Volcanoes can entirely transform worlds, and play a major role in shaping their atmospheres. Volcanic outgassing is a primary source of a planet’s atmosphere, releasing nitrogen, water vapor, carbon dioxide, and sulfur dioxide. These gases influence surface conditions, climate stability, and even the potential for life. But in the search for life on exoplanets, volcanic emissions pose a challenge: they can mimic the chemical signatures that astrobiologists rely on to detect living organisms.
Volcanism may even be prerequisite for habitability. On Earth, it has played a key role in maintaining a stable climate and cycling essential elements. If life requires a planet with an active interior, then volcanism may be a common thread among habitable worlds. The history of Earth suggests that volcanic activity could have been crucial to the emergence of life itself. If this is true, then exoplanets with persistent volcanic activity could be prime candidates for hosting life.
Scientists searching for biosignatures—chemical traces of life—must tread carefully. Some gases, such as methane, are often associated with biological processes. However, volcanic outgassing can also produce methane abiotically, leading to false positives. High-temperature volcanic emissions on Earth release methane, as well as carbon monoxide. If methane and carbon dioxide are detected in an exoplanet’s atmosphere without carbon monoxide, this could be a strong biosignature. But if all three gases are present together, the likely explanation is volcanic activity, not life.
Sulfate aerosols provide another complicating factor. These particles can result from volcanic eruptions, but they can also be linked to biological processes. The challenge is determining whether their presence signals life or an active geological process. Volcanic activity and biological activity can overlap in complex ways, making it difficult to pinpoint definitive signs of life.
Beyond short-term atmospheric changes, volcanism has a long-lasting impact on planetary habitability. Outgassing releases carbon dioxide and hydrogen, which serve as substrates for biological methanogenesis. Volcanism drives atmospheric evolution through a continuous cycle of outgassing, ingassing, and volatile loss to space. Even planets without plate tectonics can sustain atmospheres over geologic timescales if volcanism remains active. The redox state of outgassed volatiles—how oxidizing or reducing they are—has likely been stable throughout Earth’s history, affecting the reliability of certain biosignatures.
Volcanism is both a facilitator and an obstacle in the search for life. It helps create habitable conditions while also producing gases that can masquerade as biosignatures. To interpret exoplanet atmospheres correctly, scientists must untangle the signals of life from the echoes of planetary geology. Only by understanding the complex interplay between volcanism and atmospheric chemistry can we truly identify planets where life might thrive.
Further Reading: Detecting Volcanism on Extrasolar Planets, The Astronomical Journal
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life, Astrobiology
Venus Landscape by NASA’s Goddard Space Flight Center Conceptual Image Lab, Michael Lentz, USRA; Aaron E. Lepsch, ADNET Systems, Inc.
Leave a comment