The Ancient Rivers Of Mars

A Natural History

For centuries, Mars has captivated the human imagination. Authors such as H.G. Wells, Ben Bova, and Kim Stanley Robinson have woven tales of the iconic but dusty and dry Red Planet. For much of history, scientists believed Mars had always been this way: a lifeless, desert-like landscape devoid of geological activity. However, discoveries in recent decades have unveiled a new story, revealing that Mars once hosted rivers, deltas, and possibly even vast lakes and oceans.

How Can We Know This?

Understanding Mars’ ancient waterways requires more than a telescope. Scientists have relied on data from powerful space probes like the Mars Reconnaissance Orbiter (MRO) and Mars Global Surveyor (MGS). These spacecraft have mapped the Martian surface in extraordinary detail, uncovering geological features that strongly suggest the presence of ancient rivers.

In 2003, data from the MGS revealed an ancient river delta-like fan, showing eroded deposits of transported sediment that have since solidified into interweaving curved ridges of layered rock. Geologists describe these ridges as inverted channels, formed due to the unique composition of riverbed sediments, which made them more resistant to erosion than the surrounding landscape.

Additionally, scientists have identified features resembling ancient “meanders.” A meander is a sinuous curve in a river channel, formed as flowing water erodes the outer bank and deposits sediment on the inner bank, creating point bars. These curving patterns are strikingly similar to those found in terrestrial rivers.

Roving Mars For Clues

More recently, NASA’s Perseverance rover, a mobile laboratory equipped with advanced scientific instruments, has uncovered compelling evidence of long-flowing ancient rivers in the Hellas Impact Crater on Mars. In 2020, the rover analyzed a 200-meter-high rocky cliff composed of sedimentary rocks. These rocks form when sediment carried by water or wind settles and solidifies into stone, much like on Earth. These formations are believed to be approximately 3.7 billion years old, and the rivers that created them likely flowed for hundreds of thousands of years.

The rover has also been exploring the Jezero Crater on Mars, thought to have contained a lake and river system about 3.5 billion years ago. Clues from this site reveal even more about Mars’ hydrological history. Flat, light-coloured rocks indicate slow-moving rivers, while large boulders, likely transported later, suggest periods of intense flooding or raging torrents.

Scientific evidence suggests that there was a time billions of years ago when Mars was far more Earth-like, a world of flowing water, dynamic climates, and geological activity.