B Asteroid 2024 YR4 has a 1% risk of a multi-megaton impact in 2032 (now ruled out)

[mfb]

TL;DR Summary

A ~50 meter object has a risk to impact Earth in 2032.

Asteroid, Data - 1.2% risk of an impact on December 22, 2032. The estimated diameter is 55 m and an impact would likely release an energy of 8 megatons of TNT equivalent, although these numbers have a large uncertainty - it could also be 1 or 100 megatons.

Currently the object has level 3 on the Torino scale, the second-highest ever (after Apophis) and only the third object to exceed level 1. Most likely it will miss, and if it hits then most likely it'll hit an ocean and be harmless, but it has the potential to destroy a city.

The observation arc is only a month long, we should get improved orbit estimates soon. It is common that these will show an increased impact probability for a while until even better observations then rule out an impact. It has an orbital period of 4 years and it's currently close to the Sun. If observations can't rule out an impact by the time it gets too dim for further measurements, this would be a possible redirect mission candidate, intercepting it the next time it's close to perihelion in late 2028/early 2029. By then we should know if it's going to hit Earth or not.

 

[Drakkith]

Random information:

The minimum speed for an object freefalling under gravity to hit the Earth (specifically hitting the upper atmosphere, where it begins to slow down) is roughly 11 km/s, which is the escape velocity of the Earth.

Most objects hit the upper atmosphere at around 17 or 18 km/s. This is because they fall towards the Sun from further out than Earth's orbit, and then they fall towards Earth, picking up speed the whole way.

A long-period comet, or other object in an extremely elliptical solar orbit, can impact at upwards of 50-70 km/s.

A 1000 kg (1-ton) object travelling at 70 km/s has a kinetic energy of 2.45 terajoules, or 585 tons TNT equivalent.

The average comet mass is 500 trillion kg, or 5x10^14 kg. At 70 km/s the impact energy is a staggering 1.225 million exojoules, or 293 million megatons, the equivalent of over 5 million Tsar Bombas, the most powerful nuclear weapon every detonated.

Ref: https://www.lpi.usra.edu/exploration/training/illustrations/craterMechanics/

Notice in the above image that the minimum lunar impact velocity is about 2.4 km/s, much less than Earth's because of the Moon's lower gravity. But even with lower minimum and average velocities, even pebble-size impactors are lethal on the Moon thanks to the lack of an atmosphere. So keep that in mind when talking to your real estate agent!

 

[mfb]

It is common that these will show an increased impact probability for a while until even better observations then rule out an impact.

Now up to 2.3%, and some preliminary estimates say ~5% (taking into account non-observations to limit the range of possible trajectories). Following its trajectory until it gets too dim to observe won't improve the estimates much, but if the asteroid can be found in older observations then we might get ~0% or ~100% without waiting until 2028.

 

[Demystifier]

TL;DR Summary: A ~50 meter object has a risk to impact Earth in 2032.

if it hits then most likely it'll hit an ocean and be harmless

8 megatons of TNT corresponds roughly to a magnitude 4 earthquake, which is not sufficient for a significant tsunami. So it seems right that it would be harmless.

 

[ohwilleke]

8 megatons of TNT corresponds roughly to a magnitude 4 earthquake, which is not sufficient for a significant tsunami. So it seems right that it would be harmless.

Unless it hits a city.

I've seen newspaper reports, including the one linked above, with maps putting the most likely impact zone fairly close to the equator, by the way, where there are still some big cities, but not as many as lots of other potential likely impact zones.

Impacts near Mumbai, India, and Lagos, Nigeria would be particularly worrisome worst case scenarios.

If a planetary defense effort couldn't prevent it from hitting Earth entirely, it might try to nudge the asteroid a little bit to the north, where much of the potential impact zone involves deep deserts, or a little bit to the south, where there are fewer big cities and more oceans.

 

[DaveC426913]

I vote for south.

Who's with me? The sooner a ground-swell of voting starts, the more likely we are to win the battle.

 

[snorkack]

Bogota, Calcutta and Dhaca are also around the path.

 

[Frabjous]

We cannot tell if it will hit the earth, but we can narrow down the hit points?

 

[Ibix]

We cannot tell if it will hit the earth, but we can narrow down the hit points?

I don't know if this is the case, but it may be that they have more confidence in one dimension than another, leading to a range of probable paths that form a plane rather than a cone. That would mean that either it hits on the intersection between the plane and the Earth's surface or it doesn't hit.

