Could the reason we haven't found evidence of extraterrestrial life be that water is too abundant on some worlds?
Host | Matthew S Williams
On ITSPmagazine 👉 https://itspmagazine.com/itspmagazine-podcast-radio-hosts/matthew-s-williams
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Episode Notes
Could the reason we haven't found evidence of extraterrestrial life be that water is too abundant on some worlds? This is the essence of the Waterworlds Hypothesis, which tells us that rocky planets with the right balance of continents and oceans could be rare.
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Resources
Beyond “Fermi’s Paradox” XII: What is the Waterworlds Hypothesis?: https://www.universetoday.com/147775/beyond-fermis-paradox-xii-what-is-the-waterworlds-hypothesis/
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For more podcast Stories from Space with Matthew S Williams, visit: https://itspmagazine.com/stories-from-space-podcast
Where is Everybody? The Waterworlds Hypothesis | Stories From Space Podcast With Matthew S Williams
E76 - Waterworlds Hypothesis
[00:00:00] The authors acknowledge that this podcast was recorded on the
traditional unceded lands of the Lekwungen peoples. Hello and welcome back
to Stories from Space. I'm your host Matt Williams and today we're going to get
back into our series on the Fermi Paradox. Why is it that humanity, in spite of
the vastness of the universe and the statistical likelihood, we assume, of life, has
not found any evidence of intelligent civilizations out there?
Now, in previous episodes, we looked at various theories, including the
possibility that there is no intelligent life out there known as the Hart Tipler
conjecture, that there is something that prevents basic life from evolving into
more complex life forms and or achieving a degree of technological mastery
that would make them easy to detect, known as the Great Filter Hypothesis.
To the possibility that civilizations out there are being periodically wiped out,
[00:01:00] or simply avoiding contact with one another. Otherwise known as
the Berserker Probe Scenario, and the Dark Forest Hypothesis. Well today we're
going to explore the Water Worlds Hypothesis. Now this is not to be confused
with the Ocean Worlds Hypothesis, which we will address in a forthcoming
episode, so stay tuned for that.
To break it down, the Waterworlds hypothesis conjectures that, perhaps, on
many planets in our universe, water is overly abundant. And while this
hypothesis was not inspired by the movie Waterworld, released in 1995 and
starring Kevin Costner. The name is applicable because the scientific research
that has gone into inspiring it, it does call to mind a lot of the ideas and themes
in that movie, that in fact, our entire planet could be covered in water, thus
making life extremely difficult for the vast majority of lifeforms here.
[00:02:00] However, the origin of this hypothesis is largely the product of
recent exoplanet discoveries, but it does have foundations that go back several
decades. And this includes David Brin's seminal paper that he released in 1983,
titled The Great Silence The Controversy Concerning Extraterrestrial Intelligent
Life, in which he said, Water covers over 70 percent of the Earth's surface, yet
perhaps the Earth is towards the dry end of the habitable class of worlds.
A much smaller land area, or a lack of dry land at all, would afford little
opportunity for the evolution of tool using species. Most intelligent species in
the universe might possess the outlook of whales, and never conceive of radioor travel to the stars. In this respect, he anticipated discoveries that were made
decades later.
The current census of exoplanets has now reached well over 5, 000, and
scientists have noted that for many, the [00:03:00] size, mass, and density
estimates that they obtained indicated that many of these planets were
composed of volatile elements. Which is to say, elements that have a low
melting point. Chief among which would be water.
And this presented astrobiologists with a bit of a conundrum. All this time,
scientists have considered water to be a key biomarker, or biosignature, in the
sense that it's something that all life, as we know it, needs in order to exist. And
based on the fossil record and the evolutionary timeline that we've managed to
reconstruct here on Earth, we also know that the first life forms evolved in
water, in particular around hydrothermal vents.
The most recent evidence is indicated that fossilized bacteria dated back to over
four billion years ago emerged as a result of these deep sea fissures and vents.
Microbial lifeforms were able to get the necessary energy and [00:04:00]
elements from the planet's interior that are essential to life as we know it.
And of course, the Earth's hydrological cycle, it helps maintain the conditions of
habitability upon which all life depends. And of course, all terrestrial organisms
need water in order to properly metabolize their food and also ensure that they
don't die of dehydration and maintain bodily temperatures.
