The important thing to realize here is, first, if you imagine an asteroid as big as this image often used in stories about it, or the movies which use similarly large asteroids
it simply can't happen now.
That's actually an artist's impression of a planetoid hitting the early Earth by Don Davis. Such an asteroid would indeed be almost impossible to deflect unless you knew of it a long time in advance.
But if you look at the cratering record of the inner solar system, then there have been no impacts that large on Earth (as far back as we can look) the Moon, Mercury, Mars and its moons, or what history we can detect of Venus (which has no continental drift but massive outpourings of lava every few hundred million years of its history erasing craters).
The last impact that large on Earth was surely over three billion years ago and probably over four billion years ago.
There were impacts that large back then, as we can see for instance from the larger craters on the Moon.
Objects that big must come into the inner solar system from time to time. But Jupiter, it seems is an effective guard. Of course Jupiter is nowhere big enough to get in the way of them physically. But it has a vast gravitational influence on the inner solar system.
This is probably how it works: on its first encounter of the inner solar system, our huge hundred kilometer diameter or larger asteroid is likely to be inclined to the plane of the ecliptic - at least a bit. So it needs flybys of Jupiter to flatten its orbit into the ecliptic to hit the terrestrial planets, which are like grains of pepper in size compared to the sun (and these large impactors even tinier). To hit Earth right away, it would need to be in such a similar orbit that it is within a planet's diameter of the plane of Earth's orbit at Earth's distance from the sun, extremely unlikely to happen.
As it does these repeated flybys of Earth, it passes close enough to Jupiter for it to break it apart through tidal interactions, or it hits Jupiter, or is deflected to hit the sun after several flybys, or out of the solar system.
That's the usual explanation for the cratering record. Smaller fragments of order ten kilometers diameter remain and can hit us.
In any case something that big would be visible way beyond Jupiter in the outer solar system. Nowadays we detect objects that big out beyond Pluto. So we'd be likely to have a decade or so of warning before it does it comes in, then several flybys of Jupiter, with decades between each one, before it is likely to send fragments in our direction. This is a process that could theoretically lead to times of increased risk of asteroid impact of the one to ten kilometer range but we'd see it coming a long time in advance. We aren't in such an era at present.
So the main hazard in terms of big impactors comes from the ten kilometer scale asteroids like the one that made the dinosaurs extinct.
This is more the size to expect, about the size of New York City
Can hardly call them planet killing as many creatures survived including turtles, birds, small mammals etc. We also would survive, at least some of us, with our technology.
But those also are very unlikely. Many movie goers would suggest a risk of 50%. But if you think about it, never in the entire history of the human race, written history anyway, has a populated area been hit by a meteorite large enough to kill lots of people. We haven't even got historical accounts of an impact by the far more numerous 100 meter asteroids. So how likely is it that we are going to be hit by a gigantic one or ten kilometer asteroid this century?
The answer may surprise you. It used to be a one in a million chance (on average these impacts happen every hundred million years so a one in a million chance per century).
However recent surveys have proved that there are no ten kilometer scale asteroids in the entire Near Earth Object (NEO) population or the asteroid belt right out to Jupiter with a trajectory that will let them hit Earth in the next century.
So that reduces the chance to one in ten million. More importantly it also means the warning time is going to be several years at least.
There are some undetected one kilometer diameter asteroids. About 90% of those are now found. We are finding them at a rate of one per month and expect to find 99% of them by the 2020s. After that, the chance of a one kilometer asteroid will also be very low indeed, and we would expect a reasonable warning period for them also.
The one kilometer and ten kilometer asteroids can be deflected, given enough time, at least in principle. We know how to do this, given enough funding.
The reason we are not spending our money for asteroid defense on building asteroid deflection spacecraft for these asteroids is because
If we had $450 million we could launch the Sentinel space telescope - designed by the B612 foundation but not yet built. It could launch in 2017, and fly near to Venus looking outwards, with sufficient funding and would detect nearly all asteroids of 40 meters and diameter within 6.5 years. It would also provide early warning of the hard to detect asteroids like the Russian meteorite that approach from the direction of the sun - but would soon map out most of them so we'd know about them decades in advance.
If we had the funding to build an asteroid deflection mission, it would make much more sense to put that funding into Sentinel and various other detection and early warning systems.
If we had enough for Sentinel, and some change in addition, it makes sense to start work on building asteroid deflection spacecraft also.
