Impact odds continue to rise for 'city-killer' asteroid 2024 YR4
We're probably still safe from this space rock, but at the moment, the chances of having a very bad encounter in 2032 have gone up!
A predicted close encounter with asteroid 2024 YR4 in late December 2032 looks to be getting even closer.
In late January, it was reported that, shortly after its discovery, a newfound 'city-killer' asteroid named 2024 YR4 had rocketed to the top of NASA's asteroid impact risk list. At the time, NASA's Center for Near-Earth Object Studies (CNEOS) had the odds of this small space rock impacting with Earth as 1.3 per cent, or about a 1 in 77 chance, for December 22, 2032.
As of February 7, NASA and the ESA had increased those odds to 2.2 per cent, or a 1 in 45 chance of impact.
Update: With new observations added up until February 18, the odds have gone up again. NASA now gives a 3.1 per cent (1 in 32) chance of impact on Dec. 22, 2032. The ESA's Near-Earth Object Coordination Centre (NEOCC) has a 2.8 per cent (1 in 35) chance of impact on that date.
The Earth Impact Risk Summary for 2024 YR4 shows a 3.1 per cent chance of impact on Dec. 22, 2032, along with five other close approaches with far lower chances. Since several different orbits are calculated for the object, due to uncertainties in its path, each of these six entries represents one specific calculated path that intersects with Earth. Sigma VI reflects how close that particular impact orbit is to the object's most likely orbit (closer to zero = greater threat), Palermo scale gauges overall impact risk, while Torino scale represents the risk based on potential damage (with higher number = worse risk for both). (NASA CNEOS)
These chances are still quite low. As shown above, a 3.1 per cent chance of an impact is still a 96.9 per cent chance of a miss.
In fact, based on NASA's calculations, the most likely closest approach distance for 2024 YR4 on December 22, 2032 will be 122,539 km (compared to 120,137 km from the Feb. 7 calculations). That's a completely safe pass at about one-third of the distance to the Moon. The asteroid's farthest close-approach distance on that day is now just over 580,000, which is still over 1.5x farther than the orbit of the Moon.
The uncertainty region of asteroid 2024 YR4's Earth encounter on December 22, 2032 is shown in this diagram. Each orange dot in that uncertainty region represents the closest approach of one possible orbit of this asteroid, based on the observations up to date and the uncertainties that still exist in its orbit. (ESA NEOCC)
However, due to the potential damage caused by an asteroid impact, any object with any level of risk is worth keeping an eye on. With at least one of 2024 YR4's possible orbits resulting in a direct strike on Earth, astronomers are collecting as many observations of this space rock as they can to refine its orbit and determine just how much of a threat it truly represents.
Although each day the asteroid is getting farther away, and thus dimmer and harder for telescope to see, astronomers have proposed using the James Webb Space Telescope to track it for some time in the spring of this year. The telescope's sensitive instruments could give us a better idea of its exact path through space, as well as providing a more exact estimate of its size.
Still likely no real threat
Even with the odds of an impact increasing slightly, in all likelihood there's still no reason to worry about this asteroid.
"Whenever a newly discovered NEA [near-Earth asteroid] is posted on the Sentry Impact Risk Page, by far the most likely outcome is that the object will eventually be removed as new observations become available, the object’s orbit is improved, and its future motion is more tightly constrained," NASA CNEOS says on their website. "As a result, several new NEAs each month may be listed on the Sentry Impact Risk page, only to be removed shortly afterwards. This is a normal process, completely expected. The removal of an object from the Impact Risk page does not indicate that the object’s risk was evaluated mistakenly: the risk was real until additional observations showed that it was not."
This diagram shows the possible encounter distances of 2024 YR4 on December 22, 2032, with each red dot representing a different computed path for the asteroid as it flies past Earth, based on the current uncertainties in its orbit. The collected line of red dots is the asteroid's 'uncertainty region', which will become more narrow as more observations are taken. Since Earth is off-centre in the uncertainty region, it is more likely that this encounter will be a miss, and once Earth exits that uncertainty region, the asteroid will likely be removed from the Sentry Impact Risk Page. (ESA)
READ MORE: Newfound 'city-killer' asteroid has chance of hitting Earth in 2032
We have already seen examples of this process over the years.
"The most famous case was (99942) Apophis, which reached level 4 in December 2004, shortly after its rediscovery. A few days later its impact probability reached 3%, the highest ever recorded for a significantly large asteroid," the ESA stated in their most recent Near-Earth Object Coordination Centre newsletter (pdf). "Precovery data from early 2004 quickly clarified that the object was not going to impact in 2029."
For asteroids, "precovery" refers to the process of scanning through telescope observations taken in the days, weeks, and months leading up to when an object first came to their attention. This can add a significant amount of data to help refine an object's orbit.
"Unfortunately, for 2024 YR4, careful searches for precovery detections have so far come up empty handed," the ESA added.
Even so, as astronomers continue to record the asteroid's motion, night by night, they will get closer to knowing for sure if 2024 YR4 will hit or miss in 2032. Another predicted 'close' approach, at a distance of roughly 8 million kilometres in December of 2028, will likely help them refine the object's orbit even further.
What if?
If astronomers make all the observations they can, and perform all of the orbit recalculations possible, and the odds of impact still keep increasing, we do have a fairly good idea of where this asteroid may end up hitting.
Taking into account both the uncertainties in 2024 YR4's orbit, and the rotation of the Earth during the window of impact, German amateur astronomer Daniel Bamberger plotted its impact risk corridor across the map.
The narrow impact risk corridor for asteroid 2024 YR4. (Daniel Bamberger/Wikimedia Commons (CC BY-SA 4.0))
The most likely scenario for this impact is that it would hit somewhere over water, whether that's the Pacific, Atlantic, or Indian Ocean. However, the narrow risk corridor does cross parts of northern South America, central Africa, Yemen, Oman, central India, and Bangladesh.
Wherever it hits, based on the size and speed of the asteroid, the impact would be the equivalent of setting off a 7 megaton bomb.
For comparison, the Chelyabinsk impact of February 15, 2013, released the equivalent energy of about 440,000 tonnes of TNT. It shattered thousands of windows across the city, caused some minor structural damage, as well as roughly 1,500 injuries.
If 2024 YR4 impacted over a large urban area, like Mumbai, India (which does lie along the impact risk corridor), the effects would be far more devastating, potentially destroying a large section of the city.
Is there anything that could be done?
If 2024 YR4 turns out to have a real threat of impact, there is one proven method of protection that could be deployed.
In late September, 2022, NASA's DART spacecraft, the Double Asteroid Redirection Test, successfully slammed itself into Dimorphos, the tiny moon of asteroid Didymos, in NASA's very first 'kinetic impactor test'.
This graphic shows the concept behind the DART mission, to change the orbit of Dimorphos around Didymos by crashing the spacecraft into the smaller asteroid. (NASA/Johns Hopkins APL)
The mission was a success, putting Dimorphos onto a brand new orbital path around its parent asteroid, and proving that this could be an effective method to use on any asteroid that posed a significant threat to Earth.
Thus, if 2024 YR4 was a danger to us, a similar spacecraft could be launched prior to the 2028 encounter, to knock the asteroid onto a path that would prevent it from coming anywhere near us for the foreseeable future.
(Thumbnail image is an artist's impression of an asteroid entering Earth's upper atmosphere, produced by Kevin M. Gill (CC by 2.0))