Around Jupiter and Saturn, orbiting their respective planets in the unforgiving darkness, are Europa and Enceladus: two scarred, ice-covered moons concealing vast subterranean oceans. Astrobiologists, salivating at the prospect of life within them, hope that they will one day be explored – not by humans, but by submarines controlled by artificial intelligence.
But to build vehicles capable of plumbing the depths of the Solar System’s oceans, scientists are turning to one of Earth’s most inhospitable environments. In November, a NASA-funded expedition put three autonomous submersibles through a literal trial by fire: they were left to their own devices to explore Kolumbo, a nightmarish, hyperactive, underwater volcanic mountain in the South Aegean Sea, just north of the Greek island Santorini.
“This is most dangerous place you could operate underwater vehicles,” says Richard Camilli, an associate scientist at the Woods Hole Oceanographic Institution (WHOI) in the United States and the expedition’s leader.
These droids were certainly up to the challenge. Their on-board computer systems conjured up their own navigation plans on the fly. The submersibles also worked in coordination with other, with each acting as a component of a single electronic superorganism.
Thanks to their shared intellect, all three robot divers survived; not only that, but their remarkable adaptability allowed them to make brand-new scientific discoveries. One, a metropolis of hydrothermal vents teeming with strange microorganisms, may not have been found if human operators were in charge. Perhaps one day, these mechanical marvels will be doing much the same in the murky depths of those watery alien moons – although there are still plenty of logistical and technical obstacles to overcome before any such mission becomes a reality.
The South Aegean Sea has a violent volcanic history. Around 3,600 years ago, Santorini Island blew a hole in its heart when a cataclysmic volcanic eruption let rip, wrecking the city of Akrotiri and dealing a potentially fatal blow to the archipelago’s seafaring Minoan civilization.
Kolumbo Seamount, located seven kilometres northeast of Santorini, may not have reached quite the same paroxysmal heights, but it’s no small fry. Sitting just beneath the waves, this three-kilometre-long volcano made itself known in 1650 when an ear-splittingly loud eruption triggered a destructive tsunami and spewed so much suffocating volcanic gas that 70 people on or near Santorini asphyxiated.
Kolumbo remains furious today. In-between 100-metre-high spiralling columns of frozen lava are forests of towering, hydrothermal vents shooting out 220C fluids. Paraskevi Nomikou, a geological oceanographer at the University of Athens and member of the expedition, explains that a diverse cornucopia of life thrives on these vents. That, along with the chaotic volcanic architecture of the site, makes it an ideal testing ground for submersibles that will one day hope to do much the same off-world.
Exploring the oceans of Europa and Enceladus will be profoundly difficult. Manually controlling robots on either would be too cumbersome; it would take us 43 minutes to send a command to Europa, and 79 minutes to Enceladus. Not only would a high-radiation environment befuddle our transmissions, but communiques from Earth would struggle to penetrate those rigid ice shells, which have been estimated to be tens of kilometres thick.
These submersibles will have to be entirely autonomous, says Samuel Royle, a planetary geochemist and astrobiologist at Imperial College London who wasn’t involved in the expedition. They need to be energy-efficient navigators, able to manoeuvre around unexpected dangers in never-before-explored alien oceans, find sites of scientific interest, and only pop up to the surface when they needed to send data back home.
Kolumbo is as good a stand-in for these hostile environments as you can find. Autonomous submersibles already exist, but they have largely been used to explore the less cramped sections of the sea, a bit like flying around an open valley. Navigating through Kolumbo’s volcanic labyrinth, says Camilli, “is the equivalent of hang-gliding in midtown Manhattan.” If robots could survive Kolumbo, they could survive the aquatic hells on other worlds too.
NASA’s Planetary Science and Technology Through Analog Research (PSTAR) program, which aims to lower the risk of future planetary exploration through terrestrial trials, agreed the dangers of Kolumbo were worth venturing into, and funded the mission. The team, comprised of scientists based in the US, Greece, Australia and Germany, sailed to Kolumbo this November, bringing with them three special robots.
