![]() You hope you can deflect it enough that it will miss the whole planet, but by doing so you set the asteroid on a course over other parts of the world. The hope is that as the orbits progress, the difference in motion ensures that the asteroid and the Earth are not at the same place at the same time.Īs the asteroid hurtles toward the Earth, it’s possible to deflect it, but when it’s deflected it will either go east or west, along an arc. As the surface expands rapidly outward, this creates a “rocket reaction” that subtly changes the asteroid’s orbit, causing it to steadily fall behind or get ahead of its original position. The NED will be detonated alongside but not too close to the asteroid, so the surface of the asteroid is partially vaporized. That could only increase the number of objects hurtling toward Earth. The idea, however, is not to blow the asteroid up, as in Armageddon. The combination of size and short timeline leaves just one possible deflection method: a nuclear explosive device – a NED. The asteroid is indeed large and headed for Lagos, Nigeria, population 28 million. The robotic spacecraft is launched the next year and reaches the asteroid in 2025. They approve a “reconnaissance” spacecraft to gather information about the asteroid’s size, composition and trajectory. As the hypothetical scenario unfolds, real-life diplomats play the role of decision makers. Nature also has a sense of humour: On Friday the 13th, April, 2029, the need for planetary defence will become visible, when a large, very real asteroid will – with 100-per-cent certainty – narrowly miss Earth. On the first day of the conference, a UN guard spotted “planetary defense” on a security pass and asked, “Should I be watching out for aliens?” Others’ imaginations take them elsewhere. ILLUSTRATION BY GRAHAM ROUMIEU/THE GLOBE AND MAIL The average time between impacts causing widespread damage is measured in tens of thousands of years, but nothing precludes a catastrophic impact this century.Īs low-probability, high-consequence events, impacts by asteroids and comets fall outside the lived experience of most people and therefore seem fantastical – the Bombardment of Earth in The Expanse, or a plot line from a Bruce Willis or Jennifer Lawrence movie. The larger the Earth impactor, the longer the typical timescale between events. The airburst injured more than 1,000 people, most of them hurt by shattered glass after they rushed to windows to observe the bright flash in the sky. A decade ago, in February, 2013, an asteroid about 19 metres in diameter exploded 30 kilometres above the Russian city of Chelyabinsk, with the energy of about 500 kilotons of TNT. The percentage is even lower for smaller NEOs.Įach year, dozens of asteroids with diameters around a metre explode harmlessly in the upper atmosphere. ![]() However, only about 40 per cent of NEOs with diameters above 140 metres have been identified. But if you wait long enough, some will come, and can do so at relative speeds of 20 kilometres a second or more.Īpproximately 31,000 NEOs have been identified so far, including most of those with diameters greater than one kilometre. Not all NEOs will actually come “close” to Earth. An AU is a vast distance – 149.6 million kilometres, about 21,640 times the distance between Vienna and Toronto. Asteroids and comets that pass within 1.3 AU of the sun are called near-Earth objects (NEOs). These leftovers from planet building are formed from metals, rocks and ice that coalesced in the solar nebula – the disc of dust and gas that surrounded the nascent sun.Īn “astronomical unit” (AU) is the distance from the sun to Earth’s orbit. A 300-metre asteroid would strike with an energy equivalent of a billion tonnes of TNT.Įarth has been bombarded by asteroids and comets throughout its history. “This is an exercise” was repeated at every stage, and for good reason. ![]()
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