TEOTWAWKI 9: It Came From Outer Space (2017 Podcast Transcript)
TEOTWAWKI SPECIALS: IT CAME FROM OUTER SPACE
On the 30th June, 1908, the people of Russia got lucky (for once.)
In an incredibly remote region of Siberia, near the Tunguska river, there was an explosion with the power of a thousand atomic bombs. People on the ground reported hearing a tremendous pounding, as if they were being bombarded by heavy artillery fire. The explosion was powerful enough not only to be seen for hundreds of miles, but to knock people off their feet for hundreds of miles around. 80 million trees were blasted aside, and the explosion magnitude was big enough to be measured on the Richter scale as a 5.0.
A local newspaper described the event:
As the body neared the (forest), the bright body seemed to smudge, and then turned into a giant billow of black smoke, and a loud knocking (not thunder) was heard as if large stones were falling, or artillery was fired. All buildings shook. At the same time the cloud began emitting flames of uncertain shapes. All villagers were stricken with panic and took to the streets, women cried, thinking it was the end of the world.
This was the Tunguska fireball event, and it got its name for good reason; the spreading fireball and blast wave from the initial shock was huge. When scientific investigators reached ground zero for the event; they saw an amazing sight; for eight miles around, the trees were still standing, but they had been burnt to a crisp from the tips of the branches down to the roots. Further out, further than the eye could see, the trees had been flattened. The Tunguska event was caused by a meteorite or comet that intersected with Earth’s atmosphere, and rapidly heated up as a result. Under the immense pressure, the meteoroid exploded in mid-air, unleashing the massive fireball. This explains why the trees near the centre were still standing: the blast wave, expanding in a sphere from several miles up in the sky, was traveling almost directly down from the atmosphere, and not horizontally, in this zone. Had the Tunguska meteoroid impacted around a centre where anyone lived, there would have surely been thousands of fatalities; if it hit a city such as Moscow or New York, millions would have died in the searing heat of the explosion. It is fortunate that the impact hit a sparsely populated region and there were very few casualties.
The Tunguska event was unusual; such impacts occur maybe only once every three hundred years. Yet the Earth is constantly being bombarded by debris and detritus from outer space; twenty to forty tonnes of it hits us every day. Even a rock the size of a fist can be moving quickly enough, and burning brightly enough, to be seen as a shooting star in the sky. The object that caused the Tunguska event was likely a few dozen yards across. Had it actually struck the ground, rather than exploding in mid-air, the crater left behind would likely be a few miles across.
It’s now pretty much accepted universally that, sixty-five million years ago, an asteroid impact caused the last great mass extinction — at least, before the present one, caused by humans — and wiped out the dinosaurs. A rock the size of Mount Everest, around six miles in diameter, smashed into the Earth off the Gulf of Mexico; the explosion was a million times more powerful than if every single nuclear weapon on Earth was simultaneously detonated. A big chunk of the Gulf would have immediately evaporated into steam as the asteroid approached; its impact threw vast amounts of molten rock and steam into the air in a vast plume, which rained fire down upon the rest of the world, with many smaller chunks of the Earth being caught in its gravitational pull and smashing back down in places hundreds of miles from the initial event, causing a devastating chain of forest-fires which filled the sky with smoke. The tsunami that spread from the event would have been hundreds of metres high — for scale, a normal tsunami like the Boxing Day tsunami in 2004 might have waves up to 30m high. What’s more, while a normal tsunami might move at the speed of a car, this tsunami would have moved faster than the speed of sound, smashing into the coastline around Mexico and North America. Whatever creatures did survive the initial apocalypse of this event would not have it easy; as you might imagine from our episode on supervolcanoes, this impact threw a vast amount of dust into the atmosphere which kicked off another ice age. Any surviving dinosaurs couldn’t adapt to the changing temperatures, and quickly died out. Yet it was a good time for the small mammalian creatures that would one day evolve into humans. If such an impact occurred today, there’s no question that the human race would struggle to survive. Billions, not millions, would be killed.