Or it could just be garbage, as your question implies. I don't know.

 

[DaveC426913]

We cannot tell if it will hit the earth, but we can narrow down the hit points?

If you look at any diagrams of potential impacts for space junk, they are invariably a long, narrow ellipse, with its semi-major axis as much as ten times longer than its semi-minor axis.

I am not a meteor scientist, so this is (informed) speculation. The unpredictibility occurs mostly in when it will fall - it's coming in at an oblique angle, so a small range in longitudinal error corresponds to a very large range in the actual moment it hits the atmo. Unlike in the lateral case, where a small lateral range corresponds to only a small change in its lateral location when it hits.

Think about a tennis ball gun being fired low over a pond. An error of one degree to left or right will cause it to hit a few feet to left of the right of the target. But one degree high or low could make a vast difference in whether it falls long or short of the target. And yes, in theory, it could go so long as to miss the pond altogether.

I suspect there are actually two factors:

1. the margin of error, as demonstrated
2. the changing path, as imparted by gravity as it approaches Earth (which adds another element of error).

• Earth's pull won't have much effect pulling it off-course to one side or another. In fact: I suspect lateral drift is a negative feedback loop - the more laterally the object moves, the more it is pulled back to centre.
• Whereas longitudinal drift, is a positive feedback loop - the more it is pulled down, the more it is pulled down, as it were. Likewise, the less it is pulled down the less it is pulled down (these are all very technical terms).

Finally, considering that the prediction is 98% or so that it won't hit, the full predicted area of passage probably looks more like this (not to-scale):

 

[Frabjous]

One of the replies (Horton-Smith) in this article seems to address my question
https://skyandtelescope.org/astrono...ance-of-earth-impact-in-2032/#google_vignette

 

[ohwilleke]

One of the replies (Horton-Smith) in this article seems to address my question
https://skyandtelescope.org/astrono...ance-of-earth-impact-in-2032/#google_vignette

Recapping that discussion:

Glenn Horton-Smith
February 15, 2025 at 9:14 am

I'm confused why the "risk corridor" is so narrow. The JPL Horizons prediction for the asteroid's 2032 close approach has a 3 standard deviation uncertainty of about 20,000 km in the J2000 "Z" coordinate (which is the direction perpendicular to the equatorial plane, i.e., north/south on the map). That's 3 times the radius of the Earth. The uncertainty in the other directions is even larger.

In any case, the center of the most likely "corridor" for 2024 YR4 passes 160,000 km away from Earth. (Give or take 700,000 km or so.)

Is there some incredibly huge correlation between the orbital uncertainties that makes the band of possible trajectories so compressed in "Z" this far from the best fit trajectory?

Glenn Horton-Smith
February 16, 2025 at 7:00 am

So just to answer my own question: yeah, there is indeed a really huge correlation between the 6 orbital parameters.

If you ask JPL's Small Body Database API the right question you can get the covariance matrix of the orbital elements. A little principal component analysis reveals a nearly 100% correlation between eccentricity, perihelion distance, time of perihelion passage, argument of perihelion, and inclination So just to answer my own question: yeah, there is indeed a really huge correlation between the 6 orbital parameters.

Also, if you ask JPL's "Horizons" system the right query (CA_TABLE_TYPE="extended"), it will give close-approach ellipse in coordinates perpendicular to the track of the asteroid, and it is indeed really narrow in one dimension, like less than 1 km. They do warn that the these uncertainties can be off by factors of a few or more.

Anyway, the thinness of the line on the map by Daniel Bamberger is not inconsistent.

 

[Ken Fabian]

If it is a "loose rubble pile" it may largely break up in the atmosphere and may not cause tsunami over oceans or a single big impact on land, with the damage that goes with that. That doesn't make it harmless; a mid-air break up of a mere 10 ton meteorite blew out windows and was so bright that eye injuries were common. (Chelyabinsk Meteor, 2013).

I'm not aware of eardrums being burst but would not be surprised that a meteor breakup could do that, affecting people over a wide area.

I've read that it is probably, but not certain, S-type - stony - which could be lots of loose rocks. Not as dense as M-types, they are still dense, ie a lot mass for the size.

Getting better observations seems to be the correct near term response. Whether and how to divert or explosively disperse - contingency planning - seems worthwhile.

