Interactions between life and planets in the modern
Cave air as an indicator of planetary habitability
Cave air flows much slower than the atmosphere and because of this the composition of cave air is sensitive to the inputs of trace gasses. The drivers of the difference in the chemical composition of cave air on Earth are biological and geological activity. The presence of biological and/or geological activity on a planet are two the best indicators of habitability. When cave air is less buoyant than the atmosphere it rises and displaces the more buoyant atmosphere. Under these conditions the chemical composition of cave air on Earth and other planets can be measured through remote spectroscopic methods and orbitally assess habitability. I am currently developing ideas related to the astrobiological implications of the composition of cave air with colleagues from the USGS.
In the above figure redrawn from Cushing et al., (2007) a skylight cave on Mars is imaged using the infrared wavelengths. Note the strong thermal signature from the cave during the morning in panel C. During times like these, cave air is likely venting to the atmosphere and its composition could be determined spectroscopically from orbit.