If you want to stay awake at night, you should know that there are plenty of chunks of space debris of similar size to the asteroid that wiped out the dinosaurs. Not only that, but there are several orbiting around the Sun whose orbits actually cross Earth’s orbital path. Every orbital period, we manage to miss each other; but, at some point in the future, we’re not going to be so lucky.
And asteroids are far from the only astronomical phenomenon that has the power to kill us. As you can imagine if you listened to our early Physical Attraction episodes on stellar formation — there are processes out there with ridiculous amounts of energy that would vaporise the earth without breaking a sweat. A gamma ray burst, for example, that had Earth in its path would fry the planet easily. Massive solar flares are also a concern and could disrupt our technology. A nearby supernova could shower us in deadly cosmic rays if it doesn’t toast us directly. And, of course, as everyone knows, the Sun will eventually expand and engulf the Earth. To my mind, the really scary aspects of this kind of apocalypse is that there’s no good news; it’s completely outside of human control, and the forces involved can be so dramatic that there’s really nothing we could possibly do to shield ourselves, short of colonising other planets. The other scary aspect is that, due to the finite travel time of light, a nearby supernova could have already occurred. Even now, the deadly explosion could be hurtling towards us at the speed of light, and it would take years for us to realize. If the Sun vanished tomorrow, it would take eight minutes for anyone on Earth to know about it. There’s a grim sense of fate about this kind of destruction, then; maybe the asteroid is already on course, maybe the gamma rays are already flooding towards us, and it’s already too late for any human actions to prevent our doom. But how likely are any of these Earth-scale astronomical apocalypses to actually happen?
Working this out is almost like dividing two massive numbers. One is the vast array of things and events in the Universe that could kill us without batting an eyelid, and the other is the vastness of space that means that chances of being in the same coordinates as such a deadly event might be quite low. And, on the whole, the vastness of space does win.
Let’s look at asteroid impacts first. I mean, there are people out there who are tracking this stuff, right? Right?
Well, yes, thankfully, there are, and these people have some of the coolest jobs out there in my opinion — keeping the world safe, albeit from an event that has a low probability of occurring. In 1992 NASA first started the search for “Near Earth Objects” — those asteroids of greater than 1km across that would cause truly global destruction if they hit. Since then, the target for tracking these objects has been continually revised upwards as it’s proved more difficult; scientists pushed back the date by which they wanted to have discovered 90% of NEOs several times. They now hope to have them tracked by 2020 — although it’s worth pointing out that there are still plenty of smaller objects, the size of the one that caused the Tunguska fireball event, such that it’s just too difficult for us to see and track all of them + we likely won’t get warning of an impact until it happens. Given that we expect a Tunguska-event type impact every few hundred years, there’s a decent chance that another might occur in your lifetime. Hopefully it will once again miss the populated regions of the Earth. Even amongst the larger NEOs, new discoveries are being made all the time — in 2009, another large NEO was discovered that was previously unknown to astronomers. So far, none of these are projected to hit the Earth any time soon — although there are occasional “near-misses” where scientists worry that slight deflections could cause impact; for example, there was an NEO that they calculated had a 1/10000 chance of being diverted to impact Earth sometime in the next century. Also in 2004, our best observations of 99942 Apophis, a 370m asteroid, suggested that it had a 3% chance of impacting the Earth in 2029. Better observations have since decreased this possibility to zero — we’re now very confident that it will be another near-miss event. When we say a near-miss, in these terms, it will miss us by around 6x the radius of the Earth; which is a close-approach, but not hugely threatening — although it will be closer to Earth than many weather satellites! Observing these objects is difficult; we can never be completely certain of our measurements, so, like all good scientists, things are expressed in terms of probability — and you can look up the various probability tables that each near-miss could in fact be a collision. They don’t add up to all that much at the moment.
So there is a small chance that there could be some large NEO that we somehow missed that might impact us, but it seems unlikely — we’re pretty good at tracking them now, and calculating their orbits. There is always some uncertainty — in the case of Apophis, people were concerned that, in 2029 — if it passes through a particular region of space around the Earth — Earth’s gravity might disturb its orbit enough that it *will* hit us on the next approach at 2036. This now seems unlikely, but it shows you why uncertainties in the orbit are concerning. The smaller objects are trickier to see, but don’t pose an apocalyptic threat — unless you happen to be underneath one. (You might not believe this, but people actually have been hit and have had their cars destroyed by small meteorites in the past few decades. It’s exceedingly rare, but it does happen. Imagine trying to get your insurance to pay out on that.)
