I was researching a fun post about the apocalypse today when I suddenly came across a disaster scale I’d never even heard of before. It’s the Volcanic Explosivity Index, which is a way of measuring the magnitude of volcanic eruptions via the amount of ejecta they produce – not a perfect way of ranking volcanic eruptions, if you ask me, but probably the only one that’s really possible given all the different ways a volcano can explode. It then struck me that it might be a good idea to spend a little while talking about the major disaster scales and why they’re set up the way they are, since it’ll be a good setup for whenever I do get around to the apocalypse, as well as ensuring that next time you read a news report about an earthquake you’ll have some idea of what the experts mean when they say it measured 5.8 on the Richter scale.

So let’s start with the Richter scale, which is the obvious one everyone thinks they know about. The Richter scale operates on a logarithmic scale, which is a method of measuring quantities that increase exponentially while keeping them all on the same piece of graph paper – or in this case, on the same ten point measurement device. This means that each point on the Richter scale represents an increase of ten times the power of the previous point on the scale; an earthquake measuring 3.0 on the Richter scale is ten times more powerful than one which measures 2.0, and a hundred times more powerful than one which comes in at 1.0. It’s this measurement quirk more than anything else that leads to most local reported earthquakes coming in at around the 4.0—5.5 mark, since the scale has to cover the entire range of possible earthquakes from tiny microtremors to vast world-ending ruptures in the earth’s crust. 4.0 is the point at which earthquakes become noticeable by the majority of humans, and at 5.0 they start causing minor property damage; these sound like large numbers on a ten point scale but you have to remember that even a 5.0 earthquake is a thousand times less powerful than the 8.0s which cause tsunamis and kill thousands of people in places which are – hopefully – a long way away.

Anyway, what you should take away from this is that the first six points on the Richter scale represent comparatively weak earthquakes that have little chance of killing anyone; the news reports are usually just quoting them to make them seem bigger than they really are. The lethal stuff doesn’t really start until after 6.0, and the good news is that you only tend to experience one of those if you live in close proximity to a tectonic plate boundary. I would also draw your attention to the final point on the conventional Richter scale – 10.0 – which says that an earthquake of this magnitude has never been recorded. That’s not to say it can’t happen, just that it would take something rather extraordinary to prompt that sort of geological upheaval, like the earth being walloped by a bloody great asteroid. We don’t notice earthquakes below 4.0 and the range of known earthquakes only goes up to 9.9, so as far as most people are concerned the Richter scale actually operates between 4.0 and 9.9, and suddenly your local earthquake measuring 5.1 on the scale doesn’t really seem like all that much.

Then there’s the Volcanic Explosivity Index, which works much the same way as the Richter scale (except at lower bounds between 0 and 3 due to the way low-end volcanic eruptions work) except it measures the quantity of volcanic ejecta rather than the amplitude of the shockwaves passing through the earth. The difficult thing to get your head around here is that the VEI measures things in terms of volume, and it can be quite hard for the human mind to comprehend just how large a cubic kilometre of ash really is. It’s one of the questions of scale that often trips up undergraduate physicists, actually¹: how many cubic metres go into a cubic kilometre? The answer isn’t a thousand, as a lot of people think; it’s actually one billion, which is a very large number of cubic metres indeed.

Now, unlike earthquakes volcanoes are usually only locally devastating in the short-term, which is one of the reasons why the VEI is focusing on the amount of ejecta – or in other words, the amount of ash – they release. Not only is this a handy way to rank the violence of a given volcano’s eruption, but it’s the ash and gas output over the long-term that will do the major damage on a global scale.  Eyjafjallajokull shut down all flights over Europe with its ash when it erupted in 2010, and that ranks at a relatively titchy 4 on the Volcanic Explosivity Index with 0.1 cubic kilometres of ash output. Krakatoa in 1883 turned the skies around the world an attractive shade of blood red and dropped global temperatures by a full degree Celsius – and Krakatoa only comes in on the VEI index at six out of eight. Once you get out to eight out of eight – the so-called supervolcano eruptions of Yellowstone and Toba, each spewing out over a thousand cubic kilometres of material – you start to see why volcanic eruptions can be globally threatening events. Both Yellowstone and Toba spread so much ash into the atmosphere and onto the Earth’s surface that not only was there a significant drop in the global temperature for years afterwards, but the human, animal and plant populations of the world started to suffer mass dieoffs as the ash either polluted their food/water sources or made it impossible to get enough light to grow. There’s even a theory that posits Toba was responsible for reducing the human race to just a few hundred living individuals, which is why the seven-billion-odd modern humans are descended from a relatively small number of ancestors. Personally I think this is just a little bit too sensational, but it’s inarguable that supervolcano eruptions on this scale would seriously mess up civilization as we know it.

