In the 18th century, an international group of astronomers referred to as the “Celestial Police” devoted themselves to the search of the “missing” planet between Mars and Jupiter. A planet was expected in that zone based on the extrapolations of the Titius-Bode law, a mathematical formula developed by Johann Titius in 1766 and popularized by Johann Bode, both German astronomers. The law calculated the expected spacing between planets in the solar system, and had gained credibility in 1781, when William Herschel discovered Uranus exactly where the Titius-Bode law had predicted it. Since Titius-Bode also predicted a planet between Mars and Jupiter, the Celestial Police were determined to find the elusive body.
In 1801, Giuseppe Piazzi seemed to have delivered on the law’s promise when he discovered dwarf planet Ceres. However, on March 28, 1802, Heinrich Olbers was attempting to observe Ceres when he discovered asteroid Pallas. Though both were large – today we know Ceres and Pallas as the largest and third-largest objects, respectively, in the asteroid belt – Olbers realized that both were far too small to be the mythical missing planet. His search for the source of Ceres and Pallas would, however, lead him to discover the second-largest asteroid belt member, Vesta, on March 29, 1807.
