Quirks & Quarks·Analysis

Strong evidence that an ancient ocean once covered Mars

Bob McDonald's blog: It has long been suspected that liquid water once flowed on Mars. Now the latest research shows that billions of years ago, Mars had a deep ocean covering hundreds of thousands of square kilometres.

Bob McDonald's blog: A massive ocean like this increases the potential for life on the red planet

A Martian landscape scene, showing what appears to be rocks of various shades of brown lined with ridges.
Stitched together from 28 images, this view from NASA's Curiosity Mars rover was captured after the rover ascended the steep slope of a geological feature called 'Greenheugh Pediment.' The floor of Gale Crater can be seen in the distance (at the top of the image), near a region called Aeolis Dorsa which researchers believe was once a massive ocean. (NASA/JPL-Caltech/MSSS)

It has long been suspected that liquid water once flowed on Mars. Now the latest research outlines evidence that billions of years ago there were more than lakes and rivers on the Red Planet. It likely had a deep ocean covering hundreds of thousands of square kilometres. 

Scientists from Penn State University used topographic maps of Mars created from data taken by the Mars Global Surveyor, an orbiting spacecraft. The spacecraft is equipped with a laser altimeter that has mapped the surface of the planet. The topography reveals features that resemble the shoreline of a vast northern ocean. 

A map of ridges, coloured from blue to red, with each colour representing the depth of the region represented. Blue is in the foreground, with green and red rising in the background.
This recently released topographic map shows a roughly 3.5-billion-year-old shoreline, with over 6,500 kilometers of fluvial ridges. It also shows substantial sedimentary accumulation, at least 900 meters thick, that covered hundreds of thousands of square kilometers. (Benjamin Cardenas/Penn State)

In a region called Aeolis Dorsa, features resembling river deltas and underwater marine channels extend for 6,500 km along the edge of a low lying basin. The features show depots of sediment up to 900 metres deep, believed to have been created when fast-moving river water met with the slower-moving ocean, forming deltas.

This ocean would have existed 3.5 billion years ago when Mars was a much warmer and wetter world, and much more Earth-like. 

That was also the time when life was emerging on our planet, so of course it's natural to ask if it's possible that life emerged there too?

That is one of the most fundamental unanswered questions in science.

A black and white drawing with a grid overlaying a tangled mess of thick and thin lines, each labelled with a different name.
Giovanni Schiaparelli's map of Mars is seen here. Compiled from 1877 to 1886 and taken from telescope images, it used names that were either based on classical geography or simply descriptive, such as the Mare Australe (Southern Sea). (NASA)

This is not the first time evidence for water on Mars has been found. In fact, the much of the history of Mars exploration has been focused on the search for water, dating back to 1877 when Italian astronomer Giovani Schiaparelli thought he saw lines on Mars through his telescope. He called these lines canali, which is Italian for channels.

American astronomer Percival Lowell took it one step further claiming in publications in the first decade of the 20th century, that the lines were artificial canals, suggesting a civilization of Martians who were great engineers. Of course, that helped inspire many of the science fiction stories of invasions from Mars by little green men in menacing machines, most famously H.G. Wells' enormously influential War of the Worlds.

It was not until 1971 that NASA's Mariner 9, the first spacecraft to orbit Mars, spotted what indeed looked like river channels, although not large enough to be seen through Earthly telescopes. Since then, robots that have visited the planet have found more evidence of water that flowed in the past. The two rovers currently operating on the surface, Curiosity and Perseverance, were sent to craters that were thought to have once been lakes. 

A black and white low quality photo showing a dried up river stretching across the screen.
This view of channels on Mars came from NASA's Mariner 9 orbiter. In 1971, Mariner 9 became the first spacecraft to enter orbit around Mars. (NASA/JPL-Caltech)

The researchers in this latest study do not estimate how long the ocean on Mars could have existed, whether it was there for millions of years or a period too short for life to take hold. What we do know is that at some point Mars transformed from a water world into a desert. The atmosphere became thin, temperatures dropped and the planet's liquid water froze in the polar ice caps and underground permafrost. 

To try to answer the question of whether life emerged while that water was liquid, NASA and the European Space Agency are planning a Mars Sample Return mission to collect dirt and rock samples that are currently being gathered by the Perseverance rover. The robotic mission is meant to land, load the samples, and return them to Earth for detailed laboratory study.

If no signs of life or fossils are found in those samples it's not the end of the story. Perhaps we just need to dig deeper -– perhaps in the ocean basin — to find evidence of life from a time when the Red Planet was blue.


  • A previous version of this article misidentified the orbiting satellite that collected data for this work. It was the Mars Global Surveyor.
    Nov 21, 2022 12:39 PM ET


Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.