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I'm having a weirdly difficult time finding some basic ELI5 answers. - What is the probability that this asteroid will hit us? - What is the time interval

I'm having a weirdly difficult time finding some basic ELI5 answers. - What is the probability that this asteroid will hit us? - What is the time interval where that probability applies? - Do we have a probability distribution for where it might hit? I don't know anything about anything, but I assume we know what *general direction* it's coming from? - Do we have a probability distribution for the potential blast radius? In general, I am very confused by this news because "400m diameter asteroid 3% chance of impact" is something I would expect literally everybody to be talking about all the time. It's also something where if I learned that everything north of Kansas has a 5% chance of getting hit but everything south of Houston has a 1% chance, I'd seriously consider taking an impromptu vacation.

lijok 3y ago
Spotted 3 days ago. There's an incentive not to publicize this. Lots of close passes only get coverage after the fact.
1970-01-01 3y ago
We need an expert to explain these facts and numbers. Until then, please buy necessary amounts of toilet paper.
Analemma_ 3y ago
When a new potentially-hazardous asteroid is discovered, it's normal for the probability of impact to go up a couple times before abruptly plummeting to zero, as the radius of uncertainty shrinks until it shrinks past the Earth. See https://en.wikipedia.org/wiki/Torino_scale#/media/File:Apophis_ellipse.svg https://en.wikipedia.org/wiki/Torino_scale#/media/File:Apoph.... A 3% chance of impact right after discovery with the initial error ellipse isn't all that unusual; it will almost certainly be revised to 0 with more observation (and if it's not, you'll hear about it).
- apatil 3y ago
  This makes sense, thanks. However, it doesn't mean that the 3% estimate of the chance of impact was wrong at the time of initial observation given data available, and that still makes it a huge deal at that time. At minimum, it would seem to justify using the best available instruments to characterize the asteroid more precisely as soon as possible. If these large numbers happen so often that asteroids with initial impact probabilities of 3% are known to actually impact much less frequently than that, then the model is poorly calibrated, no? In other words, the reported probabilities aren't really probabilities and that is what has caused the confusion and anxiety in these comments.
  - abathur 3y ago
    I don't know, but I suspect this is more about the limits of the observations (which I imagine are mostly from terrestrial observatories) needed to obtain much certainty about the object's size, course, speed, density, etc.
  - cfraenkel 3y ago
    It's not a model that is poorly calibrated - you seem to be taking a software-centric concept far away from where it's useful. The uncertainty at initial observation is because when you first observe an object, you only have observations covering a tiny bit of the orbit, resulting in very wide error bars. The "model" (Newtonian orbital dynamics) is one of the most precise models we have. Doesn't help when the observations are noisy.
    - MauranKilom 3y ago
      Unless one in every 33 asteroids that have 3% impact probability at some point in time actually impacts earth, there is clearly some unwarranted assumption in the error bar/distribution calculation. "The measurement data has noise" does not explain why the noise has a bias towards "the asteroid will hit earth" whereas reality so far has been biased towards "the asteroid will not hit earth". (This assumes that significantly more than 33 asteroids have had >= 3% impact probability predicted at some point. The opposite would not be less concerning.)
      - noduerme 3y ago
        One explanation would be the Anthropic Principle. In 3% of universes you were killed today, you're just not living in one of those.
        jacquesm 3y ago
        In 97% of the universes dinosaur descendants rule planet earth. But on this one they got unlucky.
        MauranKilom 3y ago
- mortehu 3y ago
  What percent of the times when the initial probability is 3% will it later be revised to zero? Is it more than 97%?
  - jacquesm 3y ago
    To date the percentage that got revised to zero is 100%. And the only time we had a really close call we didn't see it coming.
    - Mrkvak 3y ago
      That's not correct at all: https://newton.spacedys.com/neodys2/NEOScan/index_past_imp.html https://newton.spacedys.com/neodys2/NEOScan/index_past_imp.h...
      - jacquesm 3y ago
