One could argue that almost any body in the
solar system is habitable so long as you have the technology to colonize it. But that would involve this solar system’s
elephant in the room, which is our civilization. For the sake of this list, I leave us off
it; we know that life on earth is possible. But as we’ve learned more about our solar
system, it is becoming increasingly evident that other places could have evolved life
independently of earth. So here are ten places where life is possible
in this solar system other than earth, plus a few bonuses tossed in, since hypothetical
habitability is by no means rare in this star system, and probably isn’t rare in the rest
of the universe either. 10. Venus This possibility is a long shot, though life
can be tenacious and surprising so it remains a possibility, at least for microbial life. Venus was once like earth, it may have had
abundant liquid water early in its history, and seems to have had it long enough for life
to arise. But the story of Venus is a sad one; several
contributing factors led to an eventual runaway greenhouse effect on that world that turned
it into a vision of hell. But that transformation would have been a
gradual process as far as we know and any life that was present on the surface may have
had time to adapt to the changing conditions and find a niche in which to survive. That niche lies in the upper reaches of Venus’
atmosphere. There exists a zone that is temperate and
cool that may allow for airborne life to exist and it’s possible that we may have already
detected it. This option for microbial life a huge maybe,
Venus’s atmosphere is quite acidic and this life would be radically different from most
life on earth, but there is a hypothetical way for life to exist in that kind of acidity
through a molecule known as an S8 molecule. An organism could hypothetically incorporate
S8 molecules as a sort of armor, as these molecules are resistant to the effects of
sulfuric acid. S8 has been detected in the atmosphere of
Venus, and could have been put there by life. Such life could also use ultraviolet light
from the sun as an energy source, and oddly enough, when we look at Venus in ultraviolet,
we see mysterious unexplained dark streaks in the atmosphere. One of the possibilities on the table for
whatever causes those streaks is microbial life. 9. Pluto For this option, we go from the inner solar
system, to the outer solar system. One of the most surprising discoveries of
recent years was that Pluto and its moon Charon were not merely frozen solid worlds but in
fact dynamic bodies with active geology and even abiotic organic chemistry occurring. With this, Pluto has gone from seemingly being
one of the last places you would expect to find life to one where it is hypothetically
possible. For life, you need energy, organics and water. Pluto has all three, though on the surface
the water is frozen. But it may have a liquid water ocean beneath
the surface heated by radioactive decay in the planet’s core. This has potentially enormous implications
for life in this solar system. Pluto is thought to essentially be a nothing
special Kuiper Belt object, one of hundreds or thousands. But if it does have that mix of radioactive
decay and subsurface liquid water, then potentially many Kuiper Belt objects have this as well. If that’s the case, then we may someday
discover hundreds of new candidates for life in this solar system. 8. Triton Speaking of Kuiper belt objects, our next
candidate is thought to also have originated from the Kuiper belt. There’s a good reason to think this, it
orbits in the opposite direction of Neptune’s rotation, suggesting that it did not form
along with that planet. Plus, it looks similar to Pluto in a number
of ways. But it does stand out in one very odd way,
it’s currently geologically active but instead of volcanoes, it has cryovolcanoes that spew
out nitrogen contributing to a thin atmosphere. Another thing that sets Triton apart from
most of the other moons of the solar system is that because it was likely captured, it
would have been subject to tidal heating from Neptune as it settled into a stable orbit. This could have created a Europa-like situation
where there might have been subsurface oceans, and they would likely have persisted for a
long period of time, but how long? Are they still there? One clue is that Triton appears to have a
young surface, thought to be only about a hundred million years old and may have resulted
from an extrusion from the ocean below. And something is driving the cryovolcanism,
so one possibility is that there is still a subsurface ocean present there. If so, it would likely be rich in ammonia
as well as water, and could contain life. 7. The Moons of Uranus As we work our way inward from the outer solar
system, we next arrive at a planet that really doesn’t get enough attention. I’ll admit my own bias here; I’ve never
talked extensively about Uranus or its moons on this channel, despite having said the word
Europa like a hundred times. Perhaps it’s simply because Uranus is not
exactly the most photogenic of the planets, all Voyager II saw was a featureless blue-green
sphere, though subsequently clouds and other activity have been seen. As a result, not a lot of attention has been
paid to this planet. But looks can be deceiving, Uranus hosts mysteries
just like all other bodies in the solar system, including how it came to be that this planet
rotates on its side compared to the other planets. Best guess there is that early in its history
