How Deep Was Mars' Ocean?

By Ryan F. Mandelbaum on at

Our little red neighbour may be a rocky red wasteland now, but lots of people think it was once an ocean-covered world just like our own. After scientists found some evidence of flowing water back in 2015, folks started to take these claims even more seriously. Heck, maybe Mars even supported life.

A team of American researchers have a guesstimate for the next logical question: Okay, if there was water, how much was there? Oceans? Lakes? Puddles?

Their estimate: 686 quadrillion meters cubed (that’s one followed by 15 zeros) of the stuff. If that seems meaningless, it’s around twice the volume of the Atlantic Ocean, or half the total volume of all the Earth’s oceans.

NASA/JPL-Caltech/Arizona State University

The researchers didn’t just pick any old number. Mars is covered with valley networks carved into highlands that, on first look, just scream “water did this.” The researchers built a new kind of model that looked at the depths of each valley based on their colour, and calculated just how much water would be required to have created those features. They also estimate how big an ocean would have to have been, with what kind of climate, in order to have a water cycle capable of forming rivers that drain into oceans. They published their estimates in the journal Nature Communications today.

The researchers point out that, well, there’s really no way to tell if they’re right, nor will there ever be. But they do say their estimates seem to confirm what others have arrived at via different methods of calculating volumes.

Image: Luo et al, Nature Comms (2017)

Researcher Tanya Harrison was sceptical of this study’s results, and others that have tried to model Mars’ oceans. “My main issue with most of these modelling types papers dealing with Mars’ Ocean is that we don’t see strong morphological evidence to support the former presence of an ocean,” she told Gizmodo in a cell phone photo of an email delivered via a Twitter direct message. Basically, yes, the valleys look like they were carved by water. But images taken by the Mars Global Surveyor of the Northern Lowlands—the place where the ocean should have been—don’t reveal evidence that they were under an ocean. And where are the shorelines?

Harrison pointed did point out that one of the papers the researchers cite show some evidence for water in the Northern Lowlands, but not at the same volumes they estimated in their paper.

So, just how wet was Mars, really? Who knows, it’s dry now. The solar winds have since stripped Mars of its atmosphere and soon the rest of its water. But maybe we’ll end up there and find fossils. Maybe we won’t.

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