This video is a sort of subset of my recent video on detecting dead alien civilizations.
The paper I reported on in that video by Stevens, Forgan and O’Malley James, link in the description
below, had a section that I found to be of separate and particular interest because while
it wouldn’t necessarily be a necromarker for a civilization that destroyed itself,
it may indicate a civilization that may still be around but has, in the past, behaved stupidly.
This is a serious potential problem for us too, to the point that if we aren’t careful,
which means all space faring countries on earth, we could set off a cascade of colliding
space junk that would completely ruin some areas of low earth orbit and severely hamper
our abilities to launch and use satellites.
This effect is known as Kessler Syndrome, and perhaps most famously was depicted in
the movie Gravity as everything started colliding with everything else causing a cascade effect.
It’s possible that a civilization whose planet has undergone this effect could be
detectable at a distance, call it Kessler SETI or dumb alien detection.
Kessler syndrome has to do with the density of objects in low earth orbit.
If that density becomes high enough through space junk launched from the surface, the
likelihood of collisions grows.
This leads to the cascade, somewhat like the domino effect, where more collusions creation
more debris which creates more collisions.
Collisions in orbit are already a problem, on average we lose one satellite per year
in LEO to one of the 600,000 pieces of space junk in orbit.
Very low earth orbit is generally safe, due to residual air drag clearing things out.
But in higher areas where there is little air drag, things can stay in orbit for a much
longer time.
In higher orbits than LEO, this is less of a problem because the density is lower, things
get more spread out.
What’s particularly worrying about the Kessler effect is that during a war on this planet,
country A might wish to destroy country B’s satellites by deliberately setting off the
Kessler effect, effectively ruining low earth orbit for all other countries for centuries.
But it doesn’t lock you in completely, launching through LEO to higher orbits is still possible
because the chances of hitting debris as the rocket passes through are low.
Efforts of avoiding Kessler syndrome are under way, for example the US Federal Communications
Commission requires satellite designers to include a way to deorbit old satellites, or
boost them into a high orbit where they pose no threat.
And there are potential methods of clearing out LEO by using laser technologies that show
promise.
But that’s’ the reason that this might be a necromarker.
If there is no civilization left to clear out their planet’s low orbits, or they’ve
been knocked back to the stone age so to speak, the Kessler syndrome debris disc might persist
for a very long time and be detectable at a distance.
The paper details how this might be accomplished.
The interesting thing is that if you wait long enough after a Kessler Syndrome event,
a debris ring very similar to a natural planetary ring might form.
We can detect planetary rings in light curves as ringed planets transit across the face
of their stars.
The authors note that it may be possible to tell the difference between icy natural rings
and technological debris due to different reflective properties.
Technological ring systems like this would not last forever before atmospheric drag and
other factors would clear them out, a few tens of thousands of years to maybe a hundred,
but out of the necromarkers, that’s among the longest visible, and it may be possible
to detect them using photometry and polarimetry techniques and could be done concurrently
with studies of natural exoplanet rings.
Thanks for listening, I am futurist and science fiction author John Michael Godier currently
battling a Kessler-like effect with the weeds in my garden, the more I pull the more they
sprout 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.