Uranus got smacked by an earth-sized protoplanet. The first candidate moon for liquid water
is Titania, though unfortunately so little is understood of this body’s evolution that
it’s candidacy is up in the air. But it is possible, at least as far as we
know, for an ammonia rich or salty liquid water layer to exist deep under this moon’s
surface. It’s much the same story for Oberon, another
candidate; we just don’t know enough, but a subsurface liquid layer is on the table. Less likely is Umbriel, it’s been suggested,
but there doesn’t seem to be much room there for anything but ice and rock. Uranus is a place where life is unlikely,
but marginally possible, at least as far as current thinking. And with all candidates mentioned for Uranus,
you need more than mere water for oceans to persist, you need ammonia and or salt as a
sort of antifreeze to keep everything liquid. But, life is in principle still possible here,
so on the list the Uranus system goes. 6. Space Itself That last place you might choose to look for
alien life is space. As in actual space itself. We tend to automatically think that life must
be intrinsically linked to planets or moons. And that’s certainly a fair point; it’s
hard to see life arising in the cold vacuum of space. But nothing says that life can’t leave its
planet. Stating the obvious, one way to do this are
rockets and spacecraft, whether you are a human intentionally going into orbit, or you’re
a dog or chimpanzee being put there by a human. Or even a stowaway bacterium, tardigrade or
lichen unintentionally leaving earth, either by way of a spacecraft, or through various
methods of natural panspermia. But the possibility of natural panspermia
comes with another possibility: that life could adapt, survive and live in space on
its own. We know that certain examples of earth life,
rare though they are, can survive the conditions of space. But what of something that can go much further. Freeman Dyson envisions one such possibility. Termed Dyson’s sunflowers, these would be
organisms that might originate on ice shell moons, growing up through cracks in the ice
with a connection to the water below like the roots of a plant. It might adapt itself to keep itself warm
through natural mirrors, and might create its own supply of liquid water. It might even eventually be knocked off its
planet and move into deep space and might adapt. I think this option is possible, but not probable. I doubt we would see life like this very often
when exploring the universe. But it pays to remember that life often surprises
us down here on earth, and I see no reason that it wouldn’t surprise us in space. 5. Titan Here we move to a moon that not only has one
possibility for life, but two. It is a body different from all others in
the solar system, save for earth. On its surface, it boasts liquid hydrocarbons
mimicking the water cycle on earth. It has been advanced that hydrocarbons in
liquid form could serve as a solvent for life, like water does for us. This life would be very different from what
we’re used to, it would need to exist at much lower temperatures than here, but Titan
is also so sufficiently strange that the possibility is worth consideration. One thing in favor of life on the surface
of Titan are, again, abundant organics. And there may even be hints that there might
be life there, such as difficult to explain methane levels at the surface, though there
also are natural possibilities for creating that, life is merely one option. But how might that life work? One thing that’s been advanced are cell
membranes involving acrylonitrile that could work with liquid methane as a solvent. And, lo and behold, acrylonitrile was found
at Titan by the Cassini mission. Only time and more study will tell if there
is life on the surface of Titan. But, it too is an ice shell moon, thought
to have a liquid water ocean, high in ammonia, below the surface where life may also have
arisen. Perhaps there are two separate forms of life
on this little orange moon. But Titan also presents an interesting future
scenario where life is concerned. Say it has arisen there or someday will. In the future, as the sun goes red giant,
Titan may get substantially warmer and undergo a greenhouse effect. In which case, the life on the former surface
may extinguish, but the life below may get a few hundred million years in the sun in
the form of a surface ocean. 4. Enceladus Enceladus is a place where the possibility
of subsurface water is far more than a maybe. The stuff literally sprays out of surface
cracks into deep space right before our eyes. And, it’s very nutritious water for life
as we know it, very likely made so by subsurface volcanic vents. This is a tantalizing environment, but there’s
a problem. It may not be old enough for life. The problem here is that some of Saturn’s
moons orbit in such a way that suggests that they couldn’t have been doing it this way
for long. It places an age on Enceladus, at least as
we know it now, of about 100 million years. That doesn’t leave life much time to arise,
but the question is open. However, there is one particularly odd feature
of Enceladus that may be related to number one on this list, do you see those cracks
on the surface. Do you see how the extruded material is bluish,
like clean ice? Take note of that for later. But in the end, even if there is no life there
now, Enceladus seems well-suited for it to arise, leading to the possibility that it
