A delta on Mars, left, is compared with a modern delta on Earth. Scientists at Caltech discovered the Martian delta, the best evidence to date that suggests a massive ocean once covered the red planet.
Scientists at Caltech have found the “strongest” evidence yet to suggest a massive ocean once covered much of Mars’ now-dry northern hemisphere.
Scientists estimate this huge body of water would have covered at least 100,000 square kilometers, or 38,610 square miles – 10 times the size of Los Angeles County.
The findings are far from proof, but they do provide some of the most convincing support to date, lead author Roman DiBiase said in a Caltech news release Tuesday.
At the heart of the hypothesis is a 100-square-kilometer portion of a "hypothetical coastline" -- an ancient delta where a river might once have emptied into a vast ocean, pictured below.
Most of Mars’ northern hemisphere is flat and at a lower elevation than the southern hemisphere, suggesting that the border between the two would have been where a Martian ocean met land.
If it existed, the ocean could have covered nearly a third of the red planet and may have harbored life, researchers said.
"Scientists have long hypothesized that the northern lowlands of Mars are a dried-up ocean bottom, but no one yet has found the smoking gun," said Mike Lamb, an assistant professor of geology at Caltech and a coauthor of the paper describing the results.
Previous images of this region show it covered in ridge-like features called inverted channels, which are created after a river dries up, leaving behind coarse materials – like large gravel and cobbles – that were carried along the river bed by flowing water.
Martian deltas have been discovered before, but most are inside a geological boundary, like a crater, which means they likely would have flowed into smaller bodies of water, such as a lake, not an ocean.
The HiRISE camera on the Mars Reconnaissance Orbiter (MRO) captured the images of the hypothetical ocean's coastline. The findings are published in Journal of Geophysical Research.
"Both the ancient environments on Mars and the planet's sedimentary archive of these environments are turning out to be surprisingly Earth-like," Lamb said.