Astronomers often use mathematical equations in order to find out more about a planet. Since planets are quite far from earth, calculating their mass, size, speed, volume and density gives astronomers an idea as to how big a planet is, and what it is made up of. The first step in this getting-to-know process is determining the distance of the planet from Earth. Once you’ve covered this, then you can calculate for its mass, size and volume.
A planet’s density is the ratio of its mass to its volume. The density tells astronomers how much space the planet occupies. Planets made up of the same material will always have the same density regardless of their size and mass. The four terrestrial planets or the planets closest to the sun, are considered the densest planets in the Universe, with earth topping the list. These planets, namely, Mercury, Venus, Earth and Mars, are made of silicate rock that surrounds an iron-nickel core.
On the other hand, Jovian planets, so-named because of their similarity to Jupiter, are very large planets that have a low density. This is because they are predominantly made up of gases and liquid hydrogen that surrounds a small rocky core.