Is Interstellar Object 2I/Borisov a Stardust Comet? Predictions for the Post Perihelion Period

Abstract

The detection of interstellar bodies passing near the Sun offers the opportunity to observe not just objects similar to those in the solar system, but also unfamiliar objects without solar system analogues. Here I show that Asymptotic Giant Branch (AGB) stellar evolution may lead to the creation, out of stardust, of substantial numbers of nomadic Post-Main-Sequence Objects (PMSOs). ABG nucleosynthesis will produce three broad classes of PMSO chemistry, oxygen, carbon and nitrogen rich (O-rich, C-rich, N-rich, respectively), depending largely on the original stellar mass. I further show that the Interstellar Comet 2I/Borisov (2I) belongs to a kinematic dynamical stream, the Wolf 630 stream, with an age and galactic orbit consistent with its origination as a stardust comet; the apparent lack of water in the 2I coma is consistent with it being a C-rich PMSO. I also provide predictions for distinguishing stardust comets from more conventional interstellar comets and asteroids ejected during planetary formation; these can be applied to 2I in its upcoming observational phase in early 2020 as it moves away from the Sun. In particular, isotope ratios of the CNO elements could be dispositive, IR detection of the 11.3 {\mu}m SiC line, the 30 {\mu}m line, or the IR PAH lines would provide strong evidence for a C-rich PMSO and detection of Na or Li enhancement would indicate an N-rich PMSO.