Today Mars is a dry, rust-colored rock.
But it wasn't always that way. One of science's biggest recent revelations is that, billions of years ago, the red planet used to be blue.
Now, a study published Thursday in Nature Scientific Reports not only adds to the evidence that Mars did indeed have vast oceans, but also suggests tsunamis that were hundreds of feet tall — also called mega-tsunamis — once ravaged those ancient seas, playing a major role in shaping the geography of the planet.
Researchers used imagery from NASA's Mars Odyssey and Orbital Reconnaissance programs to discover geologic evidence of at least two mega-tsunamis, each separated by millions of years, that flooded and scoured the face of a wet, ancient Mars.
The ancient coasts of Mars
The discovery emerged from a riddle posed by major variations in elevation on Mars.
Those variations revealed the coasts of an ancient Martian ocean, yet larger variations conflicted with the relatively consistent height of shores seen on Earth.
Researchers involved with the new study, however, realized one thing could account for the discrepancy: Mega-tsunamis.
"The finding that tsunami deposits actually dominate the coastal morphologies of the early Mars ocean comes as a surprise," lead author J. Alexis Rodriguez told Tech Insider in an emailed statement.
A huge meteorite crashing into the ocean of Mars' northern hemisphere likely triggered the first tsunami some 3.4 billion years ago, Rodriguez said.
Both waves were absolutely enormous. When they plowed into the Martian shore, they ranged from 32 feet to 400 feet in height, and had a surface area of 386,000 square miles — large enough to cover much of the western US.
That's not larger than the biggest-known mega-tsunami on Earth — that 1,720-foot colossus hit Lituya Bay, Alaska, in 1958.
But even average-sized tsunamis on Mars, which the geologic data suggest reached 164 feet, would be tall enough to submerge the Statue of Liberty.
The highest waves would have almost entirely drowned a 40-story building.
Anatomy of a Martian tsunami deposit
The bigger, second tsunami was also triggered by a meteor impact in the ocean, but the climate of Mars had cooled and sea levels had dropped in the millions of intervening years.
Like on Earth, the flood of water created channels and dragged sediment and rocks toward the ocean to create irregular patterns in rocks and soil.
Erosion typically hides such deposits or makes them disappear rather quickly, or at least here on Earth. But the process is much slower on Mars, which rapidly lost its water and atmosphere, allowing the scientists to discover evidence of the mega-tsunamis with satellite images billions of years later.
When the 400-foot-tall mega-tsunami approached the shore, ice crystals began formed in the moving water and turned it into an icy slurry. The slush eventually froze solid as it spread out over the land, reaching 400 miles or more inland.
When the tsunamis froze, they became "lobes" still visible on the surface of Mars today. These landforms were rocky and icy, but contained enough salt to delay freezing for millions of years.
Rodriguez said the possibility of ancient mega-tsunamis occurred to him while he was examining the geology of Mars' northern plains. These flows, he realized, were very similar to ones on Earth.
"There are not many processes in nature that can produce these kinds of features," he said.
Many of these lobes are so well-preserved that the researchers believe we may be able to analyze them to find if the composition of the oceans was potentially suitable for life.
Similar conditions — briny, liquid solutions sitting at temperatures below freezing — are "known to be habitable environments on Earth," co-author and Spanish astrobiologist Alberto Fairen told Tech Insider in an emailed statement, "and consequently, some of the tsunami deposits might be prime astrobiological targets."
Join the conversation about this story »
NOW WATCH: A mysterious ocean on a frozen moon may have the perfect conditions for alien life