Italian scientists have discovered evidence of a lake with liquid water below the surface of Mars, according to a report published in Science on Wednesday. The researchers examined the planet’s southern icecaps between 2012 and 2015, using the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). MARSIS sent radio waves through the icecaps and determined the rate at which they reflected back. A mile below the surface, the pulses changed, leading to the discovery of the 12.5 mile-wide lake, which is similar to lakes found beneath Earth’s ice sheets. Scientists said the reflections’ brightness signified that there was water. This is the first evidence of stable liquid water on the planet, although scientists have hypothesized its presence for many years.