EARTH cannot defend itself against the thousands of “city killer” asteroids that are zooming around space near our planet, Nasa chiefs warn.
They reckon there are about 15,000 undetected medium-sized rocks in striking distance of the globe.
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Illustration of what a devastating asteroid impact would look like from spaceCredit: Getty
A mission in 2022 demonstrated how knocking an asteroid off course could be achievedCredit: NASA
The Dart mission was considered a successCredit: NASA/ASI/University of Maryland
A 2022 mission called Dart proved that in an emergency we could bash one off course with a rocket.
But the expedition leader said we are not prepared to do it again if in danger.
Dart mission chief Dr Nancy Chabot, from Johns Hopkins University in Maryland, US, said: “We worry about these city killer asteroids.
“Dart was a great demonstration but we don’t have that sitting around ready to go if there was a threat we needed to use it for.
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“We don’t know where 50 per cent of the 140-metre asteroids are, which is a concern.
“We would not have any way to go and actively deflect one right now.
“We could be prepared but I don’t see that investment being made.”
She warned that space agencies do not have the cash to keep defences on high alert.
Dr Kelly Fast, Planetary Defense Officer at Nasa HQ, said the medium asteroids are the ones that worry her most.
Speaking at the conference of the American Association for the Advancement of Science (AAAS) in Arizona, she said: “What keeps me up at night is the asteroids we don’t know about.
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“Small stuff is hitting us all the time so we’re not so much worried about that.
“And we’re not so worried about the large ones from the movies because we know where they are.
“It’s the ones in between, about 140 metres and larger, that could really do regional rather than global damage and we don’t know where they are.
“It’s estimated there are about 25,000 of those and we’re only about 40 per cent of the way through.
“It takes time to find them, even with the best telescopes.”
Nasa is launching a mission called Surveyor in 2027 in a bid to find at least 90 per cent of asteroids measuring wider than 140m within a decade.
What’s the difference between an asteroid, meteor and comet?
Asteroid: An asteroid is a small rocky body that orbits the Sun. Most are found in the asteroid belt (between Mars and Jupiter) but they can be found anywhere (including in a path that can impact Earth)
Meteoroid: When two asteroids hit each other, the small chunks that break off are called meteoroids
Meteor: If a meteoroid enters the Earth’s atmosphere, it begins to vapourise and then becomes a meteor. On Earth, it’ll look like a streak of light in the sky, because the rock is burning up
Meteorite: If a meteoroid doesn’t vapourise completely and survives the trip through Earth’s atmosphere, it can land on the Earth. At that point, it becomes a meteorite
Comet: Like asteroids, a comet orbits the Sun. However rather than being made mostly of rock, a comet contains lots of ice and gas, which can result in amazing tails forming behind them (thanks to the ice and dust vapourising)