In the quest to understand how life on earth came to be, and indeed how common such an
occurrence is in the universe, scientists have put a significant amount of thought into
just what environments could potentially host life, and even alien civilizations on distant
exoplanets.
In our search however, we find that the traits Earth possesses to support life, and the genesis
of it, are not unique in our own solar system.
Especially for microbial life.
These places include some low hanging fruit.
In addition to Earth, Mars once was very earth like with oceans and liquid water, and may
still possess it deep below its surface leading NASA and others to search for evidence of
life on that world.
Also famously are Enceladus and Europa, the most famous ice shell moons where the ice
covers oceans that may not only harbor microbial life, but maybe, just maybe, even complex
oceanic life.
We’ve even considered the very cold environment of Saturn’s moon Titan as a possible abode
of low temperature life as we do not know it.
But aside from those more famous places, the potential for life in our solar system other
than that of earth is actually much broader than the more famous candidates.
So here are 10 Mysterious, more obscure places in the solar system where life could conceivably
exist above and beyond the most famous candidate worlds.
Number 10.
The Atmospheres of Jupiter and Saturn
Gas giants at first glance do not seem to be ideal planets for life to arise.
It would actually be enormously difficult for abiogenesis to occur, due to the nature
of it having to occur in an atmosphere rather than on land or water.
But there have been ideas of it potentially being able to occur in floating water droplets
if the right conditions happen.
This is still a stretch however, based on what we do know about how life arises, but
on the other hand we do not have a full understanding of that.
However there is another way for life to inhabit a gas giant.
It’s panspermia, so if a star system has an inhabited planet that infects a gas giant
with life, which is also a rather tall order but not in principle impossible, then that
life might find a niche in the upper atmosphere of a gas giant planet and evolve there.
Carl Sagan once envisioned what this life might look like, large gas bag type creatures,
flying creatures and so on that might take advantage of the atmospheric conditions present
in the upper atmosphere of these worlds.
Looking for this kind of life would be extremely difficult however, and also a low priority
for robotic space missions due to the slim chances for it to have occurred at either
Jupiter or Saturn.
Still, it remains a possibility and in the coming centuries maybe we’ll go to those
planets and take a closer look.
Maybe there will be a surprise awaiting us.
Number 9.
The Asteroid Belt
Another scientist that waded into the speculative life arena was none other than Freeman Dyson.
Dyson’s idea, known as Dyson’s Sunflowers, goes like this.
Life arises in an ice shell moon with a subsurface ocean.
That life evolves to grow up through the cracks and essentially flower, with a reflective
energy gathering apparatus.
Imagine a flower with highly reflective petals gathering solar energy.
Through further evolution, these sunflowers might sever their connection to the ocean
beneath and become essentially a space faring plant.
It’s hard to envision such a thing living in deep space indefinitely for a lack of nutrients,
but Dyson suggested that they may colonize asteroids for that purpose, or you could also
envision it as a dandelion that scatters its seeds into deep space to colonize whatever
they can.
This would open up the asteroid belt as a long shot, but plausible abode for life.
For any life evolved for it, asteroids are rich sources of minerals, many of them already
are loose conglomerates of soil and rocks, and they also tend to contain volatiles and
water ice.
At the same time however, we’ve examined a handful of asteroids at this point and nothing
like this has been seen.
But that;s not the only place where this might occur.
On the list for this as well would be the rings of saturn.
There’s even one particular asteroid that might be a very good candidate for something
like this to happen or be the original origin of it.
It’s the asteroid Ceres, which is believed to harbor a slushy subsurface ocean where
life could have arisen.
Number 8.
Pluto
One of the great surprises in astronomy in recent years was the New Horizons flyby of
Pluto which revealed not a boring frozen unremarkable world, but a vibrant active world with no
shortage of surprises.
It had always been assumed that Pluto formed very distantly from the sun in the Kuiper
Belt out of cold rock and ice slowly clumping together.
Pluto is also believed to have a subsurface liquid ocean, not unlike Europa.
This ocean also was assumed to have formed after Pluto's formation, in other words the
heat built up below ground due to radioactive elements decaying in Pluto’s core.
Recent work however has shown that may not have been the case, and Pluto’s formation
was actually hot and the liquid water was there from the start.
This is hinted at by the rather surprising surface geology of Pluto which shows the action
of freezing water expanding creating characteristic cracks due to stretching.
If Pluto had formed very cold, you’d see compression as the water melted from the radioactive
decay.
This is not seen in the most ancient areas of Pluto’s surface.
The fact that Pluto’s ocean may have been there for the entire history of that world,
means that it’s had every bit as much time for life to arise as earth did.
That a minor planet like Pluto can have a hot start and support liquid water oceans
long term bears significant implications for the Fermi Paradox in that if something can
happen at Pluto, which is far outside the sun’s habitable goldilocks zone, then the
possible environments for life pervade most star systems in the universe.
It’s then possible that habitable ice shell worlds may indeed outnumber stars in this
universe.
