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Nuke an asteroid? Russian plan may target Apophis

Scott Sutherland
Meteorologist/Science Writer

Thursday, February 18, 2016, 5:00 PM - Russia's new plan for protecting Earth from potential asteroid strikes has some chilling aspects. Not only would it violate a 49-year-old international treaty, but it involves nuking potentially-hazardous asteroid 99942 Apophis.

On February 15, 2013, a 13,000-metric-tonne asteroid plummeted into Earth's atmosphere and exploded over Chelyabinsk, Russia. Although the incident did not result in any fatalities, it highlighted exactly how important our asteroid detection and monitoring programs are, and that we should be investing considerably more in both these programs and into future plans to protect ourselves should we discover one of these space rocks on a collision course with Earth.

Teams of scientists from around the world have come up with many novel ideas on how to do this so far. Some of the more inventive ones put the Sun to work for us, by sending spacecraft to splatter asteroids with bright paint, so that light pressure from sunlight will divert their path, or propose to use the universe itself, by putting a spacecraft next to an asteroid and using the gravitational attraction between the spacecraft and asteroid to "tractor" the asteroid into a safer orbit.

An old standby from science fiction has been to simply "nuke" asteroids. The two latest examples of blockbuster "doomsday from space" films - Armageddon and Deep Impact - followed this philosophy, although with slight alterations and slightly different targets (asteroid vs comet).

It seems that Russian scientists have taken some cues from these scripts now, as Russian News Agency TASS reported on February 11 that a new project is in the works to convert some of the nation's complement of Intercontinental Ballistic Missiles (ICBMs) into planetary defense missiles. Rather than targetting exceptionally large asteroids, however, these upgraded ICBMs would be aimed at smaller objects, between 20-50 metres across.

On the one hand, this makes a certain amount of sense. Nuclear weapons are the most powerful ones at our disposal, and ICBMs can be launched at a moment's notice. If we detected an asteroid inbound with only a short lead time, it is possible for an ICBM to intercept it before it could impact with Earth.

On the other hand, though, there are several problems with such a plan.

The very first issue is that putting nuclear weapons into space violates an important part of the Outer Space Treaty of 1967, which Russia both signed and ratified (with 103 other parties around the world). Along with the basic issue of the potential political tensions that could result from stationing nuclear weapons in space or simply aiming them in that direction, if a nuclear weapon were set off close enough to Earth, the resulting electromagnetic pulse could cripple satellites and spacecraft in orbit, and knock out power grids and computers here on the ground. This is preferable to a devastating asteroid impact, however it is not an ideal choice.

Beyond that, if a special exception was made in the Treaty for planetary defense, even science fiction has been quick to point out that some asteroids are simply too large and dense, and moving too quickly, to be noticeably affected by a blast from a nuclear weapon. Smaller asteroids, such at the one that exploded over Chelyabinsk or a bit larger, could be dealt with in this way, however that particular asteroid was only spotted when it entered the atmosphere. Not the best time to be targetting it with a nuclear missile. Others of the same size, caught further out in space, could be effectively destroyed, however.

For larger ones, a few hundred metres wide or bigger, the best you could probably do is divert it slightly from its path. If you have a very long lead-time before an impending impact, this is actually an effective strategy: Blow up several bombs in its vicinity, each one nudging it further off course, and you could put it on a trajectory that will take it safely past us (and lock it into a safe path for the foreseeable future).

Get a little more aggressive with one of these larger asteroids, such as by directly targetting the rock itself in an attempt to destroy it, and the likely result would be turning a single large space rock into a cloud of smaller pieces. In this case, unless you can guarantee that you've broken it down so the largest chunks are only about a metre wide or so (which would burn up fairly harmlessly in the atmosphere), you've probably made the situation worse. Rather than one massive strike, there would be multiple impacts, spread out over a large area, which could result in just as much damage, or possibly even more.

Credit: NASA/JPL-Caltech

Why is this alarming?

According to TASS, the Russian scientists say that they want to test out their new system on a very specific asteroid - 99942 Apophis.

Apophis has already caused some concern in recent years. Discovered in 2004, plots of this asteroid's orbit showed that it comes around for an encounter with Earth every three years or so, with some of those encounters involving close approaches. Two of these close approaches, in 2029 and 2036, were especially worrisome to start, since the 2029 pass had the potential to alter Apophis' orbit just enough that the 2036 encounter could result in an impact.

NASA has since ruled out any possibility of impact from Apophis, ever, but if Russia launches one or more nuclear missiles at the asteroid during its March 28, 2036 pass - which seems to be the plan, according to TASS - it could cause unintended consequences.

The asteroid is expected to be quite distant during that flyby - at least 34 million km away, or roughly 88 times farther away than the Moon. Thus, one or even a few nuclear "nudges" wouldn't likely cause any immediate problems. The biggest concern for such a test, though, is that Apophis is quite a bit larger than the size group of asteroids this defense system is apparently intended for. At roughly 325 metres across and tipping the scales at an estimated 60 million metric tonnes, this is not an asteroid you want to mess around with, especially now that it has been deemed safe. Without knowing Apophis' exact characteristics and composition, detonating nuclear weapons near it, or using them to break it apart, could result in a raised threat level for future passes.

There's no word yet on whether the plan has been funded or been given the final go-ahead. Hopefully the rest of the world will be able to weigh in on the feasibility of this plan before it would go into effect.

(Update: A previous version of this article referred to the Chelyabinsk asteroid as having a mass of 20 metric tonnes. The asteroid that exploded over Chelyabinsk, Russia on Feb 15, 2013 was roughly 20 metres wide, but its mass was estimated at 13,000 metric tonnes. The article has been updated to reflect this. Hat-tip to reader Ryan Norton for spotting this discrepancy.)

Sources: TASS Russian News Agency | United Nations | NASA

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