Predictions of Stellar Occultations by Haumea and the Event of 4 May 2026

Abstract

Haumea is the third-largest of the five officially recognized dwarf planets and one of the four that reside in the trans-Neptunian region. It is among the most exotic bodies in the Solar System, with an exceptionally rapid rotation, a highly elongated triaxial shape, and a ring that orbits about three times more slowly than Haumea itself. Because of its large heliocentric distance, direct exploration by dedicated space missions is not feasible in the short term, so progress must rely on ground- and near-Earth facilities. Stellar occultations are among the most powerful tools to investigate trans-Neptunian objects. We present new predictions of stellar occultations by Haumea and its ring for stars down to Gaia G = 21, and assess their scientific potential, with special emphasis on the 4 May 2026 event. We computed occultation opportunities for the coming years and evaluated the 4 May 2026 geometry in detail, including Haumea's rotation phase, known 3D shape, pole orientation, and sky-plane motion, to estimate the expected shadow-path width. Because the target star has a very large Gaia RUWE, we also carried out a dedicated reliability analysis, including speckle observations. We identify eleven valuable events through 2030. For 4 May 2026, we derive an expected sky-plane shadow width of $2224 \pm 30$ km, substantially larger than conservative nominal assumptions and therefore highly favorable for observations. Speckle imaging reveals a companion at $\sim 0.12$ arcsec and $\Delta m \sim 3.1$; this companion is also expected to be occulted and shifts the nominal main-star path prediction on Earth by about 8 mas. These results confirm the strong scientific return expected from coordinated observations of upcoming Haumea occultations, especially the 4 May 2026 event, and provide an updated framework to improve constraints on Haumea's shape, density, ring properties, and environment.