A new view from Mars Express's High Resolution Stereo Camera (HRSC) showcases Caralis Chaos, an area believed to have been rich in water. The lower-right part of the frame features the remains of an old lakebed, visible in the associated topographic view in shades of blue. The boundaries of this lakebed curve from the bottom-center of the frame to the top right, skirting a large central crater.
This ancient lakebed now contains numerous raised mounds, thought to have formed as ancient martian winds swept dust across the planet. This dust was later covered and altered by water before drying out again and breaking apart.
The broader region around Caralis Chaos contains several old lake basins that have eroded over time. Together, these basins form the remnants of a vast ancient lake known as Lake Eridania. Covering over a million square kilometers, Lake Eridania once held more water than all other martian lakes combined and was larger than any known lake on Earth. It contained enough water to fill the Caspian Sea nearly three times over and likely existed around 3.7 billion years ago. Initially, it was one large body of water, but it later dried out into smaller isolated lakes before disappearing entirely along with the rest of Mars's water.
Alongside water, signs of volcanism are evident in and around Caralis Chaos. Two long cracks, known as the Sirenum Fossae faults, run vertically down the image, cutting through the lakebed and the smoother ground to the left. These faults formed as Mars's Tharsis region - home to the largest volcanoes in the Solar System - rose up, putting immense stress on Mars's crust.
Volcanic stress also created the many wrinkle ridges seen here, appearing as wriggly lines weaving horizontally across the frame. These ridges are common on volcanic plains and form as new lava sheets are compressed while still soft, causing them to buckle and deform.
Impact craters in the region also tell a story. The large central crater shows signs of flowing material and carved-out valleys on its southern rim, suggesting that water existed here even after Lake Eridania vanished. The smaller crater to its south has been eroded by small gullies, while the rightmost part of the image displays several ancient craters that are barely recognizable due to erosion.
Mars Express has been orbiting the Red Planet since 2003, capturing images of Mars's surface, mapping its minerals, analyzing its atmosphere, and exploring its crust. The HRSC has revealed much about Mars's diverse surface over the past 20 years, showing everything from wind-sculpted ridges to impact craters and ancient lava pools. The mission has significantly enhanced our understanding of Mars.
The Mars Express High Resolution Stereo Camera (HRSC) was developed and is operated by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR).
Related Links
Mars Express at ESA
Mars News and Information at MarsDaily.com
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