A scientist recently proposed a simple test to separate planets from non-planets — sadly, Pluto still would not make the cut.

UCLA professor Jean-Luc Margot said the current official planet definition from the International Astronomical Union, which demoted Pluto to dwarf planet status in 2006, has created a “definitional limbo” for newly discovered bodies as it only applies to those in the solar system.

Presenting his paper at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society, Margot said that the new approach would need only estimates of the star’s mass as well as the planet’s mass and orbital period, all of which can be determined easily via Earth or space telescopes.

Margot highlighted the striking differences that set real planets apart from others.

“The sharp distinction suggests that there is a fundamental difference in how these bodies formed,” he says.

To the disappointment of Pluto’s fans, the dwarf planet would remain classified as such and bundled together with others like Eris, a rocky body in the Kuiper asteroid belt beyond Neptune’s orbit, bigger than Pluto and whose discovery led to the official definition in 2006.

The IAU definition states that in order to be considered a planet, a celestial body must be fairly round, orbit a star, and clear the orbital path around its own star. It’s this last criterion that evicted Pluto out of the planet club, and it is the same ability to dominate its region of space that Margot focused on in his classification system for planets outside the solar system.

Pluto flunked Margot’s test yet again, staying within the league of dwarf planets such as Ceres, Eris, Haumea, and Makemake.

There are at least a hundred dwarf planets of Pluto’s size in the solar system alone, which worked against the still-dwarf planet's favor as far as astronomers are concerned. If it stays a planet, scores of new, smaller bodies will be named official planets.

“There are over 100 objects like Pluto, so we’re not going to have the schoolchildren of the world memorize over 100 planets,” says Jay Pasachoff, Williams College’s Hopkins Observatory director.

Leading the New Horizons science team studying Pluto, planetary scientist Alan Stern however argues that all this comes from a conservative point of view.

“Pluto is much more similar to the planets of our solar system than anything else… Astronomers don’t seem to understand that attributes matter,” he says.

Photo : NASA Goddard Space Flight Center | Flickr