One thing that’s very unclear within the field of exobiology is what role the exact
circumstances of earth had on the formation of intelligent life on this world.
There are a wide array of questions here, what happens if you remove the moon and tides
from the equation?
What would have happened if there hadn’t been plate tectonics on this world?
Would life still have arisen?
These are all open questions with no ready answers, and there are many more of them.
But one emerging addition is the question of how unique our solar system itself actually
is.
For one, we’re missing an entire class of apparently common planet, the super earths,
with no examples in our system.
Why are the inner planets of the solar system so low mass?
Another oddity is a lack of very close in planets to the sun.
We seem to find a lot of hot exoplanets in the universe that orbit so closely to their
stars that their “year” passes in a matter of days, in fact it seems that more often
than not planets congregate close to their stars rather than the case here.
For example, as close as it is, it still takes Mercury 88 days to complete an orbit of the
sun, which is fairly far away compared to some exoplanets.
So why is there nothing closer?
The answer may lie in how Jupiter behaved early in the solar system’s history, and
if a 2015 paper by Konstantin Batygin is correct, the interactions of Jupiter with the first
generation of planets in this system may have been chaotic even to the point that the sun
may have swallowed earth’s precursors in the inner solar system, tossed in by a wandering
Jupiter’s gravity and a bombardment by planetessimals being drawn along by it.
In order to account for the solar system the way it is, Jupiter had to have migrated around
at some point early on.
The main model for this is the Grand Tack Hypothesis, which suggests that Jupiter formed
about 3.5 astronomical units from the sun, but wandered inward to nearly the current
orbit of Earth due to gravitational effects of the sun on gas and debris still present
in the solar system, but then moved back out as it came into an orbital resonance with
Saturn before both stabilized in their current orbits.
In other words, had Saturn not saved the day, Jupiter too might have fallen into the sun.
Had none of this happened, Earth might not be here, the material having instead been
incorporated into a super earth planet.
While super earths can be more like miniature Neptunes rather than giant earths, rocky giant
earths are possible and may be ideal for life to get a foothold.
But there’s another effect of Jupiter, and also Saturn, on the solar system that may
have also been crucial as far as complex life is concerned.
The solar system’s early history was one of cataclysm where planetessimals were in
constant collision, for example an impact between earth and a mars sized object is thought
to be responsible for the formation of our moon.
Impacts like that are not good for life to arise.
But that period in the solar system ended relatively quickly due to Jupiter and Saturn,
and the sun for that matter, helping to clear out the system and make for enough stability
so that life could arise.
Even then, mass extinctions due to comet or asteroid impacts still occurred, and can still
occur, but they are not enough to reset life on earth completely, they are merely setbacks
when they occur.
At first glance, this might seem disheartening.
We are merely the product of a certain set of chance circumstances involving gas giants
and many other factors, perhaps so much so as to be a unique situation within the Milky
Way, but I would never want to say that there aren’t other circumstances, perhaps even
better than our own, that could allow for complex life and eventual intelligence to
evolve.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently adding Jupiter and
Saturn to my holiday greeting card list, where would we be without them 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.