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Should We Have 100+ Planets in Our Solar System?

Under a size cutoff of 10,000 kilometers, there are two planets, 18 or 19 moons, 1 or 2 asteroids, and 87 trans-Neptunian objects, most of which do not yet have names. All are shown to scale, keeping in mind that for most of the trans-Neptunian objects, their sizes are only approximately known. Montage by Emily Lakdawalla. Data from NASA / JPL, JHUAPL/SwRI, SSI, and UCLA / MPS / DLR / IDA, processed by Gordan Ugarkovic, Ted Stryk, Bjorn Jonsson, Roman Tkachenko, and Emily Lakdawalla.

Remember Pluto?

Ever since it was kicked out of the family of planets of our solar system, it's been trying to get back in. This time, in an effort spearheaded by Kirby Runyon of Johns Hopkins University, Pluto wants itself and its 100 closest pals to be called planets.

Runyon proposed that a planet is redefined to focus on its own geophysics: "A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters."

In a scientific poster submitted to the upcoming Lunar and Planetary Science Conference, Runyon pointed out that this new definition of planet would emphasize its intrinsic as opposed to extrinsic properties. For school children and lay people, the definition of planets is easy: "Round objects in space that are smaller than stars."

But what about memorizing the names of all those new planets? No need to do that, Runyon said, instead schools should focus on teaching Solar System's zones and why different types of planets formed at their respective distances from the Sun.

Read more about the new effort to reclassify Pluto as a Planet over at Universe Today.

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Technical jargon is created and define to be useful. Sometimes words diverge from common use or even other fields, e.g. metal is defined very differently in stellar astronomy from chemistry and common use, because it is more useful that way in that field. There are many different ways to group the bodies in our solar system, some groupings more useful to specific areas of research than others. At the end of the day, whatever definition is given to planet, no science is changed, only the words used to write about the science. This means some papers will get to use a single word to describe the grouping relevant to that situation, while others might have to use a qualifier or a couple words. Spending more time on the debate than it would save in such writings is mostly a waste, with the exception of some arguable public outreach.
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