New Evidence Suggests Mars Had a Longer, Wetter Past

Recent research from separate scientific teams has presented new geological evidence suggesting Mars had a more extensive and longer-lasting history of surface water than previously confirmed. One study proposes a large-scale feature as a remnant of an ancient ocean, while another reveals subsurface evidence of earlier, prolonged river delta activity.

Proposed Evidence for an Ancient Martian Ocean

A study published in the journal Nature proposes that a flat band of land encircling Mars's northern plains could be evidence of an ancient ocean. Researchers Michael Lamb and Abdallah Zaki used computer simulations modeling the drying of Earth's oceans to identify enduring geological features. They identified the continental shelf as the most distinct and long-lasting feature from these simulations.

Using topographic data from NASA's Mars Orbiter Laser Altimeter (MOLA), the team reports finding evidence for a "coastal shelf," described as a band 200 to 400 meters wide, which they argue is larger and more resistant to erosion than a simple shoreline.

The hypothesis that an ocean once existed on Mars originated with data from NASA's Viking missions in the 1970s, but earlier evidence was not considered conclusive.

Other scientists not involved in the study have commented on the findings:

• James W. Head, a professor at Brown University, stated that the formation of a sharp coastal shelf boundary on Mars is debatable due to the planet's lack of plate tectonics.
• Brian Hynek, a professor at the University of Colorado Boulder, noted that Earth's continental shelves are partly shaped by plate tectonics, making a direct comparison difficult.
• Bryony Horgan, a professor at Purdue University, stated that whether Mars had a large ocean remains a long-standing controversy in Mars science.

The European Space Agency's Rosalind Franklin rover, scheduled for launch in 2028, is planned to explore Mars's northern hemisphere and may provide further data on this proposed feature.

Subsurface Radar Reveals Earlier Delta System

In a separate discovery, NASA's Perseverance rover has identified evidence of an ancient delta system buried deep beneath the Jezero crater. The findings, published in Science Advances, were made using the rover's RIMFAX ground-penetrating radar instrument.

• The radar probed more than 35 meters into the subsurface during 78 traverses covering approximately 6.1 kilometers.
• The data revealed sloping layers of rock and lobe and channel structures consistent with sediment deposition from flowing water.
• This evidence indicates an earlier deltaic environment existed beneath the currently visible delta in Jezero crater.

The research suggests this delta system was functional as early as the Noachian period, approximately 4.2 to 3.7 billion years ago. This implies that water flowed in the region for a significantly longer duration than previously understood.

This extended period of water activity improves the likelihood of preserving biosignatures in the subsurface, extending the window of potential habitability.

Context and Ongoing Investigation

These studies contribute to a broader body of evidence for water on ancient Mars, which includes:

• Sedimentary layers detected by the Chinese Zhurong rover interpreted as ancient beaches.
• Geological remnants of river deltas identified from orbital imagery.
• Scientific consensus that most of Mars's water was lost as its atmosphere thinned over time.

The new findings from Perseverance's subsurface radar and the proposed coastal shelf hypothesis both point toward a more complex and extended hydrological history for Mars. Future missions, including the Rosalind Franklin rover, are designed to investigate these features further to better understand the planet's past climate and potential for harboring life.