This is something you hear said so often - that we risk being hit by an asteroid that could make humans extinct. But do we really? This is the article I’m commenting on, a recently breaking news story: Earth woefully unprepared for surprise comet or asteroid, Nasa scientist warns. Some are already worrying that it means that we are all due to die in the near future from an asteroid impact. Well, no, it doesn't mean that. So, what is the truth behind it? 

The source of all this is a comment by Dr Joseph Nuth who warns:

“But on the other hand they are the extinction-level events, things like dinosaur killers, they’re 50 to 60 million years apart, essentially. You could say, of course, we’re due, but it’s a random course at that point.”

Photograph of comet Siding Spring by Hubble - right hand image is more processed. This comet did a close flyby of Mars and at one point was predicted to have a tiny chance of hitting Mars. In the end it missed Mars by more than a quarter of the distance from Earth to the Moon

If you read the rest of the article, it’s a worthy goal, to prepare us for asteroid impacts of all sizes from the small Chelyabinsk one up to really large 10 km ones. There are a number of things potentially confusing about this statement however, if you read it as a non scientist.

  • Although there is a risk of “mass extinction” if a large asteroid hit Earth, “mass extinction” there doesn’t mean “extinction of humans”, we are such a resilient species that we would certainly survive a giant asteroid impact.
  • We are not “due” an extinction at all. Next giant impact is most likely to happen many millions of years into the future. As we'll see, there is almost zero chance of a giant impact in the next century.
  • There is however much we can do to protect ourselves from smaller asteroids.

As a result of extensive asteroid surveys over the last couple of decades:

  • We can be pretty sure (as in perhaps 99.999999% sure) that there isn’t an extinction level asteroid  headed our way in the next century. We know the orbits of all the Near Earth Asteroids that could do this and none will hit Earth over that timescale. That leaves comets, and the chance of that is something like 1 in 100 million per century, as a very rough guess (since 99% of the impacts are thought to be from asteroids). This risk has been pretty much retired due to the automated asteroid searches by the likes of Pan STARRS.
  • But the chance of a smaller asteroid impact is still high enough to make it worth working on it, especially since this is the one natural hazard we can not only predict to the minute, decades in advance, with enough information but also prevent also, given a long enough timeline.
  • We are already close to completing the survey of 1 km asteroids (90% done). With a bit more funding we could also find most of the asteroids down to 45 meters in diameter. As a result of new developments in the science of asteroid detection, this could be done for a cost of only $50 million to protect the entire Earth. We would then be able to deflect asteroids decades before they are due to hit, which is a far easier task than a last minute deflection.
In more detail:


First when he said  "You could say, of course, we’re due, but it’s a random course at that point.”" - that is a scientist speaking as a scientist. But of course people sharing this on social media, retweeting, writing new stories about it, pick up the “we are due” and omit the scientific qualification “but it’s a random course at that point”.

To say that we are “due” a mass extinction is a bit like saying that after you throw nine heads, you are due to throw a tail. Not true. The chance that the next coin toss is a tail is always going to be 50/50 for a fair coin no matter how many heads you throw.

It's the same with extinctions. So long as it is a random process, then an extinction that happens every 60 million years could happen tomorrow or it could be 60 million years or 120 million years before it happens. On average we would still expect to wait 60 million years for the next such mass extinction even if the last one happened hundreds of millions of years ago. It’s just as for the coin toss. Same for an extinction event of a size that happens every 100 million years. If you look at the diagram the big five are irregularly spaced. The last one happened 66 million years ago. But they are irregularly spaced so we can't conclude either that we need to wait 44 million years for the next big extinction either.

Some scientists have tried to discern a periodicity in the extinctions of perhaps 26 to 30 million years. If they are right then we are due the next extinction perhaps 15 million years or so from now. But that is very controversial and if true, it wouldn’t cover all mass extinctions. At any rate that's so far into the future it makes no difference to us now, if they are right or wrong. We could get a mass extinction in the next few millions of years. But it is nearly impossibly unlikely in the next century.


This graph shows some of the major extinctions - note that some of the extinctions spread over several tens of millions of years. This probably doesn’t mean that the extinction took tens of millions of years as this is a graph of the fossil species and due to the Signor–Lipps effect - that a species may seem to go extinct in the fossil record before it actually is extinct because typically you get only a few specimens scattered over time so can easily miss the exact moment of extinction. The extinction that ends the Permian era is thought to have lead to extinction of 96% of all marine species. and 70% of land species.