Finally there’s the Torino scale, which is used to rate asteroid impacts. Given that the vast majority of asteroids tend to miss the Earth completely, the Torino scale differs from the others in that it combines both the potential magnitude of the impact event with the probability that the asteroid will actually hit the Earth to produce a single number that indicates just how much we should be worrying about it. Small asteroids that will definitely hit us but will burn up in the atmosphere rank in low positions on the Torino scale. Large asteroids that could explode a small country but which have low probabilities of impacting are also ranked in low positions on the Torino scale. It’s only a combination of a (reasonably) large asteroid and high probability of impact which results in an asteroid having a Torino number attached to it which is larger than one, and if you look at the chart it is impact probability which is the dominant factor in an asteroid managing to place on the higher regions of the scale.  Which is fair enough, really; an object with a 1% chance of impact is something we should definitely keep our eye on, but until we get improved observations of its trajectory and know for sure it’s not a huge worry unless it’s something large enough to potentially end all life on Earth.

So any object with a Torino scale value of 1 or 0 is basically completely non-threatening, and as far as I’m aware the only asteroid that has made it past 2 was 99942 Apophis back in 2004, which was briefly ranked at 4 due to its size (350 metres diameter, which isn’t world-ending but is still pretty big) and the fact that it had a whopping 1% chance of impacting. That it was eventually downgraded to zero should tell you something about the Torino scale: since the bottom four rungs of the scale are based on impact probabilities calculated before detailed observations, this range of numbers basically exists to tell astronomers what they should be focusing their attention on and not to panic the general public. Not that this stops the media from completely misinterpreting what the scale means, of course;  they actually had to rejig the scale categories at one point because asteroids with a Torino value of 1 kept cropping up in news reports as potential threats when in fact these objects posed no unusual danger and just needed a double-check to make sure there was no chance of them hitting.  (This is why 1 is now in its own category as “NORMAL” instead of “MERITING FURTHER ATTENTIONS OF ASTRONOMERS”.)

But what about the upper regions of the scale? It’s the last three points we should really be interested in, which represent certain impacts with increasing levels of destructiveness. Number 8 is localised destructive potential, which basically equates to the detonation of a large nuclear weapon – annoying if you happen to be standing nearby, but not unduly threatening to everyone else. Number 9 represents regional  destructive potential, which is… hmm. If it was an ocean impact we’d probably be talking about something on the level of the 2004 or 2011 tsunamis, but I’m not sure there’s a good analogue for a land impact. Earthquakes don’t really translate that well into asteroid strikes, but maybe just imagine a similar level of devastation to one which wrecks an entire country (so Haiti 2010, Lisbon 1758 etc.) and you’d have some idea of the amount of damage we’re talking about. And then there’s a Torino number of 10, which has the interesting wording of global climactic catastrophe.   An asteroid that ranks at 10 doesn’t have to be large enough to kill millions of people through direct impact damage (although it probably would just as a byproduct), it just has to be able to throw up enough impact debris to cause mass species dieoffs similar to a supervolcano (or a nuclear winter).

Now, if you ask me there should be a number beyond 10. An impact of 10 on the Torino scale is small enough that it still leaves a fair chance of survival for the human race, albeit with vastly reduced numbers. If there was an impact event powerful enough to crack the earth’s crust open there’d be no survivors whatsoever, so maybe there should be a number 11 in its own category of “WE’RE SO SCREWED”. On the other hand the Torino scale exists to communicate information to the public and I suspect the public would find the existence of this category profoundly depressing, so perhaps it’s for the best.

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Jiiiiim asks

Hentzau a matter of utmost importance has arisen.

According to gentlemen like http://www.youtube.com/user/gorilla199 we are on course to be hit by the planet Nibiru early in the 21st century. Obviously the freemasons are hushing this up but you are a man of science and so I ask: why do you deny that extra-terrestrials from the Zeta Reticuli star system have warned us about this impending catastrophe? It even has a wiki page if that’ll help. http://en.wikipedia.org/wiki/Nibiru_cataclysm

THE TRUTH MUST OUT.

