If Kirby Runyon has his way, Pluto will regain its standing as a full-fledged planet. Promoted into the planet club along with it: about 110 miscellaneous rocks, dwarfs and roundish celestial bodies in our solar system once considered too small to make the cut.

Our own moon would achieve planet-hood.

Runyon, a PhD student from the Department of Earth and Planetary Sciences at Johns Hopkins University, argued that the much-debated demotion of Pluto to a “non-planet” in 2006 made no sense. He presented revised standard and a paper he co-authored supporting the idea, “A Geophysical Planet Definition,” at the 48th Lunar and Planetary Science Conference on March 21 in The Woodlands, Texas.

Pluto “has everything going on on its surface that you associate with a planet,” said Runyon. “There’s nothing non-planet about it.”

Runyon and his colleagues, all planetary scientists, argue that a planet should be defined by its intrinsic, geophysical characteristics rather than extrinsic qualities, such as its orbit or other objects around it. The six scientists are team members on NASA’s New Horizons space probe mission to Pluto and the Kuiper Belt. That spacecraft’s 2015 fly-by of Pluto, the first-ever, made headlines with dramatic close-ups of the mountains, canyons and cliffs on the icy orb.

In the new formal definition, a planet is “a sub-stellar mass body that has never undergone nuclear fusion,” and that has enough gravitational heft to maintain a roughly round shape, even if it bulges at the equator because of a three-way squeeze of forces created by its gravity and the influence of both the sun and a nearby larger planet.

The short story: planets are round objects in space that are smaller than stars. Pluto and more than 100 other celestial bodies in our solar system make the cut.

The International Astronomical Union was behind the much-ballyhooed 2006 vote to demote small, icy Pluto to “non-planet” or dwarf. “Pluto is dead,” announced California Institute of Technology astronomer Mike Brown then, during a teleconference of the vote by 424 astronomers following contentious debate during an IAU meeting in Prague.

The current IAU definition differs from that of Runyon and his colleagues’ in one important way. The astronomers insist that a planet must be gravitationally hefty enough to “clear the neighborhood around its orbit,” dominating its path by bossily pushing other bodies away.

Pluto hadn’t cleared its orbit, the astronomers decided.

However, neither has the earth, Mars, Jupiter and Neptune, Runyon and other planetary scientists who reject the IAU definition have often pointed out. Asteroids constantly intersect their orbits.

Runyon isn’t waiting around for the IAU – or any other official group – to sanction the new definition. And he is especially interested in connecting with educators and young students, hoping that the new definition of planet gains acceptance and becomes the de facto definition, “The definition that people use and what teachers teach,” Runyon said.

He said he would like to see the public more engaged in solar system exploration.

“I want the public to fall in love with planetary exploration as I have,” said Runyon. “It drives home the point of continued exploration.”

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