If you look at some of the past extinction events, you might think that humans could go extinct very easily. The worst of all of those was the Permian–Triassic extinction event during which 96% of marine species and 70% of land species went extinct according to one estimate.

So based on those figures you might well think that there is a 70% chance that humans would go extinct as a result of whatever causes those extinctions.

However, even after the extinction of the dinosaurs, birds, dawn sequoia, river turtles, small mammals and many other plants and creatures survived. Many species would go extinct after a gamma ray burst or a large asteroid impact, but humans are great survivors. We were at risk in the past before we developed tools and clothing. But with clothes, tools, boats, etc, we are an extremely adaptable species, able to survive anywhere from the Kalahari desert to the Arctic, with only stone age technology. We had already colonized most of the world by the end of the neolithic period.

Overview of Pre-modern human migration - there is debate and controversy about the details, but generally agreed that humans were already present world-wide by the end of the neolithic period (which ends around 2000 BC), or shortly after.

So, as long as we retain at least stone age technology, there isn't much that could make us extinct. Even if we have to go back to beachcombing and surviving on shellfish, which was a staple of early human diet in cold places such as Canada and Scotland where I live, one way or another some humans would survive.

Conchero al sur de Puerto Desead - a shell midden in Argentina. For long periods of time ancient humans survived on shellfish, for so long that they built up these huge shell middens in many parts of the world. See Shell Midden

We are omnivores able to survive on:

  • Shellfish
  • Insects
  • Fish and other marine life
  • Nuts
  • Fruit
  • Roots
  • Seeds and cereals
  • Birds,
  • Animals
  • Reptiles.

So long as any of those survive the extinction event, anywhere in the world and so long as humans retain at least stone age level of understanding of technology - then there would be many survivors and we would not go extinct, even if more than 90% of species went extinct. The dinosaurs weren't a patch on us as far as survival goes. Without any technology, turtles, crocodiles, alligators, small mammals, flying dinosaurs (the birds), dawn redwood trees, pine trees, many lifeforms survived the dinosaur extinction impact.

We aren't vulnerable like the early hominids. So long as

  • We retain the ability to make clothes and simple tools and to make boats to cross rivers and seas to find new sources of food
  • There is something edible somewhere on Earth that we can find in our travels, and cultivate or just eat in situ as hunter gatherers
  • Then we could survive anywhere where there is such food, from the Arctic to the hottest of deserts, along the sea shores, or in tropical rainforests.  

So, for sure, some of us would survive a giant impact like that

River turtle, Boremys basking on a Triceratops dinosaur skull, Credit: Brian T. Roach, Yale Peabody Museum
How Tough Turtles Survived Dino-Killing Meteor

It did become extinct eventually, but not through asteroid impacts. Probably because it was unable to retract its neck, and succumbed to predators.

Homo Sapiens is listed in the IUCN Red list of threatened species - as one of the species of least concern

"Listed as Least Concern as the species is very widely distributed, adaptable, currently increasing, and there are no major threats resulting in an overall population decline."


We have already found all the 10 km asteroids that do regular flybys of Earth. We have found 90% of the 1 km asteroids. This makes it very unlikely that we are hit by either a 1 km or 10 km object in the next century.

We could be hit by a comet. But they are rare. He mentions the comet Siding Spring which did a flyby of Mars. But it’s important to note that it actually missed Mars by quite a distance. Also, it was only 400 - 700 meters in diameter, so of a size that would have only local effects if it hit Earth. Also even with this small size, it was discovered 22 months before the flyby, so more than a year and a half. A larger comet would be discovered several years before the flyby.

This shows the trajectory of Siding Spring:

It actually missed Mars at a distance of 140,000 km. That’s 22 times the radius of Earth and 36% of the distance to the Moon. Earth is often “buzzed” by asteroids at that distance.

It’s orbit was uncertain when first discovered, as is usual, giving a tiny chance of hitting Mars. But was eventually shown to miss. So if a comet happened to be in a similar orbit but targeting Earth instead of Mars that would be what we’d expect, that it would have a tiny chance of hitting Earth but a few months after discovery or maybe sooner, we’d know for sure that it would miss. It would be exceedingly unlikely for such a comet to hit.

