Nasa's Mars rover Curiosity has found evidence of ancient lakes and wet underground environments that changed billions of years ago.
This is an indication that the planet could have supported life for millions of years.
The rover arrived on Mars four years ago to determine if the planet ever had the ingredients for life. To answer that question, it has been been drilling into rocks, recently discovering the element boron for the first time.
"Gale Crater, which is the site where Curiosity landed, could have been a habitable environment for tens to even hundreds of millions of years and that would have been represented by ancient lakes but also groundwater systems with fluid circulating," said John Grotzinger, Nasa lead scientist for the Mars rover.
But Curiosity has had to halt its trek temporarily while engineers fix a problem with one of its key drilling instruments, although the difficulties of exploring Mars have not diminished its allure - outgoing US President Barack Obama has pledged to send people to the Red Planet by the 2030s.