Apophis to impact earth in 2036?

[joema]

Could a laser, in theory, impart enough power to an object the size of an asteroid to change its course?...

No, the military lasers fire for only a few seconds at most. They just can't deliver enough total energy to make a difference.

One of the most powerful military laser programs is the 1 megawatt Boeing Airborne Laser. It supposedly will be able to fire about 20 rounds of (maybe) several seconds each. If we take 3 sec/round as typical, that's 60 sec total firing time. Total energy emitted would be about 60 million joules, but you'd lose energy from atmospheric absorption, even if adaptive optics maintained focus.

Due to beam divergence, it would also only be useful at very close ranges. The beam divergence of a 1.35 micron, 1.5 meter dia COIL laser is about 1.15 microradians. At distances of more than a few thousand km, the beam would be much wider than the asteroid.

Even if 100% of energy was delivered, 60 megajoules is roughly the energy of 1/2 gallon of gasoline. It's just not enough, when the object weighs 2.1E10 kg.

You can hypothesize much larger ground-based lasers, but in general, they aren't an efficient way to deliver energy in quantities needed for asteroid deflection.

 

[MadScientist 1000]

http://www.lpl.arizona.edu/impacteffects/
http://en.wikipedia.org/wiki/99942_Apophis

The site is a calculator for the effects of an asteroid hitting us. Just find data on Apophis and plug it in.

Update:

I did a bit of the work here, and found some data. Credit goes to the site and wikipedia.

Impact Effects
Robert Marcus, H. Jay Melosh, and Gareth Collins

Please note: the results below are estimates based on current (limited) understanding of the impact process and come with large uncertainties; they should be used with caution, particularly in the case of peculiar input parameters. All values are given to three significant figures but this does not reflect the precision of the estimate. For more information about the uncertainty associated with our calculations and a full discussion of this program, please refer to this article

Your Inputs:
Distance from Impact: 80.50 km = 49.99 miles
Projectile Diameter: 250.00 m = 820.00 ft = 0.16 miles
Projectile Density: 1500 kg/m3
Impact Velocity: 30.73 km/s = 19.08 miles/s
Impact Angle: 45 degrees
Target Density: 2750 kg/m3
Target Type: Crystalline Rock

Energy:
Energy before atmospheric entry: 5.79 x 1018 Joules = 1.38 x 10^3 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 2.9 x 104years

Atmospheric Entry:
The projectile begins to breakup at an altitude of 82000 meters = 269000 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 23 km/s = 14.3 miles/s
The impact energy is 3.25 x 1018 Joules = 7.77 x 10^2MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 1.21 km by 0.859 km

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.

Crater Dimensions:
What does this mean? Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 3.15 km = 1.96 miles
Transient Crater Depth: 1.12 km = 0.692 miles

Final Crater Diameter: 3.68 km = 2.29 miles
Final Crater Depth: 0.438 km = 0.272 miles

The crater formed is a complex crater.
The volume of the target melted or vaporized is 0.0205 km^3 = 0.00491 miles3
Roughly half the melt remains in the crater

Thermal Radiation:
What does this mean? Time for maximum radiation: 0.129 seconds after impact

Visible fireball radius: 2.46 km = 1.52 miles
The fireball appears 6.93 times larger than the sun
Thermal Exposure: 1.88 x 105 Joules/m2
Duration of Irradiation: 38.5 seconds
Radiant flux (relative to the sun): 4.87 Seismic Effects:
What does this mean? The major seismic shaking will arrive at approximately 16.1 seconds.
Richter Scale Magnitude: 6.5
Mercalli Scale Intensity at a distance of 80.5 km:

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop. Ejecta:
What does this mean? The ejecta will arrive approximately 129 seconds after the impact.
At your position the ejecta arrives in scattered fragments
Average Ejecta Thickness: 1.69 mm = 0.0666 inches
Mean Fragment Diameter: 4.01 cm = 1.58 inches Air Blast:
What does this mean? The air blast will arrive at approximately 244 seconds.
Peak Overpressure: 10600 Pa = 0.106 bars = 1.51 psi
Max wind velocity: 24 m/s = 53.7 mph
Sound Intensity: 81 dB (Loud as heavy traffic)
Damage Description: Glass windows will shatter.
Tell me more...

