‘City Killer’ Asteroid Is Size Of Apartment Block — Webb Telescope

An asteroid that was until recently thought to be on a collision course with Earth in 2032 has been measured by the James Webb Space Telescope.

Asteroid 2024 YR4, which is now thought not to pose a threat to Earth, is about 200 feet (60 meters), which is about the size of a 15 storey building. That’s right in the middle of the 130-300 feet (40-90 meters) range that astronomers has suspected.

However, knowing how to use the Webb Telescope to study such a small asteroid could prove hugely useful if and when another incoming asteroid is on course to strike Earth in future.

Fist-sized Rocks

Astronomers used Webb’s Near-Infrared Camera to capture reflected sunlight from the asteroid and its Mid-Infrared Instrument to study 2024 YR4’s heat. The results revealed not just its size, but hints of a surface may be covered in fist-sized or larger rocks.

If 2024 YR4 were to srike Earth, it would do so at a velocity of 10.6 miles (17 kilometers) per second — about 38,028 miles (61,200 kilometers) per hour. It would most likely explode above the surface during an event equivalent to around eight million tons of TNT. That’s about 500 times the power of the atomic bomb dropped on Hiroshima, according to Wired.

Given that the size of a crater is about 20 times the size of the impacting body, 2024 YR4 would produce a crater 0.75 miles (1.2 kilometers) wide.

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Webb’s Smallest Target So Far

NASA announced at the end of February that the chances of 2024 YR4 strilking Earth during a close pass in 2032 were near-zero. So why was Webb used to get a close up? “This is the smallest object targeted by the mission to date, and one of the smallest objects to have its size directly measured,” said Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory, the principal investigator of the study. “We are interested in using the observatory to measure its properties to understand what asteroids of this size are like to help inform the hazard they could pose to Earth.”

Astronomers expect more objects like 2024 YR4 to be found in future. “Observations using the most powerful telescope we have right now are invaluable,” said Rivkin, just in case there’s a more urgent need should another asteroid pose a potential impact threat.

Wishing you clear skies and wide eyes.