Martian enthusiasts are growing increasingly excited by the presence of cracked mud on Mars. A recent study suggests that the conditions required for the formation of these cracks may have also been conducive to supporting microbial life. While the origins of life on Earth remain uncertain, one prevailing theory posits that cycles of wet and dry conditions on land played a crucial role in assembling the complex chemical building blocks necessary for life to begin.
The discovery of well-preserved ancient mud cracks by NASA’s Curiosity Mars rover has sparked excitement among the mission’s team. Detailed in a paper published in Nature, these cracks exhibit a distinctive hexagonal pattern that provides the first evidence of past wet-dry cycles on early Mars.
Lead author William Rapin from France’s Institut de Recherche en Astrophysique et Planétologie explains that these particular mud cracks form when wet-dry conditions occur repeatedly, possibly on a seasonal basis. Curiosity is currently ascending the sedimentary layers of Mount Sharp within Gale Crater.
The mud cracks were first spotted in 2021 after Curiosity drilled a sample from a rock target known as “Pontours,” located in a transitional zone between a clay-rich layer and a layer enriched with sulfates, which are salty minerals. Clay minerals typically form in water, while sulfates tend to form as water evaporates.
The different minerals present in each area reveal different eras in Gale Crater’s history. The transitional zone between these two layers provides a record of a period when long dry spells became prevalent and the lakes and rivers that once filled the crater began to recede.
As mud dries out, it shrinks and fractures, forming T-shaped junctions. Curiosity previously discovered these junctions at a location called “Old Soaker,” lower down on Mount Sharp. The mud cracks at Pontours, experiencing recurring exposure to water, caused the T-shaped junctions to soften and become Y-shaped, eventually forming a hexagonal pattern.
The hexagonal cracks in the transitional zone continued to form even as new sediment was deposited, indicating that wet-dry conditions persisted over long periods of time. The rover’s ChemCam instrument confirmed the presence of a hardy crust of sulfates along the edges of the cracks, which is not surprising considering the proximity of the sulfate region. This salty crust protected the mud cracks from erosion, preserving them for billions of years.
Rapin notes that this is the first tangible evidence of the ancient climate of Mars having regular wet-dry cycles similar to those on Earth. Furthermore, these wet-dry cycles are believed to be essential for the molecular evolution that could lead to life.
While water is essential for life, it requires a delicate balance – not too much and not too little. The conditions that sustain microbial life, such as a long-lasting lake, differ from the conditions necessary to promote chemical reactions that could give rise to life.
One crucial product of these chemical reactions is long chains of carbon-based molecules called polymers, including nucleic acids, which are considered the building blocks of life. Wet-dry cycles control the concentration of the chemicals involved in these fundamental reactions leading to the formation of polymers.
Ashwin Vasavada, the project scientist for the mission at NASA’s Jet Propulsion Laboratory, remarks that this research expands upon the previous discoveries made by Curiosity, providing ample evidence that ancient Mars could have supported microbial life and suggesting that conditions may have existed for the origin of life itself.
The discovery of the Pontours mud cracks may offer scientists their first opportunity to study remnants of life’s beginnings. Unlike Earth, which constantly recycles its surface through tectonic plate movement, Mars does not have tectonic plates, allowing much older periods of its history to be preserved.
Rapin considers it fortunate that a planet like Mars, which retains evidence of the natural processes that may have led to life, exists nearby. The Curiosity rover was developed by NASA’s Jet Propulsion Laboratory, managed by Caltech in Pasadena, California. The mission is led by JPL on behalf of NASA’s Science Mission Directorate in Washington.
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