        Fair enough, but those are all relatively small, and detected only hours before impact, their effect would not be such that anything major would happen on the surface of the planet beyond some broken windows and maybe a sunburn. Anything that size aimed straight down would most likely not reach the ground but burn up in the atmosphere and any remaining bits would just fall at regular terminal velocity. But from 10 meters and up things change and the Chelyabinsk meteor is remarkable in that it (1) was large enough to have been detected but wasn't and (2) struck while we were apparently focused on one that was more visible but that ultimately missed us. We were very lucky that it impacted where and at the angle that it did, otherwise the airburst might have happened far closer to the ground or to might have impacted directly over much more populated territory. That would have been very bad news. It doesn't matter how many 1 through 5 meter objects we can track because we have the atmosphere to protected us from the worst of these if we miss the 20 meter ones (or apparently even much larger) that travel at speeds high enough to give their relatively modest mass tremendous energy and for which the atmosphere does not give sufficient (or even any) protection.
- mabbo 3y ago
  I think, given the expected impact time windows have passed now, we can update it to 0% (this time).
apatil 3y ago
Also, is it possible to quantify the risk of unseen companion asteroids, which someone else mentioned in the comments.
mrb 3y ago
I can answer 2 of your questions: - What is the probability that this asteroid will hit us? It's listed in the article: Impact probability 0.034, meaning 3.4% chance of impact. - What is the time interval where that probability applies? It's also listed: impact was estimated to potentially occur between 2023/08/14 04:48 TDB and 2023/08/15 12:22 TDB. (TDB seems to be UTC time without leap seconds? not sure). In other words the asteroid already passed Earth, and is currently no longer a risk.
- onlyrealcuzzo 3y ago
  Probability without confidence interval is not very useful. If there's <1% confidence - this is not exactly news.
  - Enginerrrd 3y ago
    The probability takes into account the error on the measurements so I'm not sure what you're getting at
  - hollerith 3y ago
    I don't know what you mean.
- Karellen 3y ago
  TDB: https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time > [TDB] is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar System. TDB is now (since 2006) defined as a linear scaling of Barycentric Coordinate Time (TCB). A feature that distinguishes TDB from TCB is that TDB, when observed from the Earth's surface, has a difference from Terrestrial Time (TT) that is about as small as can be practically arranged with consistent definition: the differences are mainly periodic, and overall will remain at less than 2 milliseconds for several millennia. https://en.wikipedia.org/wiki/Terrestrial_Time https://en.wikipedia.org/wiki/Terrestrial_Time > TT is distinct from the time scale often used as a basis for civil purposes, Coordinated Universal Time (UTC). TT is indirectly the basis of UTC, via International Atomic Time (TAI). Because of the historical difference between TAI and [Ephemeris Time] ET when TT was introduced, TT is approximately 32.184s ahead of TAI. Phew!
Leary 3y ago
Found this tweet with an impact probability map that is around northern US/Asia/Europe : https://twitter.com/JoelSercel/status/1691549821629526219 https://twitter.com/JoelSercel/status/1691549821629526219 "If it is real this IS the worst asteroid threat ever discovered and the impact location and times are ugly (will post pics shortly). Note that the impact is in the next couple days! However, an Italian colleague of one of our astronomers suspects there is an error in the reported observations and there has been no chatter about this object and no followup. This probably means that it is not real. " - Joel C. Sercel, PhD I'm guessing the impact death area will be around 3600 km2 (I have no idea, please correct), so ultimately the chance of it falling on me is 1 in 10,000 to 1 in 100,000 provided the asteroid hits. Which means 1 in 1,000,000 to 1 in 10,000,000 in total? (assuming 1% hit probability)
- noduerme 3y ago
  If I'm looking at the time chart correctly, that basically corresponds to "daylight hours", when you're facing the sun, tomorrow within the northern hemisphere...
  - radicaldreamer 3y ago
    We should look for secondary evidence, did the gov start continuity of gov operations etc. If it is real and if nothing can be done about it, we cannot expect official confirmation.
    - noduerme 3y ago
      Well, that map tweet has now been deleted, and the guy posted this: >> I would like to make an apology to the small body community. Some information was shared with me on an internal company message board that I did not have full perspective on and I posted a tweet, which I now understand was not appropriate. It was preliminary data and I did not have full perspective on it. Does that sound like everything's gonna be okay?
- tophi 3y ago
  There is a disclaimer from the data source: “Scout data are about unconfirmed objects and all information should therefore be treated as potentially unreliable” I’m hoping this ztm0038 is an error or hoax.
vkou 3y ago
Uncertainty in measurements make it almost impossible to tell where an object like this is going to impact, until we are hours, if not minutes away from impact.
ortusdux 3y ago
I found this breakdown of JPL's CNEOS data to be every helpful. The close approach time chart shows % chance of impact vs day. From this I take it that we just didn't have enough info at the time of publishing.

lijok 3y ago

Spotted 3 days ago. There's an incentive not to publicize this. Lots of close passes only get coverage after the fact.

