One of the biggest questions regarding the bombardment of earth by asteroids or comets
is if it’s just a more or less random chance event where an asteroid happens to hit us,
or if it’s actually non-random and is caused by something in the outer solar system perturbing
comets and sending hails of them into the inner solar system periodically.
There are actually two ways this can happen, and both are equally spooky.
The first is if there is a large body in the outer solar system that periodically deflects
comets our way.
There have been a number of incarnations of this idea, going back to the 1980’s with
the concept of an actual second star termed Nemesis, which would have been a dim, tiny
red dwarf orbiting the sun at great distance.
At the time, this was invoked to explain an apparent periodicity to asteroid impact related
mass extinctions.
It turns out, it’s probably not the case, and most mass extinctions on earth were not
due to asteroids or comets, but other causes, though the one that killed the dinosaurs certainly
was.
But that didn’t kill the idea.
More recent work has found what may be a loose correlation in the ages of known impact craters
on earth that could suggest that something in the outer solar system is perturbing objects
and sending them our way on a periodic basis.
And indeed, at least two potential planets are hypothesized to potentially exist in the
outer solar system.
One these is the infamous Planet 9 hypothesis, which may explain odd orbital inclinations
of objects in the outer solar system, and the other is the lesser known Planet 10 hypothesis,
where a Mars sized object is advanced to be the cause of the so-called Kuiper Cliff feature,
where a very well defined line seems to exist in the Kuiper Belt that may suggest a planet
is shepherding it’s edge.
Whether either of those could perturb comets periodically is unknown, but there is another
option.
It’s past stellar encounters.
70,000 years ago, a star known as Scholz’s star passed within our Oort cloud.
It’s entirely possible, and recent research actually bolsters this possibility, that this
stellar encounter perturbed a hail of comets and they’re heading this way.
That could be bad news for Earth, but the good news is that it’s going to take roughly
two million years for them to get here.
Plenty of time for them to be discovered and deflected if any prove to be dangerous.
But this is all very hard to prove.
We know that comet material composed of ice and rock as opposed to iron and stone like
asteroids do periodically enter earth’s atmosphere.
Several events have relatively recently happened that might have been cometary material, the
most famous being the Tunguska blast of 1908, that seem to hint that the objects involved
weren’t particularly sturdy, and may have been composed of a large component of ice.
This would make them very likely to be cometary material, and as our periodic meteor showers
on earth like the Perseids each year show, comet material does get deposited in the inner
solar system when comets pass through, suggesting that at least some perturbation occurs in
the outer solar system all the time, with or without a planet or passing star being
involved.
But mundane explanations like more planets existing within this star system that we currently
know, there are some more exotic possibilities for an object to perturb material from the
outer solar system and send it inward.
Questions can be asked about passing black holes, for example, which, a small enough
one might act as a perturber, or how about a passing brown dwarf not bound to the sun?
These are unknowns.
But there is actually an even crazier one, and it’s been recently advanced that it
may have actually been the one that ended the reign of the dinosaurs.
It’s dark matter, one of the most mysterious materials in the universe.
Here it pays to revisit just what dark matter is, and why scientists think it exists.
The core problem that gives rise to the notion of dark matter is that most galaxies don’t
behave as they should.
When you calculate the gravity needed to hold them together, it doesn’t mesh with the
amount of matter contained in those galaxies, not by a long shot.
By all rights, there are galaxies in the universe that should be flying apart, but they’re
not.
So either our understanding of gravity at very large scales is wrong, which observation
doesn’t seem to indicate, or there is some form of otherwise undetectable, invisible
matter contributing to the overall gravity of these galaxies.
In fact, most of the matter in the universe must be of this invisible variety.
And that’s why most astronomers think that dark matter must exist.
But the opposite argument can be made, dark matter is not something we’ve detected in
nature before, so how much of a stretch is it to invoke something that has never actually
been observed?
Well, the reality is that something like it has.
It’s the neutrino, and while neutrinos alone do not account for dark matter, they are very
weakly interacting particles that pass through most matter undetected.