I note that (according to Pew Research) searching for potential impactors is/was the most supported objective for NASA amongst the US public. Not sure that funding priorities reflect that - but nor am I convinced priorities should be a popularity contest. I know that I think meteor defense is an objective for space agencies that I favour - long term, quite technologically ambitious with potential for peaceful international cooperation.

Pew Research -

Monitoring asteroids that could potentially hit the Earth ranks at the top of the public’s priority list for NASA. Monitoring the planet’s climate system also ranks highly as a priority for NASA.

 

[Ken Fabian]

Whilst meteor defense is apparently the single most popular NASA objective for US citizens I am not convinced that level of popularity applies to preventing lesser meteor strikes that are not expected to hit or directly harm the USA.

 

[DaveC426913]

Whilst meteor defense is apparently the single most popular NASA objective for US citizens I am not convinced that level of popularity applies to preventing lesser meteor strikes that are not expected to hit or directly harm the USA.

"American Congress approves trillion dollar budget for meteor shield.
Everybody who matters breaths sigh of relief."

 

[russ_watters]

Here's a good visual of the prediction/uncertainty region, and how it has shrunk over the past few weeks:

https://blogs.esa.int/rocketscience...s-apophis-as-riskiest-asteroid-ever-detected/

You can see why the likelihood of an impact goes up as the uncertainty region gets smaller -- but that doesn't necessarily imply the likelihood will keep rising to 100%. The uncertainty region is not centered on Earth but rather is offset perhaps half a moon distance from Earth. So while a trend of increasing likelihood of impact is not good, it does seem to be likely to increase a bit more and then drop to zero once the uncertainty region is around 1 lunar distance from Earth wide. Probably.

 

[mfb]

Improved measurements have dropped the risk to 0.3%. Earth is now at the outer edge of the uncertainty region, follow-up measurements (JWST can likely see the asteroid until May) will most likely rule out an impact completely.

Where the trajectory of the asteroid crosses Earth's orbit is well-known, the uncertainty is basically all in the timing. If it arrives "early" then it misses Earth, if it arrives "late" then it misses Earth, in between there is a time where it crosses Earth's orbit just as Earth is there.

 

[ohwilleke]

Improved measurements have dropped the risk to 0.3%. Earth is now at the outer edge of the uncertainty region, follow-up measurements (JWST can likely see the asteroid until May) will most likely rule out an impact completely.

Where the trajectory of the asteroid crosses Earth's orbit is well-known, the uncertainty is basically all in the timing. If it arrives "early" then it misses Earth, if it arrives "late" then it misses Earth, in between there is a time where it crosses Earth's orbit just as Earth is there.

I can confirm this: https://www.space.com/asteroid-2024yt4-impact-risk-drop-nasa

 

[Ken Fabian]

Correction to my @13 post, re eye injuries; I assumed the eye injuries were from the bright flash but may have been from broken glass. The reports I read didn't specify. Apologies.

(Update - I subsequently tried to find out and that led to https://www.sciencedirect.com/science/article/abs/pii/S0019103518305104 )
From that article -

A population of 1.7 million people lived in the affected area (Popova et al., 2013). About 1% of the 1758 people who chose to submit an online report in the weeks after the event reported some form of injury, mostly sunburn, hurting eyes, temporary deafness and headaches (Popova et al., 2013; Kartashova et al., 2018). A fraction of 4.4% of respondents who were outside ended up with some level of sunburn, suggesting an energy dose of far-UV radiation >0.7 kJ/m2 (Huang et al., 2010). More than half reported they could feel the heat from the fireball. No fires were ignited by the event. Ignition of ground litter requires about 350 kJ/m2 (Glasstone and Dolan, 1977) and this limit was not reached. Eardrums will typically rupture at about 16 kPa (Mannan, 2005), but no reports of such injuries were made. Instances of both glass cuts and being hit by (or blown into) obstacles were usually found at similar frequencies in the area where overpressures were >1 kPa, independent of the distance from the Chelyabinsk meteoroid trajectory out to about 50 km (Kartashova et al., 2018).

- which means my initial assumption of the bright flash doing eye damage was not incorrect - but only by luck. No burst eardrums but there were ear injuries.

Where it might hit? I have seen a prediction of a 2032 impact risk corridor, a band running from tropical Eastern Pacific Ocean, crossing North of S. America, middle Africa, Yemen and across India to Burma.

