[carl_dr]

https://phys.org/news/2021-06-space-orbit-oort-cloud.html

The asteroid that wiped out the dinosaurs was between 3 and 10 miles diameter. 2014 UN271 is 100km-370km.

Would we have discovered 2014 UN271 earlier had its orbit brought it closer to Earth? It’s making its closest approach in 2031 (ok, 11AU away!), only 17 years after discovery.

And sure, incredibly unlikely something that size would hit Earth, but just an example of something that is very large, and discovered shortly before it makes its closest approach.

[willis936]

Objects with highly eccentric orbits are both very uncommon and very unlikely to intercept Earth. The period in which they have near misses is on the order of thousands of years at least. Even if we could see them from their high altitude we don't have enough information to predict where they'll be on the next intercept.

My understanding is that this kind of threat is usually lumped in with comets, whereas threat asteroids are lumped in with low eccentricity big rocks.

[carl_dr]

Thanks, I see the difference now.