Stories From Space

Signs of Life: What are "Ocean Worlds"? | Stories From Space Podcast With Matthew S Williams

Episode Summary

In the outer Solar System, there are multiple icy bodies believed to have warm water interiors - entire oceans where life could exist right now.

Episode Notes

Host | Matthew S Williams

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Episode Description

In the outer Solar System, there are multiple icy bodies believed to have warm water interiors - entire oceans where life could exist right now. In the coming years, the first missions will arrive at these "Oceans Worlds" and begin searching them for signs of extraterrestrial life.



NASA Ocean Worlds Exploration Program:

The NASA Roadmap to Ocean Worlds:


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Episode Transcription

The authors acknowledge that this podcast was recorded on the traditional unseeded lands of the Lekwungen Peoples.

Hello, and welcome back to another episode of Stories from Space. I'm your host, Matt Williams. And today, in anticipation of some upcoming episodes, I want to discuss the topic of ocean worlds. And this has come to be a bit of an umbrella term. And it refers to bodies that are primarily made up of ice.

And in all cases, these moons have interior oceans due to geological activity within their course, this could be the result of title flexing, which is what happens when there's gravitational interaction between two bodies. The force of that gravity causes the interiors to stretch flex contract, leading to the release of energy in the form of heat. In other cases, these oceans could be the result of antifreeze such as ammonia, which causes ice to remain in a liquid state at temperatures below the freezing point of water.

Now, the reason why these bodies have become rather popular in recent years is because of ongoing studies of the outer Solar System, which revealed that they are a lot more common than previously thought. What's more, it's anticipated that these types of ocean worlds may in fact be some of the best places to look for evidence of life beyond Earth.

And given the recent spate of exoplanet discoveries, scientists are now wondering how long before we can begin to study exomoons. We are multiplying the number of known exoplanets that are out there, and many of them happen to be gas giants. So if we can find satellites that orbit them that have similar compositions to Europa and Ganymede and other icy bodies in our Solar System, could these exobodies be a good place to look for life beyond the solar system?

Basically, if we can confirm that there is life in some exotic or familiar form, within satellites in the outer solar system, or in the case of Titan, possibly on its surface, then surely these same bodies and other Solar Systems have given rise to their own forms of life, and that certainly warrants investigation. Maybe it's not just the rocky planets that orbit close to their sons the Earth-like planets that we should be examining.

Now, to give you a little background, speculation about Ocean Worlds begin in the late 1970s, early 1980s. And it was thanks to the Voyager I and II missions that had passed through Jupiter's system of moons in 1979, on their way to the outer Solar System. Prior to that, the Pioneer 10 and 11 missions had gone through the system, and they both buzzed Europa and took pictures.

And scientists had noticed some very strange chaos terrain features as they're called. But it was the Voyager I and II missions, whose images managed to really ignite the fire in scientists' minds and fueled all kinds of speculation. In particular, the so-called chaos terrain features, they noticed that there were patches of what appeared to be younger ice based on its

coloration and based on its smoother features, compared to other parts of the terrain, which were chaotic (as mentioned).

And this indicated that there was what's known as endogenic resurfacing, so that the ice sheet on top was in motion, kind of like tectonic plates, and that there was an exchange of material on the surface or the subsurface. And also, they noticed these large red streaks which you can see in any modern image of Europa, which indicated that chemicals were deposited on the surface that did not appear elsewhere in the ice sheet.

And, this too was seen as an indication that liquid was being churned up from the interior with chemicals, it would evaporate and then rain back down and refreeze on the surface. And subsequent missions like the Galileo spacecraft, which began exploring the system in 1995.

It refined these observations and obtained magnetic data on Europa, which indicated that through the interaction of Jupiter's powerful magnetic field with the moon itself, that there was likely a subsurface ocean with saltwater in it, because that was the effect that this magnetic interaction had on the moon. It could only really be explained by the presence of a subsurface ocean that was filled with saltwater.

And from all of this, scientists began creating models of Europa's interior which made various assumptions but basically came down to that beneath this frozen ice sheet - which could be a couple 100 meters thick or roughly 600 feet thick, or as much as a few kilometers thick, known as the thick ice or thin ice model - beneath that, that there was likely to be a liquid water ocean between the core-mantle boundary.

And that the interior of Europa, based on the models they made, was likely made up of rocky material and with a metallic core, not dissimilar to the rocky planets and the Moon. And that it was interaction with Jupiter's powerful gravity that caused this interior to flex and release heat energy that kept the interior geologically active.

So it flexed and contracted, and it released heat, and this heat most likely came up through the core-mantle boundary as hydrothermal vents. So very similar to what we have on the ocean floor here on Earth. There's volcanic activity in these vents, heat and hot magma are pouring up from underneath the surface. And they provide all these chemical nutrients for extremophiles around these vents.

