Nasa’s Perseverance rover has detected underground remains of an ancient river delta on Mars, offering some of the strongest evidence that water once flowed on the planet’s surface.
The discovery was made using ground-penetrating radar, which revealed hidden geological features beneath the Martian terrain.
The six-wheeled rover identified structures up to 115 feet (35 metres) below the surface while travelling about 6.1 km across Jezero Crater in Mars’ northern hemisphere. Scientists believe this crater once held a lake and was fed by flowing rivers billions of years ago, according to Reuters.
Researchers found layered sediments and eroded surfaces typical of a river delta. They saw a fan-shaped deposit formed where a river meets a larger body of water like a lake. These features suggest that Jezero Crater once hosted a stable, water-rich environment.
The buried delta is estimated to be around 3.7 to 4.2 billion years old, indicating it formed relatively early in Mars’ history, shortly after the planet itself was formed about 4.5 billion years ago.
Scientists said this underground delta predates a nearby surface formation known as the Western Delta, which is younger.
The findings were made using Perseverance’s RIMFAX instrument, which sends radar signals below the surface and records how they bounce back. This allows scientists to create a three-dimensional map of subsurface structures.
The latest data, collected between September 2023 and February 2024 over 250 Martian days, represents the deepest radar observations made by the rover so far.
Scientists believe that the discovery is significant because water is considered essential for life. Mars, now cold and dry, is believed to have once had a thicker atmosphere and warmer conditions that allowed liquid water to exist.
“From the features mapped by RIMFAX, we believe that Jezero Crater hosted an ancient water-rich environment, capable of biosignature preservation that existed prior to the formation of Jezero’s Western Delta,” said UCLA planetary scientist Emily Cardarelli.
A biosignature refers to chemical or physical evidence of past or present life. On Earth, river deltas are known to trap sediments and create conditions suitable for microbial life.
The latest discovery adds to earlier findings from Perseverance. In 2024, scientists reported that a rock sample collected in Jezero Crater contained a possible biosignature, though it could also have formed through non-biological processes. That rock was dated to between 3.2 and 3.8 billion years old.
Since landing in 2021, Perseverance has been exploring Jezero Crater, where scientists believe ancient rivers once flowed into a lake.
“It’s very exciting that RIMFAX was able to provide such a detailed view of these deposits, and thus help solve the puzzle of their origin,” said UCLA scientist David Paige. He added that ground-penetrating radar is proving to be a valuable tool in studying planetary geology.
The findings also align with other recent discoveries. Chinese scientists previously reported that their Zhurong rover detected underground features resembling ancient ocean shorelines on Mars.
