Cueva de Villa Luz – a cave system measuring around two kilometres long – lies beneath the southern Mexican state of Tabasco.
It’s filled with hydrogen sulphide gas, and in his documentary Wonders of the Solar System, physicist Brian Cox ventured in with a mask and gas detection system to film there.
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“Although the cave is a death trap for us, that doesn’t mean that nothing lives here,” he explains.
“In fact, it’s teeming with life.”
As it turns out, this extreme environment deep under the surface provides us with clues of how extraterrestrial life could survive in hostile (and otherworldly) environments.
Cave-dwelling fish – cave mollies – are found in the shallower waters and appear pink. This is likely due to high amounts of haemoglobin (the protein that transports oxygen around the body and gives blood its red colour) within them – and is an example of how life adapts to a low-oxygen environment.
But there’s something even odder below.
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Snottites are a type of single-celled bacteria that hang from the walls and ceilings of caves. While they look like small stalactites, there’s one difference: they have the consistency of snot.
These odd specimens metabolise hydrogen sulphide, react it with oxygen and produce sulphuric acid. And while it might look harmless, it actually has a pH level similar to battery acid.
“What a strange organism,” says Cox.
“It’s alien in every sense of the word, except that it’s present just below the surface of our planet.”