It's not a lot of funding compared with the sums spent on nuclear weapons, wars, and bailing out bankrupt banks. The UK government is planning to renew Trident with an estimated cost of £31 billion or about $47 billion. Including future operating costs, that is an estimated £167 billion or about $252 billion Exclusive - Trident programme to cost 167 billion pounds, far more than expected.
This is a weapon that can only ever be used to kill millions of innocent civilians.
For that we could fund the Sentinel telescope 500 times over with some change. We could not only build Sentinel but also fund missions to deflect the asteroids it finds headed for Earth with that figure, and probably also detect the ten kilometer asteroids right out to Pluto or some such, goodness knows what you could do with that much funding for asteroid detection and deflection.
Even the $15 billion contingency figure for Trident could fund Sentinel 30 times over.
I'm not sure we have our priorities right here.
The price is low enough that a public minded billionaire could fund the Sentinel mission in one go, if they got interested in the project. Or for that matter, the likes of a public spirited company like Google (which has shown interest in space with its Lunar X prizes etc).
It could fly by 2017. We could know the position of just about every asteroid of 40 meters or larger from Venus orbit outwards by 2025.
As for asteroid deflection, building spacecraft to do it is expensive. But smaller scale tests are affordable, so also is theoretical work. There are many published papers on ways to do it in theory.
And actually both NASA and ESA do have asteroid deflection tests planned. These are early stage small scale tests as they don't have lots of funding for this. But they will test the effectiveness of the kinetic impact approach, one of several ways of deflecting asteroids that have been developed. The ESA one, for instance, will impact one of two asteroids in a binary system (many asteroids have small asteroid moons) and then see the effect on its period of orbit around the other asteroid, a very sensitive way to observe the change in delta v.
If we detect an asteroid headed our way with a decade or so of warning, we just need a small fraction of a meter per second delta v to deflect it. If it does flybys of Earth in between now and the impact, as is very likely, then we need even less. In some cases it might be sufficient to "paint" the surface of an asteroid white to deflect it using the Yarkovsky effect.
I think astronomers have their priorities right and are doing everything they can with current funding. What they could definitely do with though is an increase in funding and if the B612 asteroid detection telescope was funded, that by itself in one go would take us in a leap forward. Then either it finds an asteroid headed our way or it doesn't. But it would surely at least find some 40 meter asteroids or 20 meter ones headed our way as they are very common.
Then we can practice deflection of those - or we can practice early warning. For asteroids that small, then they may hit in remote places, or if they hit the sea are not large enough for a tsunami. So we could just observe them land and evacuate the impact zone if necessary unless they are headed for a city (very unlikely). Or deflect them relatively easily given enough advance warning.
Since the smaller ones are so much more numerous than the larger ones, I would expect the first successful deflection will be of an asteroid of size 20 meters upwards, like the one that flew over Russia, the Chelyabinsk meteorite. Perhaps an outside chance of a 100 meter asteroid. The one kilometer or larger ones are so rare, that though you can't rule them out, typically you'd need to wait many centuries before you get such a rare impact on Earth.
However a 100 meter impact, much more likely, would be devastating for a major city and would have serious effects over much of an entire small country like the UK.
Though there are no records of any such hitting a populated area in recorded history, we are now spread over more of the globe and with more large cities than ever before. Though still very unlikely to happen this century, it could and given that millions of people could be killed by one of these, it should be a high priority. Especially as it is perhaps the only natural disaster we can predict to the minute with early detection, and actually prevent also.
Many astronomers and astronauts have signed a petition calling for spending on asteroid detection and deflection to be increased a hundred times over current levels.
For details, see Giant Asteroid Headed Your Way? - How We Can Detect And Deflect Them
Also available as a kindle booklet:
Giant Asteroid Is Headed Your Way? : How We Can Detect and Deflect Them (Amazon)
(102 pages)
(see also the Popular Mechanics article on the topic: The Asteroid Hunters)
it simply can't happen now.
That's actually an artist's impression of a planetoid hitting the early Earth by Don Davis. Such an asteroid would indeed be almost impossible to deflect unless you knew of it a long time in advance.
But if you look at the cratering record of the inner solar system, then there have been no impacts that large on Earth (as far back as we can look) the Moon, Mercury, Mars and its moons, or what history we can detect of Venus (which has no continental drift but massive outpourings of lava every few hundred million years of its history erasing craters).
The last impact that large on Earth was surely over three billion years ago and probably over four billion years ago.
There were impacts that large back then, as we can see for instance from the larger craters on the Moon.
