New research suggests that fluorescent caves on Earth may hold the secrets to survival in extreme environments necessary for scientists to detect life elsewhere in the universe.
The pink, blue, and green shimmers come from stone-captured chemicals that may hold clues to the conditions in remote locations like Jupiter‘s ice-covered moon Europa. The research took place at South Dakota’s Wind Cave and other caves in the US, which revealed conditions believed to share many similarities with Europa, according to a team at the University of Northern Iowa led by Professor Joshua Sebree.
Spelunking for Clues to Life Elsewhere
“The purpose of this project as a whole is to try to better understand the chemistry taking place underground that’s telling us about how life can be supported,” Sebree said.
Descending into several caverns, Sebree’s students mapped natural features and the inhabitant organisms they found. The team’s major innovation was using black lights to investigate the fluorescent minerals in the cave rocks. The colors act as a sort of chemistry “fossil,” recording the organic and inorganic compounds carried by water long ago.
“The walls just looked completely blank and devoid of anything interesting,” says Sebree. “But then, when we turned on the black lights, what used to be just a plain brown wall turned into a bright layer of fluorescent mineral that indicated where a pool of water used to be 10,000 or 20,000 years ago.”
New Approaches to Underground Exploration
Sebree’s team circumvented the typical process of collecting physical samples for laboratory analysis by recording fluorescence spectra with a portable spectrometer. The spectra for each mineral are like a unique fingerprint, allowing the team to identify the compounds present without damaging the cave system.
Several of Sebree’s students are now building on the cave work with their own unique projects. Anna Van Der Weide is currently bringing the work to a broader audience by creating a publicly available database, a project that expands traditional cave maps with new layers of information. Meanwhile, Jacqueline Heggen is studying how the caves may act as simulations for extreme astrobiological environments.
Another student, Jordon Holloway, is at work on an autonomous spectrometer that would aid further measurements in terrestrial caves and uncrewed missions beyond Earth. Finally, Celia Langemo is moving in the opposite direction, investigating biometrics to advance safety when humans eventually explore extreme extraterrestrial environments.
“It was really cool to see how you can apply science out in the field and to learn how you function in those environments,” Van Der Weide said.
Rough Conditions and Future Work
The 48 °F Minnesota Mystery Cave presented some challenges for researchers as a simulacrum of extreme environments beyond Earth. The team used hand warmers to keep the spectrometer batteries from quickly dying due to the chill. Sebring’s team slid through crevasses under a foot wide but hundreds of feet long. Other times, they waded through knee-deep frigid water.
NASA
The team’s work has yielded a fountain of fresh knowledge about caves. They discovered that the waters that carved Wind Cave were rich in manganese, which grew pink glowing zebra-striped calcites. Sebree hypothesizes that because calcite was weaker than the surrounding limestone caves, the calcite shattered, allowing the cave to expand.
“It’s a very different cave-forming mechanism than has previously been looked at before,” he says.
Sebree next aims to test fluorescence spectroscopy’s accuracy by comparing the results to existing laboratory techniques. He also hopes to study fluorescent cave water to understand the connection between surface conditions and underground life. Such work would provide a new understanding of how subsurface ecosystems like those that may exist on Europa operate.
The presentations “Developing a cave science spectral database for fluorescence inventory” and “Spectroscopic analysis of caves: The influence of organic overburden on karst speleothems” occurred during the Spring 2025 meeting of the American Chemical Society, March 23-27*.*
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted atryan@thedebrief.org, and follow him on Twitter@mdntwvlf.