Comets in the near-Earth object population

Abstract

Because the lifespan of near-Earth objects (NEOs) is shorter than the age of the solar system, these objects originated elsewhere and they must have a source of re-supply. We seek to determine what fraction of the NEO population consists of dormant or extinct comets. We identify comet candidates among NEOs using three criteria: the Jovian Tisserand parameter Tj < 3, comet nucleus-like spectral parameters (generally linear spectra which correspond to C, D, or P taxonomic types), and low (<0.075) albedos. Out of 31 objects we sample having Tj < 3, we find 17 objects or approximately 55% also satisfy these comet candidate criteria. Bias corrected discovery statistics (Stuart 2003, Ph.D. thesis; Stuart & Binzel 2004, Icarus 170, 295) estimate 30% of the entire NEO population resides in orbits having a value of Tj < 3. Combining these two factors suggests that approximately 16% of the total NEO population has both dynamical and physical properties consistent with a cometary origin.