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Sixty-two feet below the turquoise waters off Key Largo, Florida, a helmeted figure explores the sea floor with gentle bounding steps. This “aquanaut” is a member of NEEMO, the NASA Extreme Environment Mission Operations project, and has been living underwater for three weeks, training to one day be an astronaut in space.

A vast expanse of the unknown, cold, dark and inhospitable, the ocean mirrors space in many ways. Both environments feature low gravity and high pressure, and potentially harbour unknown life forms lurking out of sight. Visiting either requires extensive planning and sophisticated equipment; many of the challenges aquanauts face underwater could be experienced on a mission to space, the Moon or Mars. These similarities make the ocean an excellent arena to practice space missions. 

During NEEMO missions, home is the barnacle-encrusted “Aquarius”, the world’s only underwater research base. From a distance you would be forgiven for mistaking it for a shipwreck, but the inside resembles a space station. The only giveaway is the fish swimming past the windows. Here up to six aquanauts must share the four hundred square foot confined space, enduring not-so-private bathroom facilities, freeze-dried food and the mental strains these conditions bring.

Aquarius is an ambient pressure habitat, which means the pressure inside the capsule is the same as the surrounding water pressure – two and a half times greater than at sea level. At pressure the human body gradually becomes saturated with dissolved nitrogen. If a person returns to a lower pressure too quickly, the dissolved nitrogen forms life-threatening bubbles, blocking blood flow and disrupting nerves, an affliction known colloquially as “The Bends”. After living underwater in the base it takes seventeen hours of decompression, during which time the pressure is gradually adjusted at a safe speed, before an aquanaut is clear to return to the surface. So, once in Aquarius, there is no quick escape back to land. This also means that, much like in space, mistakes or equipment failure can be fatal. In 2009, an aquanaut died when his breathing apparatus malfunctioned during a dive and in 1994 Aquarius had to be evacuated in fifteen foot seas when one of the generators caught fire.

Despite, or perhaps partially because of these risks, NEEMO missions offer opportunities to both train future astronauts and test new equipment and procedures. Inside Aquarius, this might include a new exercise machine or miniature scanning electron microscopes for the International Space Station.  Outside, the neutral buoyancy in the aqueous environment provides an excellent simulation of the microgravity of space. Kitted up with dive gear and a thirty two pound helmet, aquanauts enter the ocean from Aquarius to practise moving, using tools and assembling apparatus as though on a weightless spacewalk. Aquanauts can also be weighted with lead cubes to mimic the gravity of other planets. Previous missions have tested the evacuation of an unconscious astronaut, or lengthy communications delays to mimic the forty minute minimum time it takes for a message and its reply to travel between Mars and Earth. NASA has been using water to simulate the weightlessness of space for decades – even Buzz Aldrin practiced in the pool.

The aquanauts themselves are test subjects too, providing data on the physiological effects of the inhospitable environment on the human body, as well as the mental and psychological effects of a typical mission. Just like on space missions, their days are tightly scheduled, detailed down to the last minute, and decisions are time-sensitive. Aquanauts are constantly under surveillance by mission control via two-way radio and video access, but physically isolated from the rest of the world. Last year neuroscientist Csilla Ari D’Agostino joined five other crew members at Aquarius, tracking their cognitive performance, including reaction time, memory, and decision-making, and collecting data about their sleep quality and stress. The results of this investigation have not yet been published. 

When not in use as a proxy space station, Aquarius hosts teams of marine biologists. The easy access from the base to the neighbouring Conch Reef presents an invaluable opportunity to conduct research on marine life. Yet, Aquarius is situated relatively shallow. Delving deeper into the ocean could provide insight into the age-old question of whether we are alone in the universe. Given the parallels between the two extreme environments, scientists look to life in the deep sea to provide a hint of what alien life might look like. Even NASA is funding deep sea exploration to this end; their Systematic Underwater Biogeochemical Science and Exploration Analog (SUBSEA) project aims to determine how best to conduct future science-driven space exploration while also searching for deep sea life.

Indeed, hidden away from human eyes in the hypoxic environment of the ocean depths lies a world of intriguing and monstrous creatures. Stalking the frigid waters are fanged viperfish reminiscent of the movie Alien, and gulper eels with mouths larger than their own bodies. Giant scaled isopods, deep sea cousins of terrestrial woodlice, scavenge among feathery soft corals on the seafloor. To survive in this permanent darkness many animals have huge eyes, and some even make their own light to confuse predators or lure prey. Fish living at these depths have evolved altered protein structures to help them withstand pressures hundreds of times greater than that at the surface. Thousands of meters below water near volcanically active zones, ashy black gases rise in plumes from hydrothermal vents, heating the water to temperatures as high as over 400°C. The vents churn out rich minerals, attracting chemosynthetic bacteria which use inorganic molecules as a source of energy. These bacteria form the basis of a food web featuring a range of life from tube worms to cutthroat eels. The discovery that complex food chains can be supported by chemical energy, as opposed to light and photosynthesis has challenged previous assumptions about the limits of biology.

Water is held as the key ingredient for life as we know it, and there is now evidence of its presence on several moons in our solar system. A study published in Nature suggests Earth’s first life forms may have lived in deep-sea hydrothermal vents. Similar vents are thought to exist on the moons of Jupiter and Saturn, and may have once been present on Mars. If life on Earth began in hydrothermal vents, could the same be possible on other planets? Just as the first discovery of these vents led biologists to rethink what is possible for life, so too must they remain open-minded in the search for life in space. While extreme deep sea environments show us the boundaries of biology on Earth, it may also be possible that life in space can take forms beyond our wildest imaginations. 

In the thousands of years humans have spent exploring our world, perhaps it was inevitable that we would eventually push past the boundary of our own planet and into “the final frontier”. It is fitting that we practice in the place that life started: the ocean.

Tatjana Baleta is an MPhil Conservation Leadership student at Wolfson College. Artwork by Rita Sasidharan.