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Micro-Swimmers: Hunting Alien Life with Robot Submarines

Written by Morris M.

It sounds like something from science fiction. A plot to explore an alien ocean, hidden beneath the surface of a world hundreds of millions of kilometers away. A plot that first involves tunneling through a 25 km thick ice sheet, before releasing a swarm of robot submarines.

Said out loud like that, it sounds not just fictional, but impossible. Like something dreamed up by stoned MIT engineers between bong hits.

Yet there’s nothing fictional about any of it. Right now, scientists are developing these concepts for a future space mission. A mission they think could be a mere twenty years away.

A mission that could lead to humanity’s first encounter with extraterrestrial life.

In today’s MegaProjects, we’re delving deep into the ideas and challenges behind cryobots and autonomous swimming robots… and asking if we really will see such an ambitious mission in our lifetimes.

Target Worlds

https://flic.kr/p/dBeY8T

Millions of kilometers away from our pale blue dot, lie two of the most-fascinating moons in the solar system.

Europa and Enceladus are both small, icy worlds orbiting gas giants. In Europa’s case, it spins around the king of planets: Jupiter. Enceladus, meanwhile, clings close to mighty Saturn.

But while they may have different hosts, both remote moons have two very important things in common.

The first is that both are home to subsurface oceans: globe-spanning seas of salty liquid water, hidden beneath a crust of ice.

Now, this is unusual, but not super-rare. The moons Ganymede, Titan, Triton, and – potentially – Callisto also hide liquid oceans beneath their exteriors; as might the dwarf planets Pluto and Ceres.

What sets Enceladus and Europa apart, though, is the second important thing about them. 

Unlike all the other ocean worlds, their layer of liquid water is thought to start relatively near the surface. The global Europan ice sheet is thought to be only 25km thick. Enceladus may have ice a mere 5km thick at its poles.

And that means we might one day be able to tunnel through to explore them. 

Exactly how humans would go about getting through so much ice and investigating these lightless seas is the real meat of today’s episode. But, before we dive into all the awesome engineering, we need to take a minute to outline why we might want to. 

The answer is: because there may be life down there.

Despite being smaller than our Moon, both Europa and Enceladus are thought to contain enormous volumes of liquid water. In Europa’s case, more than all of Earth’s oceans combined.

This is exciting, because where we find water on Earth, we tend to find life. Especially when that water is in contact with mineral rich rocks. Especially when it also has a heat source.

In Europa’s case, that heat source comes from a process known as ‘tidal heating’. 

As the moon travels in orbit around Jupiter, it interacts with the gravity of two other large satellites: Io and Ganymede. This creates an odd effect whereby Europa is repeatedly pulled in one direction by its siblings, and another by its host planet – a cosmic tug of war so powerful, it literally stretches Europa’s skin. 

This creates friction, which leads to internal heating. In turn, this not only keeps the ocean liquid, but also likely leads to hydrothermal vents – chimneys on the seafloor where water interacts with the hot rock, creating a chemical-rich stew perfect for life.

Here on Earth, hydrothermal vents are usually swarming with creatures. Creatures supported not by a food chain that relies on energy from the sun, but by one relying on those same chemical reactions.

This is why astrobiologists think Europa or Enceladus represent our best chance of finding alien life. Europa’s ocean – in particular – is thought to have been stable for billions of years. Plenty of time for microbes, or even complex creatures, to have evolved.

It’s also why one of the most-exciting upcoming NASA missions is the Europa Clipper: a probe we covered in a separate post that will soon conduct multiple flybys of the Jovian moon.

But, awesome as the Clipper is, it’s not an upcoming mission we’re here to discuss today. But a hypothetical one.

As part of planning for what comes after Clipper, NASA has set up an entire department. Known as Scientific Exploration Subsurface Access Mechanism for Europa (or SESAME for short), it has one of the coolest tasks in science: to figure out how we get down to that hidden ocean. How to hunt for signs of life deep below the surface of a hostile world so far away.

The coolest part? We already have the answers.

Meltdown

https://commons.wikimedia.org/wiki/File:Cryobot_prototype.jpg#/media/File:Cryobot_prototype.jpg

Way back in the 1950s, scientists began working on probes that could tunnel deep into ice sheets.

Known as melt probes, they were initially designed for work in Antarctica. By the 1960s, they were capable of boring down to a depth of 1km – or over half a mile, for those who prefer units that function like Harry Potter money.

It’s from these original melt probes that today’s cryobots are descended: souped-up modern versions that will one day be used in space.

So, now might be a good time to explain exactly what they are.

At their simplest, melt probes work on something sometimes called the Hot Penny principle.

