Scientists have been arguing for years about ambiguous radar scans of Mars’ south pole. Do they reveal underground lakes of liquid water? Or something else? Two new papers out this week have added even more intrigue to the controversy.

In 2018, a team of Italian scientists claimed to have discovered a subglacial lake near the Martian south pole using radar data from the Mars Express satellite. The discovery was met with skepticism, with other scientists suggesting alternatives like lumps of clay that could have produced the same reflection patterns. It’s a heady debate, because of water’s implications for life. While most scientists agree that Mars used to be very wet, the H2O it has left seems to be all ice.