First planets discovered were Venus, Mars, Jupiter and Saturn. They are known since antiquity. It is easy to observe them, because any special equipment is not required - they can be seen at night without any special devices. Mercury, the Sun's closest planet, is not a good object for observation - sun's light is so bright, that it is very hard to see anything else. But the real problem is with outer planets of solar system. They are far from earth, small and dark, so catching them in telescopes without the knowledge where to point them is not easy.
Man, who discovered another planet, was William Herschel. He found Uranus by accident and become famous in one night. Then, in 1846, Johann Galle observed Neptune. But it was not a fluke - astronomers made many calculations based on irregularities in the orbit of Uranus. It led them to prediction of location of a new planet, which gravity influenced the Uranus orbit. Next Pluto was discovered in 1930 similarly - by checking on previous planet orbit fluctuations.
But even existence of Pluto did not explain all Uranus perturbations - scientist think that there should be another planet, called by them X. This hypothesis is confirmed by two independent astronomers: John Murray and John Matese. They were working on long-term comets of solar system and both think that the disruptions in cometsí orbits are made by large object in the Oort cloud. According to their calculations, the tenth planet should be about 25,000 - 32,000 au (astronomical units) from the sun, it can be bigger from Jupiter approximately 3-10 times, and it's orbital period is predicted to be from 26m to 5.8m years. The accuracy of calculations is influenced by the set of comets taken to observations.
Scientists hope to locate planet X soon with radio or infrared telescopes. The planet is so precious, because it is said to come from other solar system or be a brown dwarf - it is very unlikely that the planet with so big orbit could stay on it for 4.5 billion years. In both cases, if it is found, it can be a great opportunity for science to observe such interesting object from so small distance.
Copyright ©2001 Marcin Wudarczyk