[meteorite-list] Maximum theoretical Earth impact velocity

[Chris Peterson]

Also worth noting is that some orbital parameters (such as semi-major 
axis) are exquisitely sensitive to the value of the initial velocity. 
Unless you know that to within a few percent, there's hardly any point 
in calculating the parameters at all (although inclination can be a 
useful value).

Chris

*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On 4/14/2014 1:54 PM, Matson, Rob D. wrote:
> Hi Chris/Shawn/All,
>
> There is obviously something squirrely going on in that generated orbit.
> For one thing, look at the error bars on the velocity -- they cover all
> possible velocities (and as Chris points out, impossible velocities as
> well).
>
> I do have a comment about the oft-quoted 72 km/sec value. It is derived
> from the orbital velocity of the earth around the sun which averages
> 29.78 km/sec encountering a retrograde body at just below solar system
> escape velocity, which is around 42.1 km/sec at the earth's average
> distance from the sun. This gets you to 71.88 km/sec. However, earth's
> maximum orbital velocity (which occurs at perihelion in early January
> each year) is 30.29 km/sec. And solar system escape velocity at earth's
> perihelion distance is 42.48 km/sec. So that increases the closing
> velocity to 72.77 km/sec. However, this still isn't the theoretical
> maximum closing velocity, since I haven't included the acceleration of
> the intercepting body due to earth's gravity well.
>
> At an initial closing speed of 72.77 km/sec, there isn't a lot of time
> for the earth's gravity to act on the body before it hits the atmosphere,
> so the velocity boost is much smaller than earth's escape velocity (11.2
> km/sec). From conservation of energy considerations, it can be shown
> that the square of the impact velocity is equal to the sum of the
> squares of the escape velocity and the approach velocity. So:
>
> Max impact velocity = SQRT(11.2^2 + 72.77^2) = 73.63 km/sec
>
> So in January, it is certainly possible to have a meteor with a
> velocity above 73 km/sec. Anything above 73.63 would require the object
> to have either originated outside the Solar System, or (as Chris
> mentioned) to have been involved in a slingshot encounter with
> another planet prior to encountering earth.
>
> --Rob