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  • Print publication year: 2010
  • Online publication date: June 2012

9 - Minor Planets


I have announced this star as a comet, but since it is not accompanied by any nebulosity and, further, since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet.

Giuseppe Piazzi, 24 January 1801, commenting on the object that he had discovered 23 days earlier, which was later determined to be the first known minor planet, 1 Ceres

In addition to the eight known planets, countless smaller bodies orbit the Sun. These objects range from dust grains and small coherent rocks with insignificant gravity to dwarf planets that have sufficient gravity to make them quite spherical in shape. Most are very faint, but some, the comets, release gas and dust when they approach the Sun and can be quite spectacular in appearance (Fig. 10.1); comets are discussed in Chapter 10. In this chapter, we describe the orbital and physical properties of the great variety of non-cometary small bodies ranging in radius from a few meters to over 1000 km that orbit the Sun. We refer to these bodies collectively as minor planets.

Minor planets occupy a wide variety of orbital niches (see Fig. 1.2). Most travel in the relatively stable regions between the orbits of Mars and Jupiter (known as the asteroid belt), exterior to Neptune's orbit (the Kuiper belt), or near the triangular Lagrangian points of Jupiter (the Trojan asteroids).