No Bomb Powerful Enough To Destroy an On-Rushing Asteroid, Sorry Bruce Willis

coondoggie writes "Maybe it's the doom predictions about the end of the Mayan calendar this year, or maybe these guys are obsessed with old Bruce Willis movies. Either way a class of physics students from the University of Leicester decided to evaluate whether or not the premise of Willis' 1998 'Armageddon' movie — where a group of oil drillers is sent by NASA to detonate nuclear devices on an asteroid that threatens to destroy Earth — could actually happen. The students found it would take a bomb about a billion times stronger than the biggest bomb ever detonated on Earth."

Comments

how they did it

[phantomfive]

I'm not sure why this is news, but here's what they calculated:

The students devised a formula to find the total amount of kinetic energy needed in relation to the volume of the asteroid pieces, their density, the clearance radius (which was taken as the radius of Earth plus 400 miles), the asteroid's pre-detonation velocity, and its distance from Earth at the point of detonation. Using the measurements and properties of the asteroid as stated in the film, the formula revealed that 800 trillion terajoules of energy would be required to split the asteroid in two with both pieces clearing the planet. However, the total energy output of Big Ivan "only comes to 418,000 terajoules. The asteroid is approximated as a spherical object 1000km in diameter

Re:how they did it

[subreality]

The biggest that the US ever actually popped was Castle Bravo. Design yield: 4-6Mt. Actual yield: 15Mt, resulting in the dry bit of island it was sitting on turning into a deep spot in the reef and destruction of the monitoring equipment two islands over, not to mention dropping fallout all over the local civilians. Oops. The Castle-* designs were weaponized into the Mk-17/Mk-21/Mk-24 with a 5-15 Mt range.

The biggest the US ever deployed was the B41, at a perfectly practical 25Mt.

Yields peaked in the 60s because the complete assemblies were huge and if you could only cart around one bomb on your plane or missile, it might as well be a big one. Since then the trend in big bombs has been toward the 0.5-1 Mt range, like the B83. The reason doesn't really have much to do with "arsenal reduction"; the real story is they figured out how to shrink midsize ones down to a much smaller package, and it's simply more efficient (more stuff blown up per kg of plutonium) to drop a half dozen 1Mt bombs in a pattern than to drop a single 25Mt one and having most of the energy end up in a stratosphere-bumping mushroom cloud.

Of course that Soviet triple-stage monster takes the cake. There's simply no possible use for a larger one, even as a national dick waving status symbol. 50Mt is basically the most you can ever drop from a plane and live to tell about it, and you HAVE to drop it from a plane because a ground burst would create stupid amounts of fallout while not even being that impressive (air bursts work better); and no one's going to bother building a missile big enough to carry a 27,000 Kg firework just to show off. I hope.

So now you know, and knowing is how we get the next generation interested in one upmanship.

Re:Bruce still has a shot

[Anonymous Coward]

The biggest one ever detonated, the so called "Tsar Bomba", was 50 megatons of TNT. It could have been made 100 MT, but was scaled back to reduce fallout, and was therefore a very clean bomb for its size.
There was however no point in building bombs of this size, so no one has attempted it since, opting instead for clusters of smaller bombs to carpet an area or using modern targeting to accurately take out small targets with great precision,
Bombs that big where shere lunacy and just a demonstration of power.

For those who don't RTFA.

[Bongoots]

This is the real paper, coming in at only 2 pages it's a light read: https://physics.le.ac.uk/journals/index.php/pst/article/viewFile/390/243

You weren't going to RTFA anyway, now were you?..
--

P1_1 Could Bruce Willis Save the World?
Back A, Brown G, Hall B and Turner S
Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH.
November 1st, 2011

Abstract
The film Armageddon (1998) puts forward the possibility of using a nuclear weapon buried deep within an Earth-bound asteroid to split the asteroid in two, each half clearing opposite sides of the Earth with only relatively minor damage. This article investigates the feasibility of such a plan and shows that even using the largest nuclear weapon made to date, the bomb comes over 9 orders of magnitude short of the yield required.

[...]

Re:not about destroying

[mosb1000]

If you'd read the article, you'd know that the calculation was to determine how powerful the explosion would need to be to split the asteroid in half so that the two pieces would pass by the earth. Basically, the same thing that was done in the movie. Only, in their calculation, the explosion occurred when the asteroid was still 8 billion miles away.

Re:1000 KM?

[tp1024]

Even worse: There are no asteroids with a diameter of 1000km. The largest of them, Ceres, is 950km and at a very safe distance in a very stable orbit. The second largest, Vesta, is less than 600km in diameter.

In fact, the main "danger" nowadays is seen in objects of about 0.1km in diameter, since that is the size at which asteroids are still damaging, but also escape early detection. That takes about 15 orders of magnitude off the energy requirements. But at this point, you wouldn't even need a bomb. Just shoving a few tons of stuff at a few km/s in front of the asteroid is enough to tear it apart. (The kinetic energy of 1t of material at 2.8km/s is equivalent to 1t of TNT.)