Mars was not always red, according to a new theory for how the planet took on its characteristic ruddy hue.
Until recently, Mars’ color was thought to be a product of liquid water, which scientists think flowed over the planet’s surface billions of years ago, rusting rocks. But after the Mars Exploration Rovers Spirit and Opportunity landed on the planet in 2004, they found evidence of certain minerals that would have been destroyed by water, suggesting that the red dust on Mars never came into contact with flowing water.
“That was a surprise to everybody,” said Jonathan Merrison of the Aarhus Mars Simulation Laboratory in Denmark.