What would happen if we observed a new, or existing near-earth-object and calculated that it had a very high probability of smashing into Earth? Bruce Willis’ strategy — nuking the asteroid to blow it up — is unlikely to be especially successful. For a start, most asteroids are less dense than solid rock — this means that it’s far less likely to be fragmented by an explosion. An explosion might heat up the asteroid somewhat, but wouldn’t destroy it completely. Even if you could detonate a warhead with enough power to fragment an asteroid and it succeded. Some NEOs are thought to be more like piles of rubble, loosely bound by gravity — you could fragment these with an explosion, but then you just have a shower of smaller meteorites that would be smaller, and more difficult to track, on similar orbits that would likely still impact the Earth. Unless you could guarantee that the big “lumps” in the NEO would be broken down, it’s a risky strategy. So asteroid impact avoidance strategies tend to be focused on deflecting them instead. The logic behind this is simple; if you can hit the asteroid at a far enough distance away, even a deflection of a tiny angle would easily take the asteroid’s orbit out of the path of the Earth. Equally, if you can slow down the asteroid as it approaches, it would “give the Earth time to move out of the way”, and the orbits would no longer intersect such that the asteroid would be in the same position as the Earth at the same time. These methods are generally considered more feasible than destroying the asteroids outright. Scientists confirmed the potential for these methods using the brilliantly-named Z-machine. This machine is the closest thing we’ve ever developed to a giant death ray; it produces the highest frequency electromagnetic radiation humans can make. (Go back and listen to our episode on radiation if you want some details.) It can produce plasmas with temperatures up to two billion Kelvin, and has been used for weapons and nuclear fusion research in the past. It was used to fire X-rays, of the same kind that would be generated by a nuclear bomb, at some asteroid-type material — and it confirmed that they would be capable of deflecting an NEO. The key is to detonate the bombs a few hundred metres away from the object, so as to push it aside without fragmenting it. A non-nuclear alternative would involve ramming the asteroid with a high-speed projectile to knock it out of the way — and, again, if you can hit it at a far enough distance, you’ll be able to divert the orbit by a tiny bit — enough, however, to miss the Earth. And scientists have some success with “kinetic deflectors”, as such a method is caused; we smashed a one-tonne brick into a comet in 2005 to study its composition and that went off without a hitch. And it’s even been suggested that we could manipulate the asteroids in more subtle ways. If you can get a rocket up to the asteroid + still have control over its thrusters, the gravitational pull of the rocket’s mass on the asteroid can actually disrupt its orbit enough to cause it to miss the Earth. Philip Plait, in his wonderful book Death From The Skies which deals with these threats, notes that you could even try to use this type of technology to drag an asteroid into an orbit around the Earth — and then we could even use it to our advantage! Trillions of dollars of valuable minerals might be buried in an asteroid of the right composition; instead of being an existential threat, it could be a lucrative asset.
So what’s the present state of play for the threat from asteroids? None of our methods for deflecting them are “mature technologies” yet — but neither are they so far from being realized that they could never happen. It seems pretty likely that the only lack here is a lack of investment. Providing we had a decent amount of notice — maybe 10–20 years of a potential impact, which seems fairly probable as the kind of timescales — a concerted effort on the part of humanity should be enough to avert this kind of disaster. It wouldn’t be cheap, and it wouldn’t be pretty, but actually — don’t you think this is amazing? — we can genuinely imagine that we might be able to knock a comet aside and save the planet. This has never been true for any species before us. Eventually, there will be an impact. But odds are pretty good we’d be able to avert it.