If it did hit, a comet the size of Siding Spring is probably not quite large enough for a tsunami depending on whether it hit into deep or shallow seas and how much it breaks up in the atmosphere. It would be seriously bad news locally if it landed in a heavily populated area, and such an impact zone would have to be evacuated if it could not be deflected. However, most of the Earth surface is sea, ice fields or desert.

Probably only one impact in 100 is by comets. So it doesn’t really make a lot of sense to focus on defense from comets first. We can deal with 99% of the threat by looking at Near Earth Asteroids and they are also easiest to deflect, as if we can find them decades in advance, just the gentlest of nudges will deflect them away, just microns per second of delta v.

Now I totally agree that we need to put more work into searching for asteroids and detecting them and preparing to deflect them. And eventually also good to speed up detection of comets too, which will happen anyway as a side effect of the asteroids search.

As for having a rocket on standby to deflect a comet, well I think you need to bear in mind that though it could be needed right away, it might also not be used for several thousand years. So - is that our priority? And as for deflecting asteroids - there are so many different ways to do it and what we use would depend on the exact scenario. For instance for some asteroids, it might be sufficient to “paint” the asteroid white with a white dust. So we would need a spacecraft able to dust it uniformly with white dust to deflect it using the effect. Here is a short video of professor Dave Hyland talking about the idea:

And article
Asteroids No Match For Paint Gun, Says Prof | Texas A&M Today
(or How to Deflect Killer Asteroids With Spray Paint | WIRED)

It's due to the Yarkovsky effect. When the sun heats up a rotating object, then the rotation carries it around some distance before the thermal photons are emitted as heat. The amount of the effect depends on how rapidly the object rotates, but also on how light or dark it is Since most asteroids are very dark, the obvious way to change the amount of this effect is to paint it white. So long as you discover it long in advance, then this may be enough to shift its orbit to miss the Earth (orbital predictions have to take account of the Yarkovsky effect).

I think that with unlimited funding we would devise half a dozen ways of deflecting asteroids, test them, and have them in a “ready to launch” state ready to deflect any conceivable asteroid, even if they may have to wait ten thousand years before we need some of the solutions. However in the situation as it is now, with limited funding then I think it makes much more sense to focus our efforts on detection.


There are new developments in asteroid tracking which may help here. Especially, use of synthetic tracking. The idea is explained in techy detail in this paper. Finding Very Small Near-Earth Asteroids using Synthetic Tracking. For an easier to read summary of it, see “Synthetic Tracking” Set to Revolutionise Near-Earth Asteroid Discovery

The idea is that instead of doing a 30 second exposure, you do many shorter 2 second exposures. With conventional CCD's that adds to the read noise so you get more errors but there are new CCD's developed for medical imaging that permit fast accurate reading, called Scientific CMOS detectors. The Andor Zyla is an example here.

Andor Zyla 5.5 | sCMOS Camera medical imaging camera capable of fast read out with low read error

You can then use this to simulate tracking the asteroid with the camera, which makes the asteroid far brighter in the images.

This image shows a the result of stacking many photographs of asteroid 2009BL with camera set to follow the stars on the left - notice how the asteroid is shown as a streak, and rather faint. On the right, the same photos are stacked to follow the asteroid which then shows as a much brighter spot, and the stars are streaked and fainter.


When the asteroid is small and traveling faster across the field of view, the trail can be so faint it can’t be distinguished from background noise when the camera follows the stars. If you know its velocity you can make it much brighter by following the asteroid. But what can you do if you haven’t detected it yet and don’t know which way it is moving? The idea of synthetic tracking is that you take lots of short exposure photos and just try stacking them in many different ways until you find the right velocity and an asteroid pops into vie win the photo. This is time consuming but modern graphics cards permit fast parallel processing which makes synthetic tracking feasible.

This approach can make it easier to spot fainter asteroids. It might mean for instance that you can spot an asteroid ten times further away than before. That means a thousand times the volume of space covered. So this technique can lead to a huge increase in the detection of asteroids.


The researchers found that fewer than eight cubesats, fitted with 15 centimeter synthetic tracking telescopes could find more than 70% of NEO's larger than 45 meters in diameter in less than six years (these are the asteroids that are most hazardous for us). The total cost would be $50 million. With larger 30 cm telescopes then eight satellites could find 95% of the NEOs larger than 45 meters in diameter in the same time period of less than six years. For details see their 2016 Annual Progress Report.

