Universe Today
Although astronomers have ruled out a smash-up between Earth and an asteroid known as 2024 YR4 in the year 2032, the building-sized space rock still has a chance of hitting the moon. In fact, the chances — slight as they are — have doubled in the past month.
The latest assessment from NASA puts the probability of a lunar impact on Dec. 22, 2032, at 3.8%. That's an increase from the 1.7% figure that was reported in February. Since then, further observations made by ground-based telescopes and NASA's James Webb Space Telescope have somewhat reduced the uncertainty over where exactly the asteroid will be when its orbit intersects Earth's orbital path (and the moon's).
Over the course of observing 2024 YR4, astronomers had set the chances of a collision with Earth in 2032 as high as 2.3% — but that wasn't because of what the asteroid may or may not do over the next seven years. Instead, it merely reflected how little was known about YR4's precise orbit. The chances of an Earth impact fell to zero more than a month ago as more observations came in.
Something similar might well happen to the chances for a lunar impact. If the calculations progress the way they usually do for asteroid orbits, the chances may go up for a while but then vanish completely. Stay tuned: The Webb telescope is due to check in again with YR4 in late April or early May.
What if it turns out that the asteroid is truly on course to hit the moon? "There might be an unbelievable light show," former NASA astronaut Ed Lu, who's in charge of the B612 Foundation's Asteroid Institute, said last week at the University of Washington.
The Asteroid Institute's researchers and collaborators are using computerized analytical tools to keep track of 2024 YR4 and thousands of other asteroids in our celestial neighborhood. Its estimates of lunar impact probabilities parallel NASA's assessments.
If YR4 does hit the moon, it's likely to happen near the lunar south pole, sometime around noon GMT on the appointed day in 2032, Lu said.
Over the course of billions of years, lots of space rocks have peppered the lunar surface, but this one could leave a mark. The latest estimates suggest that 2024 YR4 is 174 to 220 feet wide (53 to 67 meters wide), about the size of a 10- to 15-story building. Lu said an asteroid that big could create a crater as wide as 2 kilometers (1.2 miles).
"If anyone here has been to Meteor Crater [in Arizona] ... that's about 1 kilometer wide. So we could be witnessing the formation of a crater roughly double that size on the surface of the moon," Lu said.
"That's a lot of material thrown up that will basically end up in orbit around the moon, or surrounding the moon," he said. "If it hits, you will be able to see that from the Earth with the naked eye. A pretty big explosion — it will throw a lot of stuff up. In fact, I will bet that there will be meteor showers on Earth."
The study of 2024 YR4 serves as good practice for what astronomers are likely to face when the Vera C. Rubin Observatory begins science operations in Chile later this year.
"The Rubin Observatory is going to be about 10 times more effective at finding and tracking asteroids than all other telescopes combined, worldwide," Lu said. "For sure we're going to find ones that are going to come very close to the Earth. Now, are we going to find something that might hit the Earth? Actually, I think it's likely."
