The Red Planet was once a vibrant blue water-world, home to raging rivers, active volcanoes, and even an ocean. But as the young planet’s core cooled, its magnetic field and protective atmosphere faded, eventually exposing it to the wrath of the sun. With its volcanoes extinguished and its water lost to space, Mars became the frozen desert planet we know today. But if it once had many of the ingredients necessary to form life, how far along might that process have gotten?

• Konstantin Batygin
• David Grinspoon