|Feb26-07, 10:26 AM||#35|
Apophis to impact earth in 2036?
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
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)
|Feb26-07, 11:05 AM||#36|
that doesn't scare me..let him come
|Feb26-07, 04:18 PM||#37|
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.
|Feb26-07, 05:15 PM||#38|
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.
|Feb26-07, 06:20 PM||#39|
Dave and Tony, I used your advice, and inserted 17 km/sec:
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
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 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
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.
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
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:
Much of the body suffers third degree burns
Deciduous trees ignite
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.
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
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)
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.
|Feb26-07, 07:12 PM||#40|
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.
|Feb26-07, 08:45 PM||#41|
|Feb27-07, 08:32 AM||#42|
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.
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/I...n/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.
|Feb27-07, 09:16 AM||#43|
|Feb28-07, 03:15 PM||#44|
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 lets 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.
|Mar2-07, 09:29 AM||#45|
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?
|Mar2-07, 03:51 PM||#46|
I think the radioactivty would only be in a 100 mile radius if that.
|Mar2-07, 05:30 PM||#47|
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.
|Mar2-07, 06:56 PM||#48|
|Mar2-07, 11:03 PM||#49|
|Jun23-07, 05:12 PM||#50|
|Jun23-07, 05:26 PM||#51|
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