Fluorescent caves show how life could exist on one of Jupiter’s moons

By Stephen Beech

Fluorescent caves deep below America show how alien life could exist on one of Jupiter's moons, say scientists.

The chemistry in Wind Cave, South Dakota, means that, under an ultraviolet (UV) light, chemicals fossilized within shine in brilliant hues of pink, blue and green.

Scientists are using the fluorescent features to understand how the caves formed and how life is supported in extreme environments.

They say their research, part-funded by NASA, may reveal how life could persist in faraway places, such as on Jupiter’s icy moon Europa.

The team explained that the chemistry in the American cave is likely similar to places such as Europa.

Astrobiologist Professor Joshua Sebree, of the University of Northern Iowa, went hundreds of feet underground to investigate minerals and lifeforms in the cold, dark conditions.

He said: “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.

As Sebree and his team began to venture into new areas of Wind Cave and other caves across the United States, they mapped the rock formations, passages, streams and organisms they found.

As they explored, they used black UV lights to look at the minerals in the rocks.

Sebree says that, under the black light, certain areas of the caves seemed to transform into something otherworldly as portions of the surrounding rocks shone in different colors.

Thanks to impurities lodged within the Earth millions of years ago, the hues corresponded with different concentrations and types of organic or inorganic compounds.

Sebree says the shining stones often indicated where water once carried minerals down from the surface.

He said: “The walls just looked completely blank and devoid of anything interesting.

“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.”

The team collected the fluorescence spectra - which they say is like a fingerprint of the chemical makeup - of different surfaces using a portable spectrometer. That meant they could take the information with them while leaving the cave intact.

One of the team, Anna Van Der Weide, is using data collected during the fieldwork to build a publicly accessible inventory of fluorescence fingerprints to help provide an additional layer of information to the traditional cave map and paint a more complete picture of its history and formation.

The team faced several challenges collecting data in caves. For example, in the chilly Mystery Cave, Minnesota, they had to bury the spectrometer’s batteries in hand warmers to keep them from dying.

In other locations the team had to squeeze through spaces less than a foot (30 centimeters) wide for hundreds of feet, sometimes losing a shoe in the process.

But their efforts have revealed a wealth of information.

In Wind Cave, the team found that manganese-rich waters had carved out the cave and produced the striped zebra calcites within, which glowed pink under black light.

The calcites grew underground, fed by the manganese-rich water.

Sebree believes that when the rocks shattered since calcite is weaker than the limestone also comprising the cave, the calcite worked to expand the cave too.

He said: “It’s a very different cave-forming mechanism than has previously been looked at before."

Undergraduate Van Der Weide added: “It was really cool to see how you can apply science out in the field and to learn how you function in those environments."

Sebree now plans to investigate how similar, mineral-rich water may support life in the far reaches of the solar system.

The researchers presented their findings at the spring meeting of the American Chemical Society (ACS) in San Diego, California.