Minor Planets

Minor Planets.

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Minor Planets.
Venus Mercury Mars Jupiter		Saturn Uranus Neptune Pluto

The Italian astronomer Giuseppe Piazzi discovered the first asteroid just after midnight on January 1st 1801. He named it Ceres after Sicily's patron goddess. The next year Pallas was discovered and in 1804 Juno followed by Vesta in 1807. Over the next few years first tens then hundreds were discovered mostly between the orbits of Mars and Jupiter. They all appeared star like through a telescope so they were called asteroids, the modern term for these asteroids is minor planets or planetoids. The tradition of naming these minor planets after mythological figures soon ran into problems as they started to run out of names. So astronomers started to name them in order of discovery. The discoverer was also allowed to name them what ever they liked once they have been approved by the International Astronomical Union. Minor planets have been named after people, sweethearts, cities, plants, dogs and cats, breweries and many more strange things. We get names like 511 Davida, 153 Hilda and 747 Winchester. Minor planets are the only astronomical objects that are allowed to be named after living people. Most of the minor planets lie between 315 million KM (2.1 a.u.) and 495 million KM (3.3 a.u.) from the Sun.
If the minor planet comes within Earth's orbit at its perihelion, it is called an Apollo type. The few that are never farther from the Sun than the Earth is are called Aten types. The sidereal period for an average minor planet in the middle of the asteroid belt is around 4.5 Earth years. Minor planets are the remains of mater that did not form a major planet when the solar system was created some 4.6 billion years ago. They range in size from the largest, Ceres, which is about 914 KM in diameter down to boulders to small to be seen from Earth and even dust particles. There about 4000 minor planets named and numbered so far with several hundred found each year. The total number is probably in the billions with only a few dozen larger than I00 KM across. If all the minor planets were added together it would make up a planet slightly smaller than the Moon. Most of these minor planets are quite dark reflecting only about 4% of the sunlight falling on them. The chemical composition of minor planets varies from metallic through stony to even organic (though not biological) compounds such as carbon, water and other volatile materials. There chemical composition resembles that of meteorites found on Earth and are probably the origin of most of these meteorites. They have a variety of shapes such as elongated and dumbbell shaped. Some astronomers speculate that some minor planets even have smaller objects orbiting them.