So, water is the key to life. However, there is a growing body of research that
suggests that too much water may actually be an impediment to the evolution of
life. In 2016, the PaleRedDot team, who actively search for rocky planets
around M type red dwarf suns, they determined that of the many recent
findings, which included Proxima b.
Assuming that these are, in fact, rocky bodies that don't have a particularly
[00:05:00] dense atmosphere, they concluded that water likely made up 50
percent of the planet's mass fraction, which would mean that it is most likely an
ocean planet with a frozen icy shell on top. And, in addition, a similar study
from researchers from the University of Bern, they examined the formation of
rocky planets around red dwarf suns, and their results indicated that these
planets could range from being 50 percent to 1.
5 times the size of Earth, and that in 90 percent of the cases, water would
account for more than 10 percent of the planet's mass. And consider the fact thaton Earth, water only accounts for 0. 023 percent of our total mass. So once
again, you've got a water world scenario. And then you have the case of the
TRAPPIST 1 planets, which consists of 7 rocky planets orbiting a red dwarf
sun.
And [00:06:00] multiple studies have indicated that it is likely rich in terms of
water, and a 2018 study by Arizona State's School of Earth and Space
Exploration calculated the water content, and based on their results, they found
that these planets could range from 15 percent of water by mass for those that
were closer to the star, and therefore drier, while the uttermost were likely 50
percent water by mass.
And last but not least, another study conducted in 2018 by a team of researchers
from Harvard University, they examined data from the Kepler Space Telescope
and the European Space Agency Sky Observatory to try and come up with an
estimate of how common water worlds are. And they did this by creating a
model that showed the relation between A exoplanet's mass and radius, and they
found that planets that have a radius 2.
5 times that of Earth, [00:07:00] and a mass of about 10 times that of Earth, are
most likely to be water worlds, where water is roughly 50 percent of the mass.
And so far the exoplanet census has indicated that 35 percent of all known
exoplanets out there are larger than Earth and up to several times the mass, aka
super Earths, and therefore should be very rich in water.
Now what this would mean for the evolution of life as we know it? Well
Implications could be very significant, in that planets like Earth that have the
right kind of land mass to ocean ratio are quite rare, thus echoing the Rare Earth
Hypothesis. For example, in a 2018 study, Harvard professor Abraham Loeb
and Dr.
Manisavi Lingam, they conducted a series of simulations that examined the role
played by oceans and continents in the emergence of life, which is something
scientists considered a foregone conclusion, that both are [00:08:00] necessary
in order for there to be species diversification and evolution. And in the end,
they came up with two likely scenarios.
On the one hand, their calculations indicated that a balance between oceans and
landmasses is crucial to the emergence of complex biospheres. And
furthermore, that planets such as Earth, which has a 3 to oceans ratio, is
probably quite rare in our universe. And so, looking for stars within habitable
zones, especially around M type red dwarfs, which appear to be very, very goodat forming rocky planets, as indicated by finds like Proxima b, the TRAPPIST 1
planets, RAS 128b, LUTON b, GLIES 667cc, and the list goes on.
And these are all planets that are within roughly 40 light years of Earth. So, in
each of these cases, [00:09:00] wherever there is a planet that is several times
the mass of Earth, the likelihood that it is a water world is strong. And this
would mean that, yes, not only does it lack the crucial balance that some
scientists believe is absolutely necessary for life, land masses and oceans
coexisting, But it would likely have an effect where the planet would become
what's known as an ice ball planet.
So, for those planets that are particularly large and have a large mass fraction of
water, and are also missing a dense atmosphere, Then the outer shell of the
planet is likely to be composed of solid ice with an interior ocean floating
beneath that. But lower than that, you'd have water that is at such great depths
and such great pressures that it would solidify.
And so you'd have this big layer of ice between the liquid ocean and the rocky
and metallic core. Which would mean that there wouldn't be exchange between
the core [00:10:00] and the ocean itself. Any hydrothermal vents that could
exist down at the rocky core would be unable to send their chemicals and their
energy and their heat up to where it's needed the most into that ocean.
