The first dwarf planet was found, lost, then found again by pure math
Giuseppe Piazzi spotted Ceres on New Year's night in 1801, exactly where a controversial spacing law predicted a missing planet should be — then it vanished behind the sun before anyone could confirm the sighting. A 24-year-old Carl Friedrich Gauss worked out its orbit from Piazzi's sparse data well enough that astronomers found it again almost a year later.