The water on Mars is gone. Maybe that’s where it happened.

The problem with this story, said Renyu Hu, a scientist with NASA’s Jet Propulsion Laboratory and another author of the current science article, is that Mars did not lose hydrogen quickly enough. Measurements made by NASA’s Mars Atmosphere and Volatile Evolution orbiter, or MAVEN, have shown that the current rate, extrapolated over 4 billion years, “may only represent a small fraction of the water loss.” Hu said. “This is not enough to explain the great drying up of Mars.”