Imagine a tiny, single-celled creature—much like a bacterium—gliding through a pitch-black ocean on another world. Its body is a translucent sphere just a few micrometers across, powered by chemical energy rather than sunlight. From its membrane sprout dozens of hair-like flagella, whipping rhythmically to propel it through the frigid depths. This “water-based microbial cell” may sound like science fiction, but a growing body of research—from Mars to the icy moons of Saturn and deep beneath Earth’s oceans—suggests that such life could exist beyond our planet.
Evidence from scientific research can be found in the following:
1. Organic Molecules in Martian Mudstone (Curiosity)
• In 2018, NASA’s Curiosity rover uncovered some of the most compelling evidence yet that Mars once hosted the ingredients for life. Inside 3-billion-year-old mudstone at Gale Crater, Curiosity’s Sample Analysis at Mars (SAM) instrument detected a suite of complex organic molecules—chlorobenzene, thiophenes, benzenecarboxylic acids, and more. These carbon-rich compounds are the very building blocks life on Earth uses to assemble proteins, DNA, and cell membranes.
Even more exciting, these organics appear embedded in sedimentary layers that were once clay-rich lakebeds, implying a wetter past with stable bodies of water. While none of these molecules prove microbes once lived on Mars, their presence shows that the Red Planet’s ancient environment could have provided the raw materials for microbial life—perhaps even tiny “Martian bacteria” swimming amid shallow lakes nearly 4 billion years ago.
• Learn more on the JPL site
2. Methane Spikes in Mars’s Atmosphere (Curiosity SAM)
Methane is a gas that, on Earth, is produced in large part by microbial activity—think of the bogs, wetlands, and digestive tracts of grazing animals. Curiosity’s SAM instrument has measured background methane at about 0.7 parts per billion (ppb) in Gale Crater’s atmosphere, punctuated by seasonal spikes up to 21 ppb. These transient bursts occur mostly in late summer and early fall, fading back to baseline over months.
Scientists are divided on the source of these methane plumes. Possibilities include:
- Underground microbial “methanogens” alive beneath the surface, releasing methane through cracks and vents.
- Geological reactions, such as water-rock interactions (serpentinization) that generate methane abiotically.
Either way, the fact that methane appears, then disappears, argues for a dynamic subsurface process—biological or not—that could fuel a lone bacterial cell drifting through a shallow Martian aquifer.
• Read the SAM methane report
3. Molecular Hydrogen in Enceladus’s Plumes (Cassini)
• Turning to the outer solar system, Saturn’s moon Enceladus has emerged as a prime target in the search for life. Cassini’s fly-throughs of Enceladus’s south-polar plumes in 2015 revealed something extraordinary: molecular hydrogen (H₂) mixed with water vapor, carbon dioxide, and organic compounds. On Earth, hydrothermal vents on the seafloor produce H₂ when hot water reacts with rock. That hydrogen then powers entire ecosystems of chemosynthetic microbes—bacteria that oxidize H₂ to produce energy and build biomass.
The detection of H₂ in Enceladus’s icy jets tells us that active hydrothermal reactions are likely occurring beneath its icy crust. If so, the moon’s subsurface ocean could host microbial life very much like our hypothetical water-based microbial cell—tiny organisms feeding on hydrogen, carbon dioxide, and salts spewing from underwater vents.
• See NASA’s “Ingredients for Life” summary
4. Earth Extremophiles at Hydrothermal Vents
• Back on Earth, we have living proof that chemosynthesis can sustain rich ecosystems in total darkness. Along the mid-ocean ridges, hydrothermal vents spew super-hot, mineral-laden water into the frigid deep. There, chemosynthetic bacteria of genera like Arcobacter and Thermodesulfobacterium form thick microbial mats on rock walls, oxidizing hydrogen sulfide (H₂S) or hydrogen (H₂) to produce organic matter.
These mats anchor tube worms, clams, shrimp, and myriad other creatures—an entire food web built without a single photon of sunlight. The analogy to Enceladus is striking: if microbes can thrive in Earth’s deep-sea vents, then tiny, flagellated cells could similarly exploit chemical plumes on distant ocean worlds.
• Click here to visit the evidence website
Why These Discoveries Matter
From ancient Martian lakebeds to the icy plumes of Enceladus and Earth’s deepest vents, the evidence converges on one clear theme: life is not confined to sunlit realms. Tiny, water-based microbial cells—propelled by flagella and powered by chemical energy—could plausibly exist wherever liquid water meets a source of reduced compounds. As missions like Perseverance, Europa Clipper, and future Enceladus landers press on, we edge closer to answering the age-old question: Are we alone, or is the cosmos teeming with microscopic life?