Meteor strikes

[Traab]

Something I was curious about. When a meteor comes flying into our atmosphere and hits the ground, I assume when it first hits the atmosphere it is going well beyond terminal velocity, but does it slow down to that speed before it hits ground? Or is the wind resistance not enough to counter the momentum behind it in the time it takes to impact the ground?

[hamishspence]

I'd say that the visual effect- of a bright glowing streak- is of the meteor slowing down to terminal velocity (with that friction burning much of it off). If it survives without being completely burnt up- the remaining fragment will hit the ground as normal.

Only the largest meteors would retain most of their velocity all the way from atmosphere to ground.

[factotum]

Just to correct you there, it's not friction--the heat you see from a re-entering body (whether a spacecraft or a meteor) is almost entirely down to the compression of the air in front of it. What will tend to happen is that a superheated plasma forms in front of the meteor, and this will start to boil away the surface of it and will also slow it down. How fast the remnant hits the ground (and if it hits the ground at all, for that matter) will depend how large the original rock was.

(As an example, Barringer Crater in Arizona was formed by a nickel-iron rock perhaps 50m across travelling at about 30,000mph--they estimate it lost half its mass during the descent through the atmosphere).

[Spiryt]

It probably depends on meteor really. Size, angle, and so on.

Terminal velocity of even large rock is something relatively low, and it's absolutely tiny fraction of velocities at which it's traveling trough the space.

Meteors which leave any sort of crater/damage are absolutely not traveling at terminal velocity.

[Traab]

Yeah thats what I figured. The thought popped into my head from another topic on falling bodies damaging the ground. My first thought was, "Duh, of course it would. Human sized meteors hitting the ground leave noticeable damage" Then I thought to myself, "Double duh! Those things are traveling at tremendous speeds well in excess of terminal velocity when they do that!" Of course the first voice in my head wasnt putting up with that crap, "Triple duh! It has to fall through increasing wind resistance from the furthest outer reaches of our atmosphere to the point of impact, thats a LOT of drag slowing it down!" And finally, that teeny tiny voice of reason that I rarely listen to whimpered, "Um, excuse me sirs, but why dont we ask on the message board? There is always at least a couple relative experts on any subject willing to help." The other voices clubbed him into a coma, but not before my original post. :smallbiggrin:

[hamishspence]

The Hoba meteorite may be one of the largest ever to hit the ground at only terminal velocity:

http://en.wikipedia.org/wiki/Hoba_meteorite

[Jimorian]

The PBS show Nova (http://video.pbs.org/video/2358778286) covered a lot of the technical details about the Russian meteor and how they figured them out, but also talk a lot about what it takes for any meteor to strike the ground and with what force, etc.

It's also available on YouTube if that link is territory blocked.

[The Succubus]

Meteor strikes don't happen very often because they have a good union.

[Ravens_cry]

Jokes aside, I am guessing it would depend to at least a degree on the angle it hits the atmosphere. A steep angle could mean it hits the ground before it has time to slow down to terminal velocity.