Mars may only be half the size of Earth, but – in part due to Mars’ low gravity – the geologic features are big. The red world has canyons and volcanoes far larger than any on our planet. Now there’s evidence that one of Mars’ ancient lakes was also bigger than any known lake on Earth. The European Space Agency (ESA) said on August 7, 2024, that its Mars Express orbiter obtained new views of the ancient lakebed in a region called Caralis Chaos. This lakebed – which presumably contained water billion of years ago – once covered more than a million square kilometers (386,000 square miles).
That’s about three times larger than the Caspian Sea, the largest inland body of water on Earth. Earthly scientists call this ancient Mars lake by the name Lake Eridania.
The ancient lakebed, now dry for billions of years, is filled with raised mounds. Scientists say they were formed by Martian winds blowing dust. Later, it appears, water covered the dust. And still later – as water disappeared from Mars’ surface – the dust dried out again and broke apart into the mounds we see today.
There are still a few old lake basins visible in Caralis Chaos today. But Lake Eridania is the biggest one. It’s the biggest lake on Mars, larger than any known earthly lake. The water in this huge lake ultimately disappeared, along with all the rest of the water on Mars. How did that happen? Again, due to Mars’ low gravity, the planet couldn’t hold onto much of an atmosphere. So, today, Mars’ atmosphere is thin. Plus Mars is farther than Earth from the sun. So, without an atmosphere to help warm it, Mars became cold. Scientists say that, over time, the one massive lake, Lake Eridania, became a series of smaller lakes as it dried out.
When it was still one lake, it contained enough water to fill the Caspian Sea almost three times over. The Caspian Sea is Earth’s biggest inland body of water. It’s about 750 miles (1,200 km) long by 200 miles (320 km) wide.
Caralis Chaos is what scientists call chaotic terrain. That is areas where mountains, plateaus, cracks and rifts are arranged in jumbled patterns.
So there’s evidence for past liquid water in this region. and there is also evidence for past volcanism in Caralis Chaos: two huge faults, or cracks, that run through the region. These are the Sirenum Fossae faults. They formed when the Tharsis plateau region formed. That upwelling caused stress in Mars’ crust, creating the faults. The planet’s largest volcanoes, including Olympus Mons, are found in the Tharsis region. And in fact, Olympus Mons itself may have once been an island!
There are also many “wrinkle” ridges in Caralis Chaos. They are also volcanic in origin and a common feature on volcanic plains. They form when new sheets of lava become compressed. Since the sheets are still soft, they easily buckle and become deformed. Wrinkle ridges are also common on the moon.
As on much of Mars, impact craters are also common here. Notably, a large central crater in this region has valleys carved out of its southern rim. Scientists say that this may be evidence for some water still existing even after the lake itself dried up. Other craters also feature small gullies, while others have been heavily eroded over time by Martian winds.
Speaking of how Mars’ water disappeared, it now seems that much or even most of it may simply have gone underground. You can read about the new evidence for a vast ocean’s worth of liquid water still existing in Mars’ crust today. That may include Lake Eridania and other lakes, as well as a possible ocean that once covered much of the northern hemisphere on Mars.
Bottom line: Lake Eridania was once the largest known lake on Mars. It was bigger than any lakes on Earth and contained three times as much water as the Caspian Sea.
Read more: Oceans of water on Mars deep underground?
Read more: Mars mission to send Blue and Gold satellites to red planet
The post Ancient Mars lake was larger than any on Earth first appeared on EarthSky.
