What gives the soil on Mars its red colour, lending our planetary neighbour its moniker the Red planet?

By Penny Wozniakiewicz

Published: Friday, 24 March 2023 at 12:00 am

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When viewed from the Earth, either through a telescope on the ground or by the more sophisticated optics of Earth orbiting space telescopes, the reddish colour of Mars is evident.

Indeed, Mars’s striking colour has led to it commonly being referred to as ‘the Red Planet’.

A plethora of spacecraft, including several landers like Curiosity rover and Perseverance rover, have now visited and documented Mars in some detail, revealing the surface to be more butterscotch in tone.

 

Mars’s red colour is not restricted to its surface either – its atmosphere also exhibits a reddish hue.

Mars’s red colour stems from the presence of an iron oxide mineral called Haematite, which is red when powdered, and this is present in a thin surface covering of soil over the planet.

These Haematite grains are extremely fine.

Some are so fine that even in the thin Martian atmosphere they can become lofted up, adding red colour there too.

How did Mars get its red colour?

How did the haematite powder that gives Mars its red colour form?

The exact process is still debated, with possible explanations put forward including chemical reactions of precursor metallic iron or another iron oxide mineral called magnetite with water, molecular oxygen or even hydrogen peroxide.

It has also been suggested that haematite can be produced simply by physically breaking up magnetite grains alongside other minerals, which provide additional oxygen to convert it to haematite.

Has Mars always been red?

Mars has not always been red – in its distant past, Mars is thought to have been more like Earth, with large bodies of liquid water on its surface, a much thicker atmosphere and active volcanoes.

When the atmosphere and water disappeared and the volcanoes went quiet, wind based – or Aeolian – erosion took over and the red soil we see today formed.

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