The numbers
- Diameter
- 3,032mi(4,879 km)
- Distance from the Sun
- 36,000,000mi(57,900,000 km)
- Length of a day
- 4,222.6hours
- Length of a year
- 88days
- Average temperature
- 333°F(167 °C)
To get an idea
A day on Mercury lasts almost twice its year: the Sun rises twice for every trip around the Sun.
By day its surface would melt lead, by night it is colder than any place on Earth.
Fun facts
These are not in the book: there was no room on paper.
It is shrinking: as it cools, its crust wrinkles up and forms long cliffs.
It is made mostly of metal: its core is huge compared with the size of the planet.
Only two probes had visited it before BepiColombo, the European and Japanese mission.
It is named after the messenger of the Roman gods, because it moves across the sky faster than anything else.
Even though it is the closest to the Sun, it is not the hottest planet: that record belongs to Venus.
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
Which is the smallest planet in the Solar System?
Question 2 of 5
How long is a day on Mercury compared with its year?
Question 3 of 5
What did probes find in Mercury's polar craters?
Question 4 of 5
Why are hot and cold so different on Mercury?
Question 5 of 5
How many moons does Mercury have?
Riddles
I live next to the biggest fire there is, and yet ice has always hidden in some of my dark corners. I have no air, no moons, and my face is full of holes. What am I?
The ancients named me after the messenger, because they saw me move across the sky faster than anyone else. You can spot me only at dawn or at dusk, never in the middle of the night. What am I?
Try it yourself
You need an open horizon, with no houses or trees. Try from a hill or a beach, and bring someone to help you search.
Draw a circle the size of a coin and next to it one a little smaller: they are the Earth and Mercury side by side.
The words
- atmosphere
- The layer of gas that wraps around a planet and spreads its heat.
Sources: Wikidata (Q308), Wikipedia (Mercurio (astronomia)) and NASA.