It is much easier to do if you have a lot of warning. The one that made the dinosaurs extinct doubtless must have done many flybys of Earth first, and if they had telescopes and rockets they could have spotted it decades or centuries before it hit, and done something about it.
It is easy to deflect an asteroid, even a big one, if you spot it many years or decades in advance. One reason for that is because a small delta v makes much more difference if you can apply it long in advance of the impact.
Change the delta v by a tenth of a meter per second along the direction of travel (say) - just a few days before impact, and it's not going to make a big difference. But do it say a year before impact and that changes its position by 365*24*60*60*0.1 = 3,153.6 kilometers. Do that two years before impact and that changes its position by more than the radius of the Earth, enough to miss even if it was a dead center hit before. Just the same one off delta v. It wouldn't make for a thrilling movie, but it would be easier and more effective.
The other reason is that the asteroid is particularly sensitive to changes in delta v when it does a flyby of Earth. Make it so it passes Earth just a bit closer or further away on its last flyby before the impact (typically a few decades before) and you get a much larger change in position later on. There's a tiny "keyhole" perhaps of just a few hundred meters in diameter that it has to go through in order to impact next time around - and if you can deflect it enough to miss that keyhole, you have prevented the impact..
So, at the moment the main focus is on detection. And they have made tremendous progress at the large end of the meteorite size. It's thought that we have already found all the asteroids of size ten kilometers diameter or larger out to the outer edge of the asteroid belt. Mainly due to the activities of the PAN-STARRS telescope, which takes which takes a 1.4 gigapixel image of a three degrees span of the night sky several times a minute every clear night, and it is in a place where typically every single night is clear.
It's low magnification - but it has a very wide field of view and reasonable apperture, and its CCD cameras are very sensitive to low levels of light. That's exactly what you need for asteroid hunting. It can detect an asteroid of only 300 meters in diameter right out to the outer edge of the asteroid belt.
This shows how the detection of NEOS is going - notice the red curve of large ones is leveling off because we have found nearly all of them. 90% of the ones above 1 km and finding one of those every month, due to reach 99'% in the 2020s. And all the ones above 10 km.
As a result of its activities we know for sure there are no 10 km size asteroids in the population of NEOs able to hit Earth in the next century. So we would be bound to get a reasonably long warning time.
As a result we are now 99.9999% certain that we won't get a dinosaur era ending event this century. Most movie goers would probably put that at 50% :). But if you think about it, it's 66 million years since the last one, and they happen roughly every 100 million years - how likely is it that it would happen in this century when it happens on average once every million centuries? And then the discovery of all the 10 km NEOs makes it ten times less likely again.
Anyway as to how we could deflect one, if discovered.
Then there are many ideas. And both the ESA and NASA are planning asteroid deflection test missions in space. ESA plan to target one of the two asteroids in a binary asteroid as that will make it very easy to see the effect. That's just impact. They are mainly focusing on deflecting small asteroids since nearly all the big ones are found anyway.
There's not really much point trying to develop a way of deflecting a large asteroid right now. Because you get so much of an advantage from early detection, that any money you have is much better spent on that.
For instance if you had $450 million dollars, that would be enough to put a space telescope between here and Venus which would hugely speed up detection until you find many of the NEOs of 40 meters upwards,. many even of 20 meters upwards, would no longer be possible to be surprised by a meteorite of any size. It could do that within six and a half years of launch. The space telescope is already designed, developed by the private B612 foundation, and could be launched a couple of years from now if the funding was made available.
There are many other ways of deflecting the asteroids.
Here is a short video of professor Dave Hyland talking about the idea:
And article
Its 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
Then there's kinetic impact. In the planetary defense conference early this year (2015), delegates practiced a scenario with a hypothetical incoming 365 meter meteorite, how it would play out, with kinetic interceptor spacecraft.
The US-ESA Asteroid Impact and Defection Mission AIDA is a concept study at present, but if it goes ahead, will send two small spacecraft to an asteroid with a moon (many asteroids have moons). One of them will impact the moon, the other will monitor what is happening close up, and it will also be monitored from Earth. The idea is to get some experience with deflection and find out for sure how big an effect it is. That's where the idea of targeting a binary asteroid is so clever. Though the amount of the effect is tiny in this case, just a small impact should make an easily detectable difference in the motion of the satellite.
