Imagining what exoplanets are really like on the ground is a difficult thing, at least
if you keep within the confines of hard science.
We’ve gotten pictures of the surfaces of planets and moons in the solar system such
as Mars, Venus and Titan, but those pictures tend to be of areas where in the case of Mars
were chosen with keeping the safety of the rover in mind, or by landing by chance as
with Venus and Titan.
You play it safe, or you go with the lottery odds, both of which tend to place you in boring
places.
What we haven’t done is visited the grand canyons or Mount Everests of those worlds,
or looked at the truly alien vistas they might present.
Look at the history of how envisioning alien worlds has been done in sci fi.
Arthur C. Clarke’s Thalassa from Songs of Distant Earth, an ocean world where 95% of
the surface is covered in water.
Or in a complete opposite grain, the alien landscapes imagined by George Melies in the
earliest science fiction films over 100 years ago.
As a science fiction author, this is a large part of what I do when I sit on my porch on
warm summer nights coming up with scripts for videos, questions for Event Horizon guests
and concepts for novels.
But for me, it all predates that, long before the internet revolution in the late 1980’s,
the days when 13 year old me was wondering what alien worlds were really like laying
on a blanket looking at the rural Missouri stars before St. Louis’s skyglow forever
dimmed them, before we even knew for sure exoplanets even existed.
Today we can get hints at what might be from our instrumentation, certain gasses present
in exoplanet atmospheres, or detecting worlds analogous to Jupiter and Saturn, some even
with ring systems that outdo Saturn, even planets so hot it rains rock, but earth-like
exoplanets are actually the hardest to try to imagine, simply because they are so similar.
They are the most interesting ones, to be sure, but it can be a bit difficult to imagine
because they would be so much like earth, because that forces you to envision ever greater
details on so little data.
The term Earth-like world is tricky.
You could make the case that both Venus and Mars are earth-like, in that they are in or
near the habitable zone of the sun, and Mars was certainly once a water world like earth
and Venus very well may have been and is very nearly the same size as Earth.
Earth-like is common in our solar system, and our search for exoplanets seems to suggest
that such worlds are common at large, as the Trappist 1 system shows, at least three earth-like
planets exist there in the habitable zone of that star.
But that doesn’t mean they are earths.
That’s actually an interesting thought though, and a major indicator that life may occur
across the universe very commonly.
It’s amazing, just the notion that this star system alone produced three water worlds
that at various points in time could have supported abiogenesis and life.
But only one could support a sustained long term experiment of evolution leading to complex
life and subsequently long term existence.
It was our world, the blue jewel of the solar system so precious to everything we are.
In addition to the blue jewel and the large terrestrial worlds, we face an even bigger
prospect for at least simple life in the solar system.
The probably dozens or more moons and even the minor planets of the outer solar system,
and even the large Asteroid Ceres, that also could harbor subsurface liquid oceans, or
slush zones including Titan which might host an ocean kept liquid by the presence of Ammonia
acting as antifreeze.
But what we don’t have with all these worlds other than earth is a very obvious, unambiguous
signature saying that they have life.
There are hints to be sure, but in contrast to earth which screams its biosphere so loudly
and has done so for so long that anyone in the Milky Way potentially knows about the
blue jewel if they have the right technology.
Maybe they know exactly what to look for.
Perhaps they have a blue jewel of their own.
But we simply don't yet know the answer to whether subtle life in the solar system exists
alongside our very unambiguous earth life.
Do we share this star system with others, even microbial but still neighbors?
We simply don’t know, nor do we know the extent of what the word “others” really
means.
In this video I’m going to introduce a few new terms that have been floating around within
astrobiology lately as we hammer out what that protoscience really will entail.
That’s if it ever truly exists.
It still needs a subject to study, earth life alone isn’t enough, but the framework is
being laid for a day when we do have something to study be it an alien technosignature or
a microbe from Mars.
One of these terms is Prepanspermia.
Obviously, panspermia is a subject I’ve covered many times on this channel, the transfer
of life from one body in a star system to another, or more broadly the notion that maybe
life from other star systems can infect each other in a meteorite, at least at the microbial
level, though you could also in principle include advanced alien civilizations colonizing
other star systems into that mix.
A star ship to another world is a form of panspermia, as much as a microbe hitching
a ride on a meteorite.
But prepanspermia may well precede the advent of life anywhere in the universe.
It’s the transfer of the building blocks of life, the movement of elements and compounds
within star systems that allow for the chemistry of abiogenesis to occur on suitable worlds.
