The greatest threat nature presents to us is the possibility of an asteroid impact.
They have happened before, and if left unchecked, they will happen again.
Such an event is horrific beyond comprehension, mass extinction by other means can often be
a slow process of habitat changes and degradation, leading to fewer numbers of a species until
there simply aren’t any left.
An asteroid impact however can cause extinction very rapidly, and very unpleasantly.
To illustrate this, let me tell you the story of the aftermath of the end Cretaceous impact
event.
For the unlucky, or perhaps actually the lucky, that happened to be within 1000 kilometers
of the impact itself, they were instantly vaporized along with an enormous swath of
the seafloor that was lofted high into the atmosphere.
More distantly, say two thousand kilometers, the situation was hellish.
First would be the earthquakes and aftermath of the asteroid strike, as its energy rippled
through the planet.
These may have been amongst the most powerful earthquakes this planet has ever experienced,
going off scale by our standards.
Interestingly, there may actually have been more than one impact at this time.
In 1994, comet shoemaker-Levy 9 broke up into pieces and impacted Jupiter in a staggered
manner.
I well remember this, I had just graduated high school and trained my then relatively
newly built 8 inch Dobsonian on Jupiter wondering if I could discern the impact sites as they
rotated into view.
And, yes, they were very clearly visible.
It reminded me that the solar system is not static and unchanging, but dynamic and had
that comet hit earth instead of Jupiter, it would have been curtains for homo sapiens.
But that Comet Shoemaker-Levy 9 broke up actually a couple years before the impact raises the
point that staggered impacts can and do occur.
And there is some evidence that the end Cretaceous comet or asteroid, it’s debated which it
was, may have broken up and caused several concurrent impacts.
There are several other candidate craters that date roughly from the same period in
the geologic record.
All of them are buried, but geologically detectable.
One of these is the Silverpit Crater off the Coast of England in the North Sea.
This is an odd area, the silver pit itself is a submerged valley that was once part of
a river valley during one of the glaciation periods when sea levels were lower, it’s
still debated which.
This feature was discovered by fishermen in the 19th century, noteworthy for fairly abundant
stocks of fish.
But it had a secret, and we didn’t know about it until it was accidentally discovered
in 2002.
A routine check of seismic data taken to explore the area for natural gas deposits showed what
was clearly a buried crater near the Silver Pit.
At 20 kilometers wide, it’s much smaller than the 180 kilometer buried crater in Yucutan,
but it’s still hotly debated as to whether it actually is an impact crater or was caused
by some other oceanic process.
If it is a crater, its age seems to fit into the timeframe of the extinction of the dinosaurs,
though an exact age isn’t yet established.
Another candidate is the Boltysh crater in Ukraine.
This 24 kilometer buried crater is also disputed, it appears to be an impact crater, but its
age range is really wide.
It does include the end cretaceous extinction however, but may also have been unrelated
to the yucutan impactor and fell later, and wouldn’t in itself have been a mass extinction
causing impact, but it does open up the question as to whether it may have interfered with
the recovery from the extinction.
It’s also possible that more craters may have been formed for which there is no preserved
geologic evidence, and there is also a rather large feature known as the Shiva crater that’s
actually significantly larger than the Yucutan crater, and is estimated at about 66 million
years old.
This one could go either way, if it’s an impact crater, it could have been what set
off the Deccan traps period of volcanism and almost certainly was a mass extinction event
if it happened.
But it seems more likely that it’s really a giant sinkhole caused by salt withdrawal,
a known phenomenon, just a really huge example of it.
So it remains an open question if the end cretaceous impact was a single event, or a
string of impacts, but the bottom line is that for the extinction to have happened,
you only need one, the Yucutan crater impactor.
The aftermath of that event also would have created hurricane force winds across large
areas of the planet, and an enormous tektite fall as molten glass solidified out of the
cloud of material lofted into the atmosphere and rained back down.
Indeed, microtektites have been found associated with this event.
All of this would have really messed up earth’s atmosphere by very rapidly heating it.
This would have favored spontaneous global wildfires in a period of a heavily forested
earth.
This period would have killed an enormous amount of animals anywhere near the impact
site, in fact in some areas it would have been most animal life within just a few hours.
And that’s when the heat ended.
The next stage of the aftermath of the impact would have been the massive amounts of smoke
from the wildfires blotting out the sunlight, leading to a global winter of several years
where ash and vaporized material would have clogged everything, including the lungs of
animals.
This period also saw a worsening of volcanism, compounding the chaos, but another factor
was the vaporization of the sea floor unleashed enormous amounts of carbon dioxide setting
up for a severe warming trend after the end of the asteroid winter that would slow ecosystem
recovery for thousands of years.