1970-01-01 3y ago

We need an expert to explain these facts and numbers. Until then, please buy necessary amounts of toilet paper.

Analemma_ 3y ago

When a new potentially-hazardous asteroid is discovered, it's normal for the probability of impact to go up a couple times before abruptly plummeting to zero, as the radius of uncertainty shrinks until it shrinks past the Earth. See https://en.wikipedia.org/wiki/Torino_scale#/media/File:Apophis_ellipse.svg https://en.wikipedia.org/wiki/Torino_scale#/media/File:Apoph.... A 3% chance of impact right after discovery with the initial error ellipse isn't all that unusual; it will almost certainly be revised to 0 with more observation (and if it's not, you'll hear about it).

apatil 3y ago
This makes sense, thanks. However, it doesn't mean that the 3% estimate of the chance of impact was wrong at the time of initial observation given data available, and that still makes it a huge deal at that time. At minimum, it would seem to justify using the best available instruments to characterize the asteroid more precisely as soon as possible. If these large numbers happen so often that asteroids with initial impact probabilities of 3% are known to actually impact much less frequently than that, then the model is poorly calibrated, no? In other words, the reported probabilities aren't really probabilities and that is what has caused the confusion and anxiety in these comments.
- abathur 3y ago
  I don't know, but I suspect this is more about the limits of the observations (which I imagine are mostly from terrestrial observatories) needed to obtain much certainty about the object's size, course, speed, density, etc.
- cfraenkel 3y ago
  It's not a model that is poorly calibrated - you seem to be taking a software-centric concept far away from where it's useful. The uncertainty at initial observation is because when you first observe an object, you only have observations covering a tiny bit of the orbit, resulting in very wide error bars. The "model" (Newtonian orbital dynamics) is one of the most precise models we have. Doesn't help when the observations are noisy.
  - MauranKilom 3y ago
    Unless one in every 33 asteroids that have 3% impact probability at some point in time actually impacts earth, there is clearly some unwarranted assumption in the error bar/distribution calculation. "The measurement data has noise" does not explain why the noise has a bias towards "the asteroid will hit earth" whereas reality so far has been biased towards "the asteroid will not hit earth". (This assumes that significantly more than 33 asteroids have had >= 3% impact probability predicted at some point. The opposite would not be less concerning.)
    - noduerme 3y ago
      One explanation would be the Anthropic Principle. In 3% of universes you were killed today, you're just not living in one of those.
      - jacquesm 3y ago
        In 97% of the universes dinosaur descendants rule planet earth. But on this one they got unlucky.
      - MauranKilom 3y ago
mortehu 3y ago
What percent of the times when the initial probability is 3% will it later be revised to zero? Is it more than 97%?
- jacquesm 3y ago
  To date the percentage that got revised to zero is 100%. And the only time we had a really close call we didn't see it coming.
  - Mrkvak 3y ago
    That's not correct at all: https://newton.spacedys.com/neodys2/NEOScan/index_past_imp.html https://newton.spacedys.com/neodys2/NEOScan/index_past_imp.h...
    - jacquesm 3y ago
      Fair enough, but those are all relatively small, and detected only hours before impact, their effect would not be such that anything major would happen on the surface of the planet beyond some broken windows and maybe a sunburn. Anything that size aimed straight down would most likely not reach the ground but burn up in the atmosphere and any remaining bits would just fall at regular terminal velocity. But from 10 meters and up things change and the Chelyabinsk meteor is remarkable in that it (1) was large enough to have been detected but wasn't and (2) struck while we were apparently focused on one that was more visible but that ultimately missed us. We were very lucky that it impacted where and at the angle that it did, otherwise the airburst might have happened far closer to the ground or to might have impacted directly over much more populated territory. That would have been very bad news. It doesn't matter how many 1 through 5 meter objects we can track because we have the atmosphere to protected us from the worst of these if we miss the 20 meter ones (or apparently even much larger) that travel at speeds high enough to give their relatively modest mass tremendous energy and for which the atmosphere does not give sufficient (or even any) protection.
mabbo 3y ago
I think, given the expected impact time windows have passed now, we can update it to 0% (this time).