Usually I wouldn’t stoop to laughing at the mentally ill. The true horror of everyday existence is pretty stark and unforgiving — especially in our media-driven first world where everybody has to be the central character in their own particular narrative — and the realisation that you’re just another schlub who isn’t going to get any special treatment from the universe and will be dead and likely entirely forgotten a century from now can be difficult to cope with. So, you know, it’s kind of understandable that your mind might snap (or at least buckle) under the strain and you start to believe that out of all the seven billion people on Earth you and you alone have been chosen to receive thought transmissions from extra-terrestrials in the Zeta Reticuli star system. Perhaps it provides these people with the personal validation and sense of purpose that they’d been so sorely missing up till then, and if it helps them get through life then who am I to judge? Usually, therefore, I would simply pity these people and refrain from mocking them.

Usually.

However, I do have to draw a line somewhere, and that for me that line is etched into the fucking ground right at the point where the public start to give these crazy people more credence than actual accredited scientists, because after that point it starts to bleed into what I have to deal with in my everyday life. I used to do very bad planetarium presentations for school classes as part of my outreach job. Would you like to know what was by far the most popular question I got asked at the end of these presentations? The question that I could pretty much guarantee would come up, and which I actually had to spend valuable minutes of my time coming up with reasoned, logical answer to? The question was this:

“Is the world going to end in 2012?”

Thanks, Mayan civilization. Thanks, Hollywood. Five hundred years of scientific progress have led to a comprehensive, detailed model of the Earth and the surrounding universe which is easily accessible to anyone with an internet connection, but people just don’t want to know. They’d prefer to believe that the Moon landings were fake because it makes them smarter than the people they think covered it up; they’d prefer to believe that climate change isn’t real because it means they won’t have to feel guilty every time they fill their SUV with 32 gallons of petrol; and they’d prefer to believe that there’s some kind of impending apocalypse which flies in the face of all currently established scientific orthodoxy because… actually I’m not really sure about that one. Believing that we’re all going to die tomorrow in some kind of horrifying nightmare cataclysm is a little bit grim, isn’t it? Especially when there’s so much stuff out there that can actually kill us, and which would likely do so with little to no warning. If I were going to pick a personal delusion to shape my view of the world I’d pick one that was a little more pleasant, one which allowed me to avoid exactly the sort of feelings of abject misery and despair that an imminent global catastrophe would tend to promote in the general population.

But anyway. I must say I hadn’t heard of this particular end of the world theory before, but that’s okay because it’s hardly original. People have been tossing around the idea of rogue planets/stars/black holes taking a little jaunt through our solar system and screwing with things in a decidedly terminal manner for years, although usually in a more appropriate venue such as a science-fiction novel. Briefly, here is why none of these things are going to be happening any time soon:

Rogue star: We’d see it coming. Even if it were a dead one that’s stopped burning or a brown dwarf that never quite made it, we’d still see it coming in the same way that we can see Jupiter as it makes its leisurely way around the Sun.

Rogue black hole. We wouldn’t see this coming directly, but that’s okay because a black hole’s gravitational footprint is a dead giveaway. We’d notice little things like the outer planets being wrenched out of their orbits, thousands of objects being punted inwards from the Oort cloud turning the inner solar system into a celestial shooting gallery, stuff like that.

Rogue planet: The most popular version of this apocalypse scenario because idiots think that a planet can be small enough that it can somehow escape detection. They are wrong. We have some of the most sensitive observational equipment in existence, both on the ground and in space, scanning the heavens for precisely this sort of thing. In order for astronomers to miss it a rogue planet would have to be actually physically hiding from us somehow as in the hilarious counter-Earth scenario, and even then we’d see evidence of its existence in the way it affected the orbits of the other planets. Even if we did somehow completely miss a planetary interloper barging its way into the solar system from outside, it wouldn’t be a problem because sooner or later Jupiter and/or one of its orbital resonances would give it a gravitational bum’s rush out of the neighbourhood. So while rogue planets may be popular, they’re actually the most scientifically implausible apocalypse mechanism of them all. The gravitational interactions of planetary-scale bodies are very well understood and it is physically impossible for a hypothetical planet such as Nibiru to pose any kind of threat to the Earth.

Honestly, if I were a believer in Nibiru I’d be more worried about the Zeta Reticulans. Think about it: you’re an alien scooting through some faraway star system in your flying saucer and you notice that an inconveniently large chunk of rock is due to strike a nearby populated planet. Do you

a)      Inform the governments of the world so that they can do something about it.

b)      Inform one random woman so she can tell everyone via the internet.

If your answer is b), then you are a dick alien. I’m sorry, but there it is.

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