By: Reilly Sleater
A cave is comparable to the oh-so-dreaded cavity your dentist may or may not find upon your next check-up. However, unlike a sugar-induced cavity, most caves were formed many thousands of years ago by Mother Nature! Caves can often be defined as natural openings or chambers in the Earth (sometimes also referred to as caverns when there is more than one chamber). There are many different types of caves, all categorized by how they were formed. For example, sea caves can be found along coastlines and are formed by the continuous crashing of waves against rock. Caves can even be made of ice – also known as ice or glacier caves. Glacier caves form when flowing water enters cracks in a glacier, and over time, these cracks become bigger and bigger through erosion. Another kind of cave is made of soluble rock, such as limestone, and is called a solution or karst cave. These caves form when acidified water seeps into underground rock and erodes the rock through a combination of chemical and physical processes. While solution caves are amongst the most common, one specific kind of cave is at the forefront of astrobiological research for extraterrestrial life.
Lava tubes are the research focus for scientists who are currently studying microscopic, resilient creatures present in these caves. The microbial life found in these lava tubes could possibly be present on another planetary bodies in the cosmos. Unlike any other kind of cave, lava tubes form through the aftermath of volcanic eruptions. Lava that reached temperatures of up to ~1200 °C, or ~2200°F, was once ejected out of a volcano, flowed downhill, and eventually cooled and solidified on the tops and sides while liquid remained underneath. Once the eruption had stopped, the lava proceeded to drain from the inside of these hardened lava tubes, creating a hollow cave tube inside. This is all made possible due to the chemical composition of the lava. Lava tubes were formed from basaltic lava, which doesn’t contain a lot of silica. Silica is the chemical agent that determines how thick the magma is. Thus, lava with a low silica concentration has a low viscosity (resistance to flow), meaning it is able to move quicker and easier from a tube.
Lava tube cave in Hawai’i [Photo Credit: Nāhuku- Thurston Lava Tube (NPS Photo/D. Boyle)]
Lava tubes are of particular interest to astrobiologists for more than one reason. The geochemical composition of rocks and minerals found in these caves, along with the living organisms and the things they do within the caves, can assist scientists in their endeavor to discover life on other planetary bodies. For example, Mars and the Moon have lava bed caves present under their rocky surfaces. In fact, the Mars Odyssey and Mars Reconnaissance Orbiter spacecrafts have detected complex networks of what appear to be intersecting tunnels created by the flow of lava. Such caves may be important models for understanding potential biological life on various other planetary bodies. Through studying similar caves here on Earth, scientists are able to look for and target tiny, microbial life forms that may be examples of cave life we might discover on other worlds.
Water droplets on biofilm & glowing microbial colonies in lava tubes upon ultraviolet exposure (Photo Credits: NASA BRAILLE Team)
There is no secret that Mars is a relatively hostile planet with extreme environmental conditions. For example, Mars has a very thin atmosphere compared to Earth. The Red Planet also lacks an intrinsic magnetic field that shields it from the Sun’s radiation. This means that radiation is not deflected, therefore harmful ionizing particles are able to penetrate Mars’ surface. This is definitely not the most ideal condition for biological life, since ionizing radiation causes mutations in an organism’s DNA and can destroy other biological molecules. However, caves have a built-in defense mechanism against this harmful radiation – their habitable surface is underground, thus covered by thick layers of impenetrable rock. Despite Mars’ desert-like terrain and cold temperatures coupled with life-destroying radiation, there still may be hope. Extant microbial life may be preserved and may even be detectable in its underground lava tubes…if only we could go there and find it!
Intersecting valleys on Mars created by lava flow, NASA 2001 Mars Odyssey (Photo Credit: NASA / JPL)
Here on Earth, a group of scientists are currently working on NASA’s BRAILLE (Biologic and Resource Analog Investigations in Low Light Environments) Project, and are venturing into North America’s largest system of lava tubes – more commonly known as the Lava Beds National Monument, located in California and home to over 900 lava bed caves. The BRAILLE team embarked on their research by deploying their cave rover, CaveR, in Valentine Cave. The Valentine Cave is approximately 15 feet high and 70 feet wide, with rocky terrain that’s comparable to what a Martian lava cave is theorized to be like inside. Additionally, the BRAILLE team is collaborating with NASA’s JPL robotics team, CoSTAR (Collaborative SubTerranean Autonomous Resilient Robots). The CoSTAR and BRAILLE teams have deployed Boston Dynamics SPOT robots, which utilize a software system called NeBula Autonomy Solution. These new-era SPOT robots are of special significance because they have four legs that are able to walk with movements comparable to a dog. The legged robots are designed to traverse extreme terrains without human guidance, which is especially promising for future missions to Mars and the Moon.
Three JPL SPOT robots working in Valentine Cave, Lava Beds National Monument (Photo Credit: NASA / BRAILLE Team)
A JPL SPOT robot in Valentine Cave, Lava Beds National Monument (Photo Credit: NASA / BRAILLE Team)
Mother Nature’s cavities, I mean caves, are of significant importance for the detection of extraterrestrial life. A good portion of people reading the term ‘extraterrestrial life’ may or may not immediately think of a little green alien that travels in a flying saucer. However, rather than searching for little green aliens elsewhere, scientists are microscopically zooming in on caves here on our home planet. With the help of autonomous robots, the research in lava tubes is more efficient than ever. Who knows, maybe the research currently being done will lead to our first discovery of extraterrestrial life!
Reilly Sleater graduated from Florida Atlantic University with a Bachelor’s in Biological Sciences. She is both a Communications Intern for BRAILLE and a Research Associate for BMSIS in the Young Scientist Program.
References:
Astrobiology Institue. (2016). Why Caves – Astrobiology. ESA. http://www.esa.int/ESA_Multimedia/Videos/2016/06/Why_CAVES_Astrobiology.
Blue Marble Space. (n.d.). NASA BRAILLE – Biologic and Resource Analog Investigations in Low Light Environments. https://nasa-braille.org/.
Greicius, T., Jackson, R., & Hartono, N. (n.d.). Nebula-SPOT. JPL. https://www.jpl.nasa.gov/robotics-at-jpl/nebula-spot.
Léveillé, R. J., & Datta, S. (2010). Lava tubes and basaltic caves as astrobiological targets on Earth and Mars: A review. Planetary and Space Science, 58(4), 592–598. https://doi.org/10.1016/j.pss.2009.06.004
NASA. (n.d.). NeBula Autonomy Solution. JPL. https://costar.jpl.nasa.gov/#nebula_up.
Swanson, D. A. (2015, April 8). Volcano Hazards Glossary – Basalt. USGS. https://volcanoes.usgs.gov/vsc/glossary/basalt.html.
Tavares, F. (2019, June 26). Using a ‘Cave Rover,’ NASA Learns to Search for Life Underground. Astrobiology at NASA. https://astrobiology.nasa.gov/news/using-a-cave-rover-nasa-learns-to-search-for-life-underground/.
U.S. Department of the Interior. (n.d.). Lava Beds National Monument (U.S. National Park Service). National Parks Service. https://www.nps.gov/labe/index.htm.