This is part 2 of a collaboration between Fraser Cain and myself on the subject of planetary
migration, covering both its implications in the past but also the future, both in nature
and what we as an advanced civilization could do with artificial migration.
You can watch part 1 on Fraser’s channel, link below or through the end screen of this
video.
As Fraser discussed in part 1, planetary migration has had profound effects on our solar system
ultimately leading to the arrangement we have now, in turn that planetary dance allowed
earth to be what it is and allow for life to arise.
But it also affects many other systems in the universe and favor, or disfavor their
chances for life.
This could allow for situations where a star in its younger phases is too active to allow
for life to arise within its habitable zone, but as it calms down, should a planet migrate
inward, the equations could change meaning that the conditions for life might be favored
in certain circumstances, such as with the red dwarf stars.
But it will also continue to affect our solar system long into its future
Future migration, whether natural or artificial, may some day affect the outcome of life on
earth if it’s still present and may even make other places in our solar system habitable,
such as Saturn’s moon Titan which it is thought could someday form surface oceans
as the sun swells into a red giant.
While we sometimes see planetary migration in terms of the past, in our solar system
it’s never really stopped.
It just moves very slowly, but in geologic time scales it is still quite evident.
For example, Pluto.
While it is in a stable orbital resonance with Neptune, it’s position evolves, and
after about 10 million years from now it becomes increasingly difficult to accurately predict
Pluto’s orbital position.
This chaos gets worse the longer you go.
Some planets may evolve into more elliptical orbits over time, which may present some problems
should the human race still be around billions of years from now.
One is that Mars’s orbit may eventually evolve to cross Earth’s, which is just asking
for a planetary collision.
This has happened before, the formation of our moon is thought to have been the result
of a collision with a Mars sized object.
Another related issue is a bit closer in time, within a billion years Mercury’s migration
may bring it into close enough proximity to Venus that it may get ejected out of the solar
system entirely.
But it’s also possible, though the chances here are exceedingly low, that Mercury might
slam into venus or be hurled in our direction making for a second way our planet might someday
get smacked again by a planetary object.
One wonders if we’ll end up with a second moon out of it.
But ultimately, none of this is very predictable, these are based on truly massive time scales
with huge amounts of uncertainty.
But one thing is certain, and you can take this one to the bank, our sun has a limited
life in the form that it currently is and it will change over time.
As the sun ages, it will change in both size and mass.
As far as size, it will some day swell into a red giant star, greatly altering the gravitational
balance of the solar system.
But at the same time, the sun loses mass over time further altering the gravitational equation
and the balance of the solar system.
Solar mass loss occurs in two ways.
The first comes from nuclear fusion.
The second is the solar wind, particles constantly stream off the surface of the sun into space,
to a combined tune of 5.5 tons per second.
Over time, this loss changes the sun’s gravitational field, causing the planets to alter their
orbits.
This has already created an issue for astronomers.
Originally, an astronomical unit within astronomy was equivalent to the distance between the
earth and the sun, about 93 million miles.
In time, this has changed, albeit very slightly, and now Earth is just a bit over one AU from
the sun thereby making the astronomical unit an arbitrary way of measuring distance.
Migration also has implications on another unit in astronomy, the solar mass, which used
to be the mass of the sun, but not anymore.
These two units will increasingly become detached from what originally was their basis.
The net effect of all of this is that as the sun ages, there is a small chance that, like
Mercury, Earth too could get gravitationally ejected from the solar system.
If this were to occur, could life survive?
The answer really depends on what kind of life and what that life is doing.
For example, humans could well alter the equation if we’re still around and by that time a
class II or III civilization on the Kardashev scale.
Barring that, as the sun’s luminosity increases well before it reaches the red giant phase,
it will have still long ago stripped earth of most surface life.
But probably not completely, microbial life is extraordinarily resilient and may well
survive that phase of the sun’s life, only finally succumbing when and if the sun engulfs
the earth.
But, needless to say, anything left alive on planet earth during an ejection would need
to be really tough, and would need to be able to make use of geothermal energy, such as
ocean vents.
