's sense of proportion for the planetary orbits led him to believe that an invisible planet lay between the orbits of Mars and Jupiter. In 1596,
Johannes Kepler wrote, "Between Mars and Jupiter, I place a planet," in his
Mysterium Cosmographicum, stating his prediction that a planet would be found there. While analyzing
Tycho Brahe's data, Kepler thought that too large a gap existed between the orbits of Mars and Jupiter to fit his own model of where planetary orbits should be found. In an anonymous footnote to his 1766 translation of
Charles Bonnet's
Contemplation de la Nature, the astronomer
Johann Daniel Titius of
Wittenberg noted an apparent pattern in the layout of the planets, now known as the
Titius-Bode Law. If one began a numerical sequence at 0, then included 3, 6, 12, 24, 48, etc., doubling each time, and added four to each number and divided by 10, this produced a remarkably close approximation to the radii of the orbits of the known planets as measured in
astronomical units,
provided one allowed for a "missing planet" (equivalent to 24 in the sequence) between the orbits of Mars (12) and Jupiter (48). In his footnote, Titius declared, "But should the Lord Architect have left that space empty? Not at all." , discoverer of Ceres, the largest object in the asteroid belt: Ceres was known as a planet, but later reclassified as an asteroid and from 2006 as a dwarf planet. On January 1, 1801,
Giuseppe Piazzi, chairman of astronomy at the
University of Palermo, Sicily, found a tiny moving object in an orbit with exactly the radius predicted by this pattern. He dubbed it "Ceres", after the
Roman goddess of the harvest and patron of Sicily. Piazzi initially believed it to be a comet, but its lack of a
coma suggested it was a planet. Thus, the aforementioned pattern predicted the
semimajor axes of all eight planets of the time (Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, and Uranus). Concurrent with the discovery of Ceres, an informal group of 24 astronomers dubbed the "
celestial police" was formed under the invitation of
Franz Xaver von Zach with the express purpose of finding additional planets; they focused their search for them in the region between Mars and Jupiter where the
Titius–Bode law predicted there should be a planet. About 15 months later,
Heinrich Olbers, a member of the celestial police, discovered a second object in the same region, Pallas. Unlike the other known planets, Ceres and Pallas remained points of light even under the highest telescope magnifications instead of resolving into discs. Apart from their rapid movement, they appeared indistinguishable from
stars. Neither the appellation of planets nor that of comets can with any propriety of language be given to these two stars ... They resemble small stars so much as hardly to be distinguished from them. From this, their asteroidal appearance, if I take my name, and call them Asteroids; reserving for myself, however, the liberty of changing that name, if another, more expressive of their nature, should occur. By 1807, further investigation revealed two new objects in the region:
Juno and
Vesta. The burning of
Lilienthal in the
Napoleonic Wars, where the main body of work had been done, , the first asteroid imaged by a spacecraft, as viewed during
Galileo's 1991 flyby; colors are exaggerated The expression "asteroid belt" came into use in the early 1850s, although pinpointing who coined the term is difficult. The first English use seems to be in the 1850 translation (by
Elise Otté) of Alexander von Humboldt's
Cosmos: "[...] and the regular appearance, about the 13th of November and the 11th of August, of shooting stars, which probably form part of a belt of asteroids intersecting the Earth's orbit and moving with planetary velocity". Another early appearance occurred in
Robert James Mann's
A Guide to the Knowledge of the Heavens: "The orbits of the asteroids are placed in a wide belt of space, extending between the extremes of [...]". The American astronomer
Benjamin Peirce seems to have adopted that terminology and to have been one of its promoters. A total of 1,000 asteroids had been found by 1921, 10,000 by 1981, and 100,000 by 2000. The detection was made by using the
far-infrared abilities of the
Herschel Space Observatory. The finding was unexpected because
comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids". ==Origin==