NASA's Perseverance rover has discovered an ancient river delta buried beneath Jezero Crater's surface using ground-penetrating radar. The rover's RIMFAX instrument detected structured sedimentary layers extending over 35 meters deep, revealing what scientists believe to be a delta system that predates the visible Western Delta by billions of years.

This hidden delta formed during Mars's Noachian period when the planet was significantly warmer and wetter, between 4.2 and 3.7 billion years ago. The radar data shows classic deltaic features including clinoforms and rollover points that indicate multiple episodes of continuous sediment deposition over vast geologic timescales. The discovery suggests early Mars maintained long-lived aqueous conditions rather than brief wet periods.

The Margin unit's carbonate-rich composition makes this site particularly promising for finding biosignatures, as carbonates on Earth excel at preserving life's chemical fingerprints. With only 6.1 kilometers of data analyzed from a planned 40-kilometer traverse, scientists anticipate many more discoveries about Mars's watery past and potential for ancient microbial life.