Experts want Pluto to get its planet status back

Kirby Runyon is a Johns Hopkins University scientist behind a renewed effort to restore Pluto’s lost title

The increase would make understanding the solar system more hard - but ultimate more rewarding, the astronomers said.

That definition change meant Pluto was no longer considered the "ninth" planet, but instead a dwarf planet and Kuiper Belt Object. That used to be one of the most popular mnemonic devices for remembering the order of the planets in our solar system - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

The effort is being led by Kirby Runyon, a doctoral student at Johns Hopkins University. Their argument and supporting information will be on display at next week's Lunar and Planetary Science Conference in Texas.

The researchers argue for a definition of "planet" that focuses on the intrinsic qualities of the body itself, rather than external factors such as its orbit or other objects around it. Even more, he says that a host of moons (including Europa and the Moon) and other bodies (like these guys here) in the Solar System should be planets, too.

Pluto was demoted to "non-planet", according to definition approved by International Astronomical Union (IAU) in the year 2006 and the number of planets from then dropped from nine to eight. The round shape also includes any bulges at the equator caused by a three-way squeeze of forces from its own gravity, coupled with the influence of both a star and a nearby larger planet.

Otherwise Pluto does fit the IAU definition - it orbits the sun and it is massive enough that the forces of gravity have made it round.

Based on IAU definition, a planet is recognized as such as having cleared the neighborhood around its orbit, has enough mass for its self-gravity and is in orbit around the Sun, according to Conservation. And that whopping increase is actually a good thing, Runyon says, as he thinks it will engage the public in space exploration. As the very word "planet" seems to carry a "psychological weight", he figures that more planets could encourage that public interest.

The team's definition doesn't require approval from a central governing body for scientists to start using it - in fact, it's already been adopted by Planet Science Research Discoveries, an educational website founded by scientists at the University of Hawaii. "It drives home the point of continued exploration". This is because, they add, most of the members of the team are closely affiliated with geology and other geosciences, and that their new geophysical definition is more useful than the IAU's astronomical definition. Majority are closely affiliated with geology and other geosciences, thus making the new geophysical definition more useful than the IAU's astronomical definition, they said.

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