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When the last humans returned from the Moon, they did so with lifeless samples of lunar rock. While geologically interesting, it taught us little about how life started on Earth, or whether similar places in the Solar System might support living things. At the time, it seemed unlikely that anything would be living out there, but the next time we visit a planetary neighbour, seeking life will be high on the list of priorities.

Should humans once again set foot on another planet in our Solar System and begin to search for life, they will do so having trained in some of the most demanding environments on Earth – because caves are the best preparation for these intrepid explorers.

That’s why the European Space Agency, Esa, have sent astronauts on two-week expeditions to reach, map and live in Sardinia’s caves since 2011.

Caves and some arid above-ground environments give astronauts the chance to train for the surfaces of other worlds (Credit: iStock)

The cave network used by Esa for the exercise this summer certainly looks the part. Descending 800m (2,640ft) underground, six astronauts from the US, China, Japan, Russia and Spain spent six days in darkness exploring and charting one of the last unexplored environments on Earth.

The chosen location, ‘Sa Grutta’, has been formed by life-giving water running through the tunnels, dissolving away the rock. The caves range from tiny crevices for the astronauts to crawl through to cathedral-like chambers. Some tunnels are dry while others require diving gear to navigate.

The mission is called Caves – Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills. It is an Esa initiative to teach a multicultural team the skills required to work closely in confined spaces and under high pressure, while still performing scientific research or reconnaissance. Not only is it difficult to move through the caves, the lack of daylight affects the astronauts’ circadian rhythms, altering their perception of time and disrupting sleep patterns – just as would happen in space.

The procedure for moving through a cave network, tethered on safety lines, making critical decisions and communicating clearly, is very similar to spacewalking  

The procedure for moving through a cave network, tethered on safety lines, making critical decisions and communicating clearly, is very similar to spacewalking. Speleologists and astronauts both use the ‘buddy system’ when on spacewalks or while caving, and instructors reiterate the same learning techniques of ‘slow is fast’ and ‘check your gear and then trust it’.

Scientific research forms a core part of the astronauts’ daily routine in the caves, just like it would on the International Space Station (ISS). They perform up to five experiments each day, taking geological and microbiological samples from the environment to find evidence of unique lifeforms that have adapted to the challenges of living without light and many life-supporting minerals.

Caves’ missions also train astronauts above ground in environments analogous to the surface of other planets. The Lanzarote Geoparque is the perfect place to train for missions to Mars, for example, with its rocky terrain. It’s here that geologist, explorer and Caves course designer Francesco Sauro offers his expert guidance on how to recognise biologically interesting rock samples in space-like environments. Sauro’s focus is on sedimentary processes that hint at the presence of water and telling the difference between meteorites from rocks.

Astronauts like Tim Peake already train in caves before their space missions (Credit: Science Photo Library)

“We created a course that enables astronauts on future mission to other planetary bodies to spot the best areas for exploration and the most scientifically interesting rocks to take samples for further analysis by the scientists back on Earth,” says Sauro.

Sauro is perfectly placed to educate the team of astronauts about finding life in the most challenging environments on Earth. He has not only found life in caves already, but has also become an expert in finding the caves in places most would not think to look. His greatest achievement to date was discovering the Imawari Yeuta cave in South America.

Also known as ‘The House of the Gods’, the Imawari Yeuta cave network are quartzite caves located in the Tepui table-top mountains of Venezuela. Ordinarily, you would not expect to find caves in mountains made from quartzite (rock which is made from 95% quartz) as it is highly resistant to being dissolved by water – so this network is particularly unusual. The fact there are caves means that they – and the landscape around them – must be very old. It’s thought that these caves are among the oldest in the world – some 50-to-70-million-years-old.

Also known as ‘The House of the Gods’, Imawari Yeuta is a network of quartzite caves  

Sauro is exploring Imawarì Yeuta with a group organised through La Venta – an international team of speleologists. When indigenous people said there were caves hidden high in the rainforests of Venuzuela, an exploration team from La Venta began searching for them. The quest began in 1995, but as late as 2003 they remained completely out of sight.

Initial images showed crevasses and fractures further down the mountain, but an accidental find by a group of trekkers encouraged the team to look higher up.

Using satellite images and aerial surveys, the team identified surface collapses in the landscape that suggested cave networks beneath. Further exploration revealed a whole network of previously unrecorded caves.

Many caves on Earth contain water - could those on other planets hold it too? (Credit: iStock)

The unlikelihood of finding a cave in quartzite rock, and the difficulty of reaching the table-top mountain in which Imawari Yeuta lies, prolonged its secrecy. To reach the mouth of the cave, researchers either have to fly by helicopter – which can be dangerous – or trek for days through the rainforest.

When Sauro’s group began to explore Imawari Yeuta, they had no idea what they might find. Unlike normal cave exploration, the speleologists couldn’t speculate on what a system as old and little understood as Imawari Yeuta might contain.

It’s like a gigantic library where you can find information about your ancestors, about life in the past – Francesco Sauro  

“The most fascinating thing for me is that those caves are very ancient – millions and millions of years old – so they are a witness of the past,” says Sauro. “And entering into this environment which is untouched for millions of years, and all the information which was captured by the cave is still there, it’s like a gigantic library where you can find information about your ancestors, about life in the past.” 

By studying these ancient worlds, Sauro hopes to better understand early microbial life that has been preserved in isolation. What we can learn from these microbes could be crucial to understanding how life might exist on other planetary bodies in our solar system. Whether they live in similar dark, cold, wet environments like those he found in Imawari, or whether they’ve found other novel ways to adapt to extreme isolation – any life is likely to share many similarities with primitive microbes here on Earth.


Genius Behind 5 - Caves


In the video above, Sauro explains how he discovered in this huge cave a new mineral – rossiantonite – and examples of life that have evolved for millions of years deep underground, separated from the outside world.

“Caves are witness to geographic history,” Sauro says. “They preserve much more than the surface. They are archives of time, of the evolution of the landscape and life.”

With the lessons they have learnt from Sauro and the Caves initiative at Esa, the next generation of astronauts are better prepared. The question of when the next human will step out onto another planet is unanswered, but through the research of speleologists like Sauro, we are a little closer to understanding what any life that calls it home might look like.

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