James Webb Space Telescope to size up asteroid 2024 YR4

The James Webb Space Telescope (JWST) is to be pointed at asteroid 2024 YR4 to reduce uncertainty regarding the chances of the object impacting Earth in the coming years.

The asteroid is not particularly large – the best guess is that it measures somewhere between 40 and 90 meters (130-295 feet) – and there is an approximately 98 percent chance it will safely pass the Earth on December 22, 2032, but if it impacts the planet, the consequences for the affected region could be dire.

Although scientists won’t be able to determine definitively whether the asteroid will closely approach Earth until 2028, using the JWST will allow the significance of the impact to be predicted by reducing the uncertainty surrounding the size of the object. The European Space Agency (ESA) pointed out: “The hazard represented by a 40 m asteroid is very different from that of a 90 m asteroid.”

The problem is that astronomers currently rely on visible light reflected from the Sun when studying the asteroid. The brighter the object, the bigger it tends to be. However, as ESA noted: “2024 YR4 could be 40 m across and very reflective, or 90 m across and not very reflective.”

What to do about the asteroid hinges on the significance of the threat posed, so getting a better idea of the object’s size is crucial.

Scientists plan to use the observatory’s MIRI instrument to measure the infrared light (heat) emitted by 2024 YR4. The plan is to use this data to better estimate the asteroid’s size and feed that into response planning.

Observations with the JWST’s NIRCam instrument will complement MIRI’s thermal data. They will also provide additional measurements of the asteroid’s position once it is beyond the reach of Earth-based telescopes.

The plan is to make the first round of observations in March when the asteroid becomes observable by the JWST. A second round will take place in May. All told, the total observational time will be approximately four hours. The data will be made publicly available.

Time on the JWST is usually booked well in advance, and the telescope is in high demand. However, each year, there is a small amount of “Director’s Discretionary Time” for time-critical or new discoveries made after the annual proposal deadline.

Reducing the uncertainty around 2024 YR4 seems a fine use of it. ®