A New Explanation for Why Mars is Red

Well that’s ruined all my lectures! I’ve spent years talking about space and a go to fact is the red colour of Mars. It’s been long believed that it was caused by the same chemical process that creates rust on Earth, a new paper suggests this is not the case! The team of researchers simulated conditions of Mars in a lab and now think a chemical called ferrihydrite, an iron oxide that contains water. It now looks like the planet’s characteristic red colour is due to a time when Mars was covered in water! 

Mars, often called the Red Planet is the fourth planet from the Sun. With a thin atmosphere composed mostly of carbon dioxide, Mars features a stark landscape of vast plains, huge volcanoes including Olympus Mons (the largest in our solar system), and deep canyons like Valles Marineris. Its surface has evidence of ancient rivers and lakes, suggesting Mars once had conditions that could have been suitable for microbial life. Its extreme temperature changes and frequent global dust storms are typical of this harsh world. 

The distinctive red colour goes back centuries; the ancient Egyptians called Mars ‘Her Desher’ which translates to ‘the Red One’, the Romans named it after the God of war and the Chinese called it ‘the fire star.’ Even Babylonian records that go back to 2000 BC noted its red colour. In 1610, when Galileo first observed Mars through a telescope, he confirmed its planetary nature but also noted a more red/brown hue. This was largely due to the poor quality optics of the day and it wasn’t until optics improved that its red colour was observed in all its glory.

A team of researchers led by Dr Adomas Valantinas from Brown University in USA have published a paper in Nature Communications that has analysed the red colouration of Mars and challenge the common view that it’s a rust like material that is responsible. They used data from a number of different Mars missions from NASA’s Reconnaissance Orbiter to ESA’s Mars Express and ExoMars (which has the Colour and Stereo Surface Imaging System onboard.) The data from the orbiters was supported by data from various rovers too and further supplemented by analysis of artificial Mars-like materials in a laboratory.

The analysis, which included experiments and measurements at the University of Grenoble, Brown University and the University of Winnipeg revealed the presence of Ferrihydrite. Not only was it present in the Martian dust, it seemed to be widespread across the Martian landscape. Ferriydrite is an oxyhydroxide mineral (one that contains oxygen, hydrogen and at least one metal.)

The widespread discovery of ferrihydrite on in Martian dust helps us to understand more about the geological history of Mars and its potential habitability. The existence of the ferrihydrite tells us that there were once cooler, wet conditions on Mars since that is a neccessity for the formation of the mineral. It’s an exciting discovery because its one more reason to believe that Mars was once a hospitable world. 

The team are keen to learn more and are now waiting for Martian samples to study directly and for that, they are waiting for the Perseverance rover. It has been systematically collecting core samples of Martian soil from the Jezero Crater and storing them in titanium tubes ready for transport home. Once the team has these, they will be able to check whether their theory about ferrihydrite is correct.

Source : Why Mars could be red

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