Mars might have once held a vast ocean covering a third of its surface. Scientists believe this ocean evaporated billions of years ago, leaving behind a noticeable mark—a flat band of land that resembles a bathtub ring. This feature, known as a “coastal shelf,” could provide key evidence in the ongoing debate about Mars’ watery history.
Researchers like Michael Lamb, a geology professor at Caltech, are interested in what signs a vanished ocean would leave. They’ve identified a distinct band that may represent the ancient shoreline. “We expect to find something like a flat bench around the shoreline, similar to what we see on Earth,” he explains.
To explore this, Lamb and his team ran computer simulations mimicking how Earth’s oceans dried up. They observed that the continental shelf is a stable feature that survives through time. To find a counterpart on Mars, they examined data from NASA’s Mars Orbiter Laser Altimeter, uncovering possible evidence of a similar feature, although it isn’t an exact match.
The notion of a Martian ocean isn’t new; it originated in the 1970s during NASA’s Viking missions, which suggested signs of a shoreline. However, previous data was never fully convincing. Lamb points out that the features detected didn’t maintain a consistent elevation, which is unusual for a shoreline. He speculates that volcanic activity might have caused changes to these features over time.
The new study argues that a coastal shelf offers a more substantial indicator of ancient oceans. The size and durability of these formations make them less likely to be eroded, with some measuring between 200 to 400 meters wide. According to Abdallah Zaki, one of the researchers, this could add clarity to Mars’ ancient geography. “If we’re looking for significant evidence of oceans, then a coastal shelf is essential,” he states.
Recent findings from the Chinese rover Zhurong support this theory, revealing signs of ancient beaches in Mars’ northern plains. There’s also evidence of river deltas that further strengthen the argument for a previously existing ocean.
Despite these indications, Mars today is cold and mostly dry, retaining some water in its ice caps. Data from NASA’s InSight lander suggests there could be more water beneath the surface—enough to fill an ocean.
The European Space Agency’s upcoming Rosalind Franklin rover, expected to launch in late 2028, aims to investigate these findings further. “It will give us a definitive answer,” Zaki says.
Understanding whether Mars ever hosted a large ocean is crucial. It could answer many questions about its climate history and the possibility of past life. Lamb notes, “We know Mars had liquid water, but we still don’t understand how long it existed and what led to its current barren state.”
Experts weigh in on the controversy surrounding Mars’ hydrological history. James W. Head from Brown University emphasizes that, while the study aligns with Earth’s oceanic features, Mars’ lack of plate tectonics complicates direct comparisons. He believes we need more observations to determine whether the theory stands up against scrutiny.
While some scientists remain skeptical, many agree that the upcoming exploration missions could shed light on these long-standing questions. Bryony Horgan from Purdue University highlights the significance of this research, stating that understanding Mars’ ancient oceans could unravel mysteries about its geological past and potential habitability.
In short, the dialogue around the existence of ancient Martian oceans continues, fueled by new studies and future missions that promise to deepen our understanding of the red planet’s history.
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