Size Does Matter

Planet Mass

Together, Jupiter and Saturn make up 92 percent of the mass of all eight planets combined. On the other hand, Mercury is so light that hardly appears in this chart.

You probably know that the largest planet in our solar system is Jupiter and that the second-largest is Saturn. You also know that Jupiter is massive: 1.898 \times 10^{27} kg, more than 317 times the mass of the Earth. In fact, if you total the mass of all the planets, Jupiter would make up 71 percent of that mass.

The more interesting planet size, to me, is Saturn, the second largest planet in our solar system. Saturn is a gas giant and has a density of 0.687 \frac{g}{cm^3}. Water, by definition has a density of 1 \frac{g}{cm^3}, meaning that Saturn would float on water. Of course, being lighter than water does not mean that Saturn is not heavy. Rather, Saturn is so huge (764 Earths would fit inside it) that it weighs 5.683 \times 10^{26} kg, or 83 times the mass of Earth, and is 21 percent of the mass of all the planets, which is more that the mass of all the non-Jovian planets combined.

Bonus Fact 1: Saturn is so massive that one of its moons, Titan, is larger than the planet Mercury.

Bonus Fact 2: The third-largest planet is Uranus, which is the butt of so many jokes.

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