Imagine taking a penny and heating it to a high temperature, then placing it on an ice cube. You can imagine what happens next: the ice melts as gravity pulls the penny down, creating a tunnel. 

Of course, melt probes are more sophisticated than hot pennies, requiring an energy source to keep them warm. Normally, this comes in the form of a generator sat on the surface feeding copper wire down into the probe.

Because the wires are poor conductors, they create a lot of heat. This keeps the body of the probe warm enough to keep melting the ice.

But that’s just the classic model. Newer versions use fiber optic cables to send lasers from the surface, which zap metal plates inside the probe to provide the heat.

Still, the principal is the same: a long, rocket-shaped instrument pointing tip dowards, using mostly heat and gravity to keep on tunneling.

Note the key word there, though: “mostly”. Because melt probes often come with add-on features to ensure the journey goes smoothly.

Features like water jetting. 

Even on Earth, melt probes tunneling through an ice sheet might encounter little rocks that get in the way and impede their passage towards Hades.

Water jetting helps clear the way by sucking in all the meltwater around the probe, heating it up, and blasting it out the front in powerful streams. Other cryobots come with cutting tools that can take over and slice through layers of stone that would be otherwise impossible to melt.

Again, this is all real technology that really exists. Has existed, in fact, for over half a century.

And that means we’ve had decades to prepare for using it on an alien world.

It was in the late-1990s that the Galileo spacecraft confirmed the existence of Europa’s subsurface ocean. Since then, scientists have been working flat out to create a cryobot that could one day take us down to see it. 

The Jet Propulsion Laboratory, for example, is currently developing the 360kg Probe using Radioisotopes for Icy Moons Exploration, or PRIME. The private company Stone Aerospace has already built and tested its own cryobot called VALKYRIE. 

Just this year, NASA signed off on a project called ORCAA, which will field test this technology by sending a melt probe tunneling 1km through Alaska’s Juneau Ice Field, into a subglacial lake.

So, now we’ve got our heads around what a regular cryobot looks like, let’s turn our attention to the next stage.

The insane challenges that come with making one function on a moon over 500 million km away.

https://commons.wikimedia.org/wiki/File:Cryobot.jpg#/media/File:Cryobot.jpg

Into The Depths

The big problem with sending a cryobot tunneling to Europa’s hidden ocean is the sheer thickness of the surface ice.

We mentioned earlier that the layer is thought to stretch 25km, but that’s really just an educated guess. It could be as little as 10km or as many as 40km.

At the higher end, that would mean any melt probe will need a power source that can sustain it on a journey of well over two years. Obviously, just running a diesel generator at the surface isn’t going to cut it. 

Instead, the heating source will likely have to be nuclear.

In the long term, the goal is to create nuclear fission reactors that could be deposited on the Europan surface and feed energy down to the craft through cables.

But this technology is so far in the future, those working on PRIME at JPL have come up with a way to power a much-sooner mission: Radioisotope thermoelectric generators.

Plutonium 238 is a fun substance. As it decays, it generates heat – meaning a block of it will get hot just as it sits there.

The heat from this can be used to generate electricity, which is what keeps Mars rovers like Perseverance alive. But it could also be used to provide a multi-year heat source for a melt probe.

That means the seemingly-hard part – how to power a cryobot so far from home – is actually pretty easy. But this isn’t the only issue. 

There’s also communication. 

On Earth, you can keep the tunnel a cryobot bores open by pouring in alcohol. On Europa, though, there’s gonna be no handy cosmonaut waving a bottle of half-drunk vodka. 

As a result, we have to expect any tunnel dug will refreeze solid behind the melt probe. 

Now, in a perfect environment, this wouldn’t be a problem. Fiber optic cables are incredibly strong these days; strong enough to withstand being encased in ice. In a perfect world, you’d just attach a super long one to the cryobot and use it for communication. 

But Europa isn’t a perfect world. It’s a world constantly pulled out of shape by the cosmic tug of war between Jupiter and the other moons. A place of frightening geological activity.

Any cable, therefore, would have to survive not just being frozen, but also being pulled and stretched, as the ice it was encased in shifted over multiple years.

Hence the need for backup wireless communication.

The idea is that – as it tunneled – the melt probe would periodically release little transponders that would freeze into the ice behind it. 

Eventually, you’d have a chain of about a dozen dotted all the way down. If the probe needed to send any information without the cable, it could send it to the lowest transponder, which would pass it on to the next-lowest – and so on. 

Impressively, this could be done using either wireless technology like we have on Earth, or by using acoustic waves: physical vibrations that would travel up through the ice, carrying information.

And there’d certainly be lots of data to relay. 

