The US government is stepping up efforts to protect the planet from incoming asteroids that could wipe out entire regions or even continents.
The National Science and Technology Council released a report calling for improved asteroid detection, tracking and deflection. Nasa is participating, along with federal emergency, military, White House and other officials.
For now, scientists know of no asteroids or comets heading our way, but one could sneak up on us, so Washington wants a better plan.
Nasa’s planetary defence officer Lindley Johnson said scientists have found 95% of near-Earth objects measuring a kilometre (0.62 miles) or bigger, but the hunt is on for the remaining 5% and smaller rocks that could still inflict big damage.
Nasa has catalogued 18,310 objects of all sizes. Just over 800 are 140 metres (460ft) or bigger.
There is no quick solution if a space rock is suddenly days, weeks or even months from striking, according to Mr Johnson, but such short notice would give the world time to evacuate the area it might hit.
Ground telescopes are good at picking up asteroids zooming into the inner solar system and approaching from the night side of Earth, Mr Johnson said. What is difficult to detect are rocks that have already zipped past the sun and are heading out of the solar system, approaching from the day side.
That is apparently what happened in 2013 when an asteroid about 20 metres (66ft) in size suddenly appeared and exploded over Chelyabinsk, Russia, damaging thousands of buildings and causing widespread injuries.
A giant space rock wiped out the dinosaurs when it smacked into Mexico’s Yucatan peninsula 65 million years ago.
Mr Johnson stressed it would take years to attempt to turn away a potential killer asteroid — several years to build a spacecraft then another few years to get it to the target. Ideally, he would like at least 10 years notice.
A mission to defend Earth could involve hitting the asteroid or comet with big, fast-moving robotic spacecraft in the hope of changing its path, or in the worst case, launching a nuclear device not to blow up the asteroid but to superheat its surface and blow off enough material to divert it.
All that involves current technology, Mr Johnson said.
“Part of what this action plan is about is to investigate other technologies, techniques for both deflection and disruption of the asteroid,” he told reporters.
Scientists hope to learn more about asteroids from a pair of missions currently under way. Nasa’s Osiris-Rex spacecraft will reach the asteroid Bennu later this year and return samples in 2023, and Japan’s Hyabusa 2 is closing in on the asteroid Ryugu, with samples to be returned in 2020.
Forget about sending astronauts, Hollywood style.
“It makes a good movie, but we did not see in our study any technique that would require the involvement of astronauts,” Mr Johnson told reporters. Missions like this lasting months or years make it difficult if not impossible for humans, given current technology.