Stopping Killer Asteroids

Drog writes "Earth has had a few near misses with asteroids recently (although "near hits" would be more accurate). It's just a matter of time, though, before we detect one with our name on it. In this New York Times article, experts discuss the various ways that we might go about saving our planet. Remarkably, nuclear detonations are not a good option, as they would break the asteroid into many pieces and merely increase our odds of being hit. And a detonation some distance away may simply be absorbed by the asteroid with virtually no effect. Instead, say scientists who study asteroid hazards, a gentle sustained push is what's needed (slow and steady wins the race). Some of the approaches have been discussed in science fiction for years--a mass driver, an electromagnetic machine which hurls dirt from the surface, an orbiting parabolic mirror to heat up the surface and create a plume of vaporized material. All of these methods require one thing, however. Time. At least several decades warning."

Comments

Can't test a nuke in space

[ColGraff]

You can't test a nuclear weapon in space - there are treaties that regulate this sort of thing, and they say space has to stay demilitarized. That means no nukes - that's one of the reasons, other than the horrible amount of radioactive pollution, that the Orion project never really took off. For better or worse, the only test we'll get is when there's actually an asteroid on the way to Earth.

Re:Can't test a nuke in space

[geoswan]

You can't test a nuclear weapon in space - there are treaties that regulate this sort of thing, and they say space has to stay demilitarized. That means no nukes

I think it is more accurate to say there were treaties in place that prevented nuclear charges in space. Hasn't George Bush announced his intention to abrogate those treaties in the last year or so?

Google to the rescue. According to this article after dropping a lot of hints he made his intention to take the US out of the ABM treaty on December 31st 2001.

Reagan's SDI proponents were asked whether their nuclear pumped X-ray lasers weren't a violation of the nukes in space portion of the ABM treaty. In an example of "spin doctoring" at its most blatant, they used to respond, "that would only be true if you take a strict interpretation of the treaty".

Of course a bilateral treaty is not like a marraige contract. There is no higher authority to whom you can appeal if you think the other side is cheating. With a bilateral treaty, if the other party doesn't trust you, doesn't trust that you are complying with the interpretation of the treaty you both agreed to when you signed it, if they don't trust your new re-interpretation of the treaty, the treaty is over.

And it doesn't really matter if there were a no nukes in space clause in the non-proliferation treaty. Other clauses in the non-proliferation treaty have been routinely violated. The non-proliferation treaty prohibited both "horizontal proliferation" and "vertical proliferation" . Horizontal proliferation was defined as nations which had no nuclear weapons at the time the treaty was signed acquiring their first weapons. Vertical proliferation was defined as the nations which already had nuclear weapons increasing the size of their nuclear arsenals. Of course The USA, the USSR and China all significantly increased the size of their nuclear arsenals in complete abrogation of the treaty.

I believe the treaty also obliged the nuclear nations to give the non-nuclear nations the benefits from the peaceful applications of nuclear energy.

Re:More pieces is bad...why?

[Ralph Wiggam]

The science is right, but I think your scale is wrong. We're talking about objects measured in kilometers. The objects are WAY too big to just burn up in the atmoshere. An object that can be chopped in half and have both pieces burn up was never a real threat anyway.

-B

More pieces is bad

[maggard]

Actually it's not friction that "burns up" incoming material, it's radiated heat from the bow shock (yes, your high school science teacher over-simplified.)

That aside unless you break up the pieces into very small bits they're gonna impact and n-medium sized craters is worse then ~1 big crater. Or, absolutely devastating some large radius is better then pretty-much devastating a number of somewhat smaller radiuses.

By the way - the worst? Ocean impact. Then you're not just talking an air blast and punching a hole into the surface with some ejecta spraying but doing all of that while vaporizing some megatons of water - much worse on a global scale.

Re:Small fragments better than one large

[siphoncolder]

Relatively, your example works.

Relatively, 1000 1-meter rocks are better than 1 1-km rock.

Actually, however, a single 1-meter rock getting through will still do a boatload of damage - it won't be a planet killer, but the damage will still be more than say, those 2 aircraft that flew into the world trade center towers.

In order for any explosive asteroid deterrant system to work well, you still have to make sure that the asteroid will be sufficiently vaporized to be eaten up in the atmosphere. You have to guarantee that the asteroid will become something more like sand. A nuclear blast will probably not do that (especially not in space, where there's no atmosphere to propagate the blast).

That's why so many systems rely more on controllable methods like redirection - we can guarantee those better.

NASA's Near Earth Object Program

[Roosey]

NASA has a pretty good website that talks about "near-earth objects" (comets/asteroids with orbits that bring them close to earth). They even have a page detailing the current impact risks.

Fortunately, only one of them is meriting significant attention. I guess we're safe for a little while then.