This probably happened with Earth.
When we look at the chemistry of the outer solar system, the comet linked meteorites
known as carbonaceous chondrites, we see the chemicals of life that might have first been
delivered to the surface of the young earth through impacts of these kinds of objects.
When we look at the gigantic clouds of dust and gas present in the galaxy, we see the
signatures of those same organic chemicals and materials, other than one perhaps, there
does seem to be an absence of phosphorus in some areas of the galaxy, and it is crucial
to life as we know it.
But everything else is common, and pervades the Milky Way Galaxy to the point that we
can probably safely suspect that prepanspermia happens all over in most star systems with
planets.
That does not mean that life happens, but only that the materials that make up life
move freely about the cosmos.
You could even imagine a scenario where across the 4.6 billion year history of the earth,
an interstellar object, such as comet Borisov, entered into the mix of earth’s biochemistry
precursors through impact and that perhaps a few atoms within your body were generated
by a completely different supernova from another part of the galaxy billions of years before
the atoms that make up most matter in this solar system had been generated.
Some small share of the matter making up our planet may have been interstellar in nature,
and even prepanspermic.
But here is the problem.
We can again look at the terrestrial worlds of the solar system and really only Earth
could hold on to broad habitability.
Venus degraded into a hell world where the only hypothetical habitability lies in its
upper atmosphere, and Mars suffered from simply being too small ultimately to remain habitable.
So we have a dichotomy, three worlds that at various periods were habitable, suggesting
that habitable terrestrial worlds are common in the universe at large, but two of them
did not stay habitable.
This is an often overlooked problem.
When pondering a subject like the rare earth hypothesis as a solution to the Fermi Paradox
we tend to focus on things like a lack of plate tectonics, or lack of a moon, or magnetic
field.
Yes, those are problems, but the challenges to abiogenesis may actually be far simpler
than that.
It may simply be that most exoplanets by and large might have relatively short periods
of habitability on their surfaces, but what’s really actually rare is surface habitability
that lasts billions of years, long enough to produce a civilization.
That long period of habitability was extremely important for life on earth.
Life on earth took nearly 2 billion years to even start what we consider to be complex
life.
That process is not understood well, and maybe if the situation had been different it might
have happened much quicker, but it’s also equally possible that it happened fast here
on earth and that on most worlds 4, 5 or 6 billion years is needed for that leap.
Well that constrains just what kinds of stars can produce life, and if it is on the upper
end, then the sun itself gets knocked out as a likely star to produce life, and very
unlikely to ever produce a civilization.
Life in that situation means we are an anomaly, and the real action happens most often around
Type M and K dwarf stars that live longer than the sun.
But that doesn’t speak to simple life.
In contrast to complexity, simple life appeared on earth the very earliest moment it possibly
could.
In fact, it seems almost too early.
There was life on this world, if the evidence we have of it is being interpreted correctly,
at the end and during the late heavy bombardment when hails of asteroids and comets were hitting
earth.
Life amid constant impacts, of which only one was needed to cause the demise of the
dinosaurs long after.
And it pays to remember, we’re not even sure the earliest life on earth, the simple
microbes, were even native to this world.
For all we know, it could have happened on Mars and was transported here via panspermia
as Mars in the early days seems to have been a more hospitable place for abiogenesis to
occur than earth was.
Yes, we could be Martians.
But hidden in here may be a larger question.
If situational worlds dictate abiogenesis and how far life can get even among habitability,
what about worlds that we know probably exist but don’t happen to have examples of in
the solar system?
What of worlds entirely covered in liquid water?
Again this is probably situational.
I’ve mentioned completely water covered ocean worlds before as have others and how
it might be impossible for intelligence to arise on those worlds but due a lack of land,
they would also lack the ability to smelt metals and build computers and rockets.
But there are conceivable ways around that, we live on a planet that has coral that in
a way can build land, though in that case there is usually a sea mount involved to form
a base.
Coral atolls represent life itself creating land, so it can be imagined such things might
happen on water worlds perhaps on a greater scale.
Or even life creating floating islands or some surface otherwise where some stepping
stone to complex land life might get a foothold.
It would be different from earth to be sure, but it can at least be envisioned.
Unless there is a further problem, and a much more fundamental one.
This one can be called the water paradox, and it’s actually composed of two problems.
The first is the question of how abiogenesis actually happened, if it happened around a
hydrothermal vent in the oceans, or if it happened on land and was linked to surface
liquid water and volcanism.
