Minor Planets

Minor Planets

The first and largest minor planet was discovered on January 1, 1801, by the Italian astronomer Giuseppi Piazzi. Named Ceres, it has a diameter between 420 and 500 miles, and moves between the orbits of Mars and Jupiter in a period of about 4.6 years. Another minor planet, Pallas, was discovered by Heinrich Olbers in 1802. Karl Harding picked up a third, Juno, in 1804, and Olbers found Vesta, the brightest of all the minor planets, in 1807. The fifth, Astraea, was not discovered until 1845 (by Heneke, a postmaster at Driesen), but since then their numbers have increased by leaps and bounds. Over 1,600 have now had their orbits determined, while many more make nuisances of themselves by showing up on photographs of star fields. There are probably thousands more, but they escape detection because of their extreme faintness. The great majority are thought to be no more than chunks of rock associated with frozen gases.

Minor Planets. Minor planets - Ceres, Vesta, Pallas, Hygiea, Eris, Pluto (with satellite Charon), Makemake, Haumea (with satellites Namaka and Hi'iaka), Sedna, Orcus, Quaoar, Varuna. Image in public domain

Most of the known minor planets move in the great gap of about 350 million miles between the orbits of Mars and Jupiter. Some, however, have orbits which take them well within the orbit of the earth, while others get taken outside the orbit of Jupiter. A few can come quite close, astronomically speaking, to the Earth. In 1930-1931, for example, Eros, a cigar shaped body some 15 to 20 miles long, approached to a distance of 16 million miles. Much closer approaches were made by Adonis (one million miles) and Hermes (500,000), two tiny bodies discovered in 1936 and 1937 respectively. Although the chances of one hitting the Earth are extremely remote, the impact of a large minor planet would certainly bring about widespread devastation.