Astronomers have filled a large gap in knowledge about Mars’ water cycle. Their research on water percolating from surface to aquifer could change the picture of what early Mars was like, suggesting that less of the planet’s water may have been available to become rain and refill lakes and oceans.

Billions of years ago, water flowed on the surface of Mars. But scientists have an incomplete picture of how the Red Planet’s water cycle worked.

That could soon change after two graduate students at The University of Texas at Austin filled a large gap in knowledge about Mars’ water cycle — specifically, the part between surface water and groundwater.