From - Sky & Telescope
By - David L. Chandler
Edited by - Amal Udawatta
Daniel BambergerAstronomers — professional and amateur alike — have turned their attention to an asteroid with a slight chance of impacting Earth in 2032, based on current observations. While the possibility is slim, and more observations are needed, the object itself might be large enough to devastate a city, motivating follow-up observations as well as archival searches for pre-discovery observations.
Astronomers — professional and amateur alike — have turned their attention to an asteroid with a slight chance of impacting Earth in 2032, based on current observations. While the possibility is slim, and more observations are needed, the object itself might be large enough to devastate a city, motivating follow-up observations as well as archival searches for pre-discovery observations.
The asteroid, designated 2024 YR4, was first noticed on December 27, 2024, by the Asteroid Terrestrial-impact Last Alert System (ATLAS); searches quickly revealed that ATLAS had already imaged it two days earlier. Then, as observations accumulated, astronomers could roughly determine its orbit. That’s when the realization dawned: The object has some chance of striking Earth.
The discovery marks only the second time that an asteroid’s impact risk has reached greater than a 1% chance
Only one other object, asteroid 99942 Apophis, discovered in 2004, has ever reached that high on the scale. That asteroid peaked at 4, with a possibility of impact in 2029. But additional observations soon ruled that out, sending it back to a Torino rating of 0 — meaning no possible impact within the next century.
The chance of impact for 2024 YR4 is still slim: NASA’s Jet Propulsion Laboratory estimates 1.2%. But if it does happen, German astronomer Daniel Bamberger (Northolt Branch Observatories) has used observations in hand to constrain the possible impact in time and location: The impact would take place on December 22, 2032, somewhere along a long line that extends from the Pacific Ocean off the coast of Mexico, through Ecuador and northern South America, across the Atlantic, through central Africa (from Kenya to Somalia), and then across to northern India.
The possible impact track covers big stretches of ocean as well as populated areas and some large cities. “I’d be really excited to see an impact,” Bamberger says, “but I don’t want it to be this one. Something over Antarctica, please!”
Given 2024 YR4’s estimated diameter of 40 to 100 meters — somewhere between the size of a tennis court and a football field — its impact could result in anything from the Chelyabinsk air-blast in 2013 to the ¾-mile-wide Barringer Crater in Arizona. It all depends on this object’s true size and mass, and those remain uncertain enough that the magnitude of a potential impact could vary by more than a factor of 10, Bamberger says.
Richard Binzel (MIT), a specialist in asteroid observations and developer of the Torino scale, explains that, until more observations are obtained, the asteroid’s orbit, and thus its current position in space, can't be known exactly. “When we first discover an object, there’s uncertainty about where it’s going to be many years or decades into the future, and that uncertainty stretches out into a long thin noodle,” he says. The spaghetti shape comes about because the greatest uncertainty lies along the direction of travel.
“As we get more and more observations of this asteroid . . . most likely, the noodle will begin to shrink,” he adds. “Eventually, we expect that the pinpoint spot for that tiny leftover grain of the noodle will miss Earth. That’s what the odds favor.”
But making those observations could take some time, and with the asteroid now receding fast, obtaining data precise enough to further refine its orbit will be increasingly difficult. It will return to Earth’s vicinity in late 2028, at which point it should be possible to determine a very precise orbit, and either positively rule out the chance of impact or prove that it’s highly likely.
“More and more telescopes on Earth are making an effort to continue to follow the object,” Binzel says, “so I’m optimistic that we’ll get good tracking data over the next several weeks.”
On Closer Inspection . . .
It’s also possible that an impact is more likely than JPL’s initial estimate. Sam Deen, a California-based amateur astronomer, says that he searched through observations from the Subaru telescope in Hawai‘i taken in 2016, looking at the position the asteroid would have had if it were on possible non-impacting trajectories. He found no trace of the asteroid in areas covering roughly 80% of all such trajectories. That finding, in turn, raises the odds for a collision, which he estimates at between 3% and 6%.
“I invite people to double check me,” he says, “because it’s been just me looking at this. I could have missed something.” If his calculations are correct, it means the asteroid will pass at least within 120,000 km (80,000 miles) of Earth in 2032.
Deen tells Sky & Telescope that one way to rule out — or in — the possibility of impact is to find prior observations of exactly the point where the asteroid would have had to be if it were indeed on a collision course. If there were nothing there, then the asteroid couldn’t be on that course, and an impact would be ruled out.
Unfortunately, no publicly available images cover that particular patch of sky deeply enough to have resolved the issue. However, archives show that a telescope at Palomar Observatory did take three images of that exact region of the sky, also in 2016 — it’s just that they’re not yet not public. Deen has reached out to the observatory to see if those images could be released. If so, we could potentially resolve the question of 2024 YR4’s possible impact once and for all.
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