Four different geologic events show evidence that water may have flowed on Mars far more recently than scientists once thought. Researchers numbered the areas from one, the oldest and most heavily marked with craters, to four, the newest.

NASA/JPL/University of Arizona photo provided by Brown University

PROVIDENCE — Mars, the cold desiccated world known as the Red Planet, appears to have had water flowing across its surface much more recently than scientists had believed.

Brown University researchers have identified a formation showing repeated deposits of sediment that seem to have been deposited by flowing water. The oldest deposit is just 1.25 million years old.

“That is very young for Mars,” said Samuel Schon, a Brown graduate student who authored the new study published yesterday in the journal Geology. “This is showing we’ve had transient liquid water appearing recently.”

In contrast, many features that scientists believe were carved by water are at least 3,500 million years old.

The 1.25 million-year-old feature, which has been dated using the craters that pockmark its surface, is overlaid by even newer deposits that flowed through the gully. But whether those were made 1,000 years, 100,000 years or a million years ago isn’t known, said Schon.

The work is based on photographs from the Mars Reconnaissance Orbiter taken a year ago in a highlands area of the southern hemisphere.

When the climate was warmer in that region, Schon said, ice that was locked inside the walls of a crater apparently melted, picked up enough Martian dust to turn it into a “muddy, chocolate stream,” and flowed downhill, allowing the sediment to collect and harden in a lowland area.

It happened at least three more times, identifiable because the material that was collected is increasingly pristine. “There could have been many individual flows,” he said.

Mars has gone through three main epochs since its formation 4,600 million years ago.

The wettest, called the Noachian, ended 3,500 million years after extensive flooding and giant meteor impacts, which are still visible today. The Hesperian ended about 1,800 million years ago and is marked by lava that hardened into massive plains.

Today, Mars is in the Amazonian era, where the planet is so cold and dry that liquid water cannot exist on the surface. Scientists believe the remaining water is in the form of ice.

gemery@projo.com