Ancient traces of a giant ocean just discovered on Mars: ScienceAlert

Ancient traces of a giant ocean just discovered on Mars: ScienceAlert

You’ll no doubt be familiar with the dry, dusty appearance of Mars as it appears today – but scientists have found evidence of a massive ocean that existed on the red planet’s surface around 3.5 billion years ago, likely covering hundreds of thousands of square kilometres.

This evidence comes in the form of distinctive coastal topography, determined through numerous satellite images of the Martian surface. When these images are captured at slightly different angles, a relief map can be constructed.

The researchers were able to trace more than 6,500 kilometers (4,039 mi) of fluvial ridges, apparently carved by rivers, proving that they are likely eroded river deltas or submarine channel zones (channels carved into the sea floor).

Gale Crater Landscape
The floor of Gale Crater, near an area called Aeolis Dorsa, which researchers believe was once a huge ocean. (NASA/JPL-Caltech/MSSS)

“The big, innovative thing we did in this paper was to think about Mars in terms of its stratigraphy and its sedimentary record,” says geoscientist Benjamin Cardenas of Pennsylvania State University.

“On Earth, we map the history of waterways by looking at sediment deposited over time. We call it stratigraphy, the idea that water transports sediment, and you can measure changes on Earth by understanding how sediment accumulates. That’s what we did here – but it’s Mars.”

Using data from the Mars Reconnaissance Orbiter collected in 2007, the team applied an analysis of ridge thickness, angles and locations to understand the study area: the topographic depression known as the Aeolis Dorsa region on Mars.

It seems likely that a major change was happening in this part of the planet all those years ago, Cardenas explains. This is shown by the evidence of significant sea level rise and the rapid movement of rocks by rivers and streams. Today, Aeolis Dorsa contains the most concentrated collection of fluvial ridges on Mars.

All of this is connected to the search for life on Mars. One of the most fundamental questions scientists face regarding the red planet is whether it ever had conditions hospitable enough to be able to support life.

“What immediately comes to mind as one of the most important points here is that having an ocean of this size means a higher potential for life,” Cardenas says.

“It also tells us about the ancient climate and its evolution. Based on these findings, we know there must have been a time when it was warm enough and the atmosphere was thick enough to support so much liquid water at once.”

Researchers don’t stop at Aeolis Dorsa.

In a separate study published in Geoscience of naturesome of the same researchers, including Cardenas, applied an acoustic imaging technique used to map ancient seafloors in the Gulf of Mexico to a model of how water may have eroded the surface of Mars.

There are huge areas of fluvial ridges all over Mars, and the team’s simulations are strikingly similar to the shape of the landscape on the red planet – suggesting that there was extensive water coverage at one point.

We’re seeing more and more signs that there was once abundant water on Mars, and work continues to understand what might have led to it and where that water is now – although looking back billions of years isn’t easy.

“If there were tides on ancient Mars, they would be here, gently bringing water in and out,” says Cardenas. “This is exactly the kind of place where ancient Martian life could have evolved.”

The research has been published in Journal of Geophysical Research: Planets and Geoscience of nature.

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