Three Thousand Motion-confirmed L and T Dwarf Candidates from the Backyard Worlds: Planet 9 Citizen Science Project

June 2026 • 2026AJ....171..341S

Authors • Schneider, Adam C. • Kuchner, Marc J. • Faherty, Jacqueline K. • Meisner, Aaron M. • Kirkpatrick, J. Davy • Burgasser, Adam J. • Bardalez Gagliuffi, Daniella • Bickle, Thomas P. • Caselden, Dan • Casewell, Sarah L. • Gagné, Jonathan • Honaker, Easton J. • Kiwy, Frank • Marocco, Federico • Rothermich, Austin • Stevnbak Andersen, Nikolaj • Ruiz Arroyo, Lizzeth • Baller, Bruce • Beaulieu, Paul • Bell, John • Bilsing, Martin • Bohling, Troy K. • Colin, Guillaume • Colombo, Giovanni • Deen, Sam • Dereveanco, Alexandru • Dixon, Kevin • Durantini Luca, Hugo A. • Flores, Deiby • Frank, Christoph • Fulvi, Christopher • Gallmann, Michael • Gantier, Jean Marc • Glebov, Konstantin • Gramaize, Léopold • Hamlet, Leslie K. • Hinckley, Ken • Jablonski, Kevin • Jałowiczor, Peter A. • Kabatnik, Martin • Kasprowitz, Peter • Ly, K. • Martin, David W. • Marzak, Naoufel • McColgan, Alexander • McEwan, Neil J. • Michaels, Marianne N. • Pendrill, William • Perlin, Stéphane • Pumphrey, Ben • Rabe, James • Raway, Henry • Robledo, Walter Ruben • Roser, David • Roy, Animesh • Sainio, Arttu • Schindler, Vincent • Schonau, Manfred • Schümann, Jörg • Selg-Mann, Karl • Serio, Andrea • Sirbescu-Stanley, David • Smith, Patrick • Stenner, Andres • Sunjoto, Christine • Tanner, Christopher • Thévenot, Melina • Thakur, Vinod • Torres Guerrero, Mayahuel • Ventura, Maurizio • Voloshin, Nikita V. • Walla, Jim • Wȩdracki, Zbigniew • Weyandt, Bailey • Wilhite, Breck • Zitouni, Spartacus

Abstract • The Backyard Worlds: Planet 9 citizen science project uses data from the Wide-field Infrared Survey Explorer to detect infrared objects with significant motion. In this work, we present the majority of the L and T dwarf candidates discovered through this effort. For each candidate, we provide proper motion measurements as well as optical, near-infrared, and mid-infrared photometry (when available), photometric spectral types and distance estimates. 3006 new motion-confirmed discoveries are presented in this work, 2357 with L-type photometric spectral types and 649 with T-type photometric spectral types. We also present an additional 80 objects as likely L or T dwarfs based on available photometry, but for which a significant motion measurement could not be obtained. We identify 28 objects in this sample as new comoving companions to higher-mass stars, and an additional nine sources that are candidate binary systems made up of two ultracool dwarfs of L type or later. Follow-up spectroscopic observations will be necessary to confirm spectral types and further characterize the sources discovered through this project. This work presents the largest single sample of motion-confirmed L and T dwarf discoveries to date, which would more than double the number of known L and T dwarfs, if confirmed. We wish to sincerely thank our citizen scientist collaborators for their monumental efforts that have directly impacted this project's success.

Links

• ELECTR https://doi.org/10.3847/1538-3881/ae5b60
• PREPRINT http://arxiv.org/abs/2604.01323