What if an asteroid was about to hit Earth?

Here’s a hypothetical: a telescope detects an asteroid between 100m and 300m in diameter racing through our solar system at 14kps, 57 million kilometres from Earth.

Astronomers estimate a one per cent risk the space rock will collide with our planet on April 27, 2027. What should we do?

It’s this potentially catastrophic scenario that 300 astronomers, scientists, engineers and emergency experts are applying their collective minds to this week in a suburb here, the fourth such international effort since 2013.

“We have to make sure people understand this is not about Hollywood,” said Nasa administrator Jim Bridenstine as he opened the International Planetary Defence Conference at the University of Maryland’s campus here.

Countries represented include China, France, Germany, Italy, Russia and the United States.

The idea that Earth might one day have to defend itself against an asteroid used to elicit what experts called a “giggle factor”.

But a meteor that blew up in the atmosphere over Russia on Feb 15, 2013, helped put an end to the sneers.

On that morning, a 20m asteroid appeared out of nowhere over the southern Urals, exploding 23km above Chelyabinsk town with such force that it shattered the windows of thousands of buildings. A thousand people were injured by the shards.

But “the positive aspect of Chelyabinsk is that it made the public aware, it made the political decision-makers aware”, Detlef Koschny, co-manager of the Planetary Defence Office of the European Space Agency (ESA), said.

Only those asteroids whose orbit around our Sun brought them within 50 million kilometres of our planet — defined as “near Earth” — were of interest.

Astronomers were finding new ones each day: more than 700 this year, for a total of 20,001, said Lindley Johnson of Nasa’s Planetary Defence Coordination Office.

The majority were very small, but 942 were more than 1km across, estimated astronomer Alan Harris.

The scientist told an audience that some large ones are probably still out there: “A fair fraction of the biggest ones are hiding... basically parked behind the Sun.”

They were found mainly by two US telescopes, one in Arizona and the other in Hawaii.

ESA had built a telescope for this purpose in Spain and was planning others in Chile and Sicily.

Many astronomers demanded a space telescope because terrestrial telescopes were unable to detect objects on the other side of the Sun.

This week’s exercise sought to simulate a global response to a catastrophic meteorite. The first step was aiming telescopes at the threat to precisely calculate its speed and trajectory.

Then it boiled down to two choices: try to deflect the object or evacuate.

If it is less than 50m, the consensus was to evacuate the threatened region. According to Koschny, it is possible to predict the country it would strike two weeks ahead. Days away from impact, it could be narrowed down to within hundreds of kilometres.

What about bigger objects? Trying to nuke them to smithereens like in the movie Armageddon would be bad idea because it could just create smaller but still dangerous pieces.

The plan, instead, was to launch a device towards the asteroid to divert its trajectory — like a cosmic bumper car.

One issue that remained was politics, said Romana Kofler, of the United Nations Office for Outer Space Affairs.

“Who would be the decisionmaking authority?” she asked. “The consensus was to leave this aspect out.”