The threat of Near-Earth Objects (NEOs), while generally low, remains a significant concern due to the potential to cause regional or even worldwide devastation. These space rocks, which orbit close to Earth, are constantly monitored to assess their likelihood of impact. The Torino Scale has been developed and is used to classify the risk level of these objects, ranging from 0 (no threat) to 10 (certain, catastrophic impact). Thankfully most detected asteroids fall into the 0 or 1 category. Others, especially new discoveries can be put into higher categories but as our analysis of their trajectory is updated, they are usually dropped back down the scale.
Artist impression of the asteroid belt between Mars and Jupiter.
There are a host of observatories whose singular task is to keep an eye on NEOs but on 8 March 2025, the James Webb Space Telescope (JWST) observed asteroid 2024 YR4, confirming that it poses no threat to Earth in 2032 or beyond. This makes it the smallest asteroid Webb has ever studied and one of the smallest whose size has been directly measured. Using its Near-Infrared Camera (NIRCam), Webb captured reflected light from the asteroid, while its Mid-Infrared Instrument (MIRI) detected thermal light, helping us better understand its composition and characteristics.
Artist impression of the James Webb Space Telescope (Credit : NASA)
The team of scientists used the NIRCam and MIRI data to analyse its thermal properties, including how quickly it heats up and cools. The findings suggest it doesn’t share characteristics with larger asteroids, perhaps due to its fast spin and a rocky surface without fine-grained sand. Instead, the surface of 2024 YR4 seems to be made up of fist-sized or larger chunks of rock. Webb’s observations also revealed it’s approximately 60 metres wide, comparable to the height of a 15-story building.
It’s being closely monitored by the ESA’s Near Earth Objects Coordination Centre in Italy, working alongside NASA and other international experts to refine its orbit. The process is much like studying a game of tennis with a camera. If you take one image of the ball as it sails over the net, quick analysis can tell you exactly where it is but you can’t tell where it’s going much less predict its position at some point in the future. Instead you need to take a number of images to understand its path. After careful tracking, it was confirmed that 2024 YR4 poses no threat to Earth. Phew!
The image collage shows, among other things the vast blackness of space, scattered with small, blurry galaxies in shades of orange, blue, and white. A faint dot, representing asteroid 2024 YR4, is highlighted with a white square near the top right of the main image and on the right side of the collage, two zoomed in insets show the asteroid in more detail, or at least as much as Webb can discern.
Source : Webb snaps photographs of Asteroid 2024 YR4