For those planets that do have a dense atmosphere, on the other hand, well, the
same problem applies. If their mass fraction of water is high, and if they're
particularly large, then, yeah. Once again, you have a layer of solid ice between
the rocky and metallic core and the liquid ocean, which is going to make it very
difficult for life as we know it to take root.
So, of course, one can see how this would be a proposed resolution to the Fermi
Paradox. And that is that perhaps most rocky planets that you will find out there
in the cosmos will in fact be covered in oceans so very deep that life does not
have a chance to emerge on the ocean floor. And no continents for life to
eventually migrate onto and start diversifying and [00:11:00] creating a rich and
varied ecosystem.
So it is a fascinating theory and it happens to fit certain facts and it's backed by
research. That has come out in recent years, thanks to the huge explosion in
terms of the number of confirmed exoplanets out there. But there are limitations
to it. There are criticisms that are also supported by a great deal of exoplanet
research, as well as the fact that the current exoplanet census is limited.For example, of the 5, 690 confirmed exoplanets to date, that is to say, as of the
recording of this episode, Roughly 30 percent fall into the Super Earth category,
whereas 66 percent fall into either Neptune like gas giants or Jupiter like or
Super Jupiter exoplanets. Only 203! Which works out to about 3.
[00:12:00] 5 percent have been confirmed to be Earth like, in the sense that they
are terrestrial and are comparable in size, mass, and density to Earth. And right
off the bat, this demonstrates something about our current methods and their
limitations. Because, of all the planets that have been discovered out there,
Almost three quarters have been discovered using the same method, the transit
method, which consists of monitoring stars for periodic dips in brightness,
which can indicate the presence of a planet.
And if astronomers note that these dips in luminosity are consistent, that they
happen with a regular period, then they know that they're looking at an
exoplanet and they can also derive highly accurate estimates on its size. And
when it's combined with the radial velocity technique. Whereas stars are
monitored for how they move about in place, which is an indication of the
gravitational [00:13:00] pull on them, i.
e. from orbiting planets, astronomers are able to measure, with a fair degree of
confidence, what the exoplanet's mass is. And by comparing mass to size,
they're able to obtain estimates on density. The problem is, is that the transit
method mainly works for particularly large planets, hence the prevalence of
super Earths in the census.
And the radial velocity method, well, so far, it has turned up plenty of super
Earths as well, as well as gas giants, because these are likely to have noticeable
perturbations on their star. Thank God. And what is considered the best way to
study and characterize exoplanets, known as the direct imaging method, which
I'll explain in more detail later.
To date, the vast majority of planets detected using this method have been gas
giants that have a more distant orbit from their star. [00:14:00] To find Earth
like planets, that is to say, smaller terrestrial planets that orbit more closely to
their suns, which are believed to be the best candidates for habitability and for
supporting life, you need much more sensitive instruments, as well as
coronagraphs, which are instruments that block out the light from a star so that
orbiting exoplanets would become visible.
And they'd be visible as small points of light, which is caused by light reflected
by the planet's atmospheric surface. And from this, astronomers can gainspectra. They can see how that light that is passing through the atmosphere is
broken down into different wavelengths, and from that, infer chemical
composition.
And this is what is meant by direct imaging. In addition, you can also look at
the surface there and detect which wavelengths of light are being radiated.
[00:15:00] And if, in addition to infrared light, heat, the colors that are being
radiated are in fact within the green wavelength of the spectrum, then scientists
have conclusive proof that there's vegetation on a planet's surface.
And that is known as the Green Vegetation Edge, which scientists use routinely,
using Earth Observation Satellites to study the extent and health of plant life
here on Earth, as well as phytoplankton and other photosynthetic organisms that
live in the ocean. And the same is true of plant life that relies on retinal
photosynthesis, where they absorb light at different wavelengths from
chlorophyll based plants, and they radiate the color purple.
Thank you. So yes, looking for green and purple planets requires much more
sensitive instruments. And we are now in a position to do that thanks to
telescopes like the James Webb Space Telescope, thanks to its advanced optics
and highly [00:16:00] sensitive infrared sensors. And it will also be possible
with the upcoming Nancy Grace Roman Space Telescope, which will have the
same kind of sophisticated optics as the Hubble Space Telescope, its direct
successor.
