I put this equation together!


K = 1.26 megatons TNT { 100 ^ [ 0.3 (22-mag) ] } V^2


K = kinetic energy (becomes heat on impact)

mag = solar system scale absolute magnitude

V = speed of asteroid in kilometers/sec

A typical impact speed with Earth would be around 30 km/sec.


The equation contains three implicit assumptions: (1) the asteroid albedo is
average for asteroids, (2) the average density is three grams per cubic
centimenter, and (3) the cross section area of the asteroid when its
magnitude is observed is equal to what it would be if the asteroid were
spherical.


For example, the asteroid 2001-XU has a solar system scale absolute
magnitude of 19.01, meaning that it probably has an average radius of about
297 meters, corresponding roughly to a volume of 110 million cubic meters.
If the average density is 3 grams per cubic centimenter (rock), the mass is
330 billion kilograms. Although 2001-XU has an MOID of ~19,000 kilometers,
we can imagine that a small perturbation might shift it into striking Earth.
If that happened, the impact speed would be about 28.9 km/sec, making the
impact energy equivalent to 65.6 gigatons of TNT, which is probably more
than the blast that you'd get by detonating every nuclear weapon on Earth.

My equation saves you the intermediate computational steps. K(mag=19.01) =
65488.7 megatons TNT equivalent

Jerry Abbott