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It's known that 9 planets orbit the Sun. There have been many solar system objects that have been discovered recently, but none of them have been classified as planets. These objects have been called asteroids, minor-planets, trans-neptunian objects.
Once some ancient astonaut discovered object which he first thought was a new star. But after its orbit was better determined, later, it was clear that it was not a star but more like a comet. By the end of the 19th century there were several hundred.
Several hundred thousand comets and asteroids have been discovered and given provisional designations so far. Thousands more are discovered each year.
Conventional wisdom says the Moon is devoid of atmosphere, and this may be close enough to the truth, the space just above the lunar surface is not a total vacuum. Some scientists identified helium and argon atoms there, and other Earth-based observations added sodium and potassium ions to the list.
Early on, Mars became a favorite subject of scientific study because of its obvious life potential. Why Go to Mars? A four-pound rock that left Mars 16 million years ago may hold the clues to ancient life on the planet. The rock is one of 13 Mars meteorites found on Earth. These rocks may contain clues to the ancient history of planet Mars, believed to have been a warmer, wetter place over 3 billion years ago.