In 2007, new images of Mars wowed astronomers and the general public with something out of the pages of a sci-fi comic: extraterrestrial caves. Photos produced by orbiting satellites showed evidence of “skylights” into underground caverns, and thermal imaging indicating that these caves remained at a constant temperature day and night. In recent years, caves and related structures have also been discovered on our moon and on Jupiter’s moon Titan. The concept of extraterrestrial caves has plainly moved from fiction to reality, and scientists are eager to start exploring.
Why is the scientific world so excited about extraterrestrial caves? For many, they represent the next frontier in the search for extraterrestrial life. For others, they are our best bet for someday constructing and maintaining habitable colonies on other planets.
In October 2011, an interdisciplinary group of geologists, cave explorers, earth scientists, astrobiologists and other researchers met in New Mexico for the first time to discuss the science and implications of caves on other planets. Published earlier this month in the journal Eos, the results of the meeting give us a tantalizing hint of what discoveries may come during our lifetimes as space missions begin exploring these hidden crevices throughout the solar system.
Caves are a remarkably promising location to begin looking for life, the scientists report. Because they are isolated and protected from the surface, they can provide a diverse range of microenvironments—and the greater number of different habitats, the greater the chance life will happen to evolve in one of them. The study of caves here on earth has shown us that many unusual (and in some cases, downright bizarre) life forms can evolve in caves, and many of these result from the abundance of sulfur, metals and other chemicals that are likely to be available in caves on other planets as well.
The group of researchers also theorized about possible means of exploring caves on other planets and moons. Although images produced by satellites and other spacecraft can sometimes reveal the existence of caves, new technologies are clearly necessary to actually explore their interiors and extract samples that might contain life. Exploration and mapping could hypothetically be undertaken by either human or robotic means, although the latter seems more realistic at this point.
Ground-based exploration vehicles, such as the Mars rovers, could be equipped to enter and navigate caves, but the group noted that such devices would require better autonomous decision-making. Robotic explorers would need to be able to avoid hazards and make decisions about what data to collect without communicating with earth, since the cave walls and ceilings could block the transmission of radio signals.
The scientists even considered how caves can foster human exploration of other moons and planets. They might, for example, be good places to look for ice and other resources that would help groups of humans explore and perhaps even inhabit far-flung extraterrestrial bodies. They could also provide physical protection for colonies and experiments. Close study of caves on earth—their geologic context, the means by which they formed, the microenvironments they provide and other factors—will help us know what to expect in planning cave excursions elsewhere.
Although all of this cave talk sounds a bit like it belongs in a summer Hollywood blockbuster rather than the proceedings of an academic conference, consider this: Exploration of the ocean floor and the moon were both predicted in science fiction before being taken seriously by the scientific establishment. After technology caught up with the human imagination, these ideas didn’t seem so far-fetched.
It may take decades or longer, but it appears as though exploration of extraterrestrial caves is on the same track. What’s more uncertain, though, is what marvels we’ll find when we get there.