Photo by: Getty Images

Getty Images

The Densities Of The Planets

A planet's density tells us more information than its size.

August 01, 2019

You can see the size differences among the planets in our solar system with the naked eye. Not so with their densities. While that number might seem meaningless to you or me, it tells astronomers a lot about what the planet is made of.

What's Going On

You can't predict a planet's density from its size. Earth is the fourth smallest of the planets—though in terms of the rocky planets, it's the largest—but it's the most dense. Jupiter is the largest planet in the solar system, but it's Saturn—the solar system's second largest planet—that takes the prize for least dense. It's less dense than water, which has led many people to postulate that it would float. However, even if it somehow found its way to a body of water large and deep enough to contain it, Saturn would break apart and its rocky core would sink.


What This Means

A planet's density tells astronomers important things about its inner structure. For example, Mercury is almost as dense as Earth, even though it's much smaller. Since a small planet experiences less gravitational compression than a larger planet—that is, the effects of gravity don't squish it down as much—astronomers need to look for another reason for its density. That's why they believe that it has a large, iron-rich core. Uranus, on the other hand, is the second-least dense of the gas giants, right behind Saturn. Like Saturn, it has a gaseous outer layer and rocky core, but where it differs is in an icy mantle between those layers made up of water, ammonia, and methane.

We know plenty about Earth's composition because we're here. But if we were aliens judging Earth's composition from its density, we'd see an iron and nickel core made up of a solid interior and a liquid exterior, a mantle made of viscous silicates, and a crust—where we live!—made up of solid silicates.

This article first appeared on Curiosity.com.

Next Up

Scientists Have Discovered Enormous Balloon-Like Structures in the Center of Our Galaxy

There's something really, really big in the middle of our Milky Way galaxy — one of the largest structures ever observed in the region, in fact.

The Perseid Meteor Shower Reaches its Peak

Stargazers rejoice! The annual Perseid meteor shower is upon us. Here's what you need to know...(updated August 11, 2022)

Neuroprosthetic Sensory Devices are Reconnecting People to the World

Sensory loss has a profound effect on millions of people’s everyday lives. Sight, hearing, touch, smell, and taste can all be affected, diminishing their experience of the world. But now, thanks to neuroprosthetic technology we can tap into nerve and brain function, and rewire these lost connections.

World's First Malaria Vaccine Offers Hope to Millions

Tens of thousands of lives could be saved each year from sickness and death caused by malaria following the World Health Organization (WHO) approval of a first-ever vaccine. Scientists have recommended the RTS,S vaccine for children in sub-Saharan Africa and other high-risk areas to prevent one of the world’s oldest and deadliest infectious diseases.

The Butterfly Effect Is Why It's Impossible to Predict the Weather

This is a concept invented by the American meteorologist.

Rhnull, the Rarest Blood Type on Earth, Has Been Called the "Golden Blood"

The extremely rare blood type is shared by only a handful of people on Earth.

Neuroscientists Found The Most Relaxing Song

Manage your stress with a perfect tune backed by science.

What Came Before the Big Bang?

Physicists are still trying to solve this mystery.

How to Watch the Orionids Meteor Shower in 2021

If you've seen a shooting star on a recent stargazing jaunt, you've spotted the very beginning of the Orionids meteor shower. It happens every fall in October or early November, and peak viewing hours are coming soon to skies near you.

5 LGBT Scientists Who Changed the World

Without their scientific accomplishments, the sciences would be very different today.