AIDA mission concept, artist's impression.
For details of AIDA, see "Asteroid deflection mission seeks smashing ideas".
(click to show on youtube)
Then there's the "ion beam shephard", you can also disintegrate it with a nuclear weapon, deflect a smaller asteroid to hit a larger one, disintegrate it with powerful infrared lasers, various other ideas.
By the way - a 10 km impact would make dinosaurs extinct. It would make many creatures extinct.
But we are not dinosaurs. Many creatures survived - turtles, mammals (underground), birds. With our technology we can emulate any or all of those capabilities.
At least some of us would survive in fireproof shelters, or flying to somewhere safe, or in boats, or submarines - if nothing else a submarine, far from the impact, able to stay under the sea for months, would surely survive (tsunamis are sea surface phenomena).
But our world also has many continents now unlike the dinosaur's single continent, and it's not possible that a single impact like their one could devastate the entire world so much that all humans go extinct right away.
And then there would be the years of nuclear winter type scenario, but especially as we'd be prepared, then probably large numbers could survive those also. It doesn't seem plausible to me at all that with modern technology humans would go extinct after a scenario like that.
And - there is no chance of really large impacts larger than that - the last of the really huge ones in the entire inner solar system happened over 3 billion years ago. Jupiter is very effective at shielding us from the very large ones, though it sometimes does that by breaking them up through tidal effects into the smaller ones so it's not so effective at shielding us from the 10 km or so ones.
NEOs have a typical lifetime of up to 20 million years. So almost all of them will either hit Earth or one of the other planets, sun, Jupiter or be ejected some time in the next 20 million years. And they are continually replenished.
So the threat is a very real one over those long timescales. but our technology is rapidly developing to the point where we will know where every single one is, and be able to deflect it away from Earth decades in advance of the impact.
Now that we have nearly completed the search for the larger asteroids - the search priority is turning towards the smaller ones. An asteroid of only 100 meters diameter would devastate an entire small country and kill many millions of people. And the chance of one such is much higher than for the larger ones - the smaller the asteroid the more likely it is.
Having said that, never in recorded history has even a 100 meter asteroid hit a city or populated area to our knowledge. They are much more common than the 1 km or 10 km asteroids, but still compared to the timescale recorded human history, they are very rare. But it could happen, and it will be a while before we have found all the 100 meter diameter NEOs.
Here is Brian May talking about what would happen to the UK, if a 100 meter diameter asteroid hit London.
It will be another decade or so before we have all the one kilometer ones also, which are large enough to have global effects and could seriously affect an entire continent. But they are getting less and less likely now that we've found 90% of the NEO population already. By now the risk is roughly equal between the large ones and the smaller ones because we have found nearly all the large ones and none of them are headed our way in the next century. By the 2020s then, except for the now exceedingly remote chance that we do find a really big one headed our way of course, the main risk will be the smaller ones. Also more distant larger ones that may get to us on longer timescales, perhaps reach us a few years after discovery.
That's why the B612 foundation telescope could make a huge difference right now, because it could help us find nearly all the medium to small ones right down to 20 meters in less than a decade. Especially, since it orbits close to Venus, it would be fast at spotting the hard to detect asteroids that can approach Earth from the direction of the sun, as the Russian Chelyabinsk asteroid did.
The UK is planning to build a new generation of Trident nuclear subs, only used to carry nuclear weapons to kill millions of civilians if they were ever used. For the $100 billion dollars of that project, they could fund the Sentinel space telescope to detect nearly all the smaller asteroids 200 times over. Similarly when one of the larger powers commissions a new destroyer, this costs many times the cost of a space telescope to pretty much eliminate any chance of even small rocks sneaking up on us undiscovered. Surely a shift of our priorities is needed here?
To find out more:
You can get it here:
Giant Asteroid Is Headed Your Way? : How We Can Detect and Deflect Them (Amazon)
(102 pages - and you can read it on any device using the kindle e-reader, or read it online in web page format)
It is also available to read online for free here: Giant Asteroid Headed Your Way? - How We Can Detect And Deflect Them
It is easy to deflect an asteroid, even a big one, if you spot it many years or decades in advance. One reason for that is because a small delta v makes much more difference if you can apply it long in advance of the impact.
