Re: Asteroid Problem

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

Thanks for constructive comments; I am not an astronomer.
Was the assumed speed, 10^5 m/s, realistic? In any case, it
would be useful to post an improved estimate of the amount
of energy needed to deviate an asteroid. Some of us may
like to present this problem to students but are not familiar
with realistic parameters. Can you help us, Michael?

Michael Bowen wrote (in part):

> Also, 10^20 kg is a pretty hefty (although not inconceivable) asteroid; if
> made of water ice and trace metallic impurities, this implies a volume of
> 10^20 liters or 10^17 m^3, and thus a radius (if spherical) of about 300
> km, which is comparable to the sizes of the largest observed asteroids.
> There are only a few of these known in the entire solar system. A more
> common but still respectable chunk (say, the size of Eros) would cut the
> radius by 10 and the mass, energy, momentum, and bomb count by an
> additional factor of 10^3; I think that with these modifications we're now
> down to "only" 4 million bombs.
>
> I think the needed angle of deflection is also less than 1/100 radian. To
> avoid a direct impact, one need only change the impact location by about
> than 10^4 km (less, actually, but let's build in a safety factor; we don't
> want it exploding in the atmosphere during a near miss, a la Tunguska).
> This is less than 10^-4 AU. From a distance of 100 AU, I think this makes
> the necessary deflection angle about a microradian. This is optimistic,
> however, as astronomers are unlikely to spot an object of asteroid size at
> 100 AU; it's simply too dim and far away.
>
> Here's another question that I haven't calculated yet, but that might be
> interesting: For a water-ice "asteroid" (probably "comet" would be a better
> description), how much heat would it take to simply boil the thing away
> into space, and how would that compare with the energy required to deflect
> it? One wouldn't have to heat it to 373 K; once liquefied, the surface
> should boil off readily into the surrounding vacuum, although one would
> have to supply at least the heats of fusion and vaporization, the latter of
> which is still substantial. Could a fleet of small, warm, radioactive
> robots "swim" through (or over) the ice to accomplish this, and could
> such a fleet be safely recalled or otherwise disposed of (e.g., sent into
> the sun) after its work was finished?