Is the reason Mars is red because its surface contains a lot of iron? (When dirt is red on Earth, it is sometimes caused by a high amount of iron).

If so, does Mars contain more iron than the earth?

  • 3
    $\begingroup$ Similar question on Space Exploration: How much iron is on the surface of Mars? $\endgroup$
    – called2voyage
    Commented Oct 19, 2015 at 19:07
  • $\begingroup$ here's another link space.com/16999-mars-red-planet.html $\endgroup$ Commented Oct 31, 2015 at 14:44
  • $\begingroup$ Mercury, on the other hand, has more iron throughout than Earth, which is why it's so dense despite its iron core being under less pressure than the Earth's. I don't know how the iron in its crust compares with Earth's. $\endgroup$ Commented Sep 13, 2017 at 1:47

3 Answers 3


Mars definitely has far less Iron than Earth. Mars has 10.7% of Earth's mass. On the other hand, Iron comprises 32% of Earth since there is so much Iron in its inner core, outer core, and the mantle. That means if Mars was made entirely of Iron (which it is not), Earth would still have more than 3 times as much Iron.

You are right that Mars has more Iron at its surface than Earth so it looks very red. Earth has many other metals on its surface (not to mention water to make it look blue and plants to make it look green).


Unless 100+ years of studying solar system formation didn't get us anywhere then you'd actually predict that mars would have less iron than earth (in relative terms). This is because the further out in the solar system you go, the lighter the materials that make up the celestial bodies become. You start off with the inner planets for example, which are made of rock and metal. At its most extreme is mercury, which has a metallic core that makes up the vast majority of its volume. As you start to move to the outer parts, there's much less metal. Even further out rocky material starts to peter until you're just left with frozen ices and covalent compounds. This pattern exists because when the solar system formed the heavier materials condensed near the centre while the lighter gases were blown away to the edges. Mars, being the last terrestrial planet, should have formed in an orbit that had less iron and heavy materials than earth and all the other rocky bodies.

However, its good to bet that on average there is more relative iron on mars surface than there is on earth. This would be because despite it's lower abundance of iron overall, it's much more spread out among the lithosphere rather than being entirely concentrated deep in its core like on earth. Mars being smaller planet might not have ever built up enough heat during its formation to completely liquefy its surface, which a planet needs in order for the heavier materials to sink to the centre, making differentiated layers such as the ones we see on earth like the crust, core and mantle etc. Don't get me wrong, mars does have these differentiated layers, but they probably aren't as pronounced as they are here on earth. This is what I think we can safely say is thus the reason for mar's red surface, despite it's location in the solar system.


The iron on Earth is being taken from the upper crust in well known processes of subduction. Earth has less iron on its surface because it is being depleted through the process of subduction which has been going on for billions of years on Earth. This process is yet to occur on Mars which is why there is very little granite on Mars surface as opposed to Earth where the continents cover a good portion of the planet.

Subduction cannot take place on Mars, because it sits outside the habitable zone. The good thing for Mars is that it will find itself in the habitable zone in the distant future because our star is growing in size and temperature. This will cause the habitable zone to move outward, and Earth will find itself unable to maintain water at this juncture and the viable planet will be Mars.

The key here is that Mars is inside out where the iron is on its surface causing the planet to appear smaller than Earth, because its silicate is in the inside while the iron is on the outside. Basically Earth through subduction has managed to turn the planet inside out allowing for Earth to grow from decompression. The iron is migrating toward the core in subduction processes because it does not melt and rise with the rest of the subducted basaltic plate to form continents it sinks to increase centripetal force and increase gravity because gravity stems from the core, the denser the core the deeper the indention on space time. Mars is compressed and its core is a silicate where Earths is now iron giving earth the greater magnetic field yet the magnetic field on Mars surface is greater than earths.

Mars' rotation period is 24 hours and its axis are tilted like Earth's and it will sit in the habitable zone where the iron will have a chance to work its way to the center of the planet as it has on Earth.


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