Elon Musk believes Mars can be settled by 2050, but a Rice University professor's new book reveals the many biological challenges humans would face trying to colonize the Red Planet.
Scientists have found carbon residue in Martian rocks, indicating that an ancient carbon cycle existed. It means Mars was likely once warm enough to sustain life.
In most photos, the surface of Mars looks like an empty red wasteland. But if you look a bit closer, the remnants of an ancient alien civilization begin to take shape.