Re:Solution Already Exists: Nuclear Rocket

[thgreatoz]

Dude, that's exactly what all those scientists at the conference decided WOULDN'T work!!! Did you read the article? Besides, you can't consider diameter as much...mass is the primary variable. And understand that the force of a nuclear blast is not going to be focused at the asteroid...it will be spread out in 3 dimensions around the source of the blast. The asteroid will only feel a fraction of the total tonnage, and that, the scientists are saying, is simply not enough.

Arthur C. Clarke...

[Verteiron]

... has once again predicted the future. In The Hammer of God, he laid out an entire scenario for just this "gentle push" method.

check your numbers -- asteroids are smaller

[klparrot]

An asteroid 1000 km in diameter is about 40e15 kg mass

Yes, but we're not usually talking about asteroids 1000 km in diameter hitting us. The largest known asteroid is Ceres, with a diameter of 933 km. There are only four known asteroids with a diameter greater than 340 km. They're (presumably) (relatively) easy to find, and fairly rare.

The problem is with a smaller asteroid, one that is still large enough to cause a globally catastrophic collision, but small enough that we don't see it until it's too late to do anything. The threshold diameter for an asteroid to cause a global catastrophe is thought to be only about 1 km. Try recalculating with something in that range.

Re:Solution Already Exists: Nuclear Rocket

[Wyatt Earp]

I don't know if I agree with the scientists.

Soviets and US had some experiance at using nuclear devices for moving Earth and simulating an earthquake.

http://nuketesting.enviroweb.org/hew/Usa/Tests/S to rax.html

"Up to a point, the more deeply buried an explosive charge is, the larger the crater it will make. Beyond this point much of the material is thrown with insufficient force to clear the crater and falls back in, reducing the final size. At the optimal crater depth though quite a lot of material actually ends up back in the crater bottom. This is an advantage for a Plowshare-type crater experiment since much of the radioactivity gets returned to the crater and buried. The radiation release (as measured in terms of I-131, the most important from human health risks) was 880,000 curies, about equivalent to a 3-4 kt atmospheric fission test.

Sedan was detonated at what was estimated to be the optimal crater depth in alluvial soil. 12 million tons of soil and rock were lifted into the air, 8 million tons of it falling outside the crater. The final crater was 1280 feet wide and 320 feet deep. The force of the detonation released seismic energy equivalent to an earthquake magnitude of 4.75 on the Richter Scale. The device used was similar to that used in Dominic Bluestone and Swanee and was thus a variant of the W-56 high yield missile warhead. The device had a fusion yield of 70%. The Sedan device had a diameter of 17.1 inches, a length of 38 inches, and a weight of 467.9 lb."

http://nuketesting.enviroweb.org/hew/Russia/Sovw pn prog.html

5 to 7 KT does this

"The site for the Chagan shot was the dry bed of the Chagan River on the edge of the Semipalatinsk Test Site (STS) in Kazakhstan. The shot location was chosen so that the crater lip would form a dam in the river during its period of high flow in the spring. The crater formed by the Chagan explosion had a diameter of 408 m and a depth of 100 m. A major lake (10,000,000 m 3 ) was quickly formed behind the 20-35 m high upraised lip. Shortly after the explosion, earthmoving equipment was used to cut a channel through the lip so that water from the river could enter the crater.

Spring melt soon filled the crater with 6.4 million m^3 of water, and the reservoir behind the crater was filled with 10 million m^3 of water. These reservoirs are known informally as Lake Chagan or Lake Balapan. Subsidence of the crater slopes subsequently reduced the crater storage capacity by about 25%. A few years later, a water-control structure was built on the left bank of the river to control water levels in the reservoirs. Both reservoirs exist today in substantially the same form and are still used to provide water for cattle in the area. Efrim P. Slavskiy, Minister of the Medium Machine Building Ministry (the ministry responsible for the entire Soviet nuclear weapons program)was reported to have been the first person to have taken a swim in the crater lake."

Re:Does anyone actually know what a nuke would do?

[Detritus]

A nuclear weapon detonated in space produces a burst of soft x-rays (from black-body radiation). It does not produce the blast and thermal effects seen when the device is detonated in the atmosphere. The atmosphere is relatively opaque to soft x-rays. This results in a complex sequence of events, involving repeated absorption and reemission of photons, that produce the fireball, thermal radiation and shock waves.

If you look at the films of high-altitude nuclear tests, they are rather boring in comparison to atmospheric tests. You can see an expanding shell-like cloud composed of the remnants of the nuclear device.

Could Give NASA A Reason To Stop Going in Circles

[reallocate]

The American space program has, literally, been going in circles for the last 30 years. It desperately needs someplace to go. Now, it looks like NASA is going to keep the shuttle flying for another decade or so, and pull out the old DynaSoar blueprints for a re-do. And where will it go? Well, around in circles for a few days when it ferries new crew members up to the space station.

But, building the capability to send people to investigate and deal with an asteriod or comet that has Earth in its sights would give NASA a place to go. If we don't have the courage to develop an interplanetary capability to ward off armageddon, maybe we don't deserve to survive.