There have been several discoveries in recent weeks that have me thinking about alternative
forms of life that could be far different from what we're used to on
Earth.
One of these discoveries was the possibility of yet another warm liquid water ocean lurking
under the ice of Dione, one of Saturn's moons.
This adds one more planetary body to the list of possible locations for liquid water in
our solar system.
Enceladus, Europa, Ganymede and possibly even Titan may also host liquid water oceans underneath
shells of ice.
Liquid water opens the door to life.
It is the universal solvent that most easily allows biochemistry to occur.
On earth, liquid water is abundant.
On Mars, it was once abundant.
That means that our solar system contained two worlds where life might have arisen.
But outnumbering the planets seems to be these liquid water moons, which means that it's
possible that most habitable zones in our universe are actually located beneath the
surfaces of icy moons rather than on earth analogue worlds.
But water isn't the only thing you need.
Our kind of life that we ourselves function on needs more.
We need oxygen created by an ecosystem that needs carbon dioxide and so on.
These atmospheric conditions are not present on icy moons.
So can life arise in these kinds of places?
The answer is probably yes and not just microbial life is possible.
Despite not having much of an atmosphere, Europa does actually have a way of getting
oxygen into its oceans.
High energy particles striking its surface creates oxygen.
Europa's surface is very young, evidenced by a lack of impact craters.
That means that the surface is constantly being renewed with new ice from below.
What goes up must come down, so oxygenated liquid would end up in the ocean below.
But there's something even more interesting going on.
Over the last decade, the amount of oxygen being fed to Europa's ocean has been revised
upward to the point that the oceans there may contain even more oxygen than our own
life-bearing oceans.
That would mean that complex life, such as fish, would have what they need to support
themselves.
This moon may be teeming with complex life, and in fact some scientists have said that
it would be surprising if it doesn't.
Very encouraging indeed, Europan life may be our kind of life.
But there are also other, more exotic ways for life to arise.
There are a number of types of theoretical forms of biochemistry that science allows
to exist, but we haven't seen or proven yet.
The first of these is non-carbon based life.
As far as we know, all forms of life on earth are based on carbon.
Carbon is incredibly versatile in its chemistry, allowing the complexities of organic chemistry
which life as we know it is based on.
As an added plus, carbon is abundant in the universe.
But there may be other platforms.
Silicon and Germanium may in fact also be vehicles for life chemistry.
And it may even be possible with boron, but that seems unlikely due to low abundance of
it in the universe.
Silicon is an element that some forms of life on earth already use.
Diatoms in the oceans use it in their cell walls, for example.
Silicon's chemical properties are similar to carbon, and it can also form complex molecules.
Unfortunately it is much more limited in the amount of chemical bonds it can create, which
greatly limits its potential for life.
But it doesn't entirely eliminate it, at least in theory, and there are situations in the
universe such as environments rich in sulfuric acid like Venus where silicon-based chemistry
would be more stable than carbon-based.
In an earth-like situation, things are more bleak for silicon.
Even though silicon outnumbers carbon atoms 925:1, life here is still carbon-based.
That alone says that carbon is better.
But change the chemical conditions on the surface of a planet, along with the atmospheric
conditions and temperature, and silicon life might be possible.
But with silicon, I would be remiss if I didn't point out something.
This only applies to life that arises through chance evolution in nature.
Life that arises as a creation of other life, such as living computers, would perhaps qualify
as a form of silicon-based life.
So if silicon life doesn't naturally occur, a form of it may artificially do so.
Other forms of non-carbon based life that theoretically may be possible are those based
on metals and oxygen.
Metal-oxide-based life may be possible under certain conditions, such as very high heat.
Sulfur may also be a way, though that seems to be somewhat of a stretch in comparison
to the others.
With the watery moons of the solar system potentially bearing oceans, carbon would seem
the likely candidate as a basis for any life that may be on them.
But what of other liquids?
It has been suggested that water need not be the universal solvent for life, and that
liquid hydrocarbons or even ammonia might do the trick.
A bit more out there, liquid nitrogen has been proposed as has hydrogen in supercritical
fluid form.