Click here for a pdf document that details the observations, assumptions, and equations upon which this program is based. It describes our approach to quantifying the important impact processes that might affect the people, buildings, and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions. The processes included are: atmospheric entry, impact crater formation, fireball expansion and thermal radiation, ejecta deposition, seismic shaking, and the propagation of the atmospheric blast wave.

Earth Impact Effects Program Copyright 2004, Robert Marcus, H.J. Melosh, and G.S. Collins
These results come with ABSOLUTELY NO WARRANTY

 

[bassplayer142]

I just started reading this thread and wow is all I can say. Why couldn't we send a ton of nukes at it when it is really far away. Even if it exploded into a few pieces of it will most likely not be headed to Earth after that.

 

[joema]

...Just find data on Apophis and plug it in...

Based on this NASA web site:http://neo.jpl.nasa.gov/risk/a99942.html, the impact velocity would be about 12.59 km/s. Since kinetic energy increases with square of velocity, this would reduce the energy to roughly 400 megatons.

 

[DaveC426913]

I did a bit of the work here, and found some data. Credit goes to the site and wikipedia.

Thought I'd separate the wheat from the chaff:

An asteroid 250m in diameter, traveling at 30km/s enters the atmosphere at a 45 degree angle. It begins fragmenting at 75km altitude creating an impact area roughly 1 km in diameter. The pieces strike at about 23km/s. In 1/8 second a fireball is formed 2.5km in radius


80km away:
0s: fireball appears, 7 times larger than the sun.
16s: quake arrives of Mag 6.5 (shakes dishes, topples objects, sensation like a truck has hit building)
38s: fireball fades
2m10s: scattered ejecta arrive (1 inch fragments)
6m: air blast (75km/h, sound as loud as heavy traffic, shatters windows)

 

[eaboujaoudeh]

that doesn't scare me..let him come

 

[MadScientist 1000]

that doesn't scare me..let him come

I'd hate for it to land within 2 km of me.

Thought I'd separate the wheat from the chaff:

An asteroid 250m in diameter, traveling at 30km/s enters the atmosphere at a 45 degree angle. It begins fragmenting at 75km altitude creating an impact area roughly 1 km in diameter. The pieces strike at about 23km/s. In 1/8 second a fireball is formed 2.5km in radius


80km away:
0s: fireball appears, 7 times larger than the sun.
16s: quake arrives of Mag 6.5 (shakes dishes, topples objects, sensation like a truck has hit building)
38s: fireball fades
2m10s: scattered ejecta arrive (1 inch fragments)
6m: air blast (75km/h, sound as loud as heavy traffic, shatters windows)

Thanks for doing the work for me

Based on this NASA web site:http://neo.jpl.nasa.gov/risk/a99942.html, the impact velocity would be about 12.59 km/s. Since kinetic energy increases with square of velocity, this would reduce the energy to roughly 400 megatons.

That is 8 times the Tsar Bomba... I don't think I'm scared. Yet. I took 30 km/s for the speed from Wikipedia. I'll go back and put some more case scenarios on here.

I just started reading this thread and wow is all I can say. Why couldn't we send a ton of nukes at it when it is really far away. Even if it exploded into a few pieces of it will most likely not be headed to Earth after that.

A lot of the others have asked the same question, and here is the reason why:

If the whole asteroid landed, it would impact one city, and make a really super large crater. But if it broke up, it would impact MULTIPLE cities, and make several smaller craters, but more dead people. Like someone on this thread said earlier, think about the fragments of the asteroid being like a shotgun spread, and the single asteroid being a rifle bullet.

