rel="noreferrer"><img src="https://i.sstatic.net/LT9h0m.jpg" alt="dirty pans being sand-blasted clean on the storm-plagued planet Rigel XII."></a></p>

CC BY-SA 4.0
2020-03-26T00:50:29.017Z
There is further background (and possibly some answers) in [Evidence for mechanical and chemical alteration of iron‐nickel meteorites on Mars: Process insights for Meridiani Planum](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JE003672)
uhoh
CC BY-SA 4.0
2020-03-26T02:09:23.460Z
«Shiny» or not does not need to depend the degree of oxidation.  You get shiny shoes, for example, because the polishing them eventually may smooth the surface to a roughness at magnitude equal to or below of the wavelength of observation.  Like if you grind a parabola antenna to cook a meal (e.g, first part of https://www.youtube.com/watch?v=RWX5HH6HyPI).  Beside albedo ...
Buttonwood
CC BY-SA 4.0
2020-03-26T02:10:50.647Z
@Buttonwood show me some *oxidized yet shiny iron* from a natural environment. The question is about the chemical and physical processes associated iron oxidized by environmental conditions, not shoes and parabolae.
uhoh
CC BY-SA 4.0
2020-03-26T02:14:05.673Z
A rusty surface is not smooth, it this much porous that oxidation advances till the ground.  Copper, on the other hand, passivates and is not «eaten away» this way.
Buttonwood
CC BY-SA 4.0
2020-03-26T02:19:44.100Z
@Buttonwood that's right, but *neither of those* are shiny, I've never seen a shiny oxidized coin for example. Dark surfaces can still by shiny (e.g. black marble or obsidian) but oxidized surfaces of iron or copper alloys no longer produce specular reflections. A single crystal of pure copper oxide can demonstrate Fresnel reflection but the oxidized surface of a copper crystal will be dull. This seems like it can evolve into a new question somehow:-)
uhoh
CC BY-SA 4.0
2020-03-26T12:43:06.177Z
@uhoh hematite, either crystalline, secular, or well weathered (moqui marbles).
John
CC BY-SA 4.0
2020-03-26T13:23:20.053Z
@John I'm not sure what you are saying exactly and I don't know much about how hematite is formed. Does it start as iron and then get oxidized by environmental conditions?
uhoh
CC BY-SA 4.0
2020-03-26T20:41:11.223Z
@uhoh As side note I _speculate_ `@John` referred to pictures like «A rare pseudo-scalenohedral crystal habit» https://en.wikipedia.org/wiki/Hematite (the entry equally mentiones its use as jewelery as well as occurences on Mars), the title picture for the Czech (https://cs.wikipedia.org/wiki/Hematit) and Spanish (https://es.wikipedia.org/wiki/Hematita) wikipedia of $\ce{Fe2O3}$, or the «Perfekt gewachsener Hämatit-Skalenoeder von der Insel Hormus, Iran » on https://de.wikipedia.org/wiki/Hämatit of high reflectance but still share the rust-red streak.
Buttonwood
CC BY-SA 4.0
2020-03-27T01:39:50.247Z
@Buttonwood I see!, I'm guessing that those perfectly formed beautiful crystals didn't just grow on a piece of iron exposed to the elements, it's likely some substantial amount of heat and/or pressure were involved.
uhoh
<geochemistry><meteorite>
Why don't iron meteorites on Mars rust or oxidize? Why are they shiny?
uhoh
# Why don't iron meteorites on Mars rust or oxidize? Why are they shiny?

(Asked by: username_0 on 2020-03-26)

Wikipedia's WikiNews' 2005 article [Mars Rover’s Basketball-Shaped Discovery Stirs Controversy](https://en.wikinews.org/wiki/Mars_Rover%E2%80%99s_Basketball-Shaped_Discovery_Stirs_Controversy) says:

> The surface of the meteorite was found to be remarkably free of corrosion. Researchers are as yet unsure whether this means it arrived recently or that it has possibly been sandblasted thoroughly.

and links to Space.com's [Mars Rover's Meteorite Discovery Triggers Questions](https://www.space.com/707-mars-rover-meteorite-discovery-triggers-questions.html)

On earth we don't normally see clean, shiny iron surfaces because iron is easily oxidized in a short time even at room temperature by several oxidizing components of air. Some of these are present on Mars but of course at far lower in concentration, but there are other oxidizers including [perchlorate](https://en.wikipedia.org/wiki/Perchlorate). Yet both iron meteorites discovered on Mars that I'm aware of ([Heat Shield Rock](https://en.wikipedia.org/wiki/Heat_Shield_Rock) and [Egg Rock](https://skyandtelescope.org/astronomy-blogs/astronomy-space-david-dickinson/curiosity-examines-iron-meteorite-egg-rock/)) look clean as do others shown in that Sky & Telescope article.