And in fact, scientists have even speculated that this is where life began on Earth, that simple bacteria in simple life forms grew up around these events, and they relied on the heat and chemicals as an energy source. And that's how life began.

So this, of course, fueled speculation that there could be life inside of Europa. And subsequent studies of Jupiter's satellites and then onto Saturn and beyond; they revealed that Ganymede also likely had an interior ocean one which was larger than Europas. They also noted that Ganymede had its own intrinsic magnetic field. And this was rather unique.

Basically, Ganymede is the only satellite in the solar system that has its own intrinsic magnetic field. The Gas Giants all have one and Earth has one but other than that, only Ganymede has one. And so there are two, there's strong speculation that there could in fact be life beneath the ice sheet.

And in recent years, thanks to the Cassini-Huygens orbiter and lander, we got a much better look at Saturn's system of moons. So the Cassini orbiter itself, it explored the Saturn system for 13 years and 76 days. And it managed to deploy the Huygens lander, which was contributed by the European Space Agency, onto the largest moon Titan. And it didn't quite survive the landing, but it did broadcast all kinds of data on its way down, and only for a few minutes on the surface.

And what the mission managed to reveal, all the combined data that they sent back to Earth was that Titan had an extremely exotic environment. And there were hints revealed about this moon too, by the Voyager probes. They also noted that Titan had a very dense nitrogen-rich atmosphere, and rather dense clouds have methane and other hydrocarbons in the air.

And what Cassini and Huygens revealed was that more than that, the moon also has methane lakes on its surface, and methane rain. So it has a methane cycle, which is identical to Earth's water cycle, where you have this volatile element that's in all three forms: liquid, gaseous, and in certain places, solid because it's also part of the massive ice sheet.

And so scientists speculate that Titan could also have an interior ocean. But more to the point, it's got bodies of liquid on its surface. And not only that, but all of these hydrocarbons - these are organic molecules, methane, butane, all of these things that we love to burn around here on Earth, in our rich oxygen and nitrogen atmosphere.

On Titan, these things are just straight-up organic molecules that are being exchanged. And the mission also noted indications of prebiotic chemistry. So there has been tremendous speculation that there, in fact, could be life forms, possibly in the lakes itself. It would likely be simple, but who knows? A lot of theoretical work has been done on what methanogenic life could look like. But we won't know until we send another mission there to really study the environment. And more on that in a bit.

And speaking of future missions, there's also plans to send another mission to Enceladus, another one of Saturn's moons. Because what Cassini noted, what it really got a very clear look at, was these plumes that come out from the southern polar region of the moon. And scientists had noted plume activity and these tiger stripes, as they call them, these big green stripes that are around the southern hemisphere, and all kinds of very, very interesting ice blocks-like terrain.

And Cassini managed to get a closer look at this while it was doing its multiple flybys. And so what it noticed was, yes, that plume that's coming out, you basically you're seeing the result of geological activity in the interior, so again, with the gravitational interaction causing tidal flexing in the interior. And so these plumes are likely coming from an interior ocean. That is connected

directly to the core and to some very serious hydrothermal activity because it's causing the water to shoot directly out through the ice sheet.

And other ocean worlds that certainly merit attention there. There's also Dionne in Saturn’s system of moons, and then hop, skip, and a jump over to Uranus and Neptune. So hop on over to Uranus, and you've got two particular moons that are also believed to also have interior oceans on account of their chaos terrain, and younger terrain intermixing with older terrain, and that includes Miranda and Ariel.

And then over to Neptune, where you have Triton, where there is considerable evidence that water from the interior breaks through the ice sheet onto the surface. And this is what is known as cryovolcanism. So much the same way that magma bubbles up from Earth's interior and breaks through the surface in the form of volcanoes, hot water is breaking through the surfaces on these icy bodies and causing plumes and raining back down on the surface.

And thanks to the New Horizons mission, which buzzed several of these moons on its way out of the Solar System, there's now strong indications that Pluto and its largest moon Charon, are also ocean worlds. And here too, there were notable features that indicated that there were likely resurfacing events and mobile terrain. So the icy surfaces, which contain a great deal of frozen nitrogen - at that distance from the Sun, even nitrogen will freeze solid - and they appear to be moving over time. So very similar to plate tectonics and geological activity here on planet Earth.

And in recent years, thanks to the Dawn mission, which visited the main asteroid belt, scientists have gotten a much closer and more detailed look at Ceres, the largest body in the asteroid belt, and the only one large enough to have achieved hydrostatic equilibrium. In other words, large enough that it collapsed into a spherical shape.

