The discovery of potentially vast deposits of water ice close to the surface on Mars could breath new life into the notion of sending humans to explore the red planet. This week, scientists poring over data from NASA’s Mars Odyssey orbiter released evidence indicating that large regions near the planet’s poles collectively hold enough water to fill Lake Michigan twice. As a result, James Longuski, professor of aeronautics and astronautics at Purdue University explains, large quantities of accessible water on Mars could drastically cut the cost and time required to mount a mission to the red planet by reducing the amount of material, including hydrogen, that would have to be launched from Earth. “Now scientists are telling us that the hydrogen is already there waiting for us!” Mr. Longuski says.