Is it known why? Have they landed so recently that oxidation hasn't had the time to make much change, or are they *sandblasted clean* as [Karen Steele](https://en.wikipedia.org/wiki/Karen_Steele)'s character Eve McHuron told ~~Kirk~~ one of the miners to do with a dirty cast-iron skillet† on the storm-plagued planet Rigel XII.

Photos of these two meteorites taken by Curiosity can be seen in

* [this answer](https://astronomy.stackexchange.com/a/31815/7982) to *What is the name of meteoroids which hit Moon, Mars, or pretty much anything that isn’t the Earth?*
* [this answer](https://space.stackexchange.com/a/24660/12102) to *Who discovered “Egg Rock”? The Curiosity rover or people?*

Also see [Curiosity Finds Iron Meteorite on Mars](https://mars.nasa.gov/resources/6433/curiosity-finds-iron-meteorite-on-mars/)

---

†from [this answer](https://scifi.stackexchange.com/a/229030/51174)

[![dirty pans being sand-blasted clean on the storm-plagued planet Rigel XII.](https://i.sstatic.net/LT9h0m.jpg)](https://i.sstatic.net/LT9h0.jpg)

**Tags:** geochemistry, meteorite

> **Comments:**
> **username_0**: There is further background (and possibly some answers) in [Evidence for mechanical and chemical alteration of iron‐nickel meteorites on Mars: Process insights for Meridiani Planum](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JE003672)  
> **username_1**: «Shiny» or not does not need to depend the degree of oxidation.  You get shiny shoes, for example, because the polishing them eventually may smooth the surface to a roughness at magnitude equal to or below of the wavelength of observation.  Like if you grind a parabola antenna to cook a meal (e.g, first part of https://www.youtube.com/watch?v=RWX5HH6HyPI).  Beside albedo ...  
> **username_0**: @username_1 show me some *oxidized yet shiny iron* from a natural environment. The question is about the chemical and physical processes associated iron oxidized by environmental conditions, not shoes and parabolae.  
> **username_1**: A rusty surface is not smooth, it this much porous that oxidation advances till the ground.  Copper, on the other hand, passivates and is not «eaten away» this way.  
> **username_0**: @username_1 that's right, but *neither of those* are shiny, I've never seen a shiny oxidized coin for example. Dark surfaces can still by shiny (e.g. black marble or obsidian) but oxidized surfaces of iron or copper alloys no longer produce specular reflections. A single crystal of pure copper oxide can demonstrate Fresnel reflection but the oxidized surface of a copper crystal will be dull. This seems like it can evolve into a new question somehow:-)  
> **username_2**: @username_0 hematite, either crystalline, secular, or well weathered (moqui marbles).  
> **username_0**: @username_2 I'm not sure what you are saying exactly and I don't know much about how hematite is formed. Does it start as iron and then get oxidized by environmental conditions?  
> **username_1**: @username_0 As side note I _speculate_ `@username_2` referred to pictures like «A rare pseudo-scalenohedral crystal habit» https://en.wikipedia.org/wiki/Hematite (the entry equally mentiones its use as jewelery as well as occurences on Mars), the title picture for the Czech (https://cs.wikipedia.org/wiki/Hematit) and Spanish (https://es.wikipedia.org/wiki/Hematita) wikipedia of $\ce{Fe2O3}$, or the «Perfekt gewachsener Hämatit-Skalenoeder von der Insel Hormus, Iran » on https://de.wikipedia.org/wiki/Hämatit of high reflectance but still share the rust-red streak.  
> **username_0**: @username_1 I see!, I'm guessing that those perfectly formed beautiful crystals didn't just grow on a piece of iron exposed to the elements, it's likely some substantial amount of heat and/or pressure were involved.  

---

## 1 answers

### Answer by username_1 on 2020-03-26. Score: 12 | Accepted answer

**tl;dr**: Compared to Earth, the atmosphere on Mars is very thin; in addition, it contains much less of oxygen and water (i.e., is very dry). It is much colder there. These conditions may slow down oxidation to an irrelevant rate.

For an object of pure iron, note that according to the English Wikipedia about [Mars](https://en.wikipedia.org/wiki/Mars#Atmosphere):

> "The atmosphere of Mars consists of about 96% carbon dioxide, 1.93%
> argon and 1.89% nitrogen along with traces of oxygen and water."

This contributes as *plausible contribution* for a lesser rate of oxidation than on earth because the concentration of an oxidizer (i.e., oxygen) is much lower (0.146 vol%, according to the side table, *ibid.*) if one assumes absence of processes splitting the $\ce{CO2}$ to yield oxygen. To set these values into context (entry [Earth](https://en.wikipedia.org/wiki/Earth#Atmosphere)):

> "A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen,
> 0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules. [...] Water vapor content varies between 0.01% and 4% but averages about 1%."

Equally note that the reported surface temperatures on Mars (min 130 K, mean 210 K, max 308 K) are substantially lower, than on Earth (min 184 K, mean 287.16 K, max 330 K) -- *equally* slowing oxidation.

