Comet Enthusiast

"We can now say that the planet was altered on a global scale by liquid water about four billion years ago."

John Carter of the University of Paris

Minerals in northern Mars craters observed by two NASA orbiters suggest that a phase in Mars' early history with conditions favorable to life occurred globally, not just in the south.

Southern and northern Mars differ in many ways, so the extent to which they shared ancient environments has been open to question.