Mars has been keeping me busy! This is the fourth article I have written on the red planet in twelve months and who knows how many I will write in the next twelve. This frequency of writing is not entirely surprising considering Mars' proximity to Earth, allowing us to explore it with highly sophisticated robotic assets, to study comparative planetology in great detail, and to search for extraterrestrial life. In fact, Mars is the most studied planetary body in Space after the Moon.
Recently, a comment regarding Mars' ability to support life and the difficulties we face in detecting it caught my attention. In my Ocean Worlds book, I've written extensively about the Viking landers and their attempts to find life on Mars, as it is a fascinating story. In the 1970s, scientists faced the surprisingly difficult task of determining how to detect life. The three experiments (GEX, LR, and PR) and the spectrometer for detecting organic molecules (GCMS) produced inconclusive results, leading to mixed and controversial interpretations. All the experiments used a solution of nutrients mixed with water to 'wake up' any microbial life present on the planet's surface. I even mentioned an experiment, the Wolf Trap, which wasn't included on the Viking landers due to budget constraints but would have involved placing Martian soil in a tube filled with liquid water and nutrients.
The main idea is that, based on our understanding of extremophiles that thrive in some of Earth's driest regions, we might be able to predict how life could survive under similar conditions on Mars. Given that such extremophiles on Earth thrive by being exposed to large amounts of liquid water, it cames to no surprise that the main strategy for finding life (microbial) on Mars has been the 'Follow the Water'. For many decades now, looking for evidence of ancient water activity, such as dried-up riverbeds, lakebeds, and minerals that form in the presence of water, has been the cornerstone of our astrobiological efforts on Mars. But, maybe we're wrong.
It might be time to rethink life detection on Mars. Astrobiologist Dirk Schulze-Makuch argues in his comment that traditional methods based on Earth-centric assumptions may have hindered the detection of Martian life, instead of helping it. Martian organisms have followed a different evolutionary pathway than Earth organisms and adapted early on to environments with minimal moisture, using mechanisms like absorbing tiny amounts of water from the air through hygroscopic salts. As such, the Viking landers' experiments might have inadvertently harmed potential Martian microbes by introducing too much water, which could be fatal to organisms adapted to trace moisture levels.
Schulze-Makuch goes on to explain that extremophiles residing within salt rocks in Earth's driest regions, like the Atacama Desert or Antarctica's dry valleys, acquire water using hygroscopic salts. These salts facilitate the creation of brine, enabling the organisms to thrive and reproduce. However, an excess of water can ironically harm these organisms, potentially causing them to die from osmotic shock. Heavy rainfall in arid regions has been noted to cause the widespread death of these extremophiles.
Due to Mars' extremely arid conditions, Schulze-Makuch suggests that upcoming Mars missions should tailor their exploration strategies to the planet's distinct environment. The focus should be on examining hygroscopic salts, which may contain the only microbial life capable of surviving the surface (which is easiest to study for current space missions) instead of trying to replicate Earth's conditions. This approach makes sense to me, and I wouldn't be surprised if the 'Follow the Water' strategy on Mars is eventually replaced by 'Follow the Salt', potentially leading to groundbreaking discoveries about the resilience of life and the geological history of Mars.
In the meantime, as we approach this season filled with warmth and cheer, I wish you all a Merry Christmas and a Happy New Year!
As always, onwards and upwards.
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