Discovery of Planets

Written by Hemal S. Shah

“My Very Educated Mother Just Showed Us Nine Planets”, is the sentence that an astronomy enthusiast likes. See the box given below to know the secret of the sentence. The planets Mercury, Venus, Earth, Mars, Jupiter and Saturn were already known since the ancient times. We do not have any mention of the discovery of any of these planets in any of the available ancient literatures. The one obvious reason for this is that all these planets are visible without the aid of telescopes. The motions can also be studied with respect to the stationery stars and hence it became possible to predict their positions. The planet Saturn was thought to be the farthest of all planets; the last planet of the Solar System. The day, 13th March 1781, changed the acute perception of Saturn being the last planet.

On this day, Sir William Herschel along with his sister Caroline Herschel caught sight of a new planet through his homemade telescope. Initially he thought that the object he found was a comet; later it got confirmed that the object was a new planet! The first planet discovered in the entire recorded history of mankind. Since it was the first time that a planet was discovered, a problem arose world-over for what should be the name of the newly discovered planet? After much debate and suggestions the name kept for the planet was Uranus. It was later, that the fact came to light that Uranus was sighted many times before. But, it was always dismissed as simply another star or a comet.

William Herschel was a type of person who believed that men and animals resided on Mars, Moon and Sun.

The world-renowned astronomer Galileo Galilee, the first person to use the telescope for astronomical observations, made the Science of Astronomy richer. He was the first person to have seen four Satellites around the planet Jupiter, phases of inner planets: Venus and Mercury, irregularities on the surface of the Moon (craters) and on the surface of the Sun (sunspots). He also saw something peculiar around the planet Saturn. He could not recognize what the peculiar thing was. Later Christian Huygens identified them as Rings around the planet Saturn. Galileo, through all his findings wanted to prove that the heavenly bodies are not exact and Earth does not hold any superior position, as it was strongly believed in those days.

Galileo could have struck a goldmine! While scanning the night skies, Galileo did notice the planet Neptune in the year 1612 and 1613. On both of these occasions he mistook Neptune for a fixed star.

After the discovery of Uranus, the next thing to be worked out was to plot its elliptical orbit around the Sun. Once this was done, astronomers found some discrepancy in actual orbit that Uranus was taking and the orbit that they had plotted. They soon knew that the gravitational force of some external mass was perturbing Uranus in its orbit around the Sun.

On the basis of observed perturbations, astronomers calculated the orbit and mass of the unknown external object. Then began the search for this unidentified object at the speculated positions. They were aware that this new object, if discovered would be the eighth planet of the Solar System.

Johann Gottfried Galle discovered the new planet Neptune on September 23, 1846, nearly at the same location as was predicted by Urbain Le Verrier in the year 1846 and by John Couch Adams in the year 1843.

Many observers had sighted the planet Neptune in the past before its discovery. Each time it was thought of as a fixed star or some comet and was never considered as a planet, even by Galileo as mentioned earlier.

Discovery of the planet Uranus and its exact orbital calculations helped in finding Neptune. The orbital calculations were on the basis of the laws enunciated by Sir Isaac Newton and Johannesse Kepler.

The Solar System was then known to have eight planets with Neptune as the last and farthest planet orbiting around the Sun. Almost 84 years after the discovery of Neptune, an astronomer named Clyde W. Tombaugh at the Lowell Observatory in Arizona discovered a new planet Pluto on February 18, 1930.

He didn't discover Pluto while scanning the sky through telescope; rather he discovered it when he was comparing the two photographic plates of a particular region of the sky taken on different dates, January 23 and 29. In it he noticed the displacement of a star like object indicating that either it was a planet or a comet. Later came the confirmation that it was a planet, the ninth planet of the Solar System.

Another 75 years have passed since the discovery of the planet Pluto. We have all studied about the Solar System consisting of nine planets with the Sun as the main central body. It seems that now the time has come to change the idea of our Solar System.

Astronomers have discovered a new planet orbiting the Sun. This planet is bigger than Pluto. It is situated 97 times further than the Earth from the Sun. This new planet was actually first photographed in 2003 by the Samuel Oschin Telescope at Palomar Observatory. These telescopes are robotically controlled. They are assigned the task of photographing regions of sky tile by tile. The same region is photographed again after some interval of time. Once this is done, astronomers check for the displacement of light points in the pairs of photographs. Millions of images are generated and stored in computers. Computers do analysis, and those pairs of photographs, which have even the slightest movements of objects, are short listed for more intense analysis by the scientists.

Mike Brown, Chad Trujillo and David Rabinowitz are the discoverers of the new planet. In an ongoing survey at Palomar Observatory, these scientists photographed the planet in 2003. In a reanalysis of the photographs, on January 5th 2005, they detected the new planet. The new planet is currently known as 2003 UB313. Since its discovery, the scientists have been studying the planet to better estimate its size and its motions.

A name for the new planet is suggested by its discoverers to the International Astronomical Union (IAU) and are waiting for the decision of this body to officially announce it.

A matter of pride for all of us is that an Indian Astronomer, Dr. J. J. Rawal had predicted in 1978 about the existence and location of the tenth planet. NASA accepted his scientific paper. According to him the new planet orbited the Sun at a distance of 99 AUs (1 AU is average Earth-Sun distance) and today after the discovery it is found to be at a distance of 97 AUs. His calculations are accurate enough. We hope that the due credit shall be given to Dr. J. J. Rawal for his excellent work done way back in 1978.