Key Biosignature Gases to Know for Exoplanetary Science

Biosignature gases are key indicators of potential life on exoplanets. By studying gases like oxygen, methane, and water vapor, scientists can assess a planet's habitability and uncover signs of biological activity, helping us understand the universe's potential for life.

1. Oxygen (O2)

   • Essential for aerobic life forms; high levels indicate potential biological activity.
   • Can be produced through photosynthesis, a process linked to plant life.
   • Its presence alongside methane suggests a dynamic atmosphere, possibly indicating life.

2. Methane (CH4)

   • A potent greenhouse gas that can be produced biologically or geologically.
   • Its detection in conjunction with oxygen raises questions about the presence of life.
   • Short-lived in the atmosphere, requiring continuous replenishment for detection.

3. Carbon dioxide (CO2)

   • A key greenhouse gas that plays a significant role in planetary climate regulation.
   • High levels can indicate volcanic activity or biological processes like respiration.
   • Its presence is crucial for understanding a planet's potential for habitability.

4. Water vapor (H2O)

   • Essential for life as we know it; indicates the presence of liquid water.
   • Plays a critical role in climate and weather patterns on a planet.
   • Its detection can suggest a suitable environment for life.

5. Nitrous oxide (N2O)

   • A greenhouse gas that can be produced by microbial processes in soil and water.
   • Its presence may indicate biological activity, particularly in nitrogen cycling.
   • Can also be produced by industrial processes, complicating its interpretation.

6. Ammonia (NH3)

   • A potential biosignature gas that can indicate biological processes, particularly in nitrogen metabolism.
   • High levels can be toxic to life, suggesting a delicate balance in any ecosystem.
   • Its detection may indicate the presence of certain types of microbial life.

7. Ozone (O3)

   • A protective layer in a planet's atmosphere that absorbs harmful UV radiation.
   • Its presence can indicate photochemical processes, often linked to biological activity.
   • High levels may suggest a planet with a complex atmosphere and potential for life.

8. Phosphine (PH3)

   • A gas that is typically associated with anaerobic biological processes.
   • Its detection on other planets raises intriguing questions about potential life forms.
   • Can also be produced by non-biological processes, making its interpretation complex.

9. Dimethyl sulfide (DMS)

   • A gas produced by marine phytoplankton, indicating biological activity in oceans.
   • Plays a role in cloud formation and climate regulation on Earth.
   • Its presence could suggest a planet with similar biological processes.

10. Chloromethane (CH3Cl)

    • A gas that can be produced by both natural processes and industrial activities.
    • Its detection may indicate biological activity, particularly in certain microbial processes.
    • Can also be a marker for atmospheric chemistry and potential habitability.