One of the biggest issues facing exobiology, whether dealing with life at any level or
even a full blown civilization, are biases.
We tend to think in terms of earth when hunting habitable exoplanets and we tend to think,
more or less, about ourselves when looking for civilizations.
There is a good reason for this bias.
Our planet, as far as life goes, is all we know.
And the same is true for our civilization.
We know that Earth is a habitable planet where life can arise and evolve, and eventually
develop intelligence and civilization.
But we also know of lesser places where life could hypothetically evolve, just not likely
to this level.
This includes the ice shell worlds like Europa, and even Mars or the upper atmosphere of Venus
where hypothetical simple life could exist.
But what we don't have is another earth in this system, nor have we found an exoplanet
quite like this planet.
In fact, one solution to the Fermi paradox is that planets like earth and the conditions
that led to the rise of humanity are simply so rare that it may happen only once per galaxy,
or less.
But, in a way, that too involves a bias.
That earth is perfect.
We may think this planet is perfect for life, but in reality it is simply what we ended
up with and it was good enough for the task.
But could there be worlds in the universe that aren't quite like earth, yet are better
at supporting life and evolution?
Nothing says that there aren't.
In a 2014 paper by Rene Heller and John Armstrong they detail how other worlds could be better
than earth at supporting life.
One way to determine this is to look at earth, and ask questions about why it is habitable,
what factors play into that, and are those factors are optimal for the rise of life?
As it turns out, many of them are not, and that opens the door for better earths.
To start, take the sun.
The presence of a stable G-type main sequence star is the elephant in the room as far as
life on earth is concerned.
It is vital to nearly everything alive on this world.
Everything from photosynthesis to human civilization is directly or indirectly dependent on that
star.
But it is not a perfect star for life, far from it, since as it ages it will progressively
wipe the earth completely clean of all life.
All stars that are stable enough and have the longevity to allow life to arise are to
some degree all going to be double edged swords.
They can give life and they can take it.
But not all are equal, where the sun will only sit on the main sequence for about another
5 billion years, it will also increase fatally in luminosity wiping out most life on earth
long before it gets to it's red giant stage.
But there are stars that last much longer than the sun.
Type K orange dwarfs can last between 15 and 30 billion years, allowing any life much longer
time frames in which to evolve.
But stars are not the only factor in life arising and evolving.
Let's take a few more.
Another would be plate tectonics.
This process is vital to earth life for several reasons.
Firstly is the carbon cycle which helps regulate global temperatures, in fact one factor for
Venus having gone through a runaway greenhouse effect may have been its lack of plate tectonics.
But plate tectonics also plays a role in the generation of the earth's strong magnetic
field, which is yet another major factor for life here having arisen and evolved.
But is earth perfect as far as plate tectonics go?
No.
In another paper by Noack and Brewer they point out that the optimal mass for plate
tectonics on a terrestrial planet is about two earth masses.
But there are others factors.
Another is our place within the habitable zone itself, it's not optimal, we're near
the inner edge, or so it is thought, so planets centrally located within their star's habitable
zone should fare better.
Then there are more murky factors, such as atmospheric composition, optimal temperature,
and pressure.
Are there better compositions?
There is some evidence that life on earth did better when oxygen levels were higher.
This is another double edged sword however; yes lots of oxygen is good for developing
things like fuel hungry human brains, but if you get too much oxygen, fire becomes less
of a tool and more of a liability if you live on land and are building a civilization.
If you don't, even ocean depth might be factor, aquatic life on earth tends to prefer to stay
shallow, though not in all cases.
So shallower oceans over all might be helpful.
There are many other factors, most unsettled as to what might be better, but a vague picture
of a world better than earth for life might be a superearth, just a bit larger and a little
warmer, with active plate tectonics, shallow oceans but still with land masses, along with
a thicker atmosphere right in the center of the habitable zone of an orange dwarf star.
I wonder if such a planet might also benefit if its star system were clearer, meaning that
asteroid induced mass extinctions would be less common, or not happen at all.
Imagine if life didn't get occasionally shaken up on one of these perfect worlds, would evolution
move faster?
Could a civilization arise sooner than it did here on earth and then go on to last much
longer around their comfortable orange dwarf?
One final point Heller and Armstrong make is that orange dwarf stars are among the most
common, more common than our G type sun and making up as much as nine percent of the galaxy.
Also, there seems to be no shortage of super earth sized worlds either, and some of the
factors discussed here would naturally come with an increase in size, such as longer lasting
plate tectonics.
It could well be that Earth is a rare type of small habitable planet and that superhabitable
worlds better than earth are more common in the universe.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently thinking about conceited
aliens sitting on their perfect planet looking at earth through their telescopes snickering
about our imperfect plate tectonics are and be sure to check out my books at your favorite
online book retailer and subscribe to my channel for regular, in-depth explorations into the
interesting, weird and unknown aspects of this amazing universe in which we live.