Perseverance’s radar revealed ancient subsurface river delta on Mars
When NASA’s Perseverance rover landed in Jezero Crater in 2021, its primary mission was to scour the remains of a dry Martian lake bed for signs of ancient life. Scientists focused on the crater’s spectacular western delta, a fan-shaped geological formation deposited by a river flowing into the basin billions of years ago. But now Perseverance’s ground-penetrating radar (called RIMFAX) has detected what is likely another, even older, river delta buried dozens of meters beneath it.
“I think this is a promising place to look for signs of deep biosignatures,” says Emily L. Cardarelli. “Microbial life could have thrived in these types of environments.” Cardarelli, an astrobiologist at the University of California, Los Angeles, led the team that interpreted the RIMFAX images.
Peeking underground
Perseverance’s RIMFAX, the radar imager for the Mars Subsurface Experiment, continuously sends radar waves into the ground, acquiring surveys every time the rover travels 10 centimeters. When these radio waves reach the boundaries between different types of layers of rock, ice or sediment, part of the signal bounces back. The timing and intensity of these reflections allow scientists to construct a two-dimensional vertical slice of the subsurface, much like an ultrasound of the Martian crust.
During a campaign spanning from September 2023 to February 2024, more than 250 Martian sols, Perseverance crossed a geological area known as the Margin unit. The Margin Unit is a large deposit flanking the inner rim of the Jezero Entrance Valley, occupying the space between the western fan deposits and the crater rim. It is rich in magnesium carbonates, which is one of the main reasons Jezero Crater was chosen as Perseverance’s landing site: on Earth, carbonates are exceptionally effective at preserving the chemical fingerprint of life. “You can think of the cliffs of Dover, for example, which are all made of carbonates: they have tons of fossils,” says Cardarelli.