Number 7.
The Atmosphere of Venus
Normally, Venus would not seem like a candidate world for life.
It once was however, before visiting it with a probe Venus was often envisioned as a hot
world with jungles lurking beneath its permanent cloud deck.
This was not the case however, Venus turned out to be a runaway greenhouse effect world
with crushing temperatures and immense surface atmospheric pressure.
As a result for many decades Venus was neglected as a potential abode for life and Mars came
to the forefront.
This was somewhat unfair however since the upper atmosphere of Venus hosts the most earth-like
environment in the solar system where temperatures and atmospheric pressures are comparable to
earth.
Given that we find earth’s microbial life in the atmosphere, at least to a degree, then
why not Venus?
Interest in Venus as a possible home for life has recently gained more attention from the
scientific community and indeed Venus is the first entry on this list where not only could
life exist, but we may have indicators that it does.
There are many strange mysteries that Venus presents.
The first is the unknown UV absorber, some substance in the upper atmosphere of Venus,
right at the temperate altitude, is absorbing ultraviolet light.
There have been suggestions that while UV light is generally not good for earth life,
alternative forms of life might use it as an energy source.
Another hint are sulfur compounds present in the atmosphere of Venus, which is full
of sulfuric acid, could also form a kind of chemical shield for a microbe to exist in
such an acidic environment.
These compounds have been measured by probes at Venus, they are there.
Another hint is the presence of small amounts of phosphine gas, which is linked with life
to a degree.
This finding was called into question, but it’s survived peer review and there is unexplained
phosphine in the atmosphere of Venus.
Other strange things are that the Venera probes sent by the soviets to parachute into the
atmosphere of Venus measured particles of something consistent in size with microbes.
There are enough indicators at this point to catapult Venus to the first position as
a candidate world for microbial life.
After all, Venus may have started out as an ocean world like Earth, only to slowly convert
into the hell world it is today.
It wouldn’t be that surprising if microbial life arose there early on, and as that world
died as far as habitability, it adapted whatever niche it possibly could in order to hold on
at Venus.
The good news is that we’ll likely know the answer in the not to distant future as
plans are being formulated for a Venus life finder mission geared specifically to investigate
the observed anomalies in the Venusian atmosphere.
Number 6.
Ganymede and Callisto
When discussing the question of life in the Jovian system, Europa is the elephant in the
room that we often hear about.
But it’s not the only moon in that system that is suspected to have a liquid water ocean
under a shell of ice.
Ganymede and Callisto are also on the suspect list and may both harbor extensive oceans
subsurface.
Very little is known about Callisto’s ocean other than if it exists, it lies very deep
below the surface on the level of 250 Kilometers or more deep, or 155 plus miles.
It’s possible that this ocean interacts with a rock floor, opening the way for supporting
life.
But with Callisto, we may never have an answer on whether it does or does not harbor life
due to the ocean being so deeply buried beneath the surface of this moon.
With Ganymede the situation is somewhat different.
In this case, Ganymede seems to be layered, meaning there’s a layer of ice, an ocean
beneath it, but then another layer of ice, which is a problem for life, and then rock
beneath that.
That’s at least as complicated as it could be, another analysis showed that Ganymede
may have stacked oceans separated by different types of life.
Given that water in contact with rock and thus nutrients may render Ganymede a long
shot for ice.
Strangely however, the evidence for some kind of liquid ocean is particularly strong with
Ganymede due to certain effects noted with this moon’s aurora, it actually has a magnetic
field, and that evidence suggests that Ganymede actually sports the largest ocean in the solar
system, significantly larger than that of earth.
As a bonus, Saturn’s moon Dione is also apparently an ice shell moon, though little
is currently known about it.
Number 5.
The Moon
You’d think the moon would be truly lifeless.
It’s baked surface is subject to the full fury of the sun, sterilized by it, and other
than pockets of ice is generally very, very dry.
Surprisingly however the moon does have prospects for past and current life of several different
kinds.
One is the elephant in the room, it’s orbiting an inhabited planet.
It’s easily possible for earth microbes to get blasted off earth and then land on
the moon.
Once there they might have held on in places like shielded craters where the sun never
reaches, something that NASA does have some plans to look for.
Also the moon once had a habitable time period along with a former magnetic field, at least
for a time, native life might have been possible on the moon.
But there’s also the question of subsurface water and possibly a haven of microbial life,
it’s just a matter of how deep you go below the moon’s surface and how warm it is.
So it’s at least possible that the moon might host cousins to earth life, or a truly
alien occurrence of life.
Number 4.
Kuiper Belt Objects
Pluto is particularly noteworthy in that it probably originated as a Kuiper belt object,
a distant cloud of minor planets that populate the outer reaches of the solar system.
As it stands today, there are 5 known minor planets that are comparable to Pluto.
Very likely there are more of these that remain undiscovered and we may well see a steady
stream of discovery of minor planets with upcoming survey telescopes like the Vera Rubin
observatory.
