4 ms·

why are these events always forecasted so late? some hours earlier i could have witnessed it

by singularity2001 4y ago

spenczar5 4y ago
Two related reasons. 1m is quite small, so it needs to be close for us to detect it. Since we don’t have many observations, the error in estimates of its orbital path is high. In general, it also is extra difficult to calculate the exact last little bit of a trajectory that will impact earth because the force models start getting really wild as something gets very close to earth - approximations stop working.
- Aachen 4y ago
  > it also is extra difficult to calculate the exact last little bit of a trajectory that will impact earth because the force models start getting really wild What kind of forces? I assume you're talking about the space part, before atmosphere, so I would assume it's the same gravity effects that you also get in space, just that gravity is a bit larger value. I wrote a gravity simulator at lgms.nl/p/badgravity so I have a bit of an idea but am definitely no expert (the thing doesn't do any sort of collisions and assumes 2d point masses), so I'm curious what you mean. Especially with the earth dominating the gravity and not needing to use N-body physics anymore, it should get more accurate if anything. Could you elaborate or do you have a link? Or do you simply mean the compounding effect of having used N-body approximations for the interplanetary space part of the trajectory leading to different starting points for the final approach?
  - throwaway4aday 4y ago
    My guess is that the uncertainty has little to do with gravity, although there is gravitational variation in both the Moon and Earth depending on what part you are close to but I don't think that comes into play here. The error is likely more to do with the observational data. Try pinpointing the exact distance and trajectory of a 1m rock using ground based telescopes. Hard enough but remember there is also atmospheric distortion and you only get limited time on the scope.
  - spenczar5 4y ago
    I actually do mean atmospheric effects. The strength of atmosphere effects is usually what makes the difference between a mere close approach and a collision. Those effects are hard to model exactly.
    - Aachen 4y ago
      Oh, I did not know that this 'last mile' often makes the difference between collisions and close approaches! Interesting. Indeed, I have to remember that atmosphere is a scale and not a hard boundary. Like, I kinda know that, but just how far up there are still particles that are of significance...
gpvos 4y ago
It's amazing it's forecast at all. As ESA writes: > This is just the seventh time an #asteroidimpact has ever been predicted before it happens - a sign of the rapid advancements in global asteroid detection capabilities!

why are these events always forecasted so late? some hours earlier i could have witnessed it

Two related reasons. 1m is quite small, so it needs to be close for us to detect it. Since we don’t have many observations, the error in estimates of its orbital path is high. In general, it also is extra difficult to calculate the exact last little bit of a trajectory that will impact earth because the force models start getting really wild as something gets very close to earth - approximations stop working.

Aachen 4y ago
> it also is extra difficult to calculate the exact last little bit of a trajectory that will impact earth because the force models start getting really wild What kind of forces? I assume you're talking about the space part, before atmosphere, so I would assume it's the same gravity effects that you also get in space, just that gravity is a bit larger value. I wrote a gravity simulator at lgms.nl/p/badgravity so I have a bit of an idea but am definitely no expert (the thing doesn't do any sort of collisions and assumes 2d point masses), so I'm curious what you mean. Especially with the earth dominating the gravity and not needing to use N-body physics anymore, it should get more accurate if anything. Could you elaborate or do you have a link? Or do you simply mean the compounding effect of having used N-body approximations for the interplanetary space part of the trajectory leading to different starting points for the final approach?
- throwaway4aday 4y ago
  My guess is that the uncertainty has little to do with gravity, although there is gravitational variation in both the Moon and Earth depending on what part you are close to but I don't think that comes into play here. The error is likely more to do with the observational data. Try pinpointing the exact distance and trajectory of a 1m rock using ground based telescopes. Hard enough but remember there is also atmospheric distortion and you only get limited time on the scope.
- spenczar5 4y ago
  I actually do mean atmospheric effects. The strength of atmosphere effects is usually what makes the difference between a mere close approach and a collision. Those effects are hard to model exactly.
  - Aachen 4y ago
    Oh, I did not know that this 'last mile' often makes the difference between collisions and close approaches! Interesting. Indeed, I have to remember that atmosphere is a scale and not a hard boundary. Like, I kinda know that, but just how far up there are still particles that are of significance...

gpvos 4y ago

It's amazing it's forecast at all. As ESA writes: > This is just the seventh time an #asteroidimpact has ever been predicted before it happens - a sign of the rapid advancements in global asteroid detection capabilities!