A river delta may have been present on Mars as early as 4.2 billion years ago, which is much earlier than previously thought. This is the conclusion from a new study by researchers at the University of California, Los Angeles, who have analysed ground-penetrating radar (GPR) data collected by the Mars 2020 Perseverance rover from the Jezero impact crater.
“The finding may also extend the period of flowing water and potential habitability for Jezero back further in time, says astrobiologist Emily Cardarelli, who led this research effort.
The surface of Mars carries many traces of a past watery climate, including ancient river channels, deltas, and paleolakes. Indeed, observations from space provide evidence for the existence of minerals possibly left behind as Mars’ atmosphere was gradually lost to space and its surface dried up.
Researchers are particularly interested in carbonate minerals because these preserve a record of the Red Planet’s ancient water thanks to its interactions with carbon dioxide in the Martian atmosphere at this time. How these minerals formed over the large scale in the Margin unit is unclear though.
Data collected from more than 35 metres underground
In the new work, Cardarelli and her colleagues in the Department of Earth, Planetary and Space Sciences at UCLA analysed data collected by Perseverance’s Radar Imager for Mars Subsurface Experiment (RIMFAX) instrument. They focused on a sedimentary deposit known as the Margin unit, which is rich in magnesium carbonates and lies near a fluvial inlet to the Jezero impact crater in the Nili Fossae region near Syrtis Major. The researchers already knew that this region hosts features typical of a paleolake basin and river delta deposits.
RIMFAX acquired a continuous 6.1-km ground-penetrating radar (GPR) image along the Margin unit campaign path with soundings every 10 cm and the researchers analysed 78 traverses made between September 2023 and February 2024 over 250 sols (Martian days, which are about 40 min longer than Earth days). The instrument collected data from more than 35 m underground, which is 1.75 times deeper than previous measurements at the Jezero crater.
The researchers found that the Margin unit contains a well-preserved paleolandscape with distinct river and deltaic features. These, they say, could be the remnants of a meandering river, an alluvial fan or braided river. This environment could have developed before the Jezero Western Delta viewable from orbit as early as the Noachian epoch (around 4.2 to 3.7 billion years ago).
Jezero might have hosted a habitable ancient environment
From the stratigraphic features mapped by RIMFAX, Cardarelli and colleagues conclude that the Jezero crater might have hosted an aqueous, possibly habitable environment capable of preserving biosignatures. “RIMFAX confirms that the Margin unit is distinct from a geological region known as the Upper Fan, which was deposited earlier and different in composition as well as in physical area,” says Cardarelli. “Our work suggests that there is some continuity of formation between the Margin unit and the Upper Fan, with a repeated process in Jezero crater, but at completely separate formation and deposition times.”
Indeed, a body of water might once have fed Jezero crater, she tells Physics World, and deposited sedimentary layers of varying scales, similar in size and morphology to those observed in an area known as the Western Fan. “We suggest that this was once an extensive system that included the Margin unit, although it is now a buried remnant.”
Mission to Mars: from biological barriers to ethical impediments
This study, which is detailed in Science Advances, highlighted only some of the specific features found since the mission began. To date, Perseverance has traversed around 40 km and has moved out of Jezero and onto the crater’s rim and the researchers say they will continue publishing their analyses from both these areas.
“I am also excited about one day returning to the Neretva Vallis region where we have detected the most compelling potential biosignatures. These may have a biological origin, but require additional study before determining if they may be evidence of past microbial life,” says Cardarelli.