Only occasionally does interaction happen, so it could be said that neutrinos are actually
a form of dark matter.
But experiments looking directly for dark matter as an unknown weakly interacting particle
perhaps like a neutrino have so far turned up nothing.
But most scientists still agree that dark matter must be there, or the universe wouldn’t
work as it does.
Same with the concept of dark energy, the universe just doesn’t work as observed without
invoking it.
But science is a learning process and subject to constant revision, so it’s also possible
that some model will be found that explains these observed effects and overturns the apple
cart.
But say for a moment dark matter is real.
Can it affect us in catastrophic ways?
Well, it may have, in the form of the Cretaceous-Paleogene extinction event that killed the classical
dinosaurs about 66 million years ago and left only the birds as their descendents.
In a paper by Lisa Randall and Matthew Reece, link in the description below, they detail
that dark matter could also be a perturber of comets, and may have done so with the object
that struck earth and ended the dinosaur age.
And it actually meshes well with the apparent periodicity of impact events on earth, though
the evidence for this is weak and has been disputed periodically.
The idea is this.
The sun follows the swirling of the Milky Way’s spiral arms, which incidentally involves
dark matter.
But the sun also moves independently, and bobs up and down in relation to the galactic
plane.
It’s possible that the galaxy’s dark matter gets denser in regions with denser matter
concentrations, so as the sun bobs up and down through this concentration of dark matter,
the effect could be that comets get perturbed by the gravity of the dark matter, sending
periodic hails of comets into the inner solar system.
This would correspond to a period of about 35 million years, and that’s exactly what
the correlations of impact cratering events seems to suggest.
But there’s a problem, dark matter isn’t thought to be capable of settling into such
concentrations.
It’s very weakly interacting, so the equation for concentrating changes.
But that assumes that all dark matter behaves the same.
That is an unknown, we have no idea if there are classes of dark matter or situations where
it can behave differently than what is currently thought.
Some measurements of the galactic center show that maybe dark matter does behave differently
in certain situations, and modeling shows that it may be possible for such a disk of
material to exist in the galaxy and explain the correlations with mass extinctions, if
those correlations do indeed exist.
But there are problems.
One is that we don’t really know what the nature of the impactor that killed the dinosaurs
was.
If it was Oort cloud material, it would have been rock and ice, but if it was an asteroid
it would be more like rock and iron.
The iridium rich layer that was laid down during the extinction event from material
from the impactor tends to point in the direction of an asteroid, but only weakly so.
Other evidence points to cometary material.
But if it was a near-earth asteroid rather than a proper comet, then a near-earth origin
is more likely.
If it were a comet however, then some kind of perturbation may have been involved in
the periodicity.
The question remains about just what the nature of the perturber is.
But it’s an interesting thought nonetheless in that it may be something entirely out of
our current paradigm of thinking.
It’s entirely possible that there are things going on in the universe of which we have
no conception that could cause our extinction.
It wasn’t that long ago that the very idea of dark matter would have been rejected outright
by scientific consensus.
Most of the universe’s matter is invisible and can pass through walls?
Doesn’t seem plausible, yet the need for invoking it arose because observation suggests
that it must exist.
And recent work has also suggested that the universe could go through a dramatic alteration
if it were to tunnel to a lower energy state, if it’s not already there.
In which case a bubble of changed universe would expand out at the speed of light, and
once it overtook us, it would cause not only our extinction, but an alteration to how matter
itself can exist in the universe, if it could still exist at all.
Dark matter having a hand in killing the dinosaurs doesn’t seem so far-fetched in light of
that.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently worried about the
asteroid impact.
What if we never saw it coming, and then it suddenly happened, and all the talking parrots,
ravens and other dinosaurs still living on this planet collectively looked at us and
all said “not again” and the last lesson of existence we get is that the birds were
smarter than we thought and they just didn’t have much to say until the impact hit.
I wonder if they’d make it through again and be sure to check out my books at your
favorite online book retailer and subscribe to my channels for regular, in-depth explorations
into the interesting, weird and unknown aspects of this amazing universe in which we liveeeeeeeeeeeeeeeeee.