During its descent, the probe wouldn’t just concentrate on tunneling. It would also conduct research into the ice: for example, by analyzing the meltwater for signs of microbes.

Still, even with the transponders, getting enough data back to the surface to be beamed to Earth might be hard. 

One of the lead researchers on ORCAA – Dr. Samuel Howell – explained in an interview that a really thick ice sheet might result in only 100 bits a second being communicated.

That’s so slow, it would make your first 1990s dial-up connection look like Starlink. If we want to prevent that from happening, we’ll need some serious advances in data compression. 

For now, though, let’s imagine the melt probe is able to keep up a decent connection as it plunges through the ice. Right the way through to the awe-inspiring, literally groundbreaking day when it smashes through the last layer, and plunges into the alien ocean. 

What happens next?

Well, it could just float there, sampling the water. Europa is thought to have extremely strong currents, meaning the probe might be lucky enough to have some interesting material swept into its sensors even if it stays still.

But what if we don’t want to stay still? What if we’re worried that we might have popped out in the one place devoid of funky space dolphins and need to travel around to be sure?

Sadly, the cryobot itself isn’t going to help us. Designing it to be streamlined enough to get through the ice means it would have limited mobility in an ocean environment, even if it wasn’t tethered by a fiber optic cable.

Instead, we’re going to need something much stranger. Much more exciting.

You guessed it: it’s finally time to talk about the thing we promised in the intro. 

Robot submarines.

The Swarm

Ethan Schaler is a guy with a fascinating job. Just this year, the JPL micro-robotics expert received $600,000 phase-II funding from NASA to further study his wild idea: to build a swarm of autonomous robot submarines.

https://www.nasa.gov/directorates/spacetech/niac/2022/SWIM/

Known as Sensing With Independent Micro-swimmers (or SWIM for short), the concept was born from Schaler and his team chucking around ideas for giving a cryobot extra mobility.

In the end, though, it became clear the best way to explore would be to pack the cryobot itself with dozens of swimming robots, each the size of a cell phone.

That tiny size is important. Because it needs to be streamlined to make it below the surface, the Europa melt probe will only have limited space onboard, most of which will be reserved for scientific instruments.

Schaler and co.’s genius was to design robots that are a mere 12 cm – or five inches – long, and extremely thin. 

By cramming them one atop another, they calculate they could fit 48 of the little buggers inside the cryobot: equivalent to just 15 percent of the space put aside for scientific instruments.

The best part? Even that wouldn’t be wasted.

Each micro-swimmer would carry its own set of tiny instruments. Nothing too fancy, just stuff designed to do simple-but-revealing things, like monitor temperature, acidity, and pressure. 

Simple things, like check for chemicals that may indicate life.

The current plan envisages the cryobot unleashing a first wave microswimmers not long after reaching Europa’s ocean. 

The robots would motor away from the burning hot melt probe to take measurements, each with an onboard battery capable of lasting up to three hours. 

Now, this isn’t much. Certainly nowhere near long enough for a microswimmer to go explore the hydrothermal vents of the ocean floor. 

But it’s also hopefully as long as it needs to be. 

While hydrothermal vents are the best bet for finding life, we know from experience on Earth that there’s another place creatures in icy seas like to gather: at the point where the bottom of the ice shelf meets the water.

Known to clever people as the “ice-water interface,” it could well be swarming with bacteria. 

That’s because Europa’s curst contains subduction zones, which drag oxidants deposited on the surface down into the ocean. It’s theorized a whole food chain could have evolved just below the ice of creatures that depend on this process.

So, it’s possible the microswimmers will find some strange purple algae within moments of being deployed. Even if they don’t, it hardly matters.

With 48 to utilize, the cryobot could send out wave after wave of the robots at staggered time intervals – allowing each new swarm to home in on different places. 

The word “swarm” is deliberate, by the way. The idea is that the robots would swim together like a shoal of fish, reducing the chance of any false readings from one errant probe.

Amazingly, they would do all of this autonomously. 

It takes light something in the region of 42 minutes to travel from Jupiter to Earth, meaning any real-time commands sent to the microswimmers would only arrive after they’d run out of battery.

That means they have to be capable of doing all their exploring without any input from us. Nor is communication with Earth the only potential problem.

Europa’s gravity is about 14 percent what we have on Earth. On the one hand, that’s great: it means the pressures encountered tunneling down 25km aren’t so crushing that our cryobot would fail. 

On the other, it presents a challenge for microswimmers. As Schaler told the American Society of Mechanical Engineers:

 “A lot of underwater robots now rely on having the center of buoyancy above the center of gravity to provide passive stability (…) when you have such low gravity, you don’t actually get that benefit, so control and steering is extra tricky.”