This is also considered an ocean world, which in all likelihood has an interior ocean that is maintained by possible geothermal activity, concentrations of ammonia, and possibly methane, and which also experiences cryovolcanism. So there is action in the interior that is spewing up onto the surface.

So as I said, all of these moons either have the geological flexing and activity in their interior to maintain a liquid warm water ocean, or they have sufficient antifreeze or volatile compounds and have a lower freezing point than water. Plus the presence of radioactive elements whose slow decay would generate heat, and that too, could be enough to support a liquid water interior.

Now, from a terrestrial scientific standpoint, it is quite possible - and I do believe it's assumed - that only the warm water interiors, only these would actually have a shot at giving rise to life and being able to support it. However, we may be in for a surprise there. And as I alluded to earlier, there are follow-up missions.

In recent years, NASA, the European Space Agency and others have all considered multiple proposals for follow-ups that will explore these worlds more closely. NASA is pursuing this through their Ocean Worlds Exploration Program or OWEP. And what's on the books right now is the Europa Clipper mission, which is scheduled for launch by October of next year. And as the name suggests, it will conduct multiple flybys of Europa, and study the surface in particular, it's looking for plume activity, which scientists have noted there too.

With Hubble, the Juno probe, and other observations scientists have noticed that, that yes, in fact, Europa has plumes that are erupting from the surface periodically. They're raining material from the interior down on the surface.

So what the Clipper mission is hoping to do is to find evidence of biosignatures in that water raining down on the surface. And the European Space Agency, interestingly enough, they just launched their mission, which will study the icy moons of Jupiter. It's known as the Jupiter Icy Moons Explorer, or the acronym JUICE, and it launched just 11 days ago, and it's headed on its way to study Ganymede and will also make fly-bys of Europa.

It will establish orbit around Jupiter in 2031 and begin studying Ganymede by 2034. Whereas the Clipper is going to get there a little sooner by 2030 as planned, and it will conduct a total of 45 orbits, and all of these which will take it past Europa there to gather additional data - so very much like the Cassini mission.

In June of 2027. NASA is going to launch the Dragonfly mission, which is a very ambitious robotic explorer, basically a robotic rotorcraft that is similar to a helicopter, but has four rotors and a nuclear battery. It is going to explore the atmosphere of Titan, its surface, its methane lakes. And it's going to be looking very closely there for evidence of biosignatures and life.

And NASA recently entertained proposals for an Enceladus orbiter, which would fly again to the Jupiter's system and moons, and it would focus on Enceladus and fly directly through its plumes in order to try and find traces of organic molecules and again, biosignatures.

So all of these missions are going to be shifting the focus of astrobiology to the outer solar system in the coming years, which is going to be a very fascinating thing, because right now, all of our astrobiology efforts are focused on Mars. And it is, of course, hoped that crewed missions to Mars in the same decade, by the early 2030s onward, will enhance those efforts - that astronauts will explore the surface, conduct research out of a surface habitat and bring samples back for analysis.

And speculation about there being life in the icy moons around Jupiter and Saturn and beyond, that's inspired quite a bit of fiction over the years. And I'd be remiss if I didn't mention the Space Odyssey series. Now, originally in 1968, when the film and book were both released simultaneously, there was a bit of a disconnect.

In the movie that Stanley Kubrick directed and co-wrote, the Discovery mission travels to Jupiter, and they find a monolith in orbit among the many moons of Jupiter. And that's where

Frank Bowman ends up being sucked into the monolith and having a journey beyond space and time and seeing things that an ancient alien intelligence witnessed, and basically experiencing transcendence: becoming something else entirely beyond his physical being.

But in the book, Arthur C. Clarke had said that the mission carried on to Saturn, and that it was on its moon, Iapetus, where the larger monolith - the so called Stargate - was found. But in the subsequent books, and one of which was adapted into film as a sequel - 2010 - the focus was on Europa.

And spoiler alert here. But it turns out that the monoliths were around Europa because their astrobiology experiments were continuing, they had assisted evolution on Earth ensure that hominids survived and became human beings. And now they were attempting to do something similar with the moon, Europa.

They were, they were engineering Jupiter to become massive enough that it would collapse and form a small star, and that the star called Lucifer would then be able to melt the ice sheet of Europa, creating a dense atmosphere, and that the life that was in the interior would have a chance to spring out and populate the surface.

Another example is the film The Europa Report, which is like a found-footage kind of science fiction movie that basically explores the idea of a mission that goes to Europa and it goes terribly wrong, because yes, there's life there, and it wasn't too friendly. And there's even a video game called The Callisto Protocol. And it is set on Jupiter's moon Callisto, which is the fourth of the largest moons around Jupiter. And there is speculation that it too could have an interior ocean and maybe just maybe life. And I believe the plot circulates around that life getting out.

