Indian who knew Pluto 20 years before anybody else

Astronomer Ventakesh Ketakar accurately predicted Pluto’s orbital details 20 years before Clyde Tombaugh discovered it in 1930.

WASHINGTON, DC: If you look up the pages of the Bulletin of the Astronomical Society of France published in May 1911, you’d come across a paper by Venkatesh Ketakar on an as-yet unknown planetary body that was exerting a gravitational pull on the neighbouring planet Neptune.

Ketakar’s paper featured orbital and other key calculations of this strange new planet. He named it Brahma. Almost 20 years later, in 1930, American scientist Clyde Tombaugh discovered it and called it Pluto. Ironically, Ketakar died of a severe paralytic stroke the same year.

As textbooks around the world change with the recent demotion of Pluto from a planet to a ‘Pluton’ or a ‘dwarf planet’, perhaps Ketakar’s name could be added as well along with Tombaugh. A leading American college textbook Universe by Roger Freedman and William J Kaufmann III did that in 1968. The Indian Journal of History of Science recognised him in 1984. But there are hardly any other references, and much of Ketakar’s work is confined to obscurity.

Senior astronomers at the Tata Institute of Fundamental Research, too, have not read about him. “I am not aware of his work,” said Dr Mayank Vahia of the Department of Astronomy and Astrophysics when DNA contacted him. Ketakar was not the only astronomer chasing Pluto.

The most famous of them all were Percival Lowell and William H Pickering, both of whom are given equal credit in the discovery of Pluto. However, both Kaufmann’s Universe and the Indian Journal of History of Science, say that Ketakar’s calculations were much closer to the final ones than those published by Lowell and Pickering.

For instance, Ketakar said that heliocentric longitude of Brahma is 114.23 degrees and that its mean daily movement was 14.6364 arc-seconds. To put it simply, he had calculated that Pluto’s orbital period (the time it takes to once revolve around the sun) 242.28 years and its distance from the sun was 38.95 AU (AU stands for Astronomical Unit or the average distance between the earth and the sun which is around 150 million km). When discovered, astronomers found that Pluto’s average distance from the sun was 39.52 AU. Its documented orbital period is 248.475 years.

There are some reported weaknesses in his calculations. According to some astronomers, Lowell’s and Pickering’s findings, along with Ketakar’s, could be coincidental because they were based on erroneous data about the mass of Neptune. Even so, the fact remains that Ketakar’s work remains unheralded in the world of astronomy.