Main-belt debris on comet-like orbits

Understanding the tension between the dynamical and physical characteristics of solar system debris has been a goal of astronomers and planetary scientists for a long time. This study considered a large (>1400) dataset of orbits gathered from six years of fireball observations observed by the Desert Fireball Network. We focused on the meteoroids we detected originating from short-period comet orbits (2 < T_J < 3). We examined how durable they were as they went through the atmosphere and their orbital evolution over the previous ten thousand years. Our results show that almost all of the meteoroids we see in this size range are sourced from the main belt, not the Jupiter-family comet population. The fact that we do not see these objects shows that genetically cometary material in the centimeter size range does not last long in the inner solar system. Even when meteor shower debris is taken into account, the majority of material at centimeter to meter-scales on comet-like orbits is from the main belt.

We worked with inclusive criteria to be considered cometary in origin. To be classified as cometary, a meteoroid must be at least a Type II according to the PE criterion and have a >50% probability of originating from an unstable orbit over the previous 10 kyrs. Of the 50 sporadic comet-like fireballs observed by the DFN since 2014, only 2 fulfilled this criterion (figure below). Using a Markov Chain Monte Carlo to draw samples from the posterior distribution, we found that sporadic JFC-like meteoroids in NEO space is 94.2% ± 3.2% from the main belt when considering an uninformed prior. This demonstrates that cometary debris has physical lifetimes in near-Earth space less than the decoherence lifetimes for a stream (<1000 years). Material from the main belt becomes the dominant source of debris in this size range as it diffuses out via some combination of orbital resonances, Kozai resonances, nongravitational forces, and close encounters with terrestrial planets (Bottke et al. 2002; Fernández et al. 2014; Hsieh & Haghighipour 2016; Shober et al. 2020a, 2020b).