Rubin’s Hidden Dwarf Planet: The World Lost in the Milky Way

Show notes
Astronomy Daily S05E216 — A New World in the Crowd (Thursday 29 October 2026). Hosts Anna and Avery. Lead: the Vera C. Rubin Observatory has found its first dwarf-planet candidate. 2026 ED138 lies beyond Pluto, about 46 au from the Sun. Matthew Holman (CfA) found it on 13 October with a search code built with Kevin Napier, and it was announced on 27 October at the DPS meeting in Spokane (MPEC 2026-U85). Rubin caught it 30 times on 20 nights between March and July, and Dark Energy Camera precoveries extend the orbit back to 2016. Only nine known trans-Neptunian objects are intrinsically brighter. Its size is estimated at 600–1,500 km, depending on reflectivity, so it remains a candidate until infrared or occultation measurements pin it down. It hid near the plane of the Milky Way, about 43° south of the celestial equator. Also: JWST's 37-hour phase curve shows the lava world TOI-561 b reflecting about three-quarters of its starlight, possibly through silicate clouds, with University of Sydney co-authors. ESA's Hera resolves Didymos and Dimorphos separately for the first time, with detailed Dimorphos images due 25 November. NASA's Swift is in its final weeks before re-entry, and UVEX passes a key review. Skywatch for Sydney, Los Angeles, New York and London: Mars and Jupiter closing in the pre-dawn sky (1.2° on 16 November), Saturn in the evening, Mercury's last call from the south, the waning Moon through Taurus to Gemini, and the US clock change on 1 November.

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