Searching for Planetary-Mass Objects in Nearby Young Moving Groups using SPHEREx and Citizen Science

The identification of isolated planetary-mass objects (“planemos”) is critically needed, as they provide gas giant atmosphere analogs highly suitable to spectroscopic characterization without the glare of a bright host star. Identifying nearby planemos requires locating substellar members of nearby young moving groups; these sparse associations of coeval stars have a common motion through space, and serve as age-dating benchmarks that allows to lift the mass degeneracy in substellar objects. I will present our most recent Bayesian kinematic membership analysis of new substellar objects discovered by citizen scientists through the Backyard Worlds: Planet IX project, supplemented by space-based infrared SPHEREx spectroscopy to identify, validate, and characterize planetary-mass objects in our immediate neighborhood. Our approach leverages the latest version of the BANYAN Σ Bayesian classification tool, which includes thousands of young associations. We have so far identified 390 age-calibrated planemos and brown dwarfs with masses ~ 2 to 88 Mjup, distances ~ 11 to 81 pc, and ages ~ 10 to 800 Myr. Of these objects, 299 already have SPHEREx spectra which have allowed us to confirm them as substellar objects. Our results highlight the power of combining citizen science and SPHEREx spectroscopy to uncover and characterize large populations of planemos and brown dwarfs in nearby young moving groups.