Ceres On 1 January 1801, apparently by coincidence and independent of the Celestial police,
Piazzi was working on a star catalogue and found a moving object, the first
minor planet,
(1) Ceres. He announced it as a new
comet, but due to the lack of nebulosity suspected it might be a small
planet. It was not until September 1801 that his complete observations were published.
Gauss then developed his method of determining
orbits from
astrometric observations. This confirmed not only a planetary rather than a cometary orbit, it also enabled
von Zach and
Olbers to "recover" the minor planet, i.e. to find it again after its passage behind the
Sun. Because the orbit of Ceres matched the requirement from the
Titius-Bode law, the
planet missing between
Mars and
Jupiter seemed to have been found, but it was disappointingly faint.
Pallas, Juno and Vesta In March 1802
Olbers was working on the star catalogue of his zone, in preparation of Ceres arriving in the area, when he discovered another moving star, the second
minor planet,
(2) Pallas. The presence of two minor planets between Mars and Jupiter had several consequences. It cast doubt on the
Titius-Bode law, which called for a single, large planet. It prompted
William Herschel, discoverer of
Uranus, to propose an alternative term "asteroid" instead of "planet". While the use of "planet" could not continue, "asteroid" was not generally accepted until decades later. Olbers took the presence of two minor planets to suggest that a former planet had been destroyed by a collision with a comet. This could restore the Titius-Bode law and offered hope to find more minor planets, in particular at the crossing points of the orbits of Ceres and Pallas.
Huth and von Zach favoured the opposite idea, that the minor planets were just small planets in a region where they failed to form a full-size planet. Pursuing Olbers' idea,
Harding in September 1804 found
(3) Juno, and Olbers in March 1807 found
(4) Vesta.
Further developments After discovering such a large number of relatively small objects in a similar orbit, it became clear that no planet-sized object likely existed in that region. The group members' interest waned in the search. Additionally, the
Napoleonic Wars had disrupted the work of several group members, especially when the war came to
Lilienthal, where Schröter's observatory had served as the home for many of the scientists working with the celestial police. Schröter died in 1816; other members of the Celestial police had moved elsewhere or changed the focus of their work. It would be another generation before any further major discoveries of planets (or even large asteroids) occurred. The division of labour pioneered by the celestial police, around 1850, lead to the concept of
surveys, also to the compilation of catalogues of nebulae. The most famous star catalogue of the 19th century is the
Bonner Durchmusterung with 300,000 stars, which was later extended through the work of more southerly observatories. == See also ==