If you nuke it close it is going to do tremendous damage, and the same thing applies to nuking it afar (3 moon to Earth units from earth), but if you do nuke it on the furthest point of its orbit away from earth, you can hopefully avert disaster, but that is unlikely to happen since you will need a fairly large bomb (50 mT) and a large rocket to lift it into space.

If you just let it hit, it will just make a big crater, and less people will die.

 

[tony873004]

I took 30 km/s for the speed from Wikipedia.

That's its orbital velocity, not its Earth impact velocity. Earth also has an orbital velocity of about 30 km/s. So like 2 cars driving down the freeway at 60 km/hr, if one rear-ends the other, the impact velocity is not 60 km/hr, but something much slower.

It must be at least ~11 km/s as this is Earth escape velocity, but probably wouldn't be much greater than this. The NASA website that joema links to probably has it right.

 

[MadScientist 1000]

Dave and Tony, I used your advice, and inserted 17 km/sec:

Impact Effects
Robert Marcus, H. Jay Melosh, and Gareth Collins

Please note: the results below are estimates based on current (limited) understanding of the impact process and come with large uncertainties; they should be used with caution, particularly in the case of peculiar input parameters. All values are given to three significant figures but this does not reflect the precision of the estimate. For more information about the uncertainty associated with our calculations and a full discussion of this program, please refer to this article

Your Inputs:
Distance from Impact: 10.00 km = 6.21 miles
Projectile Diameter: 250.00 m = 820.00 ft = 0.16 miles
Projectile Density: 3000 kg/m3
Impact Velocity: 17.00 km/s = 10.56 miles/s
Impact Angle: 45 degrees
Target Density: 2750 kg/m3
Target Type: Crystalline Rock

Energy:
Energy before atmospheric entry: 3.55 x 1018 Joules = 8.47 x 10E2 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 2.0 x 104years

Atmospheric Entry:
The projectile begins to breakup at an altitude of 54000 meters = 177000 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 15.7 km/s = 9.76 miles/s
The impact energy is 3.03 x 1018 Joules = 7.24 x 10E2MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 0.873 km by 0.617 km

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.

Crater Dimensions:
What does this mean? Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 3.36 km = 2.08 miles
Transient Crater Depth: 1.19 km = 0.737 miles

Final Crater Diameter: 3.95 km = 2.45 miles
Final Crater Depth: 0.448 km = 0.278 miles

The crater formed is a complex crater.
The volume of the target melted or vaporized is 0.0191 km3 = 0.00457 miles3
Roughly half the melt remains in the crater , where its average thickness is 2.15 meters = 7.06 feet

Thermal Radiation:
What does this mean? Time for maximum radiation: 0.184 seconds after impact

Visible fireball radius: 2.89 km = 1.79 miles
The fireball appears 65.6 times larger than the sun
Thermal Exposure: 1.44 x 107 Joules/m2
Duration of Irradiation: 37.6 seconds
Radiant flux (relative to the sun): 383

Effects of Thermal Radiation: Clothing ignites

Much of the body suffers third degree burns

Newspaper ignites

Plywood flames

Deciduous trees ignite

Grass ignites Seismic Effects:
What does this mean? The major seismic shaking will arrive at approximately 2 seconds.
Richter Scale Magnitude: 6.5
Mercalli Scale Intensity at a distance of 10 km:

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Ejecta:
What does this mean? The ejecta will arrive approximately 45.2 seconds after the impact.
Average Ejecta Thickness: 1.13 m = 3.72 ft
Mean Fragment Diameter: 10.8 m = 35.6 ft Air Blast:
What does this mean? The air blast will arrive at approximately 30.3 seconds.
Peak Overpressure: 557000 Pa = 5.57 bars = 79.1 psi
Max wind velocity: 546 m/s = 1220 mph
Sound Intensity: 115 dB (May cause ear pain)
Damage Description: Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

Highway truss bridges will collapse.

