2025RNAAS...9..270D

Most exoplanets known orbit stars that will evolve into red giants, then white dwarfs (WDs). Understanding the population of substellar WD companions informs the common-envelope evolution process (E. Villaver & M. Livio ), thereby shedding light on the current and future planetary population of the Milky Way. Here, we report the discovery of a low-mass (25 ± 5M_Jup) brown dwarf (BD) fully eclipsing every 2.93 hr the WD J0404+1112, which we found to be an unexpectedly large host WD (2R_Earth). The eclipsing nature of the system, the low masses of the primary (∼0.3M_Sun) and secondary, and the large day-night temperature contrast for the BD (${\unicode{10925}}$2000 K) make it a prime target amongst the dozen WD+BD systems known for a detailed study via JWST phase-curve observations.