An image captured by ESA’s Mars Express space probe’s High Resolution Stereo Camera (HRSC) shows the region of the planet Mars called Caralis Chaos. At first glance, it may seem like just another Martian area dotted with craters and wind-carved mounds, but when the red planet was young, it was home to Lake Eridania, larger than all the lakes on Earth. It covered an area of ​​more than a million square kilometers, including Atlantis Chaos, an area close to Caralis Chaos. That lake gradually dried up as the environmental collapse transformed an Earth-like planet into the one we see today.

The top image (ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)) shows the Caralis Chaos region. Today, it displays a variety of geological features that have formed over time: tectonic faults, river channels, ancient lava lakes, and impact craters.

About 3.7 billion years ago, the planet Mars was similar to Earth and this applies to both water and volcanoes so it’s not strange to find traces of both. The Tharsis region is home to the largest volcanoes in the entire solar system, and in the distant past, their activity generated fractures and other movements in the Martian crust. Among them are the Sirenum Fossae faults, which also cross the Caralis Chaos area, very clearly visible in the bottom image (ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)). However, according to scientists, those faults were created only after Lake Eridania dried up.

In the reconstruction of the history of that region of Mars, about 3.7 billion years ago, there was the large Lake Eridania. It occupied over a million square kilometers, larger than all the known Martian lakes put together. It was also larger than any Earth lake, about three times the size of the Caspian Sea.

As the Martian atmosphere began to be blown away by the solar wind, the environmental conditions also led to a slow loss of the water that flowed on the surface of Mars. The large Lake Eridania was reduced to a series of smaller lakes and eventually, they too disappeared.

The chronology of the events that created the many geological features of the Caralis Chaos area are difficult to reconstruct precisely after more than three billion years. For example, the large central crater shows evidence of material flows and valleys carved out on the southern rim, on the left in the top image. This indicates that water could have existed in a liquid state even after the disappearance of Lake Eridania.

Various studies have already been conducted to examine various aspects of the geological complexity of the area where Lake Eridania used to be. A recent study published in February 2024 in the journal “Nature Astronomy” focuses on volcanism and recycling processes of the Martian crust in the various parts of the ancient lake, therefore Atlantis Chaos, Caralis Chaos, and also Simois Colles. The examinations continue by scientists of various disciplines, also to study the conditions that in Lake Eridania could have been favorable to the birth of life forms.