Why is Mars red? Planet's appearance and lost atmosphere explained - and whether life on Mars is possible
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NASA has successfully landed its new robot on the surface of Mars.
The vehicle, thought to be in “great shape” after its landing, will spend at least two years searching the Red Planet for evidence of past life.
But why is Mars that colour - and why has did it lose its atmosphere?
Here is everything you need to know about the planet, including whether life on Mars is possible.
Why is Mars red?
Mars, the fourth planet from the sun, is Earth’s neighbour at 206 million kilometers away.
The planet is about half the size of ours, and it has a completely different surface which is littered in canyons, craters and volcanoes.
But perhaps its most recognisable feature is its red hue - precisely the reason that was named after the Greek god of war.
Mars, which often appears in the sky as a bright red star, is red as it is covered in iron oxide.
This is the same compound that gives blood and rust that distinctive colour.
Scientists are not clear on how all the iron oxide ended up on the surface of the Red Planet.
Mars formed around 4.5 billion years ago, when debris, gas and dust began coalescing, and among these materials was iron that formed within dead stars.
While the iron on Earth sank to its core when the planet was young, scientists believe the same didn’t happen on Mars because of its weaker gravity and smaller size.
This could be why so much iron is found in the planet’s upper crust.
Iron alone does not have a red colour, so Mars’ surface iron must have become oxidised at some point to form iron oxide, or rust.
It is thought that this mass oxidation happened at the time when Mars had flowing water and a thick atmosphere - conditions similar to that of modern day Earth.
If an iron-rich spoon is left outside or in water for a long time it will rust.
Scientists believe a very similar process occurred on Mars to cover it in iron oxide and turn it red.
Why did Mars lose its atmosphere?
Today, Mars has a thin atmosphere.
The volume of gases, mainly made up of carbon dioxide, is less than one per cent of Earth’s.
Yet scientists believe the planet was once much warmer and wetter, suggesting that the Martian atmosphere could have been a lot thicker to create a strong greenhouse effect that trapped the Sun’s light.
Multiple missions to the planet have shown that, up until around four billion years ago, Mars had a strong magnetic field created by currents of molten metals in its core.
However, Mars cooled internally which switched off this global magnetic field.
Without it, the planet was less protected from solar wind - the stream of energetic charged particles that flow from the sun.
Scientists think that this solar wind stripped away most of the Red Planet’s atmosphere over a few hundred million years.
The loss of a large part of its atmosphere caused Mars to transition from a warm, wet climate to the cold and dry one we know of today.
Earth has retained its magnetic field, which deflects the solar wind, so our atmosphere has stayed in tack allowing life to develop and thrive.
Is life on Mars possible?
The Perseverance rover’s main mission is to look for evidence of past life on Mars.
The 28-mile-wide crater it has landed in, Jezero, is thought to have held a giant lake billions of years ago.
Where there has been water, there is the possibility there might also have been life.
However, this life - if it exists - will most likely take the form of extinct microbes.
The rover will gather samples of Martian rocks and soils using its drill, before storing the cores in tubes on the planet’s surface ready for a return mission to bring them back to Earth in the early 2030s.
Unfortunately, modern-day Mars is too hostile a condition for life.
The planet is too cold for water to stay as liquid on its surface, and its thin atmosphere lets in high levels of radiation which could potentially sterilise the upper part of the soil.
Yet, it wasn’t always like this on the Red Planet.
More than 3.5 billion years ago, scientists think water flowed on its surface due to its river-like features and spreading deltas.
The thicker carbon dioxide atmosphere would have blocked out more of the harmful radiation.
As water is a common ingredient in biology, it seems plausible that microorganisms once inhabited the ancient Red Planet.