The magnitude distribution and evolution of short-period comets

The magnitude distribution, perihelion distribution, nucleus size variation and evolution of the short-period comet population are re-assessed. Short-period comets with perihelion distances greater than 2 au have a magnitude distribution index of about 2.3, similar to that of the long-period comets. This index progressively increases for smaller perihelion distances, owing to the pronounced effects of cometary decay. The relationship between absolute magnitude and nucleus radius is investigated, as is the relationship between cometary decay rate and perihelion distance. It is estimated that 50 per cent of the known short-period comets will decay away completely in the next 2600 yr, a further 25 per cent going in the following 2300 yr.