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Oumuamua raises some questions, but the one my mind keeps wandering to is “how common are these interstellar objects?” It poses a serious existential threat to

Oumuamua raises some questions, but the one my mind keeps wandering to is “how common are these interstellar objects?” It poses a serious existential threat to us. We are a tiny target, but we have been able to observe these objects for a very short period of time. Unlike regular solar satellites, they are only visible for a very short period of time. Like comets, if one hit us it would end life on the planet. They don’t need to be massive with how fast they are. We can estimate how many comets are out there with orbital mechanics models, but what about objects originating from outside the solar system? We could one day not wake up because we couldn’t even see one of these coming before it hit us.

avian 6y ago
> We can estimate how many comets are out there with orbital mechanics models, but what about objects originating from outside the solar system? We can estimate the frequency and size of impacts, regardless of the origin of the impacting body, from observing craters on the Earth, moon and other planets. Those show that the "end of life" impacts are pretty rare - the conclusion that also follows from the fact that we're having this discussion here.
- willis936 6y ago
  The solar system has an orbital period of 250k years. Nearby systems do not have the same orbital period. I’m not sure galaxies are considered stable to individual stellar systems.
  - breck 6y ago
    > The solar system has an orbital period of 250k years. I thought it was 250 million years, though maybe I'm misunderstanding you. [1] [1] https://www.sciencefocus.com/space/how-long-does-it-take-the-sun-to-orbit-the-galaxy/#:~:text=We%20tend%20to%20think%20of,to%20complete%20a%20single%20orbit https://www.sciencefocus.com/space/how-long-does-it-take-the....
    - willis936 6y ago
      My mistake! I didn’t check, but knew the value was in the range of “too long to assume our galactic neighborhood is static or even repeating but too short to not have had potential repetitions show up in Earth geology”.
- Gravityloss 6y ago
  The dinosaur killer was estimated to be 10 km diameter. Oumuamua is much smaller, maybe 0.1 to 1 kilometers long and narrow.
detritus 6y ago
> Like comets, if one hit us it would end life on the planet. 'Oumuamua is more of a 'city-killer' risk at its size than a comet such as Halley's, which would be more of the sort of range of size that could seriously screw up our day.
- willis936 6y ago
  True, Oumuamua itself would not have done Earth changing damage even in the worst case collision, but where there is one we have to ask “are there others?” and “how big are they?” We have a pretty good idea of the asteroids and comets in stable orbits around the sun. We know with certainty we’re not going to be hit with a planet killer asteroid in the next hundred years because we track all of them.
  - AnimalMuppet 6y ago
    We track all of them that we know of. And we think that we know most of them. I'm not sure that we know all of them; I'm not sure that the trackers think that, either.
    - willis936 6y ago
      Actually, we do. Asteroids large enough to be considered planet-killers are the easiest ones to spot. https://youtu.be/4Wrc4fHSCpw https://youtu.be/4Wrc4fHSCpw

avian 6y ago

> We can estimate how many comets are out there with orbital mechanics models, but what about objects originating from outside the solar system? We can estimate the frequency and size of impacts, regardless of the origin of the impacting body, from observing craters on the Earth, moon and other planets. Those show that the "end of life" impacts are pretty rare - the conclusion that also follows from the fact that we're having this discussion here.

willis936 6y ago
The solar system has an orbital period of 250k years. Nearby systems do not have the same orbital period. I’m not sure galaxies are considered stable to individual stellar systems.
- breck 6y ago
  > The solar system has an orbital period of 250k years. I thought it was 250 million years, though maybe I'm misunderstanding you. [1] [1] https://www.sciencefocus.com/space/how-long-does-it-take-the-sun-to-orbit-the-galaxy/#:~:text=We%20tend%20to%20think%20of,to%20complete%20a%20single%20orbit https://www.sciencefocus.com/space/how-long-does-it-take-the....
  - willis936 6y ago
    My mistake! I didn’t check, but knew the value was in the range of “too long to assume our galactic neighborhood is static or even repeating but too short to not have had potential repetitions show up in Earth geology”.
Gravityloss 6y ago
The dinosaur killer was estimated to be 10 km diameter. Oumuamua is much smaller, maybe 0.1 to 1 kilometers long and narrow.

detritus 6y ago

> Like comets, if one hit us it would end life on the planet. 'Oumuamua is more of a 'city-killer' risk at its size than a comet such as Halley's, which would be more of the sort of range of size that could seriously screw up our day.

willis936 6y ago
True, Oumuamua itself would not have done Earth changing damage even in the worst case collision, but where there is one we have to ask “are there others?” and “how big are they?” We have a pretty good idea of the asteroids and comets in stable orbits around the sun. We know with certainty we’re not going to be hit with a planet killer asteroid in the next hundred years because we track all of them.
- AnimalMuppet 6y ago
  We track all of them that we know of. And we think that we know most of them. I'm not sure that we know all of them; I'm not sure that the trackers think that, either.
  - willis936 6y ago
    Actually, we do. Asteroids large enough to be considered planet-killers are the easiest ones to spot. https://youtu.be/4Wrc4fHSCpw https://youtu.be/4Wrc4fHSCpw