One of the problems present in predicting which exoplanets in the galaxy could harbor
life is that we don’t entirely understand the ground rules for how much variation habitable
planets can have while still allowing for life to arise.
A big part of this problem is that, so far, we’ve only seen life develop on one planet,
Earth, though it may well have developed, or even still exists, on multiple worlds in
own solar system, not accounting for the universe at large.
This maybe list in our solar system is extensive, particularly for microbial simple life and
includes Venus in its past, and Mars possibly in its present, but also the many moons of
the solar system that are thought to have zones of liquid water locked under icy shells.
They are wild cards, and while it doesn’t seem likely anything much more complex than
a microbe could have had time to develop on Venus or Mars before those planet’s climates
became unsuitable, we have no idea what’s possible in places like Europa’s subsurface
ocean that’s seemingly been liquid and stable for a very long time.
The only thing we can say for sure is that such life would be, well, oceanic by nature
if it’s living in a subsurface ocean, though nothing says it hasn’t evolved to leave
that ocean.
But, if earth is any indicator, oceans, at least like those of earth, can quite easily
support the evolution of complex life, in fact a lot of it, with massive variety ranging
from microbes to clams to squid to sharks.
But we also know about past mass extinctions having occurred among earth’s ocean life,
among the worst extinction events, so life in an ocean can meet a horrible end just as
land life can.
And this brings up a question.
Given that chemically imbalancing earth’s oceans, such as an environment that makes
them more acidic, or nearly freezes them over, can dramatically affect oceanic life, what
other factors might affect water world exoplanets and their ability to sustain life?
This question is just now beginning to be explored, but one possibility is that water
worlds covered entirely by deep oceans might exist, and may be common in the universe.
But could they sustain life?
That’s been a subject of some debate.
On one side, with earth, the oceans and the atmosphere are linked in a symbiosis, they
affect each other profoundly.
But on a world with much deeper oceans there could be issues with mineral and gas exchange
that might make for a very unstable climate over all.
In other words, oceans too deep could prevent life from arising.
But a new study suggests that it may not be that simple and things may be more dependent
on the exact conditions of an exoplanet than was previously thought.
In a paper by Edwin Kite and Eric Ford, link below, they detail that planetary conditions,
such as the presence of a certain amount of carbon, help stabilize climate, but also mineralogy
such that allows carbon to stay in the atmosphere rather than getting locked away, as generally
happens here on earth.
But, their simulations showed that under the right conditions, such a water world might
stay stable enough to provide an abode for life to arise, at least for a time.
In a way though, this doesn’t seem surprising.
Exoplanets are showing themselves to increasingly not be clean cut affairs, rather a huge variety
of factors play into their ultimate conditions, which are also, in the end, subject to change
just like earth has changed.
Earth at times was a near iceball, and at other times significantly hotter, along with
having gone through profound changes to its atmosphere, such as the great oxygenation
event, or effects from heavy volcanism, such as the Siberian Traps that caused one of the
greatest extinction events in history, the end Permian.
Further, look at the variation in planets in this solar system.
Three worlds in the past seemingly could have hosted liquid water on their surfaces, Venus,
Earth and Mars.
Earth still does, and Mars also apparently still has it, though it’s now retreated
deep below its surface.
Then there are the wild card ice shell moons.
And that’s just this solar system where we have tens of chances of liquid water environments
in some form, there are yet entire classes of exoplanet that we don’t have examples
of in this solar system, such as the superearths, that appear to otherwise be very common in
the universe.
If an ice shell moon like Enceladus might harbor life, then what of a water world super
earth?
We don’t yet know the ins and outs of that, so would it be that surprising if the conditions
for life to arise can happen in any number of combinations?
Planets where there is enough time for life to arise, but maybe not last long, at least
for anything above a microbe, but also planets like earth where life can not only arise,
but last a very long time and profoundly affect the host planet?
It would seem that answering the question of life in the universe is probably very complex
and will likely lead to surprises, and as we start looking closer, which we are poised
to do with increasingly better instrumentation, and really studying exoplanet atmospheres
from afar and perhaps start glimpsing evidence of life itself on other worlds, we may well
find that biosignatures can be found in places we might not expect at this time.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently being a tease again!
I know, it’s been bad, I keep teasing the new show but I can’t help myself.
I’m obsessed with it!
But we’re now only about a week away from the debut of the first full show on September
20th, which is Dr. Avi Loeb of Harvard, perhaps the most cited scientist on this channel as
far as papers go, so be sure to subscribe to the new channel, link below and in the
end screens.
But, for fans of this channel, don’t worry, this place will never change, in fact you’re
probably going to get more videos than usual soon as I’ve come across lots of new stuff
lately to cover and be sure to check out my books at your favorite online book retailer
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unknown aspects of this amazing universe in which we live.