Mars may have been covered with lakes in ancient times

Scientists have puzzled over the surface features of Mars since robotic explorers began visiting the Red Planet in the 1960s and 1970s. These included river channels, valleys, lake beds, and deltas that appear to have formed in the presence of water. Since then, dozens of missions have been sent to Mars to explore its atmosphere, surface, and climate, and to learn more about its warmer, wetter past. In particular, scientists want to know how long water has flowed on the surface of Mars and whether it was inherently permanent or intermittent.

The ultimate purpose here is to determine whether rivers, streams, and stagnant water existed long enough for life to arise. So far missions like curiosity and persistence have collected volumes of evidence showing how hundreds of large lake beds once dotted the Martian landscape. But our current estimates of Mars’ surface water could be a dramatic understatement, according to a new study by an international team of researchers. Based on a meta-analysis of years of satellite data, the team argues that ancient lakes may have once been a very common feature on Mars.

The research was carried out by Dr. Joseph Michalsi, Associate Professor in the Department of Earth Sciences and Associate Director of the Laboratory for Space Research (LSR) at the University of Hong Kong (HKU). He was joined by researchers from the Canadian Institute for Advanced Research (CIFAR), the Center for Planetary Systems Habitability at UT Austin, the University of British Columbia (UBC), the Natural History Museum, and Brown and Georgetown University. The paper, titled “Geological Diversity and Microbiological Potential of Lakes on Mars,” describing their findings, recently appeared in the journal Nature.

As Michalski explained in a recent HKU press release, current research has focused on larger bodies of water on Mars and may have neglected the many smaller lakes that may have existed there:

“We know of about 500 ancient lakes deposited on Mars, but almost all of the lakes we know of are larger than 100 km². But on Earth, 70% of lakes are smaller than this size and occur in cold environments where glaciers have retreated. These small lakes are difficult to identify on Mars by satellite remote sensing, but there were likely many small lakes. It is likely that at least 70% of the Martian lakes have yet to be discovered.”

Lake beds are currently one of the prime targets for robotic explorers on Mars, as ancient lakes would have all the ingredients for microbial light – including water, nutrients, and energy sources such as light (for photosynthesis). Today, the lake beds of these ancient bodies of water contain sedimentary deposits rich in iron/magnesium clay minerals and carbonates, as well as sulfates, silica and chlorides. These deposits could potentially contain preserved evidence that would attest to ancient atmospheric and climatic conditions on Mars.

But as they state in the publication, most of the known Martian lakes are from the Noahian period (roughly 4.1 to 3.7 billion years ago) and lasted only 1,000 to 1 million years. From a geological perspective, this is a relatively short period of time and represents a tiny fraction of the 400-million-year-old Noahian timeline. This could mean that ancient Mars was also cold and dry, and flowing water was episodic and short-lived. Due to Mars’ lower gravity and fine-grained soil, the team also theorized that the lakes on Mars would have been turbid, making it difficult for light to reach very deep and posing a challenge to photosynthesis.

As a result, Michalski and his colleagues argue that large, ancient, ecologically diverse lakes would present a much more promising target for future exploration. “Not all lakes are the same,” Michalski said. “In other words, some Martian lakes would be more interesting for microbial life than others because some of the lakes were large, deep, and long-lived, and featured a variety of environments, such as hydrothermal systems, that may have been conducive to the emergence of simple life.”

However, there is also evidence that lakes existed on Mars in more recent geological periods, but left fewer traces. These include paleolatic lakes during the Hesperian period (3-3.7 billion years ago) and shallow marshy lakes during the Amazon (less than 3 billion years ago). These features would be similar to those found on Earth, where similarly cold conditions prevail, and would likely resemble shallow lakes found in drier regions (Hesperian) and thermoclasts (swampy sanctuaries) formed during permafrost thaw ( Amazonia) occur.

dr David Baker is an ecologist at the HKU School of Biological Sciences and co-author of the article, who is familiar with microbial systems in Earth’s lakes. As he summarized, Earth analogs could help expand the search for life on Mars by allowing scientists to look into more diverse environments:

“Earth hosts many environments that can serve as analogues to other planets. From the rugged terrain of Svalbard to the depths of Mono Lake, here at home we can define how to develop tools to discover life elsewhere. Most of these tools are aimed at detecting the remnants and residues of microbial life.”

This research supports the recently published ESA mineral map of Mars, which showed how aqueous minerals (those that form in the presence of water) are ubiquitous on the surface. It could also help inform future robotic missions, which include those by ESA Rosalind Franklin Rover currently scheduled to launch by 2028. China’s first lander and rover mission to Mars, Tianwen-1 and Zhuronglanded on May 14, 2022 and is currently exploring the plains of Utopia Planitia.

This region was once the site of an ocean that covered most of the northern hemisphere and likely contains mineralogical and chemical evidence of how and when Mars transitioned from a warmer, wetter planet to what we see today. That persistence Rover is currently collecting and storing samples to be retrieved by an ESA-NASA sample return mission in the coming years. This will be the first time samples will be brought back from Mars for a comprehensive analysis that can only take place in laboratories on Earth.

China is planning a similar sample-return mission, which could be sent to a Hesperian or Amazonian lake bed, and will likely take place by the end of the decade. These and other missions will also pave the way for manned missions that NASA and China plan to conduct by the early 2030s. These missions will land in regions that have accessible water that could also serve as a site for potential research. If there really was life on Mars billions of years ago (or there still is today), the evidence won’t be far behind!

Further reading: HKU, Natur