$50 million is not a lot. Any developed country could find that out of loose change from its defense budget. $50 million spread over the US population, say, is a one off cost of 15 cents per person. In the UK we could do it for a one off cost of £1.60 per person - that's to find them for the entire world. As an example, the UK recently voted to renew Trident at a cost variously estimated at £40 billion to £205 billion ($50 billion to  $256 billion). The cost of finding 70% of Near Earth Asteroids down to 45 meters within six years is a tiny 0.1% of that. We can certainly afford to do that.

It would still leave the risk of comets, but those are not the priority because they are so rare. If we had loads of funding it would make sense to fund a rocket ready to launch if necessary, even if it is quite possible it won’t be used for 1000 years. That’s the ideal situation, to do both. But with limited funding, detection is surely the priority.

See also my Giant Asteroid Headed Your Way? - How We Can Detect And Deflect Them


I field many questions here from people who are scared from the end of the world. Some of them are stories that for a scientist are just plain nutty such as the "Nibiru". But others are genuine possible disasters, but way over hyped. 

One of the most over hyped disasters is the possibility of an asteroid impact. As I've explained briefly here, we have pretty much retired the risk from major dinosaur extinction type asteroid impacts for the next century as a result of exhaustive sky surveys over the last couple of decades. That just leaves the smaller ones similar in scale to a tsunami, volcanic eruption or earthquake. These are very rare indeed.  We haven't had a single major asteroid impact since the invention of writing. There is no ancient asteroid version of Pompeii.

This shows figures from Pompeii in the positions in which they died, preserved as plaster casts. There are many ancient disasters from volcanoes, tsunami, earthquakes. But none like this from asteroids. Asteroid impacts can happen but they are rare. Photo by Lancevortex

 However they are well worth focusing attention on since if we can detect an asteroid well in advance, we can predict the moment and point of impact exactly to within a minute or less, even decades in advance, and we can either evacuate the region, or indeed with enough warning, it is easy to deflect it too. Given that for just $50 million we could find 70% of the asteroids of diameter 45 meters in diameter or larger within six years - and that's to protect the entire world - it is well worth spending the sums involved. 

However, scientists often use hyperbole - this is a perfectly acceptable mode of expression, using vivid imagery that is exaggerated to the point of impossibility for emotional effect. They focus on the major asteroid impacts which we are pretty sure won't happen this century, in their enthusiasm to try to get the politicians and public to do something about it. Sometimes they even mention 100 km diameter asteroids which have never hit us or any planet inside of Mars for over three billion years. But we don't need to do that in my view. The downside of it is that as a result of this, together with disaster movies, many of the general public are seriously scared of an asteroid impact wiping out humanity.

Young children and those without a scientific background are especially impacted by this. It is very natural to do this, but I think a more measured, sober approach just stating exactly what the risks are and what they are not, is more likely to lead to action rather than a kind of paralysing fear. Especially once you realize that some become so scared of these stories they even become suicidal.

I'm author of a new book available on kindle and to read free online, which gives a sober assessment of possible "doomsdays" of all sorts, scientific, prophecies, pseudoscience etc. This is one of the chapters from the Scientific section (just added it, will update on kindle within a day or so).


The kindle book may be useful if you want it formatted as a book, which you can read on your kindle, and also on most major smartphones, tablets and computers, using the free kindle reading app.


I've made a new facebook group which you can join to discuss this and other doomsday stories that you find scary. also astronomers and scientists, do join if you want to help reassure scared people and help with the debunking.

Please feel free to post any story you find scary, however silly it may seem. Also for astronomers and scientists - when commenting please bear in mind that some here may have decided long ago that astronomy and maths are not for them and others may be young children - children as young as 10 can get scared of Nibiru. Please treat any questions with respect. Ideas that seem LOL silly to astronomers can be truly scary to those without that background.

Doomsday Debunked

Also you can check out my Debunking Doomsday blog which is where I first post articles like this.


Robert Walker's posts - on Quora

And on Science20

Robert Walker's posts on Science20


And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon


If you have any comments or questions do say. Also, if you notice anything that needs to be corrected in this article, however small, even a typo, be sure to say in the comments area, thanks!