A geological map, created using data from a plethora of orbiting spacecraft, presents new evidence that lakes persisted early in Mars' history.

The map focuses on Hellas Planitia, an area located in the planet's southern hemisphere that is well known for its giant impact basin – the Hellas basin – which spans over 2,000 kilometres in diameter and plunges to a depth of eight kilometres.

Finely layered outcrops of sedimentary deposits seen in the eastern rim of Hellas point to large areas of standing water, such as lakes or seas. Deposits of sedimentary rocks suggest erosion and transport of material from higher to lower ground. Indeed, the highlands surrounding Hellas are well known to have hosted volcanic activity and sedimentary processes over time.

Using data from Viking Orbiter, Mars Odyssey's Thermal Emission Imaging System (THEMIS), Mars Orbiter's narrow-angle camera and the Mars Orbiter Laser Altimeter topographic data, planetary geologists could piece together the geological history of the area.

“This mapping makes geologic interpretations consistent with previous studies, and constrains the timing of these putative lakes to the early-middle Noachian period on Mars, between 4.5 and 3.5 billion years ago,” says Leslie Bleamaster, research scientist at the Planetary Science Institute.

Moreover, scrutinizing high-resolution images revealed that the eastern area of Hellas Planitia, where the fine-layered floor deposits were discovered, is unique in nature. It is interpreted as the meeting point of sedimentary sources, and sedimentary sinks – the locations where sediments derived from elsewhere are deposited .

“Our mapping and evaluation of landforms and materials of the Hellas region from the basin rim to floor provides further insight into Martian climate regimes and into the abundance, distribution, and flux of volatiles through history,” says Bleamaster.

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