About water and atmosphere humidity: Provided the meteorites get water wetted, said perchlorates could start to work as oxidizer of iron. In comparison to this, *dry* perchlorate will remain inactive. Again, Mars' atmosphere (0.0210 vol% of water vapour, *ibid.*) seems to be considerably more conservative than Earth's.

You can't have oxidation alone, it is a electrochemical process where some other material in contact with the one oxidized has to be reduced. Corrosion of the meteorites equally could occur if these simultaneously contain grains of metals / alloys differing in the their [electrode potential](https://en.wikipedia.org/wiki/Standard_electrode_potential) provided

* these grains were in close contact with each other, especially if their grain boundary were water wetted, *and*
* if one of the metals / alloys -- relatively speaking -- would be «less noble», i.e. a material with a more negative reduction potential, than any other grain / material in contact. The less noble grain than would become a [galvanic anode](https://en.wikipedia.org/wiki/Galvanic_anode) and eventually be "eaten away", protecting the other, more noble one, to be oxidized.([table](http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/electpot.html)) The formation of these little, local [electrochemical cells](https://en.wikipedia.org/wiki/Electrochemical_cell) could be even more important if there were *salty water* droplets on the surface at room temperature and above accelerating corrosion. (This, by the way, a reason why steel bridges and copper house roofs exposed to the climate and atmosphere of salty seas are more prone to [galvanic corrosion](https://en.wikipedia.org/wiki/Galvanic_corrosion) than similar constructions only exposed to fresh water.) Presence of phosphates in said meteorites however could slow down the oxidation of the meteorites ([passivation](https://en.wikipedia.org/wiki/Passivation_(chemistry)), as assumed for the [Iron pillar in Dehli](https://en.wikipedia.org/wiki/Iron_pillar_of_Delhi)).

*Note:* The initial answer assumed iron meteorites to contain discrete grains, occasionally altogether with grains of other metals. A comment by`@username_4` pointed out [iron meteorites](https://en.wikipedia.org/wiki/Iron_meteorite) however mainly consist of (Fe,Ni) *alloys*. Their electrochemical properties may be different to their components (e.g, [table](https://web.archive.org/web/20150516030826/http://www.corrosionist.com/Galvanic_Series_of_Metal_in_Seawater.htm)), which the edit aims to include.

> **Comments:**
> **username_3**: This pretty much sums it up. There is very little oxygen in the Martian atmosphere. Whatever "trace oxygen" is in the atmosphere, it's at an even lower total pressure, so the partial pressure of oxygen is negligible.  
> **username_4**: Note that metallic meteorites have never been found as pure iron; they are all Nickel-Iron alloys - mostly taenite or kamecite.  
> **username_1**: @username_4 Thank you for pointing out iron meteorites are an alloy.  My edit now aims to include this perspective.  
> **username_0**: Can you address the two linked items (the "Stirs Controversy" and "Triggers Questions" and see how well this agrees with [Evidence for mechanical and chemical alteration of iron‐nickel meteorites on Mars: Process insights for Meridiani Planum](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JE003672) mentioned in my first comment? I think this answer states some general principles but I don't know how well it matches what's actually known. Also I can't figure out what the answer to "Why don't...?" is exactly. Is it "because Mars is dry" or ""They do after a while"?  
> **username_0**: a **tl;dr** would be helpful for me if possible, *Thanks!*  
> **username_1**: @username_0 Your first quote (WikiNews' 2005 article) allows: a) metorites found are shiny, because they are young. b) They are old, but because they are sand blasted traces of oxidation are insignificant (Mars' dust storms). c) They are old, but low concentration of oxygen and water (wikipedia's entry about the Martian atmosphere reads almost like a low-pressure inert gas here) slow down oxidation to a minimal rate / there is no significant oxidation.  Source accessed by mine do not indicate if the time since the impact of these meteroites on Mars was determined to exclude either a), b), or c).  
> **username_0**: @username_1 I see, so would the following be at least a rough paraphrase of your answer? "For these particular meteorites we don't know because we don't know how long they've been there. In fact, *even if we did know that*, we still wouldn't know the answer because none of these can be ruled out. However, here are the underlying factors that are at play..."  
> **username_0**: I'm perfectly happy finding out that my question can't have a definitive answer. I just want to make sure I understand. *Thanks!*  
> **username_1**: @username_0 Re ruling out one in (a,b,c) / narrowing range of age of these metorites: according to http://www.meteoritestudies.com/protected_dating.htm, it is possible to date them.  While the principle is similar to the carbon clock, isotopes determined here by mass spectroscopy were Sr/Rb ratios, a technique dominant till about the 1980s. Maybe the mars rovers (will) use such an analyzer.  
> **username_5**: $\ce{CO_2}$ can reduce to the monoxide and by doing that, oxidize iron. It is way less oxidizing than oxygen though. But the important key is the low total pressure.  

---

