The first and biggest proof is that mercury has a much bigger core than a planet of its size should have, which means it was bigger than it is currently. So therefore, it was definitely bigger than Jupiter before it got struck by a bunch of meteors and made smaller.

We also can pretty much GUARANTEE that Mercury had much bigger moons than Jupiter did, which adds onto Mercury’s size, which clearly makes it bigger!

And also, since Jupiter is technically a gas giant, should we really be counting the gassy part of it? If we’re not counting the gas, which we shouldn’t, mercury EVEN AS IT IS NOW is clearly bigger than Jupiter, as are many other planets in our solar system. Because of this, gas giants in general should not be considered planets.

Mercury both was and is MUCH more sturdy than Jupiter as well as heavier. It’s been said that if you had a big enough pool you could let gas giants float in it. No one says this about the proper planets like mercury. We also see that Saitama can sneeze Jupiter away, (which is clearly only possible because its made of gas) while no rocky planet has ever shown this sort of weakness, discounting that one time when superman sneezed.

This post was about planet sizes and nothing else.