There is a lot of evidence from orbiting satellites and surface rovers indicating that liquid water was present long ago on the surface of Mars in the form of ponds, lakes, and rivers. But the idea that Mars once had a huge and long-lived ocean on its northern plains has remained a matter of debate.
Scientists have now detected what might be the contours of this putative ocean on Earth’s planetary neighbor, using data collected by a NASA probe that orbited Mars for a decade. Their research indicates the presence of the Martian equivalent of the continental shelf that defines the boundaries of Earth’s oceans.
They compared it to a huge “bathtub ring” showing where water may have once met land on Mars. Because Mars does not possess continents and lacks the geological process called plate tectonics that led to the formation of Earth’s continents, the researchers are calling the Martian landforms a coastal shelf.
Like Earth and the solar system’s other planets, Mars formed roughly 4.5 billion years ago. Early in its history, Mars was warmer and wetter than the cold and arid place it is today.
“The Martian ocean could have existed when the planet had an active hydrological cycle, with flowing rivers and lakes, nearly 3.7 billion years ago, and it likely disappeared as the planet became dry. Exactly where the water went remains highly debated,” said University of Texas planetary scientist Abdallah Zaki, lead author of the research published on Wednesday in the journal Nature.
A coastal shelf could have formed on Mars over millions of years due to rivers dumping sand and mud into an ocean, waves spreading those sediments around, and the sea level rising and falling over time. Looking from above, the sedimentary rock making up this shelf might superficially resemble the ring that remains after a bathtub has been drained.
“The northern ocean on Mars, if it existed, dried up a long time ago, and there have been billions of years of volcanic activity and wind abrasion on Mars, so interpreting ancient landforms is not straightforward,” Caltech planetary scientist and study senior author Michael Lamb said.
Taken together, Lamb said, the evidence points toward a long-lived ancient ocean.
“This means that Mars once looked much more like the Earth than it does today,” Lamb said.
The existence of an ocean would be an important factor in understanding whether Mars was ever able to give rise to life.
“If Mars once had an ocean covering roughly one third of the planet over geologic timescales, that would suggest that a large part of its surface had sustained water, which is a key ingredient for habitability,” Zaki said.
“That does not mean Mars was inhabited, but it does suggest that potentially habitable environments may have been more widespread and longer-lived than if water had only existed briefly or locally,” Zaki said.
