Potentially Hazardous Asteroid 2024 YR4
Every once in a while, the Universe likes to remind us it has the ability to kill us
On January 29, an email from the International Asteroid Warning Network notified, among others, the United Nations Office of Outer Space Affairs office, that on Dec 22, 2032, the Earth could be hit by an asteroid big enough to wipe out a city. That asteroid, cataloged as 2024 YR4, was initially found to have a 1.3% chance of hitting Earth. (Latest risk available on NASA CNEOS Sentry site)
We’ve seen this kind of notice before. Back in 2004, an asteroid that would come to be named 99942 Apophis was discovered, and initial orbital calculations gave it a 2.7% chance of hitting Earth on April 13, 2036. Back then, it felt like each new set of observations dropped our chance of being hit, and by 2013, we knew we should be safe. This experience both added urgency to our work learning how to deflect asteroids and made us foolishly trust that the next potentially hazardous asteroid would also prove to be a nothing burger.
And, in pretty much every story about YR4, journalists have correctly said, “Further observations may reduce risk of impact to basically zero”.
But so far, new observations and efforts to find the asteroid in old data sets have only increased the chances of impact. As I write this on 9 Feb 2024, the risk stands at 2.2% chance of impact, with a level 3 Torino Scale impact being possible. The Torino scale is essentially a way of combining information on both how dangerous an impact could be and how likely it is to happen. Together, these factors tell us how much we should be paying attention to a passing space rock.
Most asteroids on NASA’s list of potentially hazardous asteroids are a level 0 hazard, which is defined as “The likelihood of a collision is zero, or is so low as to be effectively zero. Also applies to small objects such as meteors and bodies that burn up in the atmosphere as well as infrequent meteorite falls that rarely cause damage.” All the asteroid alerts we have talked about on my podcast, Escape Velocity Space News - alerts where ATLAS or a similar system let us know about a meteor we’d be able to see streaking through the atmosphere as they became a couple of cm-sized meteorites - have been level 0 impacts.
2024 YR4 is holding firm at level 3 on the Torino scale, which is defined as: “A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of localized destruction. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by the public and by public officials is merited if the encounter is less than a decade away.”
The potential impact is in 2032, putting it solidly less than a decade away, and all of us need to sit up and pay attention as scientists work to figure out what is going on.
Measuring somewhere between 130 and 300 feet in width, or 40-90 meters wide, it is small enough to only be visible when it is closest to Earth and large enough to wipe out a city if it hits (or trigger a nasty Tsunami). Most recently, it made its closest approach on Dec 25, 2024, and prior to that, in 2016 and 2020. Researchers are now calculating all the possible orbits that can be fit observations taken since its discovery, and they are looking through the archives to see if they can find the asteroid somewhere that means we are safe… or find it somewhere that means we’re not.
So far, archival images from the Subaru telescope have been found that line up with a bunch of “good, doesn’t hit Earth” possible orbits, and the asteroid has been seen in none of those images. This negative confirmation caused an increase in the possibility of impact. More searching is being done, and a whole lot of new images are being taken as this asteroid races into the distance and ultimately fades out of view of even our largest telescopes.
Per his blue sky accounts, researcher Andy Rivkin and his team have successfully gotten JWST time to pin down the size of the asteroid. While we may not be able to get enough data to know for certain if we are or aren’t in danger, knowing the asteroid’s size will let us plan to move it if we need to.
The timeline to do something isn’t very long. In 2028, when next we pass near one another, Earth and YR4 will be about 8 million km apart, which isn’t going to allow precision radar measurements, but it will allow the orbit to be better determined. If we can get our act together, it may even allow us to send a spacecraft out to chase down the asteroid and acquire the kinds of observations that tell us if it is one mostly solid object or some kind of a boulder or rubble pile.
NASA and ESA have minimal experience moving asteroids, thanks to the DART mission. Planning started in earnest for DART in 2015, with design and assembly starting in August 2018 and the launch occurring in November 2021. If the will and funding were put in place, we could launch a twin in time to take advantage of YR4’s closest approach in 2028.
I expect high-level decisions to be made after the JWST observations, and I’ll be following closely as we see what international-level planning occurs around how we, as a planet, should respond.
Folks, at the end of the day, all of us humans are one people, sharing one sky in a universe that would be happy to kill us all.
Even if YR4 turns out to be of no consequence, it is necessary for us to make time to prepare for the asteroid that will be of consequence. As Dr Robin Andrews correctly points out, 2024 YR4 is just one of the some-odd 230,000 objects we estimate have near-Earth orbits and are this same, able-to-kill-cities, size. Telescopes like Vera Rubin Observatory will do one heck of a job finding these space rocks, but they won’t find all of them, and they may find some of them as them when they’re on their way in toward impact. As humans, we are good at developing technologies that can help keep us alive. From seat belts to systems that shut off subways when Earthquakes start to all manner of weather alert networks that indicate when to evacuate and when to shelter in place. We have gotten good at keeping ourselves alive in the face of terrestrial threats. Now, we just need to master the space rock threat.
If you’d like to learn more about threats from space, I recommend Phil Plait's oldie but goodie, Death from the Skies (Amazon Affiliate Link).
And if you’re in the mood to Doomscroll Mother Nature, Blue Sky seems to be the place to scroll. Follow along on hashtag #2024YR4 for asteroid updates. I, for one, am also hoping the relevant pages on NASA’s Center for Near Earth Object Studies will stay online.