Planets?

Pluto's demotion creates galactic uproar

Randy Boswell, CanWest News Service

Published: Friday, August 25, 2006

A decision Thursday by the world's top astronomical authority to strip Pluto of its status as a planet has rocked the universe, sparking an uproar in cyberspace and bringing ''personal disappointment'' to the family of the demoted spheroid's discoverer.

But the son of late U.S. astronomer Clyde Tombaugh, who identified Pluto as the ninth planet in 1930, told CanWest News Service that the scientific method ''guided my father all of his life,'' and that if reason now dictates Pluto's reclassification as a planetary 'dwarf' then ''he would have been all for it'' - provided politics didn't ''bias'' the outcome of the long-running controversy.

''This doesn't change my father's achievement,'' said Alden Tombaugh, a retired banker in New Mexico whose father's ashes are currently on a nine-year journey to Pluto aboard NASA's New Horizons spacecraft. ''Science is an evolving process, and he was a part of that process.''

Pluto has been a controversial component of the solar system ever since Tombaugh's discovery was made at Arizona's Lowell Observatory 76 years ago. Much smaller and farther from the sun than Earth and the other seven planets, Pluto's diminutive size and its oblong, steeply inclined, 250-year orbit had always troubled planetary purists.

But the 2005 discovery of a neighbouring celestial body nicknamed Xena - 100 kilometres wider than 2,300-kilometre Pluto and equally deserving of the planet designation - finally forced a scientific moment of reckoning: to make Xena the 10th member of the solar system or kick Pluto out of the club.

Last week, an executive committee of the International Astronomical Union (IAU) proposed new definitions that would have kept Pluto as a planet and extended the same status to Xena and two other large celestial objects beyond Neptune - including Pluto's largest moon, Charon.

That idea was savaged as arbitrary and unscientific by many of the 2,500 delegates attending the IAU's annual conference this week in Prague. Even the discoverer of Xena, California Institute of Technology astronomer Michael Brown, argued that expanding the number of planets didn't make sense and would ''take the magic out of the solar system.''

But Pluto backers still defended the 12-planet proposal. IAU committee member Richard Binzel, a professor of planetary science at the Massachusetts Institute, insisted before Thursday's decision that Pluto met the definition of a planet ''by a long shot.''

In the end, though, the IAU rejected the committee's plan and adopted a new three-point test for any celestial body to be called a planet. It must: orbit the sun; have enough mass and ''self-gravity'' to sustain a nearly round shape; and have ''cleared the neighbourhood around its orbit,'' establishing an independent path as it circles the sun.

''Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding,'' the IAU announced. ''This applies, in particular, to the designation 'planets.' The word 'planet' originally described 'wanderers' that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.