 

[Office_Shredder]

"American Congress approves trillion dollar budget for meteor shield.
Everybody who matters breaths sigh of relief."

View attachment 357526

Thanks to a metric to imperial conversion bug this was promptly launched into a polar orbit.

 

[TensorCalculus]

I'm not entirely sure how much we have to worry about it though. Not only do we already have asteroid deflection technology, as time goes by and we get better predictions of where the asteroid will go, and if it does seem like it might hit somewhere like a city, we're more likely to divert more time and resources to improving said deflection tech ("necessity breeds invention", as they say).

Whilst meteor defense is apparently the single most popular NASA objective for US citizens I am not convinced that level of popularity applies to preventing lesser meteor strikes that are not expected to hit or directly harm the USA.

Yeah this is the thing though, it was NASA who changed the course of that asteroid. The question is - who's going to pay for the mission to go deflect the asteroid if we do deem it a problem - the USA, or somewhere that's potentially affected? Out of those potentially affected countries, how should the cost be split? Where should everything be made? These are all interesting questions! (And unfortunately me, being an astrophysics student and not an expert, and having a fairly limited understanding of the geopolitics of space, can't offer answers)

It is very, very cool (and really fun!) to think about the path of the asteroid, areas of uncertainty etc (I tried some calculations with some info that was given then ended up with a messy soup of half-solved equations, the aftermath of my bad integrating skills among other quirky things). Though I think the probability of it hitting earth is only like 0.28%, and the probability of it hitting earth and a city is even less so - so we probably don't even get to the asteroid deflection phase. If it was on course to hit the middle of nowhere, I'd want to let it - asteroids are supposed to be pretty nice resources wise.
(please do correct me if I'm wrong - most of this comes from youtube, random websites + dodgy redditers so I could be drastically incorrect)

 

[mfb]

The impact probability has now dropped to 0.004% - it's less than the chance that another (undiscovered) asteroid that size hits Earth in 2032. Astronomers will keep watching it, but for all practical purposes the risk is gone.

 

[neilparker62]

Thanks to a metric to imperial conversion bug this was promptly launched into a polar orbit.

Polar bears will be happy anyway

 

[neilparker62]

The impact probability has now dropped to 0.004% - it's less than the chance that another (undiscovered) asteroid that size hits Earth in 2032. Astronomers will keep watching it, but for all practical purposes the risk is gone.

Is this asteroid a long time 'citizen' of our solar system or is it possibly from beyond like Oumuamua ? I mean could we be starting to see shards of some distant cosmic explosion reaching us ?

 

[snorkack]

So what will be the distance and visual magnitude on 22 XII 2032?

 

[DaveC426913]

Is this asteroid a long time 'citizen' of our solar system or is it possibly from beyond like Oumuamua ? I mean could we be starting to see shards of some distant cosmic explosion reaching us ?

"As an Apollo-type near-Earth object, 2024 YR4 orbits the Sun on an elliptical orbit that crosses Earth's orbit… Astronomers Carlos and Raúl de la Fuente Marcos have proposed that 2024 YR4 could be related to a group of near-Earth asteroids on similar orbits that also have virtual impactors: 2017 UW5, 2018 GG4, 2019 SC, and 2020 MQ61."

https://en.wikipedia.org/wiki/2024_YR4

So, it's part of a our local system. Likely, whatever created the asteroid belt: an early proto-planetoid that either failed to form - or was torn apart - by Jupiter's presence.

 

[mfb]

So what will be the distance and visual magnitude on 22 XII 2032?

Nominal 0.00182 AU = 270,000 km, minimal 0.00049 AU = 73,000 km. Could be something like magnitude 15. Certainly too dim for the naked eye, but various telescopes can see it.

 

[fresh_42]

However, as of March 13, 2025, the probability of an impact is only given as 0.000020%.

https://cneos.jpl.nasa.gov/sentry/details.html#?des=2024 YR4

 

[ohwilleke]

https://cneos.jpl.nasa.gov/sentry/details.html#?des=2024 YR4

To save folks the click, the link states that the impact probability is currently 1.9e-7, i.e. 0.000019%.

 

[DaveC426913]

To save folks the click, the link states that the impact probability is currently 1.9e-7, i.e. 0.000019%.

 

[TensorCalculus]

View attachment 358767

I mean... there's a chance for a lot of crazy things... they're just really, really, small...