Highway girder bridges will collapse.

Glass windows will shatter.

Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
Tell me more...

Click here for a pdf document that details the observations, assumptions, and equations upon which this program is based. It describes our approach to quantifying the important impact processes that might affect the people, buildings, and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions. The processes included are: atmospheric entry, impact crater formation, fireball expansion and thermal radiation, ejecta deposition, seismic shaking, and the propagation of the atmospheric blast wave.

Earth Impact Effects Program Copyright 2004, Robert Marcus, H.J. Melosh, and G.S. Collins
These results come with ABSOLUTELY NO WARRANTY

Credit goes to the same site as the one I used before.

 

[bassplayer142]

I'd hate for it to land within 2 km of me.

A lot of the others have asked the same question, and here is the reason why:

If the whole asteroid landed, it would impact one city, and make a really super large crater. But if it broke up, it would impact MULTIPLE cities, and make several smaller craters, but more dead people. Like someone on this thread said earlier, think about the fragments of the asteroid being like a shotgun spread, and the single asteroid being a rifle bullet.

If you nuke it close it is going to do tremendous damage, and the same thing applies to nuking it afar (3 moon to Earth units from earth), but if you do nuke it on the furthest point of its orbit away from earth, you can hopefully avert disaster, but that is unlikely to happen since you will need a fairly large bomb (50 mT) and a large rocket to lift it into space.

If you just let it hit, it will just make a big crater, and less people will die.

I know that multiple pieces would do a lot of damage but if the asteroid were detonated miles upon miles away I doubt any would hit the earth. Especially if more nukes were detonated after the first to further break up pieces.

 

[MadScientist 1000]

I know that multiple pieces would do a lot of damage but if the asteroid were detonated miles upon miles away I doubt any would hit the earth. Especially if more nukes were detonated after the first to further break up pieces.

You are right, but you'd need a really large bomb, and a lot of fuel to get it in the way of the asteroid.

 

[joema]

...A lot of the others have asked the same question, and here is the reason why...But if it broke up, it would impact MULTIPLE cities, and make several smaller craters, but more dead people...think about the fragments of the asteroid being like a shotgun spread, and the single asteroid being a rifle bullet.

Although the shotgun analogy may help to visualize it, the underlying mechanism is quite different.

The key damage mechanism is blast, which decreases with the cube of distance. If you're 10 km away the damage is 1/10^3 that of 1 km. It's often called the "inverse cube" law.

This has several implications:

(1) At a given distance, a hugely more powerful blast doesn't do proportionately more damage. Thus a 400 megaton blast at 10 km does only about 2x the blast damage of a 50 megaton blast: (400 / 50)^.33 = 1.98

(2) For a given asteroid mass, splitting it into fragments does much more damage, assuming they survive reentry. This is also one reason why MIRV warheads on ICBMs were adopted: ten 100 kiloton MIRVed warheads do much more damage than a single 1 megaton warhead.

Consider two scenarios: (1) A 1000 meter diameter dense rock asteroid, and (2) The same asteroid split into ten equal-mass fragments.

Note: because volume of a sphere is 4/3 Pi * r^3, ten 460 meter dia fragments equal the mass of one 1000 meter asteroid

The key metric is the 5 psi blast pressure radius. 5 psi will destroy most buildings, so that number is frequently used in nuclear war simulations as the radius of total destruction.

1000 meter rock asteroid impact effects:

Energy before entry: 54000 megatons
Energy on impact: 52600 megatons
5 psi blast pressure radius: 160 km (20096 square km)

460 meter asteroid fragment impact effects (note there are 10 of these):

Energy before entry: 5280 megatons
Energy on impact: 4670 megatons
5 psi blast pressure radius: 72 km (4069 square km * 10 fragments = 40690 square km)

So breaking it into 10 fragments results in double the damaged area.