But here’s the interesting part.
They may all be candidates for hosting microbial subsurface life, opening the way for at least
tens of new candidates to someday search.
This is for the same reasons that Pluto is suspected of having a subsurface ocean, radioactive
decay in their cores.
This is likely to be the case for any Kuiper Belt object of sufficient size.
On the other hand, this may be a search that takes centuries due to distance.
It’s not easy to get probes out that distantly, though we can do it.
We just have to wait 14 or more years for something to get out there to even begin to
image and look at these worlds close up.
Searching them for life is much more difficult in that we don’t even have the first steps
towards knowing how to do that worked out.
As such, the question of life in the outer solar system, may be open for quite some time
yet.
Number 3.
Mimas and Stealth Oceans
Saturn’s moon Mimas is strange, above and beyond a resemblance to a death star.
It’s also the newest member of the ice shell moon list, only two months ago was it proposed
to be a new one and it introduces an entirely new class of ice shell oceanic world that
was not previously thought to exist.
Mimas is in stark contrast to places like Callisto and Ganymede in that it is a very
tiny moon, the smallest in fact of saturn’s major moons.
Recent work has shown that Mimas in fact has the right circumstances of heating to keep
water liquid at some level, and evidence from its huge Herschel impact basin support the
idea of a very young, geologically speaking, liquid ocean under the surface.
In fact, the ice shell itself may still be in the process of thinning due to the accumulated
heating that seems to be going on.
The findings go back to a curious finding years ago by the Cassini mission, that Mimas’
rotation was oscillating, known as libration, which tends to point towards an object being
geologically active in this case.
An ocean however was not considered, due to Mimas appearing to have an ancient and heavily
cratered surface, suggesting that there was no interaction with liquid water.
No water, no erasing of the craters, hence the ancient surface.
In other words, ice shell moons, at least those with relatively shallow water show geysers
and surface tectonics.
But in the case of Mimas, that may have been situational, and in fact the existence of
the ocean represented a new kind of ice shell moon that does not show outward evidence of
the ocean’s existence, termed a stealth ocean world.
Modeling of the huge Herschel impact crater showed that at the time when it hit, the ice
shell had to be at least 55 kilometers thick.
Current observations however show it to be around 30 kilometers thick, meaning its thinned
during the intervening time as the ocean expanded.
This would be because Mimas is an emerging oceanic world in the process of formation.
As to the question of life, we simply don’t know the rules here.
If the ocean is young, the chances are lesser, but not that much because microbial life appeared
on Earth the very earliest moment it possibly could have.
So it may have happened at Mimas, and questions could be asked about transient water pockets
that could have been quite ancient that began to form just as soon as enough heat built
up.
In any case, Mimas shows that we don’t yet know just how many other bodies in the solar
system might have situational liquid water beneath their surfaces.
Number 2.
The Uranus System
We have only ever been to the Uranus system once, with Voyager 2.
Since then it has been a relatively neglected system due to it being difficult to get probes
there.
Uranus itself is quite strange, but it also hosts an inordinate amount of ice shell moon
candidates.
Among these are Miranda and Ariel, which both show features not unlike the surface features
of Enceladus and Europa.
Titania, Umbriel and Oberon are larger moons, and also good candidates for ice shell moons,
but would be very difficult to study in that usual magnetic measurements used to detect
these oceans aren’t present due to their distance from Uranus and the bulk of its magnetic
field.
Still it might be poetic if after searching many ice shell moons in the solar system,
while Uranus sat on the backburner only to finally find it there in conjunction with
some far future drilling mission.
Number 1.
Io
One of the seemingly least likely places in the solar system to harbor life also happens
to be one of the most dangerous solid surfaces in the solar system to land on.
Wildly volcanic, unstable and inside Jupiter’s deadly radiation torus, it rounds out the
Jupiter’s four Galilean moons as actually being potentially habitable.
The reason is, it’s thought that Io, which is the most volcanic body in the solar system,
also very likely started out with as much water as the other galilean moons.
Much of this water is now gone, but’s certainly possible that abiogenesis might have gotten
a start there early on, and there might still be enough subsurface water to allow for microbial
life to maintain some type of foothold.
While this seems unlikely, there’s another dimension to this.
Recent breakthroughs in trying to figure out abiogenesis have come to two pieces of evidence
that may push Io higher up on the list of places to look for life.
The first is that RNA generation appears to involve water and nutrients percolating through
basaltic volcanic glasses, something Io very likely has.
Another point is that the formation of protocell walls seems to involve hot springs that periodically
and repeatedly dry out, again something Io may have once conceivably had.
So this body, while surprising and volcanically violent, is a rising star in the question
of where life might be located in the solar system.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently eyeing the planet
Mercury suspiciously.
With so many speculative possibilities regarding places where life may have arisen, this is
the one planet that to this day has no prospects that I’m aware of.
All of the other classical planets have it in some form.
But Mercury simply seems to be a germaphobe that has something against microbial life.
Very unsavory 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.