Re: 2004 MN4 Asteroid Possibilities

From: Raven (jonlennart.beck.god_at_damn.get2net.that.dk.spam)
Date: 12/27/04 

Date: Mon, 27 Dec 2004 20:30:17 +0100

"Brian Jacobson" < stree.antispam@redshift.com> skrev i en meddelelse
news:9lk0t058sf58qkleqh08imsvl0u69el7pa@4ax.com...

> If it couldn't be nudged enough and did turn out to be an
> impactor, what would its impact energy be, since it would be a
> "rear-end collision" rather than a "head-on"? Would it be practical
> to try to drop it on a big desert?

   If an asteroid strikes the Earth, its minimum impact velocity will be the
Earth's escape velocity, at about 11.2 km/s. Unless by some fluke of
coincidences it grazes the upper atmosphere, is captured into a closed
orbit, and aerobrakes over several orbits until it drops wholly into the
atmosphere at "only" about 8 km/s.
   If you assume that the speed imparted to a molecule in the gas that
results from a TNT explosion is typically about 3 to 4 km/s, then the escape
velocity corresponds to ten times that in kinetic energy. So an asteroid
with a mass of x thousand tonnes will strike the Earth with an energy
corresponding to at least a 10x kilotonne nuclear warhead. If 2004 MN4 has
a diameter of 400 meters, and we assume it is roughly spherical and is made
mainly of rock (asteroids that close to the Sun probably contain little ice)
with a density of about twice that of water (assuming that it is rather
porous, like a flying rubble heap), then its mass will be somewhat less than
70,000 thousand metric tonnes. The impact energy will be near that of a
hypothetical 700 megatonne warhead - going off at ground level or a little
below, but without the radioactivity, at least.

Jon Lennart Beck.