apatil 3y ago

Also, is it possible to quantify the risk of unseen companion asteroids, which someone else mentioned in the comments.

mrb 3y ago

I can answer 2 of your questions: - What is the probability that this asteroid will hit us? It's listed in the article: Impact probability 0.034, meaning 3.4% chance of impact. - What is the time interval where that probability applies? It's also listed: impact was estimated to potentially occur between 2023/08/14 04:48 TDB and 2023/08/15 12:22 TDB. (TDB seems to be UTC time without leap seconds? not sure). In other words the asteroid already passed Earth, and is currently no longer a risk.

onlyrealcuzzo 3y ago
Probability without confidence interval is not very useful. If there's <1% confidence - this is not exactly news.
- Enginerrrd 3y ago
  The probability takes into account the error on the measurements so I'm not sure what you're getting at
- hollerith 3y ago
  I don't know what you mean.
Karellen 3y ago
TDB: https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time > [TDB] is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar System. TDB is now (since 2006) defined as a linear scaling of Barycentric Coordinate Time (TCB). A feature that distinguishes TDB from TCB is that TDB, when observed from the Earth's surface, has a difference from Terrestrial Time (TT) that is about as small as can be practically arranged with consistent definition: the differences are mainly periodic, and overall will remain at less than 2 milliseconds for several millennia. https://en.wikipedia.org/wiki/Terrestrial_Time https://en.wikipedia.org/wiki/Terrestrial_Time > TT is distinct from the time scale often used as a basis for civil purposes, Coordinated Universal Time (UTC). TT is indirectly the basis of UTC, via International Atomic Time (TAI). Because of the historical difference between TAI and [Ephemeris Time] ET when TT was introduced, TT is approximately 32.184s ahead of TAI. Phew!

Leary 3y ago

Found this tweet with an impact probability map that is around northern US/Asia/Europe : https://twitter.com/JoelSercel/status/1691549821629526219 https://twitter.com/JoelSercel/status/1691549821629526219 "If it is real this IS the worst asteroid threat ever discovered and the impact location and times are ugly (will post pics shortly). Note that the impact is in the next couple days! However, an Italian colleague of one of our astronomers suspects there is an error in the reported observations and there has been no chatter about this object and no followup. This probably means that it is not real. " - Joel C. Sercel, PhD I'm guessing the impact death area will be around 3600 km2 (I have no idea, please correct), so ultimately the chance of it falling on me is 1 in 10,000 to 1 in 100,000 provided the asteroid hits. Which means 1 in 1,000,000 to 1 in 10,000,000 in total? (assuming 1% hit probability)

noduerme 3y ago
If I'm looking at the time chart correctly, that basically corresponds to "daylight hours", when you're facing the sun, tomorrow within the northern hemisphere...
- radicaldreamer 3y ago
  We should look for secondary evidence, did the gov start continuity of gov operations etc. If it is real and if nothing can be done about it, we cannot expect official confirmation.
  - noduerme 3y ago
    Well, that map tweet has now been deleted, and the guy posted this: >> I would like to make an apology to the small body community. Some information was shared with me on an internal company message board that I did not have full perspective on and I posted a tweet, which I now understand was not appropriate. It was preliminary data and I did not have full perspective on it. Does that sound like everything's gonna be okay?
tophi 3y ago
There is a disclaimer from the data source: “Scout data are about unconfirmed objects and all information should therefore be treated as potentially unreliable” I’m hoping this ztm0038 is an error or hoax.

vkou 3y ago

Uncertainty in measurements make it almost impossible to tell where an object like this is going to impact, until we are hours, if not minutes away from impact.

ortusdux 3y ago

I found this breakdown of JPL's CNEOS data to be every helpful. The close approach time chart shows % chance of impact vs day. From this I take it that we just didn't have enough info at the time of publishing.