Change the delta v by a tenth of a meter per second along the direction of travel (say) - just a few days before impact, and it's not going to make a big difference. But do it say a year before impact and that changes its position by 365*24*60*60*0.1 = 3,153.6 kilometers. Do that two years before impact and that changes its position by more than the radius of the Earth, enough to miss even if it was a dead center hit before. Just the same one off delta v. It wouldn't make for a thrilling movie, but it would be easier and more effective.
The other reason is that the asteroid is particularly sensitive to changes in delta v when it does a flyby of Earth. Make it so it passes Earth just a bit closer or further away on its last flyby before the impact (typically a few decades before) and you get a much larger change in position later on. There's a tiny "keyhole" perhaps of just a few hundred meters in diameter that it has to go through in order to impact next time around - and if you can deflect it enough to miss that keyhole, you have prevented the impact..
So, at the moment the main focus is on detection. And they have made tremendous progress at the large end of the meteorite size. It's thought that we have already found all the asteroids of size ten kilometers diameter or larger out to the outer edge of the asteroid belt. Mainly due to the activities of the PAN-STARRS telescope, which takes which takes a 1.4 gigapixel image of a three degrees span of the night sky several times a minute every clear night, and it is in a place where typically every single night is clear.
It's low magnification - but it has a very wide field of view and reasonable apperture, and its CCD cameras are very sensitive to low levels of light. That's exactly what you need for asteroid hunting. It can detect an asteroid of only 300 meters in diameter right out to the outer edge of the asteroid belt.
This shows how the detection of NEOS is going - notice the red curve of large ones is leveling off because we have found nearly all of them. 90% of the ones above 1 km and finding one of those every month, due to reach 99'% in the 2020s. And all the ones above 10 km.
As a result of its activities we know for sure there are no 10 km size asteroids in the population of NEOs able to hit Earth in the next century. So we would be bound to get a reasonably long warning time.
As a result we are now 99.9999% certain that we won't get a dinosaur era ending event this century. Most movie goers would probably put that at 50% :). But if you think about it, it's 66 million years since the last one, and they happen roughly every 100 million years - how likely is it that it would happen in this century when it happens on average once every million centuries? And then the discovery of all the 10 km NEOs makes it ten times less likely again.
Anyway as to how we could deflect one, if discovered.
Then there are many ideas. And both the ESA and NASA are planning asteroid deflection test missions in space. ESA plan to target one of the two asteroids in a binary asteroid as that will make it very easy to see the effect. That's just impact. They are mainly focusing on deflecting small asteroids since nearly all the big ones are found anyway.
There's not really much point trying to develop a way of deflecting a large asteroid right now. Because you get so much of an advantage from early detection, that any money you have is much better spent on that.
For instance if you had $450 million dollars, that would be enough to put a space telescope between here and Venus which would hugely speed up detection until you find many of the NEOs of 40 meters upwards,. many even of 20 meters upwards, would no longer be possible to be surprised by a meteorite of any size. It could do that within six and a half years of launch. The space telescope is already designed, developed by the private B612 foundation, and could be launched a couple of years from now if the funding was made available.
There are many other ways of deflecting the asteroids.
DEFLECTING ASTEROIDS
White paint
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)
Its 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
Then there's kinetic impact. In the planetary defense conference early this year (2015), delegates practiced a scenario with a hypothetical incoming 365 meter meteorite, how it would play out, with kinetic interceptor spacecraft.
The US-ESA Asteroid Impact and Defection Mission AIDA is a concept study at present, but if it goes ahead, will send two small spacecraft to an asteroid with a moon (many asteroids have moons). One of them will impact the moon, the other will monitor what is happening close up, and it will also be monitored from Earth. The idea is to get some experience with deflection and find out for sure how big an effect it is. That's where the idea of targeting a binary asteroid is so clever. Though the amount of the effect is tiny in this case, just a small impact should make an easily detectable difference in the motion of the satellite.
AIDA mission concept, artist's impression.
For details of AIDA, see "Asteroid deflection mission seeks smashing ideas".
