Latest NASA Observations Make Asteroid 2024 YR4 The Most Dangerous Since Tracking Began

The odds of the asteroid striking Earth on December 22, 2032, are currently at 1 in 32, or 3.1 percent, rising from 2.6 percent yesterday. Though astronomers still expect further observations to show the asteroid to miss Earth, these new probabilities from NASA’s Center for Near Earth Object Studies technically make it the most-threatening space rock humanity has observed. Of these, only Bennu and 99942 Apophis have come close.

After it was first discovered in 2004, observations of Apophis placed it at level 2 on the Torino scale. However, further observations in December of that year placed it up to level 4 due to a 1.6 percent chance that the asteroid would hit us in 2029. This briefly rose to a 2.7 percent chance, before further observations ruled out a collision in 2029, as well as in 2036 and 2068, though they will still be close encounters. Asteroid 2024 YR4 has gone slightly higher in terms of odds of hitting Earth, but is smaller in size than Apophis, posing less of a threat to the planet.

While this growth in percentages may not sound too reassuring, fear not. We are not on an exponential curve here. As astronomers turn telescopes – including the JWST – towards the asteroid and narrow down its trajectory, you should expect changes to the percentage chance of it hitting Earth. 

While certainty for 2024 YR4 missing the Earth is the outcome we expect, it’s not up to us. It’s for nature to decide. In fact, nature already has settled the question. We just don’t know that answer yet. That’s why the tracking efforts continue.

Richard P. Binzel

“It is perfectly natural that the impact chances for asteroid 2024 YR4 will bounce around a bit,” Richard P. Binzel, inventor of the Torino Impact Hazard Scale for asteroids, explained in an email to IFLScience, pointing out that objects at level 3 on the scale will most likely be reassigned to 0 after further observations.

“While certainty for 2024 YR4 missing the Earth is the outcome we expect, it’s not up to us. It’s for nature to decide. In fact, nature already has settled the question. We just don’t know that answer yet. That’s why the tracking efforts continue.”

Rising percentages may seem scary, but it should reassure you to know that it is expected, and is the result of astronomers attempting to pin down its path. At the moment, the asteroid is heading out towards Jupiter. As it does so, astronomers are taking observations and attempting to narrow down its path. Think of it like placing a new dot on an imaginary line. With each new observation we get a new dot, which will eventually reveal the path the space rock is set on.

The impact odds will stabilize almost certainly in April, where the current observation window closes until 2028.

Dr Robin George Andrews

“Every new observation that comes in changes the trajectory of that line. Sometimes the final destination of this asteroid looks like it gets a little closer to Earth and sometimes it looks like it gets a little further away, so there’s still a lot of uncertainty,” asteroid-killing expert, science journalist, and author Dr Robin George Andrews told IFLScience in our exclusive feature on the global planetary defense response to asteroid 2024 YR4.

“The impact odds will stabilize almost certainly in April, where the current observation window closes until 2028.”

Should 2024 YR4 impact Earth, it would not be a world-ender due to its relatively small size of an estimated 40–90 meters (130-300 feet) wide. However, it is around the size of the asteroid responsible for the Tunguska Event, the largest impact in recorded history, which is thought to have been about 50 to 80 meters (160 to 262 feet). Depending on where it hit (if we are unlucky enough to be hit by it) it could cause similar levels of devastation. The most likely scenario is that it explodes as an airburst, though an impact could happen if it is at the larger end of size estimates made so far.

“It’s a very, very rare event,”  Richard Moissl, head of the European Space Agency’s (ESA’s) planetary defense office told AFP, adding: “This is not a crisis at this point in time. This is not the dinosaur killer. This is not the planet killer. This is at most dangerous for a city.”

For ESA’s part, they place the percentage chance of the object hitting Earth at a slightly lower 2.8 percent.

If further observations still show a risk of impact as the asteroid moves out of observation windows, then the Space Mission Planning Advisory Group (SMPAG) would begin to prepare plans for dealing with it, before passing them to the UN General Assembly. This could involve a mission similar to NASA’s DART, which altered the path of asteroid Dimorphos pretty spectacularly when it slammed into it in 2022.

There are still a lot of unknowns on this front that won’t be answered without more observations.

“There are many things you do to fight off asteroids, but you can’t fight an asteroid if you don’t know it’s coming. Hitting something that’s 40 meters versus 90 meters is quite a different kettle of space fish. You don’t want to break the asteroid into pieces unless you are sure the pieces are so small that they will burn up harmlessly in the atmosphere,” Dr Andrews explained. “So it’s a bit easier to do for 40 meters, definitely harder for 90 meters.”

For now, astronomers are hoping that further observations will lead to the percentages dropping to zero, as it has for other potential threats in the past.