Politics

Defence tactics to stop potentially-hazardous asteroids impacting Earth


In a world, maybe even universe first, plan the space agency will slam a spacecraft into the non-hazardous moonlet asteroid Dimorphos, which is about 160 metres in diameter.

The goal is to see whether it’s possible to knock the space rock off its orbit.

Planetary scientist at the University of Queensland Trevor Ireland told 9news.com.au this is one of two methods humanity has to stop a potentially hazardous object (PHO) from slamming into Earth.

The DART mission, or NASA’s Double Asteroid Redirection Test, will lift off at 10.20pm on November 23 aboard a SpaceX Falcon 9 rocket (CNN)

The other option would be to use a nuclear blast to blow the asteroid apart, Professor Ireland explained.

“What we’ve discovered over the last couple of years is a lot of the near-Earth asteroids are potentially rubble piles,” he said.

“So if you put a lot of energy into them, they are just going to fly apart.

“They are not well held together.”

Professor Ireland said this then prompts the question: “Do you let it come in as a bullet or as shotgun scatter?”

“You don’t want it blowing up too close to Earth as that generates debris,” he said.

Geminids meteor shower in 2018 over lake in Erenhot, Inner Mongolia, China.
The Geminids meteor shower photographed in 2018 over Lake In Erenhot, Inner Mongolia, China. (iStock)

Professor Ireland said he believes deflection, through the DART method, is humanity’s best option to defend Earth.

If time and proximity is not an issue, Professor Ireland said placing a sail on an asteroid could also potentially change it’s orbit.

“You could attach a parachute effectively to the asteroid, and I say attach rather glibly, that sail could produce solar wind to push and pull on it a bit,” he explained.

“But most of these methods, beyond hitting [a potentially hazardous object] with something to try and bash it out of the way, require force over a long period of time.”

Hubble Telescope captures eerie image of dying star

Is Earth currently at risk from a potentially hazardous object?

Kelly Fast is a planetary defence expert and a manager in NASA’s Planetary Defence Coordination Office.

She with certainty an asteroid would hit our planet again.

“Asteroids have hit Earth over the course of its history, and it will happen again,” Dr Fast said on the space agency’s website.

“Dust, meteoroids, and even small asteroids hit Earth all the time.

“But impacts of asteroids that affect the surface are much rarer and happen on time scales of hundreds to thousands to millions of years.”

DART team members stand outside Astrotech Space Operations processing facility with the shipment container holding the DART spacecraft. DART moved to SpaceX's payload processing facility late October.
DART team members stand outside Astrotech Space Operations processing facility with the shipment container holding the DART spacecraft. DART moved to SpaceX’s payload processing facility late October. (NASA/Johns Hopkins APL/Ed Whitman)
Professor Ireland said the asteroid Bennu poses the greatest risk to Earth.

The space rock is about 492 metres in diameter.

The good news is, it won’t pose a risk for more than 100 years.

The final four candidate sample collection sites on asteroid Bennu were designated Nightingale, Kingfisher, Osprey and Sandpiper. Credit: NASA/Goddard/University of Arizona/CSA/York/MDA
Asteroid Bennu orbits the sun every 1.2 years and makes a relatively close approach to Earth about every six years. Credit: NASA/Goddard/University of Arizona/CSA/York/MDA (AP)
OSIRIS-REx captured this image of the asteroid Bennu on April 12, 2019.
OSIRIS-REx captured this image of the asteroid Bennu on April, 2019, with the mission giving more insight into the PHO’s trajectory through the year 2300. (NASA) (Supplied)

Should it hit though, studies show it would create a crater between 10 to 20 times its size – and cause an area of devastation that could reach 100 times the size of the crater.

Professor Ireland said civilisation-ending asteroids are much rarer and would have to measure more than a kilometre in diameter, at least, to be “extinction-level”.

For reference, the Chicxulub impactor that wiped out the dinosaurs was about 9.6 kilometres.

An artist’s interpretation of the asteroid impact that wiped out all non-avian dinosaurs. (CNN)

NASA estimates about 40 per cent of asteroids larger than 140 metres have been found to date.

But this is no cause for alarm.

The better news is these large asteroids are easier for astronomers to find, meaning it’s unlikely one should suddenly “pop up” and pose a risk.

“There’s about a million one kilometre asteroids in the asteroid belt,” Professor Ireland said.

“The likelihood of one of those suddenly meandering down to Earth is very remote.”



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