Pluto

For seventy-six years it was a planet

You need a telescope

Pluto photographed up close: smooth plains of ice, mountains and the big patch shaped like a heart.

The numbers

Diameter: 1,476mi(2,376 km)
Length of a year: 90,560daysAbout two and a half centuries
Average temperature: -373°F(-225 °C)
Moons: 5The biggest is Charon
When it was discovered: In 1930, by Clyde Tombaugh

To get an idea

A year on Pluto lasts about two and a half centuries: since it was discovered it has not yet completed one.

Charon is so big compared with Pluto that the two circle around each other.

Fun facts

These are not in the book: there was no room on paper.

Charon is so big compared with Pluto that the point they circle around lies outside Pluto.
The New Horizons probe flew past it in 2015, after nine years of travel.
Those photographs showed mountains made of water ice, as tall as mountains on Earth.
On its surface there is a big pale plain shaped like a heart, smooth and with no craters.
It is one of those rare bodies that spin backward, like Venus and Uranus.

Test yourself

The first question is the one printed under the QR code, with the answer the book did not give. The other four only exist here.

Question 1 of 5★ is the one from your book

What is Pluto today?

Question 2 of 5

Is Pluto bigger or smaller than our Moon?

Question 3 of 5

How long is a year on Pluto?

Question 4 of 5

What is special about Charon?

Question 5 of 5

How did we see it up close?

Riddles

For seventy-six years I was the last in line and I was called by the same name as my big brothers. Then they changed the rules and gave me a different title, even though I did not change at all. What am I?

I am smaller than the companion that circles your world, and my own companion is so big compared with me that we go around each other. What am I?

To go once around the fire I need two and a half centuries: since you found me I have not finished yet. On my belly I carry a patch shaped like a heart. What am I?

Try it yourself

Activity 1

It is the way it was discovered: compare two pictures of the same patch of sky and look for the only dot that has moved. Try it with two photographs of the sky.

Activity 2

Draw the Moon and next to it Pluto, a little smaller. For seventy-six years the second one was a planet and the first one was not.

The words

Kuiper Belt: The icy region beyond Neptune, full of small bodies.

Sources: Wikidata (Q339), Wikipedia (Plutone (astronomia)) and NASA.