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Scientists stunned by billion-year-old ancient river on Mars

A team of European Space Agency (ESA) scientists have reportedly discovered an ancient riverbed on Mars, the latest evidence supporting the theory that water once flowed freely across the Martian surface. The photos, which were taken last year, were released late Thursday by the agency, according to a statement.

European Space Agency officials announced Thursday that they have discovered an ancient riverbed carved into the surface of the Red Planet. The images, snapped by the ESA’s Mars Express, have left astronomers around the world scrambling to better understand the stunning feature — quite possibly the most definitive evidence to date supporting the theory that water once flowed on Mars.

The area, dubbed Reull Vallis, contains a river-like channel likely formed billions of years ago. The 1500-km channel is lined with tributaries that seem to resemble tributaries found on Earth, according to the report, and the striking river is at some points wider than four miles. Astronomers say the ancient river is nearly 1,000 feet deep at some points, and it is likely one of the most geologically important features on the planet.

“These structures are believed to be caused by the passage of loose debris and ice during the ‘Amazonian’ period (which continues to this day) due to glacial flow along the channel,” the ESA wrote.

The depth of the channel has led a number of geologists to speculate that the riverbed was once occupied by water and large chunks of ice. Water likely flowed though Reull Vallis somewhere around 3.5 to 1.8 billion years ago, according to geologists, during a time known as the Hesperian period. The Hesperian period is thought to have ended around  3.5 to 1.8 billion years ago, although further research is likely needed in in order to confirm the age of the channel. The region shows a striking resemblance to the morphology found in regions on Earth affected by glaciation, and its history is likely complex as it holds a number of unusual formations.

“For example, we can see circular step-like structures on the inner walls of the sediment-filled crater in the foreground of the second perspective view,” ESA said. “Planetary scientists think that these may represent former high water or glacial levels, before ice and water sublimated or evaporated away in stages at various times.”

It remains unclear whether additional studies will seek to better understand the formation of the riverbed. A number of scientists have suggested that the channel is the result of a series of past rivers, rather than one single river. Some scientists have even suggested that the riverbed is the result not of water, but instead of lava flows. Regardless, the discovery of the formation means that the planet’s climate has changed dramatically over the past several billion years.

The discovery comes as the U.S.-based space agency NASA continues to operate its nearly one-ton rover on Mars. The rover, which is slated to begin analyzing its first soil samples, has already discovered a number of geologically relevant features, including evidence of past water and worn rocks that seem to indicate the existence of flowing, knee-high rivers.

Watch the video announcing the discovery: