Mars Organic Geochemistry—Are We Alone, and Where Did We Come From?

This review of martian organic geochemistry aims to contextualize recent findings of organic molecules in martian meteorites and from Mars missions within the broader study of origins of life on Earth. Analyzing martian organic inventories helps us understand the abiotic processes in planetary environments that are common wherever rocks interact with liquid brines and that likely contributed to the emergence of life on Earth. Mars is only the second planetary body studied for organic molecules; while carbonaceous meteorites, comet missions, and sample-return analyses of comets and asteroids have shown the diversity of organics across the solar system, studying Mars reveals what these molecules are on another planet. Although a definitive sign of extraterrestrial life has not yet been found, the findings provide insights into abiotic synthesis mechanisms that would have occurred on early Earth. At worst, these observations represent the oldest planetary record of organic and prebiotic chemical synthesis pathways that could have led to life, as inferred from the alteration of Earth's oldest rocks. They may also point to potential habitats for past martian life. Currently, samples collected by the Perseverance rover represent a unique opportunity to verify which of the two questions, "Are we alone?" or "How did we get here?" will be true for Mars. Without doubt, these questions would be best addressed through the use of higher resolution analyses by more advanced and sensitive instrumentation after sample return to Earth. Even if no definitive signs of life are found in returned samples, they would give us the opportunity to study the missing link to life on Earth, that of the primordial abiotic organic chemical processes that could have led to life. Therefore, there are no wrong answers to exploring Mars for signs of life; its secrets will illuminate our understanding of ourselves and our place in the universe, whatever the answer.