What Makes a Planet "Terrestrial"?
* Composition: Primarily rocky and metallic, with a solid surface.
* Density: Relatively high density compared to gas giants.
* Structure: Typically have a differentiated structure (core, mantle, crust).
* Atmosphere: Thin or non-existent compared to gas giants.
Pluto's Challenges:
* Composition: While Pluto has a rocky core, it also has a significant amount of ice (water, nitrogen, methane, etc.).
* Density: While it's denser than gas giants, it's still significantly less dense than the terrestrial planets.
* Structure: Its internal structure is less well-understood, but it's likely to be different from terrestrial planets due to the presence of so much ice.
* Atmosphere: Pluto does have a thin atmosphere, but it's highly volatile and varies greatly with its distance from the Sun.
Mercury's Influence:
* Size: Even if Pluto were the size of Mercury, its composition and structure would remain largely unchanged.
The Conclusion:
While a Pluto-sized Mercury would be significantly larger than the current Pluto, it wouldn't necessarily make it "terrestrial." Its composition, internal structure, and atmospheric characteristics would still differ significantly from the inner rocky planets.
More Than Just Size:
The classification of planets is based on a complex interplay of factors. Size is one piece of the puzzle, but it's not the only, or even the most important, factor.
