Deep under the ice of the Martian south pole researchers have discovered signs of a hidden lake that could hold liquid water year-round, a crucial condition needed for life to develop.

An advanced satellite radar has found a massive anomaly—a 12-mile-long lake that researchers believe must be at least a meter thick. Previous discoveries on Mars have indicated liquid water that existed only seasonally.

“This is the first potential habitat,” said researcher Roberto Orosei at the Italian National Institute for Astrophysics. “We don’t know it is inhabited, but if you’re looking for life on Mars, this is one of the prime places to look.”

Dr. Orosei and an international team of researchers probed through to the bottom of about a mile of ice on the planet’s south pole using a radar aboard the Mars Express Satellite, a European Space Agency mission. The Italy-based researchers published in Science on Wednesday the results of four years of radar readings. The lake, they say, was found because it produces different radar readings than the surrounding ice and bedrock.

“If the result can be confirmed, it would be the largest known occurrence of present-day liquid water on Mars,” said Jeffrey Plaut at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who is the U.S. leader on the joint U.S.-Italy project that developed the radar system.