If you nuke it close it is going to do tremendous damage, and the same thing applies to nuking it afar (3 moon to Earth units from earth), but if you do nuke it on the furthest point of its orbit away from earth, you can hopefully avert disaster, but that is unlikely to happen since you will need a fairly large bomb (50 mT) and a large rocket to lift it into space...

There are various ways to employ nuclear warheads to divert an asteroid. In general you'd want a precision stand-off detonation to deflect it, not try to vaporize or pulverize it.

There's no atmospheric blast wave in space, so the typical earth-bound scenarios are misleading. There's also no huge fireball, as that's also an atmospheric affect. The visual appearance would be similar to a flashbulb - a very brief bluish flash.

In a precision stand-off detonation, the x-ray and neutron radiation would vaporize a thin surface layer of asteroid material, and resultant impulse would nudge the asteroid the opposite direction.

For an asteroid the size/mass of Apophis, a stand-off detonation of a small 30 kiloton nuclear warhead would deflect it (without fracturing) about 15 centimeters/second, which is enough move it out of the gravitation "keyhole" (about 640 meters wide) in 1.2 hours (1.2 MB .pdf): http://www.llnl.gov/planetary/pdfs/Interdiction/04-Solem.pdf

OTOH if an asteroid the mass/speed of Apophis is detected closer missing the keyhole isn't sufficient -- you have to alter the trajectory to totally miss earth. A single 30 kt detonation 1 year out would do it in most cases. For closer detections, multiple detonations would be required, each changing the asteroid velocity about 15 cm/sec. In theory you could deflect it sufficiently (without fracturing) with only a few weeks advance notice by using 10-20 such stand-off detonations.

This assumes the impact trajectory is at Earth's center, thus about one Earth radius deflection is needed. In most cases less deflection than that would be needed. It also doesn't consider gravitational capture effects or atmospheric issues, which could require slightly more deflection.

 

[DaveC426913]

I know that multiple pieces would do a lot of damage but if the asteroid were detonated miles upon miles away I doubt any would hit the earth. Especially if more nukes were detonated after the first to further break up pieces.

Now you're talking about not one target, but many targets, all of which are smaller, on less predictable paths. You've just turned the problem from 'bad' to 'horribly bad'.

 

[tony873004]

But the point bassplayer142 was making was that if you detonate it early enough, none of the pieces will hit the Earth. They will all be so spread out in their orbits that their average spacing will exceed 1 Earth diameter.

Here are some screen shots of a simulation I performed. One year prior to Apophis' 2029 collision with Earth, I created a 2nd Apophis, about 200,000 km from the real Apophis, placing it on a collision trajectory with Earth. I then shattered it into 20 pieces. Each piece had a velocity of 1 meter per second relative to the original object.

After 1 year, a battery of Apophiss approaches the Earth and Moon. The green one is the real Apophis. The gray path is the orbit of Moon.

8 of them impact the Earth, while 12 miss. This shows the incoming and outgoing trajectories of the 12 surviving pieces. The green one is the real Apophis.

(why don't image tags work in this sub-forum? The Homework Help section let's you use img tags.)

So the moral of the story is either nuke it with enough force that the pieces spread faster than 1 meter per second, or nuke it more than 1 year in advance.

 

[skyraider]

Do you all think that if we chose the nuke options, there'd be concern over radioactive fallout from a nuclear blast? Any things such as EMP concerns?

 

[bassplayer142]

I think the radioactivty would only be in a 100 mile radius if that.

 

[joema]

Do you all think that if we chose the nuke options, there'd be concern over radioactive fallout from a nuclear blast? Any things such as EMP concerns?

There would be almost zero risk over radiation and EMP from a deep space nuclear detonation -- the only kind useful in deflecting an asteroid.

You can't deflect an asteroid (even with a nuke) unless it's many millions of km out. At that distance, radiation/EMP would have no more earthly effect than a nuclear bomb detonation on Mars.

