🚀 go-pugleaf

>  the risk of encounter is 1e-6

The probability of impact must be calculated with respect to the    
uncertainty in the orbit of the comet due to the astrometrics and
the action of non-gravitational forces.  This comet is a particular
comet on a particular path  - not a hypothetical comet on a 
hypothetical path.

To determine the probability of impact during a given time period
simply integrate the density of the distribution of the error in
the location of the comet over the cross section of the Earth's orbit
over the time period in question.

It will vary depending on the expected distance that the comet is from  
Earth during that time period - and thus is not a constant over equal
time periods.  For instance the apparent risk of an impact by S-T today 
is much lower (nil) than it will be on Aug 14, 2116 given our present 
state of knowledge of the S-T orbit.


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Ed Russell