This event ultimately caused the extinction of 75 percent of all species on earth, and
other than the birds, sent the dinosaurs into history.
If this happened today, we would almost certainly go extinct without some dramatic and rapid
measures to colonize space, and even then it might not work.
As a result the threat of an asteroid impact has increasingly come to the attention of
NASA as a very real, very possible threat.
We now track near earth objects, but it could also be that something from the outer solar
system might show up and pose a threat, or a near earth asteroid that in the future might
as well.
This has led to an effort that includes more than just monitoring, but in fact the idea
of altering the courses of asteroids using impactors.
Ramming spacecraft into objects in space is nothing new, if you want to see what the inside
of a comet or asteroid looks like as far as composition, you need to blow a hole in it.
We did just that with comet Tempel 1 with NASA’s deep impact mission in 2005, and
then turned cameras and instrumentation on it to study the resulting plume and reveal
its composition.
We’ve sent spacecraft to impact the moon, and even defunct spacecraft like Cassini at
Saturn were deorbited and allowed to burn up in the gas giant’s atmosphere so there
would be no chance it could impact and contaminate Enceladus.
But now we have a coming mission that will go a bit further, and try to ever so slightly
deflect an asteroid.
This involves a rather interesting asteroid system known as Didymos, which has a companion
orbiting asteroid known as Dimorphos.
This asteroid system does not pose a threat to earth, but serves as a good test bed for
deflection.
The mission itself is known as DART, or Double Asteroid Redirection Test, in which NASA will
attempt to bump the moonlet asteroid off course.
The whole idea here is to see if we actually could deflect a dangerous asteroid on a collision
course with Earth.
And further efforts continue to extend the amount of time we could have for deflection
efforts through the discovery of dangerous objects and subsequent study.
DART has already launched, it left for its mission in November of 2021 and the actual
collision is currently slated for September 25th, just a few weeks away.
The objects involved are small, Didymos is about 780 meters in diameter, and the target
Dimorphos is only 160 meters across.
They get close to our planet, on october 4th, they will pass about 30 times the distance
to the moon from earth.
Once the impact occurs, high resolution imagery and data will be taken by a small piggy back
cubesat built by Italy.
So you have the DART spacecraft impacting and photographing all the way down, and then
the cubesat left behind to record the aftermath.
In addition to this, there will be a litany of earth based telescopes monitoring the impact
and aftermath.
This will allow scientists to determine just how much DART perturbed the target object.
It won’t be enough to knock it out of orbit of Didymos, but it should change the orbit
enough for us to be able to detect it.
The asteroid system is already being monitored, they watch the system’s light curve as Dimorphos
orbits and passes in front of Didymos, so they should see a deviation in the expected
data that will determine just how much the object was moved, in the form of slowing down
Dimorphos slightly and shifting it to a lower orbit and it could slow down its orbital period
by as much as ten minutes, but that’s uncertain due to certain unknowns such as how hard the
object is.
This has been an issue,the Osiris-Rex mission that touched down on the asteroid Bennu found
that the material was so loose that it actually behaved a bit more like a liquid than something
like sand.
So we just have to do the experiment and see what it does.
But there’s going to be a further chapter to this story.
In late 2026 the European Space Agencies HERA probe will arrive at the Didymos system and
take a further look after several years have elapsed.
This spacecraft will study the resulting impact crater in detail, learn more about the impact
conditions, and the composition of the interior of Dimorphos.
As to DART itself, it has very little in the way of an instrument package, rather it’s
a 610 kilogram impactor.
Other than a host of navigation sensors, it has only one major camera which is just as
much designed for navigation as it is for taking photographs before the impact.
Driven by an ion thruster, it also employs solar panels for power generation.
What’s interesting here is that crater forming on small asteroids has in the past proven
rather strange, both because of the loose nature of asteroids in general, but also in
how slow the crater forming process is.
Japan had equipped the Hayabusa 2 mission with an impactor, and instead of the crater
forming process happening in seconds, it took over 8 minutes to settle back down.
Given the uncertainties however, it may be that DART doesn’t have the intended effect
and does not appreciably alter Dimorphos’ orbit.
That would spell bad news for future attempts to avoid asteroid collisions with earth, and
the process for doing so may not be so straightforward, especially if differences are found from asteroid
to asteroid and that one object can be easily deflected, but the structure of another may
make it harder.
Still it’s crucial we do these experiments now and be ready, instead of trying to do
it on the fly should a dangerous asteroid be found on a collision course.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently eyeing the birds
suspiciously.
The only dinosaur to survive.
I wonder why.
And they still rule the skies.
Very unsettling the birds 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 live.