There are scenarios where the incoming trajectory is close to the sun, preventing detection until it's only weeks away. In desperation you could try to pulverize (not deflect) it with nukes, for lack of any other option. There are some combinations of object mass, velocity and warning time where that's possible. It's conceivable in some cases some radioactive fragments could re-enter and partially or mostly burn up.

However there have already been over 2,000 nuclear detonations within the Earth's atmosphere, which has already released over 10 metric tons of pure Plutonium 239. We're obviously still here. You'd have to weigh the pros/cons of just letting the asteroid hit Earth vs setting off a few more nukes to try and mitigate the damage -- if it fell within the engagement parameters where that was feasible.

There's no single answer, as the possible scenarios vary so widely.

 

[MadScientist 1000]

However there have already been over 2,000 nuclear detonations within the Earth's atmosphere, which has already released over 10 metric tons of pure Plutonium 239.

The numbers seem kind of high.

 

[joema]

The numbers seem kind of high.

You're right, it's over 2,000 nuclear test detonations total (including atmospheric and below ground). Of these, about 711 were in the atmosphere or under water. Total Pu-239 discharged into the atmosphere was about 4.2 metric tons.

http://en.wikipedia.org/wiki/Nuclear_testing
http://archive.greenpeace.org/comms/nukes/ctbt/read9.html

 

[Ruslan_Sharipov]

No, the military lasers fire for only a few seconds at most. They just can't deliver enough total energy to make a difference.
...
You can hypothesize much larger ground-based lasers, but in general, they aren't an efficient way to deliver energy in quantities needed for asteroid deflection.

I think the Giant Solar Laser (see https://www.physicsforums.com/showthread.php?t=174052") is that very tool for deflecting Apophis. I think such solar lasers could be used not only for deflecting asteroids, but for deflecting planets, e.g. for to move Mars to Earth's orbit and then to implant the Earth-type life to it. Colonizing Mars, isn't it a good prospect for all of us?

 

[cristo]

I think the Giant Solar Laser (see https://www.physicsforums.com/showthread.php?t=174052") is that very tool for deflecting Apophis. I think such solar lasers could be used not only for deflecting asteroids, but for deflecting planets, e.g. for to move Mars to Earth's orbit and then to implant the Earth-type life to it. Colonizing Mars, isn't it a good prospect for all of us?

This is just speculation-- you point to a thread about a "giant solar laser" which firstly, has no details, and secondly has been locked due to idle speculation! I suggest that you should give up trying to publicise your "idea" on here.

 

[Ruslan_Sharipov]

I suggest that you should give up trying to publicise your "idea" on here.

Please, tell me what's wrong with my idea? It doesn't contradict any existing knowledge about lasers. Filling it with details is not my job since I can't build such a laser in my kitchen for to test it.

 

[cristo]

Please, tell me what's wrong with my idea? It doesn't contradict any existing knowledge about lasers. Filling it with details is not my job since I can't build such a laser in my kitchen for to test it.

I can't tell you what's wrong with your idea, since I know no details about it. But, please don't start telling us here; firstly, it will be off topic trying to describe such an idea, but secondly, and more importantly, it is an idea and, as such, belongs only in the independent research subforum (as explained to you in your last thread which was subsequently locked).

You really have to stop trying to bring up topics from threads that have been locked again and again.

 

[Ivan Seeking]

...NASA had previously estimated the chances at only 1 in 45,000 but told its sister organisation, the European Space Agency (ESA), that the young whizzkid had got it right.

The schoolboy took into consideration the risk of Apophis running into one or more of the 40,000 satellites orbiting Earth during its path close to the planet on April 13 2029. [continued]

http://www.physorg.com/news127499715.html

 

[Ivan Seeking]

I didn't notice that this thread was locked. I guess if anyone wants to discuss this you will have to start another thread.Edit: Note that a reply thread has been opened and can be found here: https://www.physicsforums.com/showthread.php?t=229482