EXTRATERRESTRIAL LAVATUBES AS REPOSITORIES OF SCIENCE, RESOURCES, AND HUMAN EXPLORATION

Lavatubes, other caves, and canyon overhangs that will be found on other planets are sites of intense scientific interest. Of course, much of this interest will center around the geological processes that have given rise to these structures. However, the contents of such caves are of equal interest. As we see here on Earth, the tendency of the subsurface to provide very different conditions from the surface means that unique mineralogy, geochemistry, and even biology or remnants of past biology are potentially to be found in lavatubes on other Solar System bodies. Increasing evidence of lavatubes on Mars and the Moon and the potential for tubes on Venus, Io, and possibly even Mercury have spurred the consideration of these structures as potential scientific targets for future missions. The dawn of comparative "tubology" is finally upon us! This has major consequences not only for planetary science but is profoundly influencing how we study the Earth examples that we can visit in person. A major focus of our work has centered around the microbial inhabitants of lavatubes across a broad set of climatic, altitudinal, and moisture gradients. We see that the mineral biosignatures that organisms create or facilitate can be diagnostic of features of the living biology and the geochemical effects that they have on their rock environments. Lavatubes are often heavily colonized with communities of novel organisms and secondary mineralogy of lavatubes can range from sulfates and sulfides, through iron and manganese compounds, carbonates, copper minerals, and silica minerals. The study of such "biosignatures" can serve as a template for life detection experiments in lavatube features in future planetary missions. Besides intrinsic scientific interest, natural subsurface cavities may present the most mission effective habitat alternatives for future human missions in the high-radiation and thermally challenging environments of Mars and Earth's Moon. They offer easier subsurface access for direct exploration and drilling, and may provide extractable minerals, gases, and ices.