Two were gliders designed by private US company Teledyne Webb Research: small, lightweight and fully autonomous submersibles, they were able to change their buoyancy and slip through the water, or zip forth using propellers, all the while draining a soupçon of their battery power. The other, the HROV Nereid Under-Ice, or NUI, was a long-range, two-tonne submersible designed by WHOI. Although also autonomous, it was attached to the boat by a hair-thin fibre optic tether, allowing for remote control operation and quick transmission of data back to base.
All three were variably equipped with a suite of sensors, from chemistry-sniffing mass spectrometers to thermometers, as well as sonar. Along with a constant input of environmental stimuli, the robots’ onboard software also took into account hazards, how much battery charge remained, if they were damaged and a bunch of pre-existing scientific information. This permitted them to invent their own navigation paths, those that maximised the scientific output of the dives while maintaining an acceptable level of risk.
Each vehicle, with its different technological capabilities, made sure to share their information with each other. They were, says Camilli, a bit like bees in a colony, all playing their part to make the hive as successful as possible. Their efficiency allowed them to make new mission plans in less than a minute, far quicker than a team of scientific experts could manage. That didn’t just streamline the mission; it kept the vehicles safe by allowing them to be effortlessly reactive to their ebullient, volcanic surroundings.
These automated planning systems had apt monikers: the executive planner was named Kirk, and the science planner called Spock. The latter was almost unnervingly good at living up to its namesake.
During one automated dive, the expedition’s geologists and biologists wanted to divert a submersible to a site on Kolumbo they knew would yield useful data. Camilli deferred to Spock, which swam to an unexplored sector. That, says Nomikou, led to one of the most satisfying moments of the expedition when it found a new hydrothermal vent site full of microbial life, all by itself.
The gliders acted like reconnaissance drones, explained expedition member Angelos Mallios, a visiting investigator at WHOI. They gathered plenty of comparatively low-resolution data, giving the more heavily equipped NUI – the equivalent of a robotic rover, like Curiosity – a more precise idea of where to explore using its more diverse sensor payload. When it arrived, it gathered samples using a camera and robotic arm, all without human input.
It could have gone so very wrong. The expedition, says Camilli, was “pretty brief and action-packed,” lasting just five days. Along with harsh weather and treacherous diving conditions, “all of the vehicles arrived damaged or with parts missing, and some equipment was even lost in shipping.”
Letting the gliders escape into the wild was always tense. “You let them go, and there’s not much you can do,” says Mallios. You only see them whenever they breach the waves to transmit their position, transmit data and receive new advice from their human masters. Much like the future space missions they hope to be emulating, “if something goes wrong down there, no-one’s going to go down to fix it,” Mallios explains.
“My gut estimate was that we stood a roughly 50 percent chance of having all the vehicles survive,” says Camilli. It was a major feelgood moment, he adds, when all three were recovered and not smashed to bits. It was unquestionably a roaring success.
Those submersibles, however, remain far from finished. Their software and designs will be continually tweaked over time; additional extreme environments, including the frigid icy waters of the Arctic, will soon be used to further test the mettle of these types of submersibles.
Along with the deeply complex logistics of sending a mission to the gas giants, it is safe to say that sending robots like these diving into Europa or Enceladus will remain a dream for some time. After all, it is difficult enough to place landers or rovers on the Moon or Mars, and we are yet to find out if we can deploy a quadcopter on Saturn’s exotic satellite, Titan. Diving into an extraterrestrial ocean is a whole new level of troublesome.
“Sending a mission to go and look under the ice is a really long way off,” says Royle. But the experiment that took place on Kolumbo is an example of one of the best things we can do to in the meantime: practise for the real thing. “We’ve got to try these things and see if they work on Earth before we even think about doing them elsewhere.”
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