Ancient River System Discovered Beneath Martian Surface

NASA’s Perseverance rover has uncovered evidence of an ancient river system buried deep beneath the surface of Mars’ Jezero Crater, suggesting the Red Planet may have been habitable for a longer period than previously thought. The discovery, made using the rover’s ground-penetrating radar (RIMFAX), reveals a delta system predating the one visible on the crater’s surface.

Peeking Beneath the Surface with RIMFAX

The RIMFAX instrument works by emitting radar waves into the Martian soil. As the rover moves, these waves bounce off subsurface layers of rock, ice, or sediment. By analyzing these reflections, scientists can create two-dimensional images of underground structures, similar to ultrasound technology used on Earth. ScienceAlert reports this allows for the visualization of layers not directly observable from the surface.

A Hidden Delta in the Margin Unit

Between September 2023 and February 2024, Perseverance traversed the Margin Unit, an area between the West Delta and the crater rim, known to be rich in carbonate minerals. Analysis of the RIMFAX data, led by Emily Cardarelli of the University of California, Los Angeles, revealed highly radar-transparent rock layers extending over 35 meters beneath the surface, with an estimated total thickness of 85 to 90 meters. Within these layers, scientists identified a geological structure resembling a river delta. Scientific American details this finding.

Evidence of Long-Lasting Water Activity

The observed layers exhibit a slanted, parallel pattern called clinoforms, characteristic of sedimentary deposits formed by streams flowing into lakes. This pattern indicates a gradual deposition process, with heavier sediment accumulating at the top, forming a sloping layer, and eventually spreading into finer layers on the lake bottom. This suggests prolonged and dynamic water activity in the region.

Perseverance’s Previous Discoveries

Since landing in Jezero Crater in 2021, Perseverance has made several key discoveries supporting the theory that Mars once had a habitable environment. These include:

• 2021: High-resolution images of the Kodiak cliff revealed a river delta formed approximately 3.7 billion years ago, indicating Jezero Crater was once a lake fed by a stable river.
• 2022: Exploration of the delta floor uncovered fine sedimentary rocks containing organic material, suggesting river flows transported material from a wide area into the calm lake.
• 2023: The discovery of large rocks and pebbles arranged in curved patterns in the Skrinkle Haven area indicated the presence of strong river currents capable of moving large rocks.
• 2023: Signs of large, periodic floods were found in the Margin Unit, suggesting the ancient Martian climate was not always stable.
• 2025-2026: Exploration of the crater rim revealed carbonate deposits, which typically form in aquatic environments like coastlines, indicating long-term interactions between water and the Martian atmosphere.

Implications for Past Habitability

While the discovery of this hidden delta is promising, scientists remain cautious. Other possibilities, such as volcanic activity or glacial deposits, could explain the underground structures. But, Cardarelli notes that the complexity and scale of the observed structures are more consistent with fluvial processes. If confirmed, this suggests Mars possessed a stable and long-lasting water system, a crucial condition for the potential emergence of microbial life.

Future Exploration

The current data analysis covers approximately 6.1 kilometers of Perseverance’s journey, with much more data yet to be published from its 40-kilometer traverse. This suggests the discovery of the hidden delta may be just the beginning of a series of significant findings within Jezero Crater.