may some day be a laboratory where the human race watches the advent of alien life in real
time. 3. Ganymede Moving from the Saturn system to Jupiter,
we find a place where all four major Galilean moons can hypothetically host life. Least likely here is Io, it’s wildly volcanic,
but it is warm and is thought to have once had water, so maybe something clings to existence
deep in a moist lava tube. Also included here is Callisto, a rather ignored
moon that could host a subsurface ocean. Then there is Ganymede, the largest of Jupiter’s
moons. Current thinking is that it doesn’t just
have one ocean, but several, all stacked one on top of each other separated by layers of
various forms of water ice. Think of it like a high rise building with
different floors. Any of these oceans may harbor life, and they
may even host different ecosystems that interact through cracks in that ice. I’m sure you’ve noticed that I ignored
the obvious candidate for life in the Jupiter system. I did that on purpose, as it tops this list. 2. Mars In both science, and the world of science
fiction, Mars has always occupied a prominent place as far as ponding extraterrestrial life
is concerned. There is something alluring about it, the
red planet, that in some ways looks very much like Earth, the solar system’s ultimate
abode for life, but also strangely alien. It’s like an alternative earth in a way,
a twin that isn’t identical, but similar enough to be a little spooky. But that similarity extends to the scientific,
Mars was once a habitat very much like earth with abundant liquid water. Now it is cold and dry. And in fact, the famous streaks that were
thought to be evidence of salty seeping water on the surface is now in question. Still, liquid water could persist on this
planet deep below in aquifers allowing a refuge for any life that might have survived the
great drying. But it would almost certainly be microbial
in nature, but in the end, life is life. But what hints have we seen that something
could still be hiding out on this world? First and foremost were the inconclusive Viking
experiments that gave positives for metabolism in samples in an experiment designed to detect
life. But unfortunately, the results were called
into question, and remain so today. It’s anyone’s guess if they did detect
life. And it’s also debatable as to how surface
life could exist in such a harsh radioactive environment. But there’s more. It’s been known for a while that something
weird is going on with Mars and the gas methane. It was detected in the Martian atmosphere
back in 2009, but the trouble is that methane is destroyed in that environment, so something
must be replenishing it. The mystery deepened when the Curiosity rover
detected a massive ten fold rise in methane levels at its location at Gale crater, only
to then see the levels drop back to normal. There are natural ways for this methane to
be released geologically, but it also happens to be that methane is also a gas associated
with active life. 1. Europa Europa probably has the best chances of harboring
life in the solar system other than Earth, and that life may even be more than microbial. It has a subsurface liquid water ocean that
interacts with its surface, it has geysers that periodically spew materials from the
ocean below into space, it has an energy source in the form of geothermal energy from tidal
flexing, essentially it has, as far as we know, the right mix for life to arise. And we may have already seen evidence of it. In 2003, a team lead by Brad Dalton looked
at the infrared signatures of the cracks in Europa’s surface where odd discolorations
are visible. He then compared that with microorganisms
here on earth located around geothermal springs at Yellowstone. They matched, opening the possibility that
the discolorations are due to the presence of frozen microorganisms from the ocean below. Taking it further, Dalton took extremophile
microorganisms native to earth and put them in conditions similar to what’s found on
Europa. He looked again in infrared, and there were
still correlations, but not a perfect match. A mineralogical answer was looked at, yet,
no combination of salts fit either. Yet, the pink and brown discoloration of the
cracks itself might be telling, salts should appear white. Yet the extremophiles used in Dalton’s experiments
are colored pink and brown. While this is by no means conclusive, the
discolorations could well be mineralogical, the mystery probably won’t be solved until
we can get samples of Europa’s ice or drill into the ocean itself. But if I had to bet on any body in the solar
system hosting life other than Earth, I’d bet on Europa. But back to enceladus for a moment. Europa and Enceladus are very similar moons. One has cracks with staining present, the
other does not. What is so radically different between these
otherwise very similar objects? Thanks for listening! I am futurist and science fiction author John
Michael Godier currently musing. If you watch a lot of space science press
conferences like I do, you notice that they often consist largely of thanking people. But they never thank the object they’re
studying, so let me take a moment to publically thank Jupiter for its awesomeness, keep up
the good work champ, be sure to check out my books at your favorite online book retailer
and subscriber to my channel for regular, in-depth explorations into interesting, weird
and unknown aspects of this amazing universe in which we live.