There is a concern, though; comets. Comets are icier and gassier than asteroids which are essentially lumps of rock. They are often in much wider, larger, more elliptical and more unpredictable orbits than asteroids — and, as they spin and emit jets of gas that can knock the comet into different orbits, they’re far far harder to predict. The Hale-Bopp comet, which was the comet that led to the mass suicide of the Heaven’s Gate cult that believed they would board a spaceship to “paradise” on the comet — that was only detected a couple of years in advance. That comet had a solid nucleus 25 miles across, much bigger than the asteroid that wiped out the dinosaurs; a comet impact would almost certainly destroy the human race, and we might end up with far less warning about a nearby comet or the fact that its orbit could change and intersect ours fairly late on. So, just in case, you should write to your local elected representative and ask them to fund research into deflecting these things!
The probability of you being killed by an asteroid or meteorite strike in your lifetime is around 1/700,000. (I should point out that this is still more likely than being killed by an act of terrorism.) But with the proper technology, we could reduce this to practically zero + actually remove a threat to the planet, for once.
But what about solar flares, gamma ray bursts, supernovae, and other astrophysical phenomena?
Let’s first describe these events, the potential impacts they’d have, and then the overall threat assessment.
The sun is a big ball of plasma; its own gravitational pull balances the outwards force of the nuclear fusion happening in its core to hold the Sun together. Yet, because it’s made of charged particles that move in complicated, convective ways — see our early episodes on stellar formation — it has a magnetic field that’s very complicated. The field of physics that studies magnetic fields in plasmas is magnetohydrodynamics, which is wonderful to say and read. Yet it can give rise to some complicated behaviour, as great tongues and conveyor-belts of gas and plasma hundreds of miles long lick their way through the Sun and generate complex, tangled-web magnetic fields. As magnetic field lines get tangled up, they interact with the plasma on the Sun’s surface as well. This can change the way the gas can move in the Sun, and prevent the hottest gases from reaching the surface in some regions. So the Sun’s surface is not uniformly bright: you get sunspots where the coolest gases are concentrated on the surface, and the sunspot activity follows an 11-year cycle that corresponds to the magnetic field activity in the Sun — sometimes there are plenty of sunspots, and sometimes none at all. But inevitably, the magnetic field can’t keep the rising, hot gas down forever — and, like springs, the magnetic field lines store more and more energy as time goes on. Eventually, the magnetic field reconfigures itself, and there’s a huge release of energy close to the Sun’s surface — a solar flare. One was observed in 1859 — and even then, with Victorian-era technology, they could measure the fluctuations of the Earth’s magnetic fields. Subsequent flares have sent bursts of protons travelling at half the speed of light towards the Earth, and flares can be accompanied by blasts of X-rays. It’s this kind of flare activity that’s part of the reason our planet badly needs its atmosphere; without something to absorb the X-ray bursts, we’d all suffer from radiation damage. Solar flares will occasionally toast communications satellites. Much more massive types of flares, such as Coronal Mass Ejections, could wreak havoc with the Earth’s magnetic field with only a few days of warning provided. Some of these events have already occurred, but luckily only produced aurorae — the Northern Lights are caused by accelerating charged particles caught in the Earth’s magnetic fields, and lots of these come from the Sun in CMEs.
The real risk to humanity from this is down to the fact that we have an awful lot of things that are very sensitive to magnetic fields down on Earth. Our entire society rests on the fact that, when you move a wire in a magnetic field, a current is generated. It’s this principle that is at play in all of the electricity generators, of any kind, on Earth. And the world is just covered in a vast network of wires — the electrical grid. If Earth’s magnetic field is severely disrupted, it can cause vast surges of current that could severely damage the grid. It would be a rare solar flare that would cause the kind of surges that would blow up power stations and set power-lines ablaze, but there’s no question that it could happen — and there’s not an awful lot we can do about it. It is possible to surge-protect the grid, but — to the woe of those who want to make it more flexible to deal with renewable energy — the electricity grid is more often than not old, overloaded, and difficult to repair and replace. And — think of it like this — how many policy-makers would even think of solar flares as a threat?
The other astronomical threats to the planet come from outside our solar system. We talked about supernovae in the stellar formation episodes, but not about their destructive potential. If our Sun went supernova (it won’t) we’d be toast for sure, and there are probably many millions of scorched planets flying around in distant regions of space which were violently ejected by a supernova. But what would happen if a supernova went off in our galaxy? How close would it have to be for us to seriously worry about it?
