NASA’s Curiosity rover recently spotted some of the most compelling evidence yet of ancient water on Mars, in the form of rippled rocks shaped by waves.
The ripples formed billions of years ago, when liquid water still covered the Martian surface. Across Mars, from the Curiosity rover near Gale Crater to Perseverance in Jezero Crater, probes are exploring these ancient waterbeds for intel on Mars’ geological history and its potential for astrobiology. Might there be fossilized microbes among all the red rocks and dust?
Curiosity began its mission in 2012 in the low elevations Gale Crater but is now on Mount Sharp, a 5 km-high mountain once covered with lakes and streams. If life ever existed on Mars, from what we know of its presence on Earth, these ancient water pathways are a good place to look.
The rover spotted the rock textures — small ripples, looking a bit like dried-up tire treads — in a layer of rock on Mount Sharp called the Marker Band, according to a NASA release.
“This is the best evidence of water and waves that we’ve seen in the entire mission,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory in Southern California, in the release. “We climbed through thousands of feet of lake deposits and never saw evidence like this – and now we found it in a place we expected to be dry.”
The Marker Band and its environs formed in drier climates than the areas Curiosity has already been through. In other words, the NASA team figured the water on Mars may have already vanished by the time the rock currently being studied was formed. There are ice sheets and ice caps on Mars’ poles, and meteorite impacts on the planet have kicked up subterranean ice, but liquid water hasn’t been on the planet for billions of years, at least as far as we know. Mars is cold and has a thin atmosphere, so water freezes at its surface, and the planet’s ancient water is thought to have mostly been lost to space (at least 87% of it, according to NASA).
The Marker Band is so hard that Curiosity has failed to take a sample of it even after several drilling attempts, but if the rover isn’t able to get a sample from softer rock, it still has exciting ventures ahead.
The Martian valley of Gediz Vallis holds an assortment of rocky debris scientists believe was swept there by ancient landslides. That makes the valley a repository of rocks from high on Mount Sharp, regions Curiosity wouldn’t be able to access. By probing those boulders, scientists will get insights about otherwise inaccessible stories from Mars’ past.
Though the recently found water ripples are some of the clearest evidence of ancient water on Mars, they’re hardly the first. Click through for other images that show how water has shaped the Martian landscape.
Mars’ ‘Dragon Scales’
The Mars Reconnaissance Orbiter snapped this picture of a distinctive ‘dragon scale’ pattern from Mars orbit. This arises from clay-bearing rock interacting with water, meaning the pattern likely formed billions of years ago.
Ius Chasma
Ius Chasma sits in Mars’ largest canyon, Valles Marineris. Researchers believe that water seeped out of the formation’s cliffs and evaporated before it could reach the canyon floor. The result is this artful geological formation.
Alluvial fans
MRO’s view of Saheki Crater on Mars reveals alluvial fans on the planet’s surface. Alluvial fans are gentle slopes formed by the flow of water. The fans also occur naturally on Earth, but on Mars they tend to be much, much older, given that water hasn’t been plentiful on the planet’s surface for ages.
Recent MRO data
European Space Agency (ESA) and NASA scientists recently teamed up to combine data from the Mars Express Orbiter and Mars Reconnaissance Orbiter, to make a map of where hydrated minerals are on Mars. The map offers a guiding document for where ancient water likely flowed. Note the amount of hydrous clays in Jezero Crater, in the map at top right. That’s why Perseverance rover scientists are exploring the crater’s river delta with such zeal. You can read more about the maps here.
‘Lineae’ slopes
This processed image from the HiRISE Camera on the Mars Reconnaissance Orbiter shows lineae (line) slopes, which could indicate where ancient water once flowed off this large ridge. Each line is about the length of a football field!
Recurring Slope Lineae in false colour
This false-colour image of a slope in Mars’ Hale Crater shows slope lineae in a yellowish-brown, again where rougher terrain meets a more gradual slope.
Very clear lineae!
This image from the MRO shows recurring slope lineae clearly, on the rim of Mars’ Garni Crater. Hundreds of feet long, the streaks indicate water once flowed down this sharp slope. Currently, Perseverance is investigating a delta on the western side of Jezero Crater, which also shows signs of ancient water flow.
A Martian ice cap
The ice cap on Mars’ south pole shows that water is still on the planet — if only in a different state. In 2021, a team of researchers published a paper suggesting that liquid water may exist in subsurface lakes on Mars. “Either liquid water is common beneath Mars’ south pole or these signals are indicative of something else,” said Jeffrey Plaut, a research scientist at NASA’s Jet Propulsion Laboratory. But more recent work has challenged that hypothesis.
Jezero’s delta
The raised remnant of a river delta on the western end of Jezero Crater, as seen by the Perseverance rover. The delta is thought to have carried water (as well as ancient Martian boulders and sediments) into a lake that once occupied the now-arid crater.
Perseverance’s path
This map shows two paths NASA’s Perseverance team charted for the rover from its landing site (white dot at right). The rover ended up taking the blue path, and now sits at the base of the raised river delta at the centre of the image. The delta is thought to have carried water from the west into the lake that occupied Jezero Crater, at right.
Jezero’s mineral map
The same research noted earlier paid particular focus to the Perseverance rover’s area of study: Jezero Crater. The crater’s western end is dominated by carbonates and hydrated minerals. It’s one of several locations on Mars that show evidence of substantial water presence in the planet’s ancient past.
Imagining Jezero lake
NASA is fairly certain that Jezero Crater was once filled with water. That would make the river delta that flowed into it a good place to search for signs of ancient microbial life, which may have looked something like the stromatolites that formed on ancient Earth (and still form in some parts of the world today.)
Read more: Abigail Allwood’s Hunt for Alien Fossils on Mars Has Begun