But with the ability to explore several hundred times more planets at a time.
And it will also be equipped with a coronagraph to assist in direct imaging
studies. And astronomers are also looking forward to the Nancy Grace Roman
Space Telescope working together with James Webb by leveraging Roman's
ability to survey countless stars and look for exoplanets at a time.
With the James Webb Superior Infrared Sensitivity, they anticipate that the
number of confirmed exoplanets is going to grow exponentially, and that the
characterization of those planets will also proceed very quickly. So from this,
the [00:17:00] exoplanet census is likely to grow by leaps and bounds and
become far more complete, which is to say we're going to get a much better idea
of the types of planets out there, just how common certain types are.
In addition to that, there's been several studies that have cast doubt on water
worlds and whether or not they are in fact unlikely to be habitable. For instance,
in 2018, geophysicist Edwin Kite and astrophysicist Eric Ford, they produced a
study titled Habitability of Exoplanet Water Worlds. And showed thatwaterworlds could in fact maintain a carbon cycle without geological activity or
landmasses and therefore produce life.
And whereas this carbon cycle wouldn't be the result of tectonic activity, as it is
on Earth, I can forward the conducted simulations that showed that waterworlds
would be able to cycle enough [00:18:00] carbon between the atmosphere and
the oceans to maintain a stable climate and thus be. Potentially habitable.
A similar study was released in 2018 that also showed that plate tectonics aren't
necessarily vital for maintaining habitable conditions on a planet. So that
stagnant lid planets, where the entire surface and mantle consists of one piece,
could in fact still maintain a carbon cycle without the need for convection and
volcanic activity.
And, of course, all of this runs into the same old question of principles, whether
the Copernican Principle or the Anthropic Principle is, in fact, the case. And, to
recap, the Copernican Principle argues that Earth is neither special nor unique in
terms of its nature or in terms of its position in the universe to view things, and
that, therefore, Earth is likely to be [00:19:00] representative of the whole.
In contrast, the Anthropic Principle asserts that scientific observations are only
possible because the laws of the universe are compatible with the development
of sentient life. And from this, cosmologists who embrace the Anthropic
Principle, they accept that, in fact, humanity and Earth are indeed in a privileged
position and are not typical of the norm.
And these two principles are of course extremely relevant here because they are
at the core of the very debate regarding the Fermi Paradox. Either Earth and life
as we know it is rare or unique, or it is not. And the only way we're really going
to be able to address that, and the fundamental arguments here, that are part of
the Waterworlds hypothesis, and every other attempted resolution of the Fermi
Paradox, is to be patient and await the returns of more [00:20:00] data, and for
more exoplanets to be discovered and confirmed, and for their characterization
to take place.
Once we have a better idea of the kinds of planets that are out there, and how
many of them are truly likely to be habitable, and even show indications of
being habitable, thanks to the aforementioned methods of characterization, Only
then can we really know if Earth is typical or atypical of the whole.
In other words, are Earth like planets with life that we would recognize, are they
statistically significant out there? And if so, what does that say about the oddsof us ever making contact with any of them? So once again, unfortunately, this
resolution does not offer a resolution per se, but is nevertheless a very
interesting theory that helps astronomers constrain their [00:21:00] searches,
and presents a possible explanation as to why we have yet to find any evidence
of life out there.
And so, we include it here in our ongoing series about the Fermi Paradox and
the many, many resolutions that have been offered and attempted over the many
decades since Fermi first asked the question. And, as I mentioned earlier, while
this hypothesis is distinct from the ocean worlds hypothesis, which we'll get into
next time, it nevertheless has some very interesting commonalities, there's some
overlap in it, especially where we're talking about ice ball planets with a frozen
outer crust and a liquid water interior surrounding a rocky and metallic core.
But we must save that for another time because it's a whole other theory and it
really deserves its own full treatment. In addition, we will soon have the final
[00:22:00] episode in our Great Migration series that addresses how human
beings may someday live in the Trans Neptunian region, which is to say, around
Neptune on its largest moon, Triton.
Pluto, Charon, and other quote unquote minor planets in the outer solar system
and the Kuiper belt. So stay tuned for all of that. In the meantime, thank you for
listening. I'm Matt Williams and this has been Stories from Space.