Asteroid ZTm0038 with a >3% impact probability • Hacker News Board

Re: Asteroid ZTm0038 with a >3% impact probability

#171

Post by snewman » Tue, Aug 15, 2023, 10:53 PM UTC

cfraenkel wrote: post #154

apatil wrote: post #136

Earlier quoted context omitted.

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 i…

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 observa…

If you have very wide error bars, shouldn't your estimate of impact probability be much lower than 3%? Most trajectories within your error bars will not intersect the Earth.

Re: Asteroid ZTm0038 with a >3% impact probability

#172

Post by vkou » Tue, Aug 15, 2023, 10:53 PM UTC

jacquesm wrote: post #159

JumpinJack_Cash wrote: post #153

Earlier quoted context omitted.

The obvious answer to that is being able to reliably detect asteroids on a collision course, and compute where is it gonna fall in order to proceed the emergency evacuation. But first you have to be able to detect it, second you have to do it with reasonable time to save as many people as possible

Again, these people aren't stupid. You will have a very large amount of uncertainty based on a series of observations which essentially project a circle of probability on the planet that shrinks as more information from newer observations comes in and then just before impact that probability will either drop to zero because it is deemed to be a near miss (sorry, George) or it will then become a certainty. By that tim…

Any links to these reports?

Re: Asteroid ZTm0038 with a >3% impact probability

#173

Post by noduerme » Tue, Aug 15, 2023, 10:54 PM UTC

MauranKilom wrote: post #166

cfraenkel wrote: post #154

Earlier quoted context omitted.

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 observa…

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 signifi…

One explanation would be the Anthropic Principle. In 3% of universes you were killed today, you're just not living in one of those.

Re: Asteroid ZTm0038 with a >3% impact probability

#174

Post by jacquesm » Tue, Aug 15, 2023, 10:58 PM UTC

vkou wrote: post #172

jacquesm wrote: post #159

Earlier quoted context omitted.

Again, these people aren't stupid. You will have a very large amount of uncertainty based on a series of observations which essentially project a circle of probability on the planet that shrinks as more information from newer observations comes in and then just before impact that probability will either drop to zero because it is deemed to be a near miss (sorry, George) or it will then become a certainty. By that tim…

Any links to these reports?

Found it:

https://www.boulder.swri.edu/~bottke/Reprints/National_Acade...

Note that Arecibo is now gone.

Re: Asteroid ZTm0038 with a >3% impact probability

#175

Post by Keyframe » Tue, Aug 15, 2023, 11:02 PM UTC

ortusdux wrote: post #150

lucb1e wrote: post #99

Earlier quoted context omitted.

That's in the submission, there's a column called H in the first table that says 19.90

The chart is H vs. Albedo, and is awkwardly formatted. H is the brightness observed on earth. Albedo is the inherent reflectivity of the object. What the chart is saying is that if we observe an object that is 19.5 H bright, it could either be highly reflective (0.30 albedo) and 310m across, very dim (0.05 albedo) and 760m across, or somewhere in between. As I understand it, we can only calculate the albedo if we kno…

True. At least it gives us a range this way unless it's a block of ice or whatever else. I still remember some of this from rendering days.

H is basically the same as M, an absolute magnitude, but for solar system objects. Difference being that for solar system objects H, as you've noted, is an absolute magnitude for an object 1 AU from Earth and 1 AU from Sun in a triangle where phase angle is zero meaning it's a straight line instead of a triangle and M is an absolute magnitude for an object (usually self illuminating) outside of solar system set at 10 parsecs from Earth. A star with M = 1 and a solar system object with H = 1 would roughly be the same brightness. It's a log scale, lower the number the brighter it is, so if you put that star at the same spot as the object it'd be a difference of about 26 where each unit is roughly 2.5 times brighter. What's interesting is that at zero it used to (roughly) be Vega (star). Both M and H are band-dependent, I guess it's V-band (visual or green-ish) if it's not mentioned. If you have B (blue) and V band, the difference between the two tells you a (visual) color which can be also interpreted as temperature, the lower the number the bluer it is and higher means red.

