On 15 February, the town of Chelyabinsk in the Russian Ural Mountains had an unexpected visitor. A meteor streaked high above the city, briefly blinded commuters and then shattered thousands of windows with a series of ear-splitting explosions. The event was recorded on mobile phones and car-dashboard cameras across the region, and YouTube soon filled with Hollywood-style disaster videos of the fireball, replete with some very colourful Russian commentary.
Local residents were not the only ones to record the blast. More than a dozen monitoring stations around the globe captured the ultra-low-frequency infrasound signal of the meteorite as it broke up in the atmosphere. The stations are part of a much larger network of sensors that has been built to detect illicit nuclear testing: the system, it is hoped, will eventually underpin the Comprehensive Nuclear-Test-Ban Treaty (CTBT), a pact to halt work on nuclear weapons worldwide. Using data from this monitoring system, scientists in Canada and the United States were quickly able to establish that the rock that broke up over Russia was the largest to strike Earth in more than a century. They found that it exploded with the strength of a good-sized thermonuclear warhead, although, luckily, at an altitude high enough for the atmosphere to absorb most of the shock wave.
To understand the value of this monitoring network, imagine that the celestial visitor had arrived 30 years earlier — no time at all in the life of the Solar System. If there had been a sudden explosion over Chelyabinsk towards the end of the cold war, without an Internet or free press to circulate images, a very different picture could have emerged. The city is fewer than 100 kilometres from some of Russia’s largest nuclear-weapon production and storage facilities: a surprise airburst would almost certainly have put the country’s nuclear arsenal on hair-trigger alert. Shortly after the strike last week, right-wing law-maker Vladimir Zhirinovsky asserted: “Those aren’t meteors falling, it’s the Americans testing new weapons.” His comments were greeted with bemusement by the Russian press; in another time, they might have triggered nuclear war.
Just a few days before the spectacular events over Russia, the CTBT network picked up a less visible but politically more significant incident. On 12 February, North Korea conducted its third nuclear-weapon test deep underground. On this occasion, the CTBT network’s seismic sensors detected the blast, and located it to within a few kilometres of North Korea’s previous nuclear tests. Independent analysis of the network’s data showed the yield of the weapon to be several kilotonnes, much smaller than the explosion of the Russian meteor.
Unlike with the Russian event, there were few other ways to verify the North Korean explosion. The North Korean Central News Agency put out a statement announcing the test, but is not particularly reliable. US, Japanese and South Korean sensors all picked up the shock from the blast, but because they belong to sovereign nations, there was no guarantee that the data would be shared in a timely fashion — or believed by adversaries.
“A ban on nuclear testing could be enforced, if a further eight nations are willing to ratify it.”
The raison d’être of the CTBT network is to catch tests such as the one conducted by North Korea. Its ability to do so shows that an international ban on nuclear testing could be enforced, if a further eight nations, including China, the United States, India and Pakistan, were willing to ratify it. The CTBT has been open for ratification since 1996, but unfortunately, in recent years, little progress has been made towards its entry into force.
The meteor strike also shows that the constructed network has great value in its own right. It has done much non-nuclear-test work since it became active: tracking earthquakes, tsunamis and nuclear accidents.
Building and running this global sensor network isn’t cheap. The CTBT organization in Vienna estimates that around US$100 million a year goes on its 321 monitoring stations and 16 laboratories worldwide, along with a data centre and other support for the treaty. Those funds are contributed by the treaty organization’s 183 member states, which are guaranteed timely access to the data collected by the network.
Many hundreds of scientists have begun using the CTBT data in the past few years, and many hundreds more are likely to sign up. As the events of the past week show, even without a test-ban treaty, the network makes the world a safer and more interesting place to live.
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