While it seems likely that engineers will be able to overcome this problem, it does bring us neatly to our final, somewhat dispiriting chapter. 

The chapter where we take this awesome-sounding mission… and try to analyze some of the ways it could go horribly wrong.

Shattered Dreams?

Back in spring of 2022, Dr. Sam Howell – the cryobot guy we mentioned earlier – sat down for a long interview with Universe Today podcast to talk about a possible Europa ocean mission.

As part of that interview, he was invited to detail all the technical challenges his cryobot might one day face. And, boy, were there a lot.

To simplify things, we can break down the problems into two categories: protecting the probe, and protecting Europa. 

Let’s start with the probe itself.

The whole time the cryobot is tunneling, and the whole time the microswimmers are doing their thing, we’ll need to have a lander on the surface beaming data back to Earth.

This is where things get tricky. Aside from the endless geological stresses, Europa’s surface is also doused in intense radiation. 

How intense? So intense that the upcoming Europa Clipper mission can’t orbit the moon. Instead, it will conduct multiple flybys, to stop all its electronics from getting fried.

Whatever lander we place on Europa will have to survive in this hostile environment for literal years, maintaining contact with Earth that entire time.

It’s a big problem, one people are trying to solve creatively. One suggestion is that the lander itself could act as a melt probe after touchdown, melting itself, say, 10 meters into the ice.

Equivalent to a depth of 32 feet, that’s easily enough to shield against Europa’s radiation. But it highlights another potential problem.

How do we even begin melting Europa’s surface?

Dr. Howell referred to this as the “start-up problem”. That’s because the theory of what happens once the cryobot is digging all works perfectly fine, as does landing the probe on the surface. 

But going from “sat on the surface” to “tunneling down”? Now that’s a problem.

With no atmosphere, the ice at Europa’s surface might not turn to water once the melt probe starts, but instead sublimate: turning straight into a gas.

https://picryl.com/media/europa-ice-rafts-c75872

This would mess up the melt probe plans, but there might be no way around it. Try and drill forcefully down for the first couple of meters, and Europa’s gravity is so weak that pushing downwards might instead push the probe upwards – away from the surface. 

Still, perhaps none of these challenges compare to the greatest of all: making sure we don’t contaminate everything.

As a world that may well be home to living creatures, Europa is at high risk of contamination from Earth-origin spores or microbes. 

Remember the end of War of the Worlds? When – 120-year-old spoiler alert! – the marauding Martians are killed off after encountering Earth viruses their systems are unprepared for?

Well, there’s a worry we might wind up doing that to a bunch of alien dolphins for real. Or we may just wind up so contaminating any area we touch down on that we can’t say for sure if the microorganisms we find are extraterrestrial or originated at home.

This is one of the major reasons why no craft are allowed to remain in the Jovian system after completing their missions, but have to be crashed – either into Jupiter, or into one of the uninhabitable moons. We need to make sure Europa remains pristine. 

And both meeting that goal while also getting to explore what lies beneath the ice is going to require a whole lot of serious science, along with serious ethical debates. Even if the journey there would kill off most contaminants, even a 1 percent chance of some surviving could be too much.

Still, we’ve no doubt that humanity is up to the challenge.

Right now, in places like JPL, the next chapter in the story of human exploration is being written. A story that will soon become so epic, it’d even give Demon Slayer a run for its money.

Within the next twenty years, it’s possible that we’ll find ourselves about to send a probe out on a voyage that could change everything. A journey to an ocean untouched for billions of years. 

A journey that could rewrite our understanding of the entire cosmos.

(Ends).

Sources:

Interview with Doctor Samuel Howell, cryobot expert: https://www.youtube.com/watch?v=f7z8Fv_CEaY 

Astronomy, overview: https://astronomy.com/news/2022/09/swarms-of-swimming-robots-may-soon-explore-alien-seas 

JPL, overview: https://www.jpl.nasa.gov/news/swarm-of-tiny-swimming-robots-could-look-for-life-on-distant-worlds 

Engineering and Technology Magazine: https://eandt.theiet.org/content/articles/2022/07/nasa-wants-to-use-swimming-robots-to-detect-alien-life/ 

CNN, Other robots that may be involved: https://edition.cnn.com/2022/07/14/world/ocean-world-exploration-concepts-scn/index.html 

Phys.org, why these moons: https://phys.org/news/2022-07-nasa-robots-habitable-ocean-worlds.html 

American Society of Mechanical Engineers: https://www.asme.org/topics-resources/content/swarming-robots-may-one-day-explore-europa 

Valkyrie test: https://www.space.com/29644-cryobot-tunneling-robot-explore-icy-moons.html 

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