Re: Is the Kepler's law of areas valid for a comet ?

The Kepler result that MdA/dt is constant follows from conservation of 
angular momentum.  When a comet loses mass by ejecting matter, it is the 
total angular momentum of the comet and all the matter it has ejected that 
is conserved.  This means that MdA/dt for the comet will decrease, but its 
dA/dt will remain constant.  The angular momentum loss by the comet will 
equal the angular momentum of the matter it ejected.