Planet Nine

Proposed by Batygin and Brown in 2016, refined in 2021. A 2025 IRAS–AKARI search found one unconfirmed candidate; a 2026 parallax search found nothing.

Rubin Observatory's LSST began on 29 June 2026 and should find Planet Nine or rule out much of the remaining space. Artist's concept — not observed.

Sources

1. Batygin & Brown 2016, Evidence for a Distant Giant Planet in the Solar System, AJ 151:22
2. Brown & Batygin 2021, The orbit of Planet Nine, AJ 162:219
3. Phan et al. 2025, IRAS & AKARI search
4. Socas-Navarro & Trujillo 2026, A targeted, parallax-based search for Planet Nine, OJAp
5. Rubin Observatory: LSST begins (30 June 2026)

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