While it may not be universally so, water is generally a good solvent for life.
It can dissolve a wide variety of compounds, it can act as an acid or a base, something
quite important for biochemical reactions.
Water is also less dense as ice than it is as a liquid.
Because of this, bodies of water freeze at the surface, they don't freeze from the bottom
up.
If this were not the case and ice sank, then bodies of water would freeze solid and that's
not good for life.
Factors such as these limit what liquids can work for life, but there are a handful of
good candidates.
Perhaps the strongest candidate is ammonia.
It's abundant in the universe.
Most organic materials can dissolve in it and numerous chemical reactions can occur
in ammonia.
But it does have some drawbacks, not the least of which is that it's flammable in an oxygen
environment, so any ammonia-based life must be anaerobic and not require oxygen to live.
But that's not impossible, such life does exist on Earth as anaerobic microbes.
Can ammonia life be complex?
We don't yet know, but if it is it would likely exist at a lower temperature than earth life
and would probably metabolize and evolve more slowly.
Another candidate is methane.
It can exist as a liquid, though at much lower temperatures than water, and, like ammonia,
there's plenty of it in the universe.
As with ammonia, there are pros and cons as a solvent suitable for biology, but what's
interesting here is that we actually have a body in our solar system that has lakes
that include liquid methane among other hydrocarbons.
It's Saturn's moon Titan, and there may be evidence that not only is this cold dark world
a home to a liquid cycle like earth with lakes and rain, it may actually have life lurking
in those lakes.
In 2010 Darrell Strobel of Johns Hopkins University found that there was much more molecular hydrogen
in the upper atmosphere of Titan than in the lower atmosphere.
Where was this hydrogen going near the surface?
One possible answer is life is removing it.
If life does exist on Titan's surface, it may use hydrogen to break ethane and acetylene
down into methane as a source of energy.
While life may not be the only answer for the missing hydrogen, and is probably unlikely,
there's also no current consensus on any other process that could cause it.
Other possible solvents include hydrogen fluoride, which is rare in the universe and thusly unlikely,
and hydrogen sulfide but their potential for supporting life are less understood as are
mixes of water and other solvents.
There's even a possible way for life to thrive in seemingly impossible environments like
lava.
A theory put forth by Gerald Feinberg and Robert Shapiro suggests just that, an organism
with a biochemistry based on silicon, oxygen and even aluminum living in a molten environment.
You may think the idea of life existing in lava might be preposterous, but life can be
a surprisingly tenacious thing that can yield some very strange surprises.
Scientists working deep in a gold mine in South Africa discovered a bacterium that breaks
all the rules.
This bacterium's energy comes not from the sun, but from radiation streaming off of uranium
ore.
That's right, a bacteria that depends on radiation to remain alive.
Also, this bacterium is the only thing that lives in its environment in the cave making
it the only known organism on earth that is alone in its ecosystem.
Not surprising, since it's environment is hostile to everything else to the point that
its comfortable in temperatures that reach 140 degrees fahrenheit.
And while it's still earth life bearing the familiar DNA and biochemistry of life on earth,
it gives a clue of what life on earth might have been like before we acquired our oxygen
atmosphere.
If life can thrive in a radioactive environment such as that cave, then where else can it
survive?
Could life evolve that derives its energy from cosmic rays in environments where there
is very little atmosphere?
Physicist and astrobiologist Dimitra Atri thinks it may be possible and backed it up
with simulations that show that a steady shower of cosmic rays could power life, though any
such life would remain simple and microbial.
Mars would be an almost perfect environment for this kind of life.
So it seems that life, at least simple microbial life, has many avenues from which to exist.
It may be that our universe really is teeming with life on a level we never thought possible.
It could be everywhere.
But it would be simple life.
Anything complex and ultimately intelligent is probably very rare.
Thanks for listening.
I am futurist and science fiction author John Michael Godier currently putting the finishing
touches on my new book "Supermind" a story based fundamentally on the subject matter
found on this channel and be sure to check out my other books and subscribe to my channel
for in depth regular explorations into the interesting, weird and unknown aspects of
this amazing universe in which we live.