Pluto Isn't A Planet — But It Gives Us Clues For How The Solar System Formed

Geophysical Definition

The debate over Pluto's planetary status hinges on the criteria used to define a planet. Wladymir Lyra advocates for the geophysical definition, which focuses solely on an object's mass. This definition suggests that any celestial body with enough mass to be round qualifies as a planet, regardless of its orbital path 1. Lyra argues that if Pluto were placed in Mercury's orbit, it would clear its path and be considered a planet, highlighting the limitations of the current definition.

There is a very good point. And that's one thing that prompted goosebumps, planetary scientists, in fact, to use another definition of planet that they call the geophysical definition planet. That depends only on the mass.

--- Wladymir Lyra

This perspective challenges the International Astronomical Union's (IAU) 2006 decision, which requires a planet to clear its orbit, a criterion Pluto does not meet.

   

Dynamical Challenges

The IAU's dynamical definition of a planet, which includes orbit clearing, faces criticism from some scientists. Wladymir Lyra points out that the decision to demote Pluto was made by astronomers, not planetary scientists, leading to ongoing controversy 2. He argues that many celestial bodies, like Europa, could be considered planets if they orbited the sun independently 3.

At the time, it felt that something had to be done about Pluto. And with that, I mean that, yeah, Pluto was always the oddball among the planet.

--- Wladymir Lyra

This debate underscores the complexity of classifying celestial bodies and the need for a more inclusive definition that reflects the diversity of objects in our solar system.