Tracking a 'city destroyer' asteroid

91���˰涶��is a founding member of the Southern Hemisphere Asteroid Research Consortium (SHARC), along with CSIRO, NASA-JPL, University of Western Australia, University of Tasmania and Curtin University. The group monitors about 10 asteroids per year which are Earth orbit-crossing and could pose a risk.

Australia is geographically important because it observes asteroids from the southern hemisphere, filling a “blind spot” most telescopes, which are located in the northern hemisphere.

91���˰涶��Space participates by analysing radar reflections transmitted from and received by CSIRO-managed radio telescopes.

“We also use our Falcon and Viper telescopes to take optical measurements to compare with radar reflections and improve orbit measurements and asteroid rotation rates,” Prof. Kruzins explained.

“These help with risk calculations and tell us about the type of asteroid – sandy, rocky or metallic.

“We share our findings with the IAWN, a United Nations-endorsed body, and the Australian government to ensure decision-making agencies have the best information possible.”

Asteroid 2024 YR4 is now moving quickly away from Earth and growing very dim. It’s on an elliptical orbit with its furthest point 360 million kilometres from Earth, or about half the distance to Jupiter.

It will require very large telescopes to observe it in February and March. After that, astronomers will need to use the Hubble Space Telescope or James Web Space Telescope to see it.

“At that stage we will likely be able to say with certainty whether it will hit the Earth.

“Astronomers will also look to determine exactly what the asteroid is made of. It is most likely that it is a mass of rocky substances that would explode in the atmosphere as an airburst, rather than metallic asteroids that are significantly denser and more likely to make landfall and cause craters.”

With the information currently available, astronomers have plotted a potential impact track that runs from northern South America across north Africa to India. But with further information in 2028 it will be possible to make a more precise estimate, if it was confirmed to be on track to hit.

“An asteroid the size of 2024 YR4 could deliver up to the equivalent of several tens of megatons of TNT. If impact was over a city or populated area it could be catastrophic and would require the evacuation of the entire area,” Prof. Kruzins said.

Even though it is highly unlikely that 2024 YR4 will hit the Earth, measures that could be taken to prevent a collision.

“In September 2022, the spacecraft purposely collided with a space rock called Dimorphis, at a speed of over 22,000 kilometres per hour, to see if it could deflect it,” Prof. Kruzins said.

“The mission was successful and proved that even a small bump, done early enough, can make a big change in the asteroid’s eventual position over a longer period. Dimorphis at 144 metres in diameter is likely to be significantly larger than 2024 YR4.”

While the Earth is pelted with many small, centimetre-sized objects every year, these burn up and are of no consequence.

About once a year a small, metre-sized asteroid will enter the atmosphere. These typically break up as airbursts but can rattle windows.

An asteroid 10 metres and above will arrive every 10 years or so. These also usually result in airbursts that can break windows and flatten small areas of forests.

A 100 metre-plus asteroid will hit the Earth approximately every 5000 years, hence the excitement caused by 2024 YR4. These can form craters or cause significant damage on a regional scale.

Note: The likelihood of impact was correct at time of publication. This figure is likely to change over time.