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Michael Byers holds the Canada Research Chair in Global Politics and International Law. Aaron Boley holds the Canada Research Chair in Planetary Astronomy. Both are at the University of British Columbia, where they co-direct the Outer Space Institute.

On Wednesday evening, depending on where in Canada you are, you might be leaving school or work, having dinner, or already fast asleep in bed.

Meanwhile, an asteroid the size of a seven-storey building – designated 2019 EA2, to reflect the fact that it is the second asteroid to pass close to Earth this year, and spotted just two weeks ago through a telescope in Arizona – will buzz by the planet we call home.

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The good news? The 24-metre-wide asteroid will miss us by 300,000 kilometres.

The bad news: asteroids do hit the Earth. Most harmlessly break into pieces as they enter Earth’s atmosphere, but even a relatively small asteroid can damage property and injure people. In 2013, a 17-meter-wide asteroid sent 1,500 people to hospital in Chelyabinsk, Russia, most of them injured by flying glass from broken windows.

The energy released by an asteroid of that size can be equivalent to 500 kilotons of TNT, about 25 times more than the nuclear bomb dropped on Hiroshima. These events seem to occur on average every 50 years, at high altitudes.

Smaller asteroids strike the Earth more frequently, but are less energetic. Just this week, the U.S. military reported that another small asteroid caused a 170-kiloton airburst last December over the Bering Sea, west of Alaska.

In contrast, a 500-metre-wide asteroid would carry the energy of 500,000 Hiroshima-sized bombs, enough to cause continent-wide destruction. Asteroids this size strike the Earth about once every 100,000 years.

And an asteroid more than a kilometre wide can have a globally catastrophic effect. Such large strikes happen on average once every 500,000 years, or longer for even larger asteroids.

Fortunately, the larger the asteroid, the easier it is to spot and determine its orbit, and calculate the possibility that it strikes the earth. For instance, we know that in 2029, a 370-metre-wide asteroid named Apophis will pass within 40,000 kilometres of Earth. While impact at that time has been ruled out, Apophis will, for a moment, be closer to us than the hundreds of valuable communications satellites in the Earth’s geosynchronous orbit.

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But while asteroids are a natural hazard, they are also time capsules that contain unique scientific information about the solar system. A NASA probe named OSIRIS-REx is currently visiting a 500-metre-wide asteroid called Bennu, where it will collect a small sample and return it to Earth. The mission is also an opportunity to test technologies for use in asteroid mining for resources.

Entrepreneurs and investors, meanwhile, are already eyeing natural resources such as platinum, cobalt and tungsten that may exist on these asteroids. They are especially interested in ice and water-bearing minerals that could be used to produce rocket fuel that, being sourced in space, will not need to be lifted – at great expense – out of Earth’s heavy gravity.

The very legality of this kind of asteroid mining, however, remains hotly debated. The 1967 Outer Space Treaty prohibits the “national appropriation of the moon and other celestial bodies,” which explains why Neil Armstrong and Buzz Aldrin did not claim the moon for the United States when they planted a flag there in 1969. Although most countries believe that asteroid mining would violate this prohibition, a few countries, led by the United States, hold that asteroid mining is similar to fishing on the high seas.

In 2015, U.S. president Barack Obama signed the Commercial Space Launch Competitiveness Act, giving U.S. citizens the right to own asteroid resources they extract in space. In 2017, Luxembourg followed suit, and offered financial incentives to support asteroid-mining companies. Earlier this month, Russia expressed an interest in partnering with Luxembourg.

Beyond the battle over resource extraction lies a more existential threat: the act of removing large quantities of mass from an asteroid could change its trajectory, potentially leading to a human-caused Earth impact. For this reason, any asteroid mining will have to be fully informed by astrodynamics, and closely regulated under international rules. And while the U.S., Luxembourg and Russia might regulate asteroid-mining companies closely with the involvement of planetary scientists, what would happen if a mining company were to incorporate a “flag of convenience state” such as Panama or Liberia? Would the same respect be paid to science and safety?

International cooperation on the Earth-impact risks of asteroid mining should be possible. In 2013, a coalition of countries including Russia and the U.S. created the International Asteroid Warning Network to facilitate cooperation between observatories in discovering, monitoring, and characterizing potentially hazardous objects. Most of the same countries belong to the Space Mission Planning Advisory Group, an association of national space agencies established in 2014 to “prepare for an international response” through the development of options for “mission opportunities.”

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If this sounds like the Hollywood movie Deep Impact, you’d be right. But instead of just planning for last-resort missions, countries should cooperate to reduce the risks. That starts with ensuring that any asteroid mining is done responsibly, and does not cause the asteroid to strike our planet.

How close is too close? Wednesday’s near-miss provides an opportunity for reflection.

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