Just over a month ago, on December 27, 2024, the Asteroid Terrestrial-impact Last Alert System (ATLAS) discovered asteroid 2024 YR4, two days after it had just made its closest approach to Earth — 515,000 miles, or a little more than twice the distance of our Moon. And while this is a fairly sizeable space rock, estimated to be between 40-100 meters in diameter (130-330 feet), or about the size of the objects involved in the 1908 Tunguska blast in Siberia, or Meteor Crater in Arizona ~50,000 years ago, things of this size actually pass by the Earth quite harmlessly with a fair degree of frequency.
What makes this particular space rock more notable is that there is now a non-negligible chance of it actually striking our planet on a future close encounter — more specifically on December 22, 2032, give or take about 1.5 days. Quoting from its own wikipedia entry:
As of 29 January 2025, 2024 YR4 is rated 3 on the Torino scale with a 1 in 77 (1.3%) chance of impacting Earth on 22 December 2032, and a 1 in 71 (1.4%) cumulative chance of impacting Earth beyond 2032.[5]
This may not sound like that big a deal yet, but the only other object to ever rate this high or higher on the Torino impact hazard scale thus far was Apophis back in 2004 when initial observations indicated a probability of 2.7% that it could strike our planet on Friday, April 13, 2029 — putting it at 4 on the Torino scale. Fortunately, further observations of its orbital trajectory soon reduced that probability to near zero, and now its Torino scale ranking is back down to 0.
Unfortunately, that is not what we’re seeing with the probability estimates with 2024 YR4. The initial estimate was actually down around 1.1%, but since then:
A search through archival Subaru Telescope images from 2016 did not find 2024 YR4, which rules out some distant approaches to Earth in 2032.[11] This raises 2024 YR4's impact probability to 3–6%, depending on whether the 25 December 2024 precovery observation is included in the orbit calculation.[13]
Again, that may not sound like something to get too excited about — going from a ~1/90 chance of a 5-20 megaton atmospheric blast in 2032 to a roughly 1/20 chance — but the probabilities are moving in the wrong direction, and that definitely makes me more than a bit nervous. The NYT also has an article out that generally tries to minimize the potential danger, except for this disturbing passage:
“The possibility that 2024 YR4 might impact in 2032 was identified right after discovery,” said Davide Farnocchia, a navigation engineer at the NASA center. But based on just a few observations, the prediction uncertainties for 2032 were initially very large. As the number of observations grew to the hundreds, he said, “the impact probability has gradually increased over the last month and has now surpassed 1 percent, an important threshold.”
...
What normally happens is that the impact odds plummet to zero as more observations come in and the asteroid’s orbit is better known with more precision.
The same story will probably unfold with 2024 YR4. “The most likely outcome is that further observations will rule out an impact,” Mr. Rankin said.
2024 YR4 is getting extremely faint as it travels away from Earth, meaning most telescopes are going to struggle to track it. “However, given this is a special case, members of the community have requested (and received) time on some of the larger and more capable facilities,” Dr. Rivkin said. “Those should do OK through April.”
Astronomers will also have an even greater opportunity to refine their predictions during the December 2028 flyby. But until then, it’s possible that an impact in 2032 won’t be entirely ruled out.
Let’s hope that the extended observations through April do lead to a lessening of the probability of a collision in 2032, otherwise we might be in for a very unpleasant surprise in 2028 when we should learn whether 2032 will really be something to worry about or not.
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UPDATE: For all those hoping there might be a chance of Mar-a-Lago being in the flight path of 2024 YR4, this is from the International Asteroid Warning Network (IAWN) pdf:
Impact Risk Corridor: The impact risk corridor for 2025 YR4, which is the region of Earth along which a potential impact could occur, extends across the eastern Pacific Ocean, northern South America, the Atlantic Ocean, Africa, the Arabian Sea, and South Asia
So with the possible exception of Hawaii, it doesn’t look like it would be a direct threat to the US — just don’t plan any Christmas vacations to the Aloha State for 2032! OTOH, that is where I live now...
I should also include a link to the Tunguska event of 1908, which seems to be the closest analog as to what 2024 YR4 might be capable of:
The Tunguska event is the largest impact event on Earth in recorded history, though much larger impacts occurred in prehistoric times. An explosion of this magnitude would be capable of destroying a large metropolitan area.[10] The event has been depicted in numerous works of fiction. The equivalent Torino scale rating for the impactor is 8: a certain collision with local destruction.
Note that if based on the 2028 fly-by, the odds of an impact actually increase to >99%, 2024 YR4 will automatically be “promoted” to a Torino rating of 8 (equivalent to Tunguska). OTOH, if its odds of impacting fall below 1% at any point, it will be downrated to a 1 or 0 the way Apophis was.
By way of comparison, a Torino 9 is capable of causing extreme damage over an entire continent, with global environmental effects that could last for several years — though not necessarily enough to end human civilization in the less affected parts of the world. That would be a Torino 10 (think Chicxulub extinction event 66 million years ago that ended the reign of the dinosaurs) — the upper end of which would effectively sterilize the planet of all life.
Finally found this graphic of the potential danger zone, from the Daily Mail. It looks like my Hawaii is fairly safe after all — unless it arrives a few minutes ahead of time. OTOH, China could also be potentially at risk if it’s a few minutes late.