Gravity tractor
Another approach is the gravity tractor. Basically you send quite a small spacecraft to sit next to the asteroid you want to move. Of course gravity pulls them together. But it thrusts against that gravity pull, so keeping them apart. You have to be careful that its exhaust doesn't impact on the asteroid you want to move. The gentle thrust of its gravity pull then moves the asteroid. With no need for it to land or make any contact with it.(click to show on youtube)
Then there's the "ion beam shephard", you can also disintegrate it with a nuclear weapon, deflect a smaller asteroid to hit a larger one, disintegrate it with powerful infrared lasers, various other ideas.
NOT AN EXTINCTION EVENT FOR US ANYWAY
By the way - a 10 km impact would make dinosaurs extinct. It would make many creatures extinct.
But we are not dinosaurs. Many creatures survived - turtles, mammals (underground), birds. With our technology we can emulate any or all of those capabilities.
At least some of us would survive in fireproof shelters, or flying to somewhere safe, or in boats, or submarines - if nothing else a submarine, far from the impact, able to stay under the sea for months, would surely survive (tsunamis are sea surface phenomena).
But our world also has many continents now unlike the dinosaur's single continent, and it's not possible that a single impact like their one could devastate the entire world so much that all humans go extinct right away.
And then there would be the years of nuclear winter type scenario, but especially as we'd be prepared, then probably large numbers could survive those also. It doesn't seem plausible to me at all that with modern technology humans would go extinct after a scenario like that.
And - there is no chance of really large impacts larger than that - the last of the really huge ones in the entire inner solar system happened over 3 billion years ago. Jupiter is very effective at shielding us from the very large ones, though it sometimes does that by breaking them up through tidal effects into the smaller ones so it's not so effective at shielding us from the 10 km or so ones.
NEOs have a typical lifetime of up to 20 million years. So almost all of them will either hit Earth or one of the other planets, sun, Jupiter or be ejected some time in the next 20 million years. And they are continually replenished.
So the threat is a very real one over those long timescales. but our technology is rapidly developing to the point where we will know where every single one is, and be able to deflect it away from Earth decades in advance of the impact.
RISKS OF SMALLER ASTEROIDS
Now that we have nearly completed the search for the larger asteroids - the search priority is turning towards the smaller ones. An asteroid of only 100 meters diameter would devastate an entire small country and kill many millions of people. And the chance of one such is much higher than for the larger ones - the smaller the asteroid the more likely it is.
Having said that, never in recorded history has even a 100 meter asteroid hit a city or populated area to our knowledge. They are much more common than the 1 km or 10 km asteroids, but still compared to the timescale recorded human history, they are very rare. But it could happen, and it will be a while before we have found all the 100 meter diameter NEOs.
Here is Brian May talking about what would happen to the UK, if a 100 meter diameter asteroid hit London.
It will be another decade or so before we have all the one kilometer ones also, which are large enough to have global effects and could seriously affect an entire continent. But they are getting less and less likely now that we've found 90% of the NEO population already. By now the risk is roughly equal between the large ones and the smaller ones because we have found nearly all the large ones and none of them are headed our way in the next century. By the 2020s then, except for the now exceedingly remote chance that we do find a really big one headed our way of course, the main risk will be the smaller ones. Also more distant larger ones that may get to us on longer timescales, perhaps reach us a few years after discovery.
That's why the B612 foundation telescope could make a huge difference right now, because it could help us find nearly all the medium to small ones right down to 20 meters in less than a decade. Especially, since it orbits close to Venus, it would be fast at spotting the hard to detect asteroids that can approach Earth from the direction of the sun, as the Russian Chelyabinsk asteroid did.
The UK is planning to build a new generation of Trident nuclear subs, only used to carry nuclear weapons to kill millions of civilians if they were ever used. For the $100 billion dollars of that project, they could fund the Sentinel space telescope to detect nearly all the smaller asteroids 200 times over. Similarly when one of the larger powers commissions a new destroyer, this costs many times the cost of a space telescope to pretty much eliminate any chance of even small rocks sneaking up on us undiscovered. Surely a shift of our priorities is needed here?
To find out more:
KINDLE EBOOK
You can get it here:
Giant Asteroid Is Headed Your Way? : How We Can Detect and Deflect Them (Amazon)
(102 pages - and you can read it on any device using the kindle e-reader, or read it online in web page format)
It is also available to read online for free here: Giant Asteroid Headed Your Way? - How We Can Detect And Deflect Them
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
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