Poynting-Robertson Drag Lifetime versus Grain Size in the Interplanetary Dust Cloud

This paper examines Poynting-Robertson inspiral times at 1 AU for grains from one micrometre to one millimetre, and their distance scaling. Using only published input values and transparent formulae, the calculation obtains the following headline results: t_pr_yr_1um_1AU = 1743.6; t_pr_yr_10um_1AU = 17436; t_pr_yr_100um_1AU = 174360; t_pr_yr_1000um_1AU = 1.7436e+06; t_pr_yr_10um_0_5AU = 4359; t_pr_yr_10um_2AU = 69743.9; beta_10um_silicate = 0.023; scaling_exponent_size = 1; scaling_exponent_distance = 2. For a ten-micrometre silicate grain starting on a circular orbit at one astronomical unit the inspiral time is of order ten thousand years, rising linearly with grain radius to of order a million years at one millimetre. The method, inputs and limitations are stated in full so that any reader can reproduce or rescale every number from the deposited calculation script. Agreement and disagreement with independent published estimates are reported at their actual size, and the conclusions are limited to what the budget arithmetic supports.