This Laser Could Find Fossil Microbes on Mars

According to Darwin, life on Earth may have first appeared in warm little ponds. This simple idea is also a cornerstone in our search for the origin of life. The ponds were rich in important chemicals, and when lightning struck, somehow, it all got going.

If the idea is correct, the same thing may have happened on Mars. If it did, and if fossilized evidence of microbes on the planet exists, a new laser could find it.

We may never know exactly how life started. It appeared to start about 4 billion years ago on Earth, confined to water for about 3 billion, until our planet developed a UV-blocking ozone layer.

If life ever appeared on Mars, it also likely occurred billions of years ago when the planet was warm and wet. There’s a strong possibility that it was also confined to water for a long time. If it did, then ancient sediments could hold fossilized evidence of microbes.

NASA’s Perseverance rover landed in Jezero Crater, an ancient paleolake with deep sediments, in an attempt to detect evidence of ancient life. Jezero also contains an ancient river delta, an excellent place for sediments to collect and potentially preserve microbial evidence.

Perseverance carries a laser as part of its Supercam instrument, an improved version of MSL Curiosity’s Chemcam instrument and laser. Supercam analyzes rocks and soils and searches for organic compounds that are biosignatures of ancient microbial life.

Now, scientists are working on a new laser that could detect microbial fossils on Mars. The device will examine gypsum deposits for signs of these fossils. The device has already been tested in Mars-analogue gypsum deposits in Algeria.

The method is explained in new research published in Frontiers in Astronomy and Space Sciences. Its title is “The search for ancient life on Mars using morphological and mass spectrometric analysis: an analog study in detecting microfossils in Messinian gypsum.” The lead author is Youcef Sellam, a PhD student at the Physics Institute at the University of Bern.

“Our findings provide a methodological framework for detecting biosignatures in Martian sulfate minerals, potentially guiding future Mars exploration missions,” said Sellam. “Our laser ablation ionization mass spectrometer, a spaceflight-prototype instrument, can effectively detect biosignatures in sulfate minerals. This technology could be integrated into future Mars rovers or landers for in-situ analysis.”

Sellam is referring to sulphate minerals, including gypsum, left behind when bodies of water dry up. The minerals precipitate out and collect as deposits, as has happened repeatedly in the Mediterranean Sea during the Messinian salinity crisis.

“The Messinian Salinity Crisis occurred when the Mediterranean Sea was cut off from the Atlantic Ocean,” said Sellam. “This led to rapid evaporation, causing the sea to become hypersaline and depositing thick layers of evaporites, including gypsum. These deposits provide an excellent terrestrial analog for Martian sulfate deposits.”

We know something similar happened on Mars because gypsum deposits are plentiful. Since these deposits form rapidly, there’s a chance for fossils to be preserved before they can decompose.

“Gypsum has been widely detected on the Martian surface and is known for its exceptional fossilization potential,” explained Sellam. “It forms rapidly, trapping microorganisms before decomposition occurs, and preserves biological structures and chemical biosignatures.”

Gypsum deposits on Earth have been extensively studied for evidence of microbes.

“Prokaryotic communities are often found dwelling within modern evaporites, such as gypsum, forming in sabkhas, lacustrine, and marine terrestrial sediments,” the authors explain in their paper. “They mainly participate in carbon, iron, sulphur, and phosphate biogeochemical cycles, extracting water and using various survival strategies to avoid ecological stresses. Consequently, investigating these fossil filaments may enhance our comprehension of the cryptic conditions that led to the formation of the Primary Lower Gypsum unit during the Messinian Salinity Crisis, the biosignature preservation potential of gypsum, and the possible preservation of such fossils in ancient, hydrated sulphate deposits on Mars.”

Detecting evidence in Earth’s gypsum deposits is relatively simple. However, doing it on Mars is rife with challenges. Since scientists already know that Mediterranean gypsum deposits hold evidence of life, Sellam went to test the method there.

Sellam and his co-researchers tested their method at the Sidi Boutbal (SB) quarry in the Lower Chelif basin in Algeria. “The Chelif Basin is one of the largest Messinian peripheral sub-basins, characterized by an elongated and ENE–WSW oriented structure spanning over 260 km in length and 35 km in width,” the authors explain in their paper. The quarry contains gypsum deposits that are tens of meters thick.

The researchers used several methods in their work, including optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and spatially resolved laser ablation mass spectrometry (LIMS). These aren’t new technologies, but combining them into an instrument that can be carried by a rover is new.

In their tests in Algeria, the researchers used a miniature laser-powered mass spectrometer, which can analyze the chemical composition of a sample in detail as fine as a micrometre. They also sampled gypsum and analyzed it using the mass spectrometer and an optical microscope. Many natural rock formations can mimic microbial fossils, so they followed criteria to distinguish between potential microbial fossils and natural rock formations. Microbial fossils display morphology which is irregular, sinuous, and potentially hollow.

In their paper, the authors report finding “a densely interwoven network of brownish, sinuous, and curved fossil filaments of various sizes.”

Their method also detects the presence of chemical elements necessary for life, carbonaceous material, and minerals like clay or dolomite, which can be influenced by the presence of bacteria. “The inner layer of the filament is morphologically and compositionally distinct from the gypsum, mainly composed of Ca, S, O, and traces of Si,” the authors write.

The authors found not only fossil filaments, but also dolomite, clay minerals, and pyrite surrounding the gypsum they were embedded in. This is important because their presence signals the presence of organic life. Prokaryotes supply elements that clays need to form and also help dolomite form, which often forms in the presence of gypsum. The only way that dolomite can form without life present is under high pressures and temperatures. To scientists’ knowledge, those conditions weren’t present on early Mars.

This is interesting progress, but there’s still lots of work to do.

It starts with identifying clay and dolomite in Martian gypsum. Along with other biosignatures, this indicates that fossilized life is there. If the system can identify other chemical minerals, that would help, too. Ultimately, finding organically formed filaments at the same time would be solid evidence that the planet once supported life.

“While our findings strongly support the biogenicity of the fossil filament in gypsum, distinguishing true biosignatures from abiotic mineral formations remains a challenge,” cautioned Sellam. “An additional independent detection method would improve the confidence in life detection. Additionally, Mars has unique environmental conditions, which could affect biosignature preservation over geological periods. Further studies are needed.”

If this method proves to be reliable, it’ll have to wait a while before being implemented.

The ESA’s Rosalind Franklin rover will launch to Mars in 2028. It will look for subsurface chemical and morphological evidence of life. Its instruments have already been chosen. Other nations and agencies have missions to Mars in the planning and proposal stages, but none of them are full-featured rovers like Curiosity and Perseverance.

However, another rover mission to Mars in the future is almost a certainty. Maybe this technology will be ready to go by then.

“Although the Messinian Salinity Crisis, during which the Primary Lower Gypsum formed, remains only partially understood, future astrobiological investigations on Mars should consider hydrated sulphate deposits as promising indicators of ancient Martian environmental conditions. This contribution underscores that hydrated sulphates serve as archives of biological history on Earth and potentially on Mars, should evidence of past life be found,” the authors conclude.

• Press Release: Laser-powered device tested on Earth could help us detect microbial fossils on Mars
• Published Research: The search for ancient life on Mars using morphological and mass spectrometric analysis: an analog study in detecting microfossils in Messinian gypsum

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