The nearest star to Earth that has a potential to go supernova is Spica, 260 light years away. In terms of the actual debris from the supernova, we’d probably be fine — although it ejects a massive amount of material, this is dwarfed by the massiveness of the distance from us to the supernova.
There was a supernova in our galaxy in 1054 that formed the Crab Nebula — it was bright enough to be visible alongside the sun during the day for several days — and, even though it was close by, only a few tons of material could ever make it to Earth, and most of that is likely to be intercepted by interstellar dust anyway. Even a supernova that was only a few light years away is unlikely to directly destroy the Earth via the matter that it sprays everywhere. The bigger risk is from radiation. There is no star close enough that might go supernova which could produce gamma rays and X-rays strong enough to sterilise the Earth for life — the atmosphere will absorb a lot of them. The only issue is that, in doing so, the atmosphere would be badly damaged; specifically, a supernova between 25 and 100 light years away would likely produce enough gamma rays to strip the Earth of its protective ozone layer. Then we would no longer be shielded from the UV radiation from the Sun, and it’s this that would cause the real damage — causing increased rates of skin cancer due to the radiation, sure, but also playing havoc with the delicate ecosystem of bacteria and phytoplankton that form the base of the food chain. Would a supernova actually wipe out life on Earth if it occurred within a few dozen light years?
One of the things that’s fascinating about this particular theory is that — most of our apocalypses, we don’t get to test, because — obviously — they’ve never happened before. But it seems that there might have been a supernova nearby a few million years ago — geologists have found a rare isotope of iron that’s only produced in supernovae deep in the Earth’s crust. Based on where it was located, and the amount that was found, we can infer that a supernova may have deposited this on the Earth’s surface a few million years ago, and it was probably only a few hundred light years away at most in order to deposit any decent amount of material on the Earth’s surface. And this is reassuring, because it means that if the gamma-ray impacts from a supernova a few million years ago weren’t enough to wipe out life then, they probably wouldn’t be now. One thing is for sure; if a supernova occurs at these kind of distances in our lifetimes, it will be a spectacular sight. You won’t need a sensitive scientific instrument or a neutrino detector to realize that this cosmic event has occurred — it could shine alongside the Sun during the day. And since one occurs in our galaxy every century or so, your chances of seeing a supernova during your lifetime aren’t that bad — but you’ll likely only get one shot, so make the most of it.
Gamma Ray Bursts are still rather mysterious events for astronomers — it’s not entirely settled what causes them. They are exceedingly rare, but very powerful — far more powerful than supernovae, the most powerful astrophysical events that we know about. The main theory is that they occur due to black hole formation, which beams matter in an explosion of heat and magnetism into highly collimated blasts. They are powerful enough that one, which occurred 8 billion light years away, was even visible to the naked eye. Philip Plait calculates that, if a GRB occurred a hundred light years away, it would create a beam 50 trillion miles across that would easily engulf the entire solar system. In the space of a few short seconds, it would dump so much energy onto the Earth that it’s equivalent to blowing up a nuclear bomb over every square mile of the Earth. It would almost certainly instantly sterilise the Earth, killing all life on the surface and a few metres down into the oceans as well. It would be left to deep-sea life (and, maybe, anyone hiding underneath thick, thick layers of lead or deep in mine-shafts) to repopulate the planet. Definitely the end of the world as we know it.
Luckily for us, there are a couple of factors that save us from GRBs. One is that they are highly beamed phenomena — which mean that, if the direction is wrong, the GRB will miss you altogether; it’s like a cosmic death ray rather than an explosion. So, for example, the nearest GRB candidate is oriented at 45 degrees to us; it will be an amazing astrophysical phenomenon when it does explode (which could be in millions of years) — but the most devastating effects will likely miss Earth. The other is distance; even this closest GRB progenitor is 7,500 light years away. At this distance, the gamma rays will still cause immense damage — including, due to their effects on the atmosphere, acid to rain from the sky — and the electromagnetic pulse from the blast would wipe out any electronic device. Bizarrely, because the GRB is so short in duration and because the EMP would be absorbed by the Earth, this effect would likely only occur on the half of the Earth that was facing the GRB when it occurred — which is difficult to imagine!
