On March 13, 1930, the Lowell Observatory in Arizona, usa, announced the discovery of the ninth planet of the Solar system, bringing an end to an exactly 150-year old search. On March 13, 1781, the German-born English astronomer William Herschel (1738-1822), more or less accidentally discovered Uranus using the biggest telescope then available. It was a momentous discovery: no one in recorded history had till then ever discovered a planet. The five planets, Mercury, Venus, Mars, Jupiter and Saturn, were easily visible to naked eye and every ancient civilisation worth its name had recognised them. But the discovery was to trigger some disquiet among astronomers culminating in the discovery of Pluto.

For, Uranus was not moving through space as astronomers had calculated using the Newton's laws of gravity. To tide over the problem some questioned the validity of Newton's laws over large distances; others suggested the existence of a planet beyond Uranus that was exerting gravitational influence on it, thereby making Uranus stray from its computed orbit.

That planet, Neptune, was discovered in 1846. Nonetheless, the discovery could not account for all observed disturbances in Uranus's orbit. Moreover, Neptune itself was seen to have orbital influences of its own. So, was another planet waiting to be discovered?

Enter Percival Lowell
Born into a wealthy and well-known Bostonian family, Percival Lowell showed interest in mathematics and astronomy even in his graduate days, but spent his first 17 years in business and served in the American diplomatic mission in Korea. Lowell called the unknown planet, Planet x