I'm all out of trivia for the night. I'm sure there are (amateur and not) astronomers and astrophotographers here that know this stuff way more about. All I knew is that without albedo you couldn't get to the size with absolute magnitude alone, we could if we had both absolute and apparent. What I didn't know if that apparently there's a rough table of correlation between H and albedo values probably based on most rocks we've seen in space around us.

Re: Asteroid ZTm0038 with a >3% impact probability

#176

Post by sfink » Tue, Aug 15, 2023, 11:08 PM UTC

jacquesm wrote: post #142

JumpinJack_Cash wrote: post #98

The public is unanimously in favor of funding asteroid protection mechanisms and research. It's even higher support than the military. Naturally what do we do with that money and goodwill instead? Yes! Let's build a massive space telescope which takes pictures that are only marginally better than the other multi-billion dollar space telescope! Protect the Earth? Fuck that, don't ya know kid? She's toast anyway becaus…

There have been many studies about what could be done to deal with asteroids that are on track to impact earth and the simple answer is 'nothing'. Frustrating, but unless you can think of something that none of the very clever people on those committees could think of it's going to stay that way.

I don't buy that. It shouldn't be that hard to launch a cloud of space drones that produce a lot of dusty debris when they hit. Have them adjust their courses when the incoming asteroid gets close.

That way, we could paint a huge smiley face on the asteroid.

I would much rather be exterminated by an asteroid with a smiley face than a big dumb pile of rocks. (Even if the smiley face keeps spinning out of view while it's coming in.)

Re: Asteroid ZTm0038 with a >3% impact probability

#177

Post by pdabbadabba » Tue, Aug 15, 2023, 11:15 PM UTC

Leary wrote: post #132

killthebuddha wrote: post #100

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 rad…

Found this tweet with an impact probability map that is around northern US/Asia/Europe : 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…

What should we make of the fact that this tweet has since been deleted?

Re: Asteroid ZTm0038 with a >3% impact probability

#178

Post by mabbo » Tue, Aug 15, 2023, 11:15 PM UTC

Analemma_ wrote: post #123

killthebuddha wrote: post #100

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 rad…

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:Apoph... . A 3% chance of impact right after discovery with the initial error ellipse isn't all that unusual; it will almost certain…

I think, given the expected impact time windows have passed now, we can update it to 0% (this time).

Re: Asteroid ZTm0038 with a >3% impact probability

#179

Post by chris_va » Tue, Aug 15, 2023, 11:17 PM UTC

throwaway5729 wrote: post #29

thatcherc wrote: post #6

I don't really know how to read this page, but it looks like the time of closest approach has already passed - > Closest approach time of impactors: t_min = 2023/08/14 04:48 TDB and t_max = 2023/08/15 12:22 TDB If so then we're all good. Can the poster or anyone else chime in with background on this?

I saw this tweet: https://twitter.com/ByronDrury/status/1691487518590402560?s=... linking to https://cneos.jpl.nasa.gov/scout/#/object/ZTm0038 It has some cool graphs that seem to show a lot of uncertainty in closest approach time [edited to fix second link]

Well, that NASA page has the closest approach going into next week and a ~10% of impact, so... hopefully the big disclaimer at the top is relevant.

Re: Asteroid ZTm0038 with a >3% impact probability

#180

Post by jacquesm » Tue, Aug 15, 2023, 11:21 PM UTC

sfink wrote: post #176

jacquesm wrote: post #142

Earlier quoted context omitted.

There have been many studies about what could be done to deal with asteroids that are on track to impact earth and the simple answer is 'nothing'. Frustrating, but unless you can think of something that none of the very clever people on those committees could think of it's going to stay that way.

I don't buy that. It shouldn't be that hard to launch a cloud of space drones that produce a lot of dusty debris when they hit. Have them adjust their courses when the incoming asteroid gets close. That way, we could paint a huge smiley face on the asteroid. I would much rather be exterminated by an asteroid with a smiley face than a big dumb pile of rocks. (Even if the smiley face keeps spinning out of view while it…

The masses you're talking about are such that you'd need to detect the asteroid well before impact (ideally: years) and that your efforts would not accidentally make matters worse rather than better. Even then it likely won't do anything at all. Calling Bruce Willis on line 3... But agreed on the smiley.