Yet gamma ray bursts are likely one of the cases where the vastness of space does dwarf the vastness of the explosion — even in the case of the biggest explosions in the Universe. It seems very, very unlikely that one is about to fry the planet; even though, if it did, there would be nothing that we could hope to do about it. Whole sections of the Universe are being wiped out by these cataclysmic events, but luckily for us, there’s a lot of Universe to go around.
I have to say: this has probably been the most reassuring episode for me to research. Going in, I knew a lot about the titanic energies and various phenomena in the Universe that could easily kill us all if we were close enough. And it’s a very scary scenario, because for a GRB of supernova, you would expect little warning, and no possibility of saving yourself from the destruction. But it seems that the distances to most of these objects are just too far for there to be any major risk from them. Asteroids and meteorites are a much bigger threat, and have been historically — just ask the dinosaurs — but we are reaching the stage where human technology is getting good enough for us to defend ourselves from flying chunks of space debris. A more robust tracking system, combined with the technology to deflect these rocks, and we should be safe. It’s lucky that the most dangerous and likely threat is also the most preventable one.
Of course, astrophysics will eventually kill us all in the end; even if we escape our planet before the sun expands and engulfs the Earth in a few billion years, we’ll still die eventually due to the inevitable heat death of the Universe. But, given that human life expectancy is pathetically tiny compared to the life expectancy of the Universe, I’m not going to lose any sleep over it.
Thank you for listening to this TEOTWAWKI special…
*** this bit should go in a final retrospective episode***
Incidentally, while we’re talking about research into the end of the world, I just want to highlight a general disparity in this field. In 2001, philosopher Nick Bostrom said:
There is more scholarly work on the life-habits of the dung fly than on existential risks [to humanity].
A startling observation. There are plenty of people working on this, including the Future of Humanity Institute which Nick Bostrom heads up, the Centre for the Study of Existential Risk in Cambridge which was set up in 2012 and includes Stephen Hawking and the Astronomer Royal Sir Martin Rees, and many others. People who look into this stuff will give you a startling range of numbers regarding how likely the apocalypse is. This makes sense, because a lot of the parameters are completely unknown or unknowable — we can’t know how close we are to a technological singularity, or how bad that would be; our knowledge of physical processes that could cause the end like climate change or astrophysical processes are by necessity incomplete, and the threat from pandemics is not entirely understood. But even so, the range of numbers is vast. The astronomer Martin Rees gives the human race a 50–50 chance of surviving the 21st century. Just think about that for a minute. There are reasons not to take his number at face value — for a start, he is in charge of the Centre for the Study of Existential Risk, who probably get a little bit more funding if people are… concerned about existential risk. Nick Bostrom who heads up the Future of Humanity Institute says that any number below 25% is misguided for near-term extinction. The Stern Review for the UK Treasury that considers the impact of climate change makes its calculations including a 10% probability for human extinction in the next 100 years. Lots of people will give you these very high numbers.
I probably won’t make it to 2100, but let’s assume that this is compensated for by the chance that the apocalypse occurs earlier in the century than we might think. Don’t you think, if you believe these numbers — that I have a decent chance of living through, or more likely dying in, a Doomsday scenario — doesn’t that change your life, just a little bit? Shouldn’t it change the way you act?
Of course, any one of us has an unknown risk of dying for any number of reasons, at any given moment. (Goodnight, kids!) So in a sense, the fact that we might just perish alongside the rest of humanity doesn’t really add much to that calculation; we all have to assume that we’re going to carry on living for the next chunk of time until the evidence suggests otherwise. But humans have been around for over a million years. The fact that we now think there’s a high chance we’ll all be dead in the next hundred years is pretty striking, and a testament to the theme I’ve been coming back to again and again on this show: we are not ordinary people. We are living through extraordinary, pivotal times. Even if you don’t believe that they’re necessarily going to pivot towards world destruction, that fact alone should — I hope — influence the way you live your life for the better.