Who Was the Last Man to Discover a Planet?
Clyde Tombaugh, a young American research student, made the last discovery of a planet while working in 1930 at the Lowell Observatory, Arizona State College. This planet is Pluto, the ninth one in order of distance from the sun, 3,670 million miles away. Although Tombaugh, who was 26 at the time, was the first astronomer to see Pluto, its existence had been suspected by Percival Lowell, builder of the observatory at Flagstaff, Arizona.
Lowell began searching for the planet in 1905, the year before Tombaugh was born. He observed that there was a difference between the predicted and actual positions of Uranus, and this led him to conclude that there must be another planet. His final calculations about “Planet X” were published in 1914, but he had still not found the planet when he died two years later.
Another American, W. H .Pickering, took up the search, concentrating on the irregular movements of the planet Neptune. He saw a clue in the movement of comets, which seem to be attracted by large planets. There were 16 known comets whose path took them millions of miles beyond Neptune, which is 2,811 million miles from the sun, and Pickering was convinced that they were being attracted by a still more distant planet.
In 1919 yet another hunt was begun by Milton Humason at Mount Wilson Observatory, Pasadena, California. Instead of mathematical calculations, Humason tried photography. He took two pictures of a series of stretches of the sky, with a gap of one or two days between exposures. In such photographs stars stay still, but planets change position.
When Tombaugh discovered Pluto, it became clear that Humason had photographed the planet twice. Once it had been masked by a star, and the second time its image had coincided with a flaw in the photographic plate. The main difficulty in the search had been that Pluto was extraordinarily faint. Pickering formed the opinion that it was not Lowell’s Planet X, but that a huge planet remains to be discovered.
Pluto was discovered by Clyde Tombaugh in 1930 and used to be regarded as the ninth planet, but it was downgraded in 2006 to a dwarf-planet or ‘plutoid’ and is now known unceremoniously as ‘asteroid number 134340.’ Mike Brown, professor of Planetary Astronomy at the California Institute of Technology, refers to himself as the ‘man who killed Pluto’ because he discovered many ‘trans Neptunian objects’ which are larger, including the dwarf planet Eris.
His team at Caltech announced they had found evidence of a ninth planet in the solar system which is travelling on a bizarre elongated orbit. The body, which has been dubbed ‘Planet Nine’ is 10 times the mass of Earth and takes between 10,000 and 20,000 years to orbit the Sun. It is so big that researchers have branded it ‘the most planety planet of the solar system.’ Evidence for Planet Nine was found by Caltech researchers who were puzzled as to why 13 objects in the Kuiper Belt – an area beyond Pluto – were all moving together as if being ‘lassooed’ by the gravity of a huge object.
Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system – one of the key tests for planet classification. In fact, it dominates a region larger than any of the other known planets–a fact that Brown says makes it “the most planet-y of the planets in the whole solar system.”
Dr Brown and other colleagues have begun searching the skies for Planet Nine. Only the planet’s rough orbit is known, not the precise location of the planet on that elliptical path. If the planet happens to be close to its perihelion, Dr Brown says, astronomers should be able to spot it in images captured by previous surveys. If it is in the most distant part of its orbit, the world’s largest telescopes — such as the twin 10-meter telescopes at the W. M. Keck Observatory and the Subaru Telescope, all on Maunakea in Hawaii — will be needed to see it. If, however, Planet Nine is now located anywhere in between, many telescopes have a shot at finding it.
“I would love to find it,” said Dr Brown. “But I’d also be perfectly happy if someone else found it. That is why we’re publishing this paper. We hope that other people are going to get inspired and start searching.” The Caltech team reported their findings in the current issue of the Astronomical Journal.