An ocean the size of the Arctic once covered half of Mars, new images hint

Image of a planet in space. The planet has red land masses surrounded by large areas of blue water dotted with white clouds. .

New evidence of ancient rivers suggests Mars may have been a "blue planet," thanks to an ocean spanning its entire northern hemisphere.

Cameras from several Mars orbiters captured the dusty remnants of apparent river deltas, which were described in research published Jan. 7 in the journal NPJ Space Exploration.