Think of weather on Mars, and sandstorms are more likely to come to mind than tsunamis. But researchers have just figured out that the Martian surface was likely struck not once – but twice – by asteroids that set off gigantic waves in seas that likely existed on the Red Planet in its early days.

It has been previously postulated that an area of Mars in the upper hemisphere known as the Martian northern lowlands was once covered in a large ocean. But, according to the researchers, there has never been sufficient proof of an ancient shoreline.

By using mapping techniques including thermal imaging, the researchers believe they have found such proof.

In a paper published on May 19 in the journal Scientific Reports, the team says it believes it has found evidence that points to the fact that the Red Planet had two enormous tsunamis wash across its surface millions of years apart, likely caused by asteroid impacts.

"About 3.4 billion years ago, a big meteorite impact triggered the first tsunami wave," says Alberto Fairén, Cornell visiting scientist in astronomy and principal investigator at the Center of Astrobiology, Madrid. "This wave was composed of liquid water. It formed widespread backwash channels to carry the water back to the ocean."

By the time the second asteroid impacted Mars, the planet had undergone a serious cooling of its atmosphere and its water had largely turned to ice. When the impact occurred, it formed rounded lobes of ice that never returned to the ocean. This implies that it was at least partially frozen at the time, says lead author Alexis Rodriguez from the Planetary Science Institute.

"Our paper provides very solid evidence for the existence of very cold oceans on early Mars," says Rodriquez. "It is difficult to imagine Californian beaches on ancient Mars, but try to picture the Great Lakes on a particularly cold and long winter, and that could be a more accurate image of water forming seas and oceans on ancient Mars."

The craters left by both asteroid impacts measure about 30 km (19 miles) across and, the researchers say, could have resulted in onshore waves that were about 50 meters (164 ft) high.

Fairén adds that the site where the ice lobes once stood might be a good spot for searching for signs of past life on Mars.

"Cold, salty waters may offer a refuge for life in extreme environments, as the salts could help keep the water liquid," he says. "If life existed on Mars, these icy tsunami lobes are very good candidates to search for biosignatures."