Objects that big must come into the inner solar system from time to time. But Jupiter, it seems is an effective guard. Of course Jupiter is nowhere big enough to get in the way of them physically. But it has a vast gravitational influence on the inner solar system.
This is probably how it works: on its first encounter of the inner solar system, our huge hundred kilometer diameter or larger asteroid is likely to be inclined to the plane of the ecliptic - at least a bit. So it needs flybys of Jupiter to flatten its orbit into the ecliptic to hit the terrestrial planets, which are like grains of pepper in size compared to the sun (and these large impactors even tinier). To hit Earth right away, it would need to be in such a similar orbit that it is within a planet's diameter of the plane of Earth's orbit at Earth's distance from the sun, extremely unlikely to happen.
As it does these repeated flybys of Earth, it passes close enough to Jupiter for it to break it apart through tidal interactions, or it hits Jupiter, or is deflected to hit the sun after several flybys, or out of the solar system.
That's the usual explanation for the cratering record. Smaller fragments of order ten kilometers diameter remain and can hit us.
In any case something that big would be visible way beyond Jupiter in the outer solar system. Nowadays we detect objects that big out beyond Pluto. So we'd be likely to have a decade or so of warning before it does it comes in, then several flybys of Jupiter, with decades between each one, before it is likely to send fragments in our direction. This is a process that could theoretically lead to times of increased risk of asteroid impact of the one to ten kilometer range but we'd see it coming a long time in advance. We aren't in such an era at present.
So the main hazard in terms of big impactors comes from the ten kilometer scale asteroids like the one that made the dinosaurs extinct.
This is more the size to expect, about the size of New York City
Can hardly call them planet killing as many creatures survived including turtles, birds, small mammals etc. We also would survive, at least some of us, with our technology.
But those also are very unlikely. Many movie goers would suggest a risk of 50%. But if you think about it, never in the entire history of the human race, written history anyway, has a populated area been hit by a meteorite large enough to kill lots of people. We haven't even got historical accounts of an impact by the far more numerous 100 meter asteroids. So how likely is it that we are going to be hit by a gigantic one or ten kilometer asteroid this century?
The answer may surprise you. It used to be a one in a million chance (on average these impacts happen every hundred million years so a one in a million chance per century).
However recent surveys have proved that there are no ten kilometer scale asteroids in the entire Near Earth Object (NEO) population or the asteroid belt right out to Jupiter with a trajectory that will let them hit Earth in the next century.
So that reduces the chance to one in ten million. More importantly it also means the warning time is going to be several years at least.
There are some undetected one kilometer diameter asteroids. About 90% of those are now found. We are finding them at a rate of one per month and expect to find 99% of them by the 2020s. After that, the chance of a one kilometer asteroid will also be very low indeed, and we would expect a reasonable warning period for them also.
As you can see the detection rate of the smaller one kilometer or larger asteroid has slowed down. We are currently finding one per month. The searches are much more sensitive, and the reason for that is that we have found nearly all of them already. We expect to find 99% of them by the 2020s.
That would leave the smaller population of Jupiter crossing asteroids still to find. We would have found those also if they are already closer to Earth than Jupiter, so that means that we have at least several years warning on the very low one in ten million probability that one of those is headed our way this century. Chances are that it would probably do several flybys of Earth before hitting as well. So the probability of finding one on a direct hit course to Earth with only a few years notice is even lower.
The one kilometer and ten kilometer asteroids can be deflected, given enough time, at least in principle. We know how to do this, given enough funding.
The reason we are not spending our money for asteroid defense on building asteroid deflection spacecraft for these asteroids is because
- There is no asteroid headed our way to our knowledge large enough to warrant an immediate crash program. If we find one due to hit Earth this century I'm sure there would be an immediate high priority program - the funds would be found somehow.
- With the larger ones nearly all detected, the priority has turned to the smaller ones, especially those of order 100 meters diameter or so. The risk per person is now equally balanced between the large and small asteroids and by the 2020s will be very much weighted towards the smaller ones. Expected number of deaths per year, averaged out, currently run at about 100 people per year for both (it was of order 1000 per year for the large ones until we did those searches and found there is none headed our way this century inside of Jupiter)
- What money we do have is much more effectively spent on asteroid detection.
If we had $450 million we could launch the Sentinel space telescope - designed by the B612 foundation but not yet built. It could launch in 2017, and fly near to Venus looking outwards, with sufficient funding and would detect nearly all asteroids of 40 meters and diameter within 6.5 years. It would also provide early warning of the hard to detect asteroids like the Russian meteorite that approach from the direction of the sun - but would soon map out most of them so we'd know about them decades in advance.
