NASA is deploying the James Webb Space Telescope (JWST) to observe a potentially dangerous asteroid, which now has a 1-in-43 chance of striking Earth. Discovered in December 2024 by NASA's Asteroid Terrestrial-impact Last Alert System, 2024 YR4 is currently at the top of the agency's asteroid watch list.
The space rock, roughly 180 feet (55 metres) across - about as tall as the Leaning Tower of Pisa - has a 2.3 per cent (up from 1 per cent) chance of hitting Earth in December 2032. While it won't cause a mass extinction, it may have the same impact as the 1908 Tunguska event, which flattened 80 million trees in Siberia.
Current models suggest that if YR4 were to collide with Earth, the explosion could be equivalent to 15 megatons of TNT - 100 times more powerful than the Hiroshima bomb. Data from JWST will be crucial in refining impact predictions and guiding response strategies by ESA, NASA, and other global space agencies.
Recognising the dire situation, an international team of astronomers has been granted emergency use of the JWST. The European Space Agency (ESA) pointed out the importance of refining size estimates, saying that a 40-metre asteroid presents a vastly different risk than a 90-metre one.
Why James Webb?
Unlike ground-based telescopes, JWST's position in space allows it to avoid interference from Earth's atmosphere, giving it a clearer view. The telescope will use its infrared instruments to measure the heat emitted by the asteroid rather than just visible light, which helps in determining its actual size. "2024 YR4 could be 40 m across and very reflective, or 90 m across and not very reflective," ESA officials explained.
The first round of observations is scheduled for March 2025, when the asteroid will be at its brightest. A follow-up observation will take place in May as YR4 moves away from the Sun, offering the last opportunity for study until the asteroid returns in 2028.
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