These vents should persist even out in deep space, keeping pockets of water in liquid
form which could, hypothetically, sustain ecosystems of some sort, if only microbial.
How long could this state of affairs persist?
The answer is a very long time.
The earth’s core contains decaying radioactive elements, and in fact there are sufficient
amounts of these to guarantee geothermal heat on this planet far longer than it will take
the sun to reach its red giant phase.
Long half-life isotopes like thorium 232 will guarantee tens of billions of years of geothermal
energy for this planet should it get kicked out into deep space.
But earth’s surface would quickly freeze under these conditions for a time.
But over a very long period of time earth might acquire a thick hydrogen envelope as
it travels across deep space.
Coupled with the geothermal heat, this might eventually provide a warm enough surface where
liquid water flows again.
Perhaps the life that once existed in those oceanic pockets could once again colonize
the planet and evolve.
But it would no doubt take a completely different path than it did earlier in the planet’s
history.
For one, there would be no sun, and that changes everything, plus the thickness of the atmosphere
would mean no stars would be visible to any complex life that might develop.
Life on earth solves this darkness problem in several ways including no functioning eyes
at all, such as blind fish living in caves, or it might solve it through bioluminesence
as happens in our oceans.
Trouble is, if this new life eventually develops a civilization, that civilization might have
no idea that there was an entire universe out there to explore.
Or, alternatively, we may still be around in one form or another but still lack any
ability to prevent our ejection.
This allows for the possibility of a technologically altered rogue planet earth where the planet
is artificially kept habitable.
Another take might be that we intentionally migrate the earth to be located further from
the sun as it ages and reorder the real estate in our solar system to however we see fit.
This goes for any other planets in the solar system.
We know that there may well be planets beyond the orbit of Neptune, indeed there is mounting
circumstantial evidence for this.
What if we found an earth sized planet out there.
Might we migrate it inward for use as a second world after terraforming?
But just how do you move a planet?
The answer would be complicated and depend on the situation of what it is you want to
move.
But to migrate earth further out from the sun, a strategy to do that was put forth in
a paper by D.G Korycanski and colleagues, link in the description below.
The concept involves using rockets to manipulate an asteroid into an orbit that encounters
both earth and Jupiter.
Over time, the transfer of energy from this object would cause earth to move outward.
The researchers conclude that to maintain our position within the sun’s changing habitable
zone, such an object passing earth every six thousand years would gradually do the trick
along with other planetary encounters over a very long period of time until we’ve survived
the sun’s red giant phase.
The authors note that this would be extraordinarily dangerous, since when you go moving orbits
you would need to have a really good asteroid map to ensure you don’t hit something.
But, then again, if your sun is going to kill you anyway, you’ve got nothing to lose.
After the red giant phase, we would need to look to migrating the planet back towards
the sun as a white dwarf, or simply abandon earth altogether in favor of building habitats
close in and harvesting what energy we can from the white dwarf.
What’s notable about this plan is how startlingly easy it is compared to interstellar space
travel.
This is already, hypothetically speaking, within our technological grasp to move an
asteroid in this fashion.
Obviously, we have thousands of years to consider this option, but the point is that we could
maintain a presence in this solar system long past the sun’s Red Giant phase, and live
on our migrating planet for tens of billions of years potentially easier than we could
if we colonized a new solar system.
And within all of this lies a SETI can of worms.
If an alien civilization were looking at our solar system long term while we orchestrated
migration, as in billions of years, what would they see?
They would see a habitable world that just happens to be migrating outward along with
the habitable zone of its star, orchestrated in such a way to have planetary encounters
to support this process.
At some point, that looks really unnatural and planned making this a potential SETI technosignature.
If you see star systems with planets with very unlikely migrations going on, you may
well have found a civilization doing the only thing it can to avoid destruction by its changing
star: migrate.
Thanks for listening, this has been a collaboration with Fraser Cain, publisher of Universe Today
and one of the best astronomy channels on Youtube and we hope you enjoyed it and be
sure to check out part 1, link below and in the end screen and be sure to like, comment
and subscribe to our channels for regular, in-depth explorations into the interesting,
weird and unknown aspects of this amazing universe in which we live.