If we had the funding to build an asteroid deflection mission, it would make much more sense to put that funding into Sentinel and various other detection and early warning systems.
If we had enough for Sentinel, and some change in addition, it makes sense to start work on building asteroid deflection spacecraft also.
It's not a lot of funding compared with the sums spent on nuclear weapons, wars, and bailing out bankrupt banks. The UK government is planning to renew Trident with an estimated cost of £31 billion or about $47 billion. Including future operating costs, that is an estimated £167 billion or about $252 billion Exclusive - Trident programme to cost 167 billion pounds, far more than expected.
This is a weapon that can only ever be used to kill millions of innocent civilians.
For that we could fund the Sentinel telescope 500 times over with some change. We could not only build Sentinel but also fund missions to deflect the asteroids it finds headed for Earth with that figure, and probably also detect the ten kilometer asteroids right out to Pluto or some such, goodness knows what you could do with that much funding for asteroid detection and deflection.
Even the $15 billion contingency figure for Trident could fund Sentinel 30 times over.
I'm not sure we have our priorities right here.
The price is low enough that a public minded billionaire could fund the Sentinel mission in one go, if they got interested in the project. Or for that matter, the likes of a public spirited company like Google (which has shown interest in space with its Lunar X prizes etc).
It could fly by 2017. We could know the position of just about every asteroid of 40 meters or larger from Venus orbit outwards by 2025.
As for asteroid deflection, building spacecraft to do it is expensive. But smaller scale tests are affordable, so also is theoretical work. There are many published papers on ways to do it in theory.
And actually both NASA and ESA do have asteroid deflection tests planned. These are early stage small scale tests as they don't have lots of funding for this. But they will test the effectiveness of the kinetic impact approach, one of several ways of deflecting asteroids that have been developed. The ESA one, for instance, will impact one of two asteroids in a binary system (many asteroids have small asteroid moons) and then see the effect on its period of orbit around the other asteroid, a very sensitive way to observe the change in delta v.
If we detect an asteroid headed our way with a decade or so of warning, we just need a small fraction of a meter per second delta v to deflect it. If it does flybys of Earth in between now and the impact, as is very likely, then we need even less. In some cases it might be sufficient to "paint" the surface of an asteroid white to deflect it using the Yarkovsky effect.
I think astronomers have their priorities right and are doing everything they can with current funding. What they could definitely do with though is an increase in funding and if the B612 asteroid detection telescope was funded, that by itself in one go would take us in a leap forward. Then either it finds an asteroid headed our way or it doesn't. But it would surely at least find some 40 meter asteroids or 20 meter ones headed our way as they are very common.
Then we can practice deflection of those - or we can practice early warning. For asteroids that small, then they may hit in remote places, or if they hit the sea are not large enough for a tsunami. So we could just observe them land and evacuate the impact zone if necessary unless they are headed for a city (very unlikely). Or deflect them relatively easily given enough advance warning.
Since the smaller ones are so much more numerous than the larger ones, I would expect the first successful deflection will be of an asteroid of size 20 meters upwards, like the one that flew over Russia, the Chelyabinsk meteorite. Perhaps an outside chance of a 100 meter asteroid. The one kilometer or larger ones are so rare, that though you can't rule them out, typically you'd need to wait many centuries before you get such a rare impact on Earth.
However a 100 meter impact, much more likely, would be devastating for a major city and would have serious effects over much of an entire small country like the UK.
Though there are no records of any such hitting a populated area in recorded history, we are now spread over more of the globe and with more large cities than ever before. Though still very unlikely to happen this century, it could and given that millions of people could be killed by one of these, it should be a high priority. Especially as it is perhaps the only natural disaster we can predict to the minute with early detection, and actually prevent also.
Many astronomers and astronauts have signed a petition calling for spending on asteroid detection and deflection to be increased a hundred times over current levels.
For details, see Giant Asteroid Headed Your Way? - How We Can Detect And Deflect Them
Also available as a kindle booklet:
(102 pages)
(see also the Popular Mechanics article on the topic: The Asteroid Hunters)
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
4.8m answer views110.3k this month
Top Writer2017, 2016, and 2015
Published WriterHuffPost, Slate, and 4 moreHuffPost, Slate, Forbes, Newsweek, Business Insider, and Science 2.0