The findings of a new study support a controversial hypothesis that Mars had oceans billions of years ago.
Astronomers from the Planetary Science Institute reported Thursday in the journal Scientific Reports that they found evidence of two giant tsunamis that could have been triggered by meteorites that slammed into the surface of the Red Planet and propelled water into 164-foot waves, or even double that. Evidence of these giant surges backs the ocean hypothesis, say paper authors.
"If you find tsunami deposits, there was an ocean," J. Alexis P. Rodriguez, a biologist at the institute in Tucson, Ariz. tells The Christian Science Monitor in an interview.
Astronomers know that there was liquid water on ancient Mars based on the planet's barren and dry landscape today, which appears to have been shaped by flowing water. There is also water frozen at the planet's polar ice caps. But how much water was on Mars, for how long, and whether in the form of an ocean, rivers, or streams are questions that scientists haven't settled. The history of water on Mars is a significant factor to nail down, since it is inextricably tied to the question of potential life on the planet.
NASA scientists last year reported on their analysis of water vapor in the Martian atmosphere. Their findings also suggested that there was an ocean in the planet's northern plains, where the landscape is more depressed, like on Earth's ocean floor, than on other parts of the planet. The body of water was vast enough 4.5 billion years ago to cover a fifth of Mars, these scientists reported.
As Mars lost its atmosphere over billions of years, it lost the pressure and heat needed to keep water liquid, so the water receded. Whatever water was leftover, suggested the team led by NASA's Geronimo Villanueva, condensed and froze at the polar ice caps.
One of the problems – and there are many – with the concept of oceans on Mars, is that there are no shorelines left to prove it.
"For more than a quarter century, failure to identify shoreline features consistently distributed along a constant elevation has been regarded as inconsistent with the hypothesis that a vast ocean existed on Mars approximately 3.4 billion years ago," said Dr. Rodriguez in a press release.
He says his team found a way to resolve this: There are no ancient shorelines, they propose, because huge tsunamis buried them, leaving behind boulders that must have been moved by a powerful force hundreds of miles inland.
Rodriguez and his team identified the two tsunamis, separated by millions of years, by analyzing images collected by Martian orbiters, and by doing computer modeling,
The first tsunami left these boulders, some of which are 33 feet in diameter, says Rodriguez. As the water retreated back to the ocean it carved out channels that cover parts of Mars today. The same channels are forged after tsunamis on Earth, say the researchers.
Before the second tsunami, Mars cooled and the sea level shrank. So when the next meteorite struck, 3 million to 15 million years later, it created a tsunami of water that was partially frozen, which would have looked like an ice surge. This even left behind icy boulders.
"This is important is because we don't really see much in the way of evidence for a backwash phase – the tsunami didn't go back into the ocean," Rodriguez told The Guardian. This could mean that remnants of that frozen ocean water could still be on Mars, according to The Guardian.
The latest research adds to the evidence that planetary scientists have been gathering to make a case for or against a watery Mars. But the case is still wide open.
"It’s still a bit unclear whether there were oceans on Mars," says Don Banfield, a planetary scientist at Cornell University who has studied the topic of Martian shorelines, in an e-mail to the Monitor.
"My work examined whether we should expect shorelines at all (i.e., would the air pressure be high enough for winds to produce waves, which are what typically makes shorelines). Others looked at this question too, and concluded that the water may not stand at the same level long enough to create a shoreline anyhow.... [I]t would evaporate and the levels would drop, so even Earth-like waves might not make a lasting shoreline. Still others suggest that any shoreline made 4 billion years ago might likely be eroded away from impacts and aeolian processes since then," he explains.