Recent work has shown that the latter might be more likely, and that has massive implications
for the search for life in the universe but more importantly within our own solar system.
The first part of the water paradox is whether it can happen in salt water at all.
There is some indication that life on earth may not have been able to arise in salt water.
It may in fact have required fresh water on land, only to then evolve the ability to colonize
the oceans.
If this turns out to be the case, then it has very serious implications for the potential
for life in the rest of the solar system.
In short, it’s going to very likely eliminate Enceladus and Europa as potential abodes of
life.
Indeed, many of the potential ice shell moons, though there is a chance that some of them
are simply not salty, and the threshold of how much salt you can have in the water and
still host the chemistry of abiogenesis is unknown.
It’s worth noting here that this aspect of the water paradox is not yet settled, but
it could mean that if water worlds are the rule of the universe and that land is rare,
then salt is a solution to the fermi paradox.
The universe being “too salty and wet” solution to the Fermi paradox aside, there
is also another issue that thickens the plot, very seriously in fact.
Recent findings in biochemistry suggest that the generation of RNA requires the presence
of water, the right chemicals, all percolating and through volcanic glasses which were and
are abundant on Earth, Mars and probably Venus early in the history of the solar system when
life first arose.
This finding points squarely at the origin of life being on land.
It also points to the formation of RNA being easy, and thus very likely to be common everywhere
in the universe, a good sign for life, or at least the probable precursor of it.
But then we come to another new finding.
In a paper by Bruce Damer and David Deamer, link in the description below and do check
out next week’s Event Horizon episode with Dr. Deamer, they report that another requirement
for life may in fact be the presence of hot springs on land that go through cycles of
drying out that may be integral to the formation of protocells.
In other words, if you have the right chemicals, many of which are found in meteorites, and
a hot spring that flows and dries out periodically, something that the authors actually verified
happening in nature in the Kamchatka region of Russia, then you have the precursors of
life.
Given that hot springs are ultimately geothermal and volcanic activity making glasses can often
be nearby, it’s not hard to imagine a link to the basaltic glasses being present along
with hot springs allowing for the circumstances of abiogenesis.
While much of the process remains unclear, but progress in understanding it is being
made, within this also is another concept and another new term coined by Damer and Deamer.
Urability.
The idea behind this concept is that, sure, you can have planets within the habitable
zone of a star, but that doesn’t guarantee that they can produce life.
Rather the conditions are situational, as they were here.
As such the solar system appears to have had two to three Urable planets in its history.
Again, Earth, Mars and Venus.
Regardless if life arose on all three of them, Venus and Mars have lost their Urability.
Life could not arise on them now, if the hot springs hypothesis is correct.
Even subsurface Mars that might still harbor microbial life, can’t produce an abiogenesis
today due to a lack of dry and wet cycles which is key to the hypothesis.
So a planet may not simply need to be habitable, but it must also meet the conditions to be
Urable.
And there may be factors here, such as changes to the atmosphere of a world, such was earth’s
great oxygenation event that actually means that Earth itself is no longer Urable, despite
hosting a huge biosphere.
That might just play into why we don’t see evidence of multiple abiogenesis events on
earth, and indeed don’t see it occurring all the time.
It’s not that the pre-existent life on earth eats any new abiogenesis, rather it doesn’t
get that far, it’s that the oxygen itself poisons it instantly.
It’s an interesting thought indeed that life itself, which was responsible for the
great oxygenation event, could actually render its own planet no longer urable even though
it’s habitable and inhabited.
But inside all of this is something else.
If it turns out that ice shell moons like Europa and Enceladus aren’t places where
life could arise even with the presence of liquid water, there is one other body that
then comes on the table.
It once had as much water as Europa, and may still have subsurface water, and it’s volcanic,
and maybe still could have lava tubes and nooks and crannies where life might persist
protected by a shell of rock.
And it’s among the last places we’d ever think to look for microbial life.
But in this model, it potentially ticks the boxes.
To paraphrase 2010, All These Worlds are yours, except Io, attempt no landing there.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently
confident in the salt!
Imagine a land world that has water, but not salty oceans, just freshwater percolating
around that spawns an invasion fleet.
They show up, and we say “accept this earth delicacy as a token of our acceptance of our
new alien overlords.
We call it a jar of pickles” and boom.
Invasion over, we got this and be sure to check out my books at your favorite online
book retailer and subscribe to my channels for regular, in-depth explorations into the
interesting, weird and unknown aspects of this amazing universe in which we live.