[version_five]

Is there an english / eli5 if you like, summary of what this means?

I gather that today or yesterday an asteroid ~400m along it's biggest dimension ultimately came within x km of earth, that was close enough there was a nontrivial chance it would hit us? And this is big enough to make a 30 mile crater? And we only found out it was coming a couple days ago? Sounds like a pretty big deal if that's accurate.

[jacquesm]

It's accurate and it could have been a pretty big deal but for now it isn't, unless there are very low magnitude companions to it that hit unexpectedly because they have not been observed at all. There is some precedent for that sort of thing.

[lucb1e]

> ~400m along it's biggest dimension

Where did you find this information? I don't understand all the fields on the page, but don't see any number being 400 within an order of magnitude

[version_five]

Everything I wrote was from skimming the comments here. This is the 400m: https://news.ycombinator.com/item?id=37138510

I was hoping someone more familiar with this stuff could write a definitive summary.

[SoftTalker]

400m in one dimension leaves a lot of room for variation. 400m x 1m x 1m is a lot less concerning than a 400m diameter sphere.

[postalrat]

400x1x1 would be a pretty nasty spear that must have been made by someone.

[radicaldreamer]

It’s the Spear of Longinus

[dougmwne]

That would sound like a kinetic bombardment weapon and that we were about to get rodded. My level of concern would be sky high!

[jacquesm]

Depending on how it is aimed... straight in that would be messy.

[version_five]

That would be an interesting analysis to see, my guess is it wouldn't be that different than if it was a sphere of equivalent mass, and vs a 400m sphere would be 400/(4*pi*200^3/3) = .0012% the volume (and so kinetic energy), and it would not penetrate in a way that does specifically worse damage. Just guessing though.

Edit: I confused radius and diameter in my calculation and revised it. I may have made other mistakes

[jacquesm]

That would highly depend on what the composition of the asteroid was and where it impacted. On a fault line? In the middle of an ocean, or a city?

For sure the depth of penetration would be different for a rod shaped object of equivalent mass compared to a spheroid, the latter would penetrate much less deep. Angle of incidence would be a factor as well as (obviously) the speed of the impacting body. But if it impacted at a higher speed than that the ejecta could get out of the way it would cause an absolutely massive crater. As though you'd exploded an absolutely enormous nuclear bomb deep underground, but not so deep that the explosion would still reach the surface. That would probably be the worst case scenario for an impact like this.

[SoftTalker]

Without fins, it's unlikely to go straight in. It would start tumbling, and probably break up and burn up. A sphere would more likely get to the surface intact.

[almostnormal]

If it has the same density than earth, it wont pierce deeper than its length. If it is made of uranium a bit over twice that (assuming earth is made of iron).

[jacquesm]

I wonder if there have been any simulations of such an impact and what the worst case would look like for equivalent mass but different shapes and asteroid compositions.

[lucb1e]

I wonder what the distribution is like; the most extreme length to height ratios we've seen for example. Not sure I've ever heard of something weirder than on the order of 2:1

[cafxx]

'Oumuamua was closer to 8:1 https://en.wikipedia.org/wiki/%CA%BBOumuamua

[zardo]

That's just measure of uncertainty in out measurements, unless we're saying there was a ~3% chance someone would do an emergency asteroid redirection to make it hit.