The point is, is that in the coming years, we will be focusing on Ocean Worlds and exomoons as part of the ongoing search for life beyond Earth, be it in our backyard or in neighboring star systems.

And there's even a Fermi Paradox proposed resolution that states that the reason we're not seeing evidence of life in the Universe is because we're not looking in the right places. That if we were looking at exomoons, we might realize that because we emerged on Earth, we became somewhat prejudiced, and we think terrestrial planets are the most likely place to find life, when in fact, the answer could be that they're most likely to be found inside icy moon interiors. And of course, that's a theory that we'll explore in a later episode as part of our ongoing Fermi Paradox segment.

So naturally, any evidence we find of life on or within these icy bodies, it's going to inform our search for extraterrestrial intelligence and extraterrestrial life. It's going to expand our frame of reference for what life is, what kind of chemical and physical characteristics it can emerge under.

And of course, it raises some tremendous ethical questions too, because much like the search for life on Mars, much like all astrobiology missions, if ever we're sending robotic or crewed

missions to explore places where we think it might reside, we run the risk of contamination. We run the risk of destroying the biome by introducing foreign bacteria and pathogens and microbes into it.

Or we run the risk of exposing our own people to life forms that could very well kill them, be they microbes or larger creatures. It's entirely possible there are aquatic species living inside Europa and other moons, and that they are much like aquatic life here on Earth, several of them have a taste for meat. So of course, that remains to be seen.

The point is that when these missions occur, planetary protection protocols are going to be in force, and there are going to have to be some very, very tough decisions made when it comes to just how invasive do we want to get.

NASA is currently exploring proposals for a Europa Lander, which would build on any success and lessons learned from the Europa Clipper mission and JUICE. They're also looking at possible submarines, vehicles that could melt through the ice sheet on Europa or Ganymede and elsewhere, and start probing the interior ocean directly.

And beyond Dragonfly, there's been several ideas floated for missions to Titan, which include a Titan submarine that would explore the depths of Kraken Mare and other major methane lakes in Titan's northern hemisphere.

So all of these run the risk of carrying Earth pathogens to these places and possibly destroying them, which would be an immeasurable loss. Part of the considerations are well, what if life out there is related to life here on Earth? If panspermia theory, the idea that the building blocks of life or even basic life forms and cells were distributed throughout the Solar System and the galaxy from other places on interstellar objects or interplanetary objects like comets and asteroids.

If in fact, that's the case, then life on Mars and life in Europa or Titan, or elsewhere, it may, in fact, be on some level related to us here on Earth. On the other hand, it's entirely possible that it emerged indigenously, and that life has a way of popping up wherever the conditions and the necessary materials are there. And if so, then life forms on any of these other bodies, we already know that they would be precious and unique, but they would be especially unique if they bore no relation to us.

And like many things, as missions to these bodies get closer and closer, that is something that's going to be completely unavoidable. And we can expect some very spirited debates, discussions, and protocols being enacted, being put in place in order to ensure that we can ensure scientific returns but not cause harm. Or at least, at the very, very least, minimize the impact that these missions will have.

And of course, no matter what we find the implications are likely to be Earth-shattering, or likely to be very huge. If, for example, we find nothing, then our astrobiology efforts are going to shift focus once again. We're very likely to focus on terrestrial planets, and that would include

exoplanets. Efforts to find and study them would certainly continue, there's a wealth of information they could teach us. But astrobiology efforts would likely prioritize rocky planets that orbit closer to their sons.

On the other hand, what if we do find life out there? This will fundamentally shake up our notions about life and the types of environments it can exist in. It will give confirmation to what has been, to this day, just speculation that perhaps life can exist in all kinds of environments, that as long as the necessary chemicals and energy are there, it can emerge even if it is just in a microbial form or in terms of simple life forms.

At the same time, it will spur on astrobiology efforts when it comes to examining moons that orbit large gaseous giants, or any icy bodies that reside in the outer regions of a star system, and even Rogue Planets. It has It's been suggested by recent research that Rogue Planets that have been kicked out of their star systems, if they have moons orbiting them, if they're particularly massive planets with icy moons, they could still maintain these warm water interiors which could support life. So this, in fact, could be how life is distributed throughout the cosmos by these moons, by entire planets carrying them.

A very fascinating subject. And I for one can't wait to see how these missions turn out. Considering that the speculation has been ongoing since the late 1970s, the fact that these missions are roughly a decade away from exploring these moons and really addressing these questions head-on is very encouraging.

And of course, I hope to explore this topic and all of its implications and where we could be looking and what we could be looking for in future episodes.

In the meantime, thank you for listening. I’m Matt Williams, and this has been Stories from Space.