TrueID: Ancient Water Ponds on Mars Reveal Clues to Lost Ocean and Potential for Past Life

A geological structure on Mars resembling a bathtub ring provides evidence that an ocean may have once covered one-third of the planet’s surface. This discovery assists researchers in determining whether ancient Mars possessed enough long-lasting liquid water to host life.

Previous research identified various geological features that look like shorelines, but these were found at varying elevations. Because sea levels on Earth remain consistent, a stable Martian ocean would ideally leave shorelines at the same elevation across the planet.

Simulating Ocean Loss to Identify Martian Features

To find more reliable signs of lost oceans, researchers used computer simulations to dry up Earth’s oceans and observe which geological details remained. They discovered that the most distinct feature left behind, other than the water itself, are flat bands of land.

These bands can be several hundred miles wide and range in elevation from approximately 15 to 410 meters (50 to 1,345 feet) below sea level. By searching for similar structures on Mars, scientists identified the bathtub ring feature that suggests a vast ancient body of water.

The Scale and Loss of Martian Water

NASA scientists have determined that a primitive ocean on Mars contained more water than Earth’s Arctic Ocean. Some models suggest that liquid water pooled to form an ocean occupying nearly half of the northern hemisphere, reaching depths greater than 1.6 kilometers in certain regions.

Other estimates indicate that about one-fifth of Mars was once underwater. However, the planet has since lost 87 percent of that water to space.

The remaining water is distributed across the planet in several forms. Some water froze into polar caps, while other portions were trapped within minerals.

Subsurface Reservoirs and Seismic Evidence

A study published May 12, 2025, suggests that a significant amount of the missing water may be concealed deep within the crust. Using seismic data from NASA’s InSight mission, researchers found that seismic waves slow down in a layer located between 5.4 and 8 kilometers below the surface.

This slowing of seismic waves is an indicator of the presence of liquid water at those depths. Calculations suggest the volume of missing water is enough to cover the planet in an ocean between 700 and 900 meters deep.

Scientists hypothesize that this water seeped into the crust during the Noachian period, when heavy meteorite bombardment created fractures that acted as channels for surface water to move underground.

Timeline of a Watery Past

During the Noachian and Hesperian periods, which spanned from 4.1 billion to 3 billion years ago, Mars featured shimmering lakes and rivers that carved valleys. As the planet’s magnetic field faded and the atmosphere thinned, the surface water vanished.

Additional evidence supports this history of surface water. On February 8, 2023, NASA’s Curiosity rover discovered rippled rock textures suggesting that lakes existed in regions where scientists had not previously expected them.

Further research provides geological clues that large ancient rivers in the northern hemisphere once emptied into a long-lasting ocean.

The presence of these ancient water systems raises the possibility that life evolved on Mars. As astrobiologist Alberto Fairen stated:

On Earth, water means life

Alberto Fairen, Center of Astrobiology in Spain and Cornell University

While the surface of Mars is currently cold and dry, the discovery of the bathtub ring and the evidence of deep crustal reservoirs suggest that the planet’s watery history was far more extensive than previously confirmed.