The Planets for Kids: How Heavy and How Old Would You Be on Mars?
The eight planets explained for kids: which is the biggest, the hottest and the fastest, how heavy and how old you would be on Mars or Jupiter, a model of the solar system to pace out and which planets you can see tonight.
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More for young space fans
Eight planets and one sun: a trip through the solar system
What is a planet?
A planet is a big, round world that travels around a star – ours travel around the sun. Planets don't glow by themselves the way stars do. They only shine because the sun lights them up, just like the moon.
Eight planets circle our sun. The four inner ones – Mercury, Venus, Earth and Mars – are made of rock. The four outer ones – Jupiter, Saturn, Uranus and Neptune – are giants made of gas and ice, without any ground you could stand on.
Planet tour: tap a planet
From the little speedster next to the sun to the stormy blue giant far out in the cold: every planet is a world of its own.
The speedster: Mercury is the smallest planet and the closest to the sun. It races around the sun faster than any other planet: one Mercury year lasts only 88 days. But it turns so slowly that a day, from one sunrise to the next, lasts 176 Earth days – two whole Mercury years! With almost no air to hold the heat, it is as hot as an oven by day and freezing cold at night.
The hothead: Venus is almost as big as Earth, but you would never want to visit. Thick clouds trap the sun's heat like a blanket, which makes Venus the hottest planet of all – hotter than a pizza oven, even though Mercury is closer to the sun. And Venus spins backwards: there, the sun rises in the west and sets in the east.
Our home: Earth is the only planet we know of with life – and the only one with oceans of liquid water, which cover about 70 percent of it. Its air lets us breathe, keeps us warm and protects us from the sun's harsh rays and from small rocks falling from space. It is the biggest of the four rocky planets.
The red planet: Mars is red because its dust contains lots of rust. It has the biggest volcano in the solar system, Olympus Mons, about two and a half times as high as Mount Everest. Robot rovers are exploring Mars and looking for signs of tiny life from long ago. A day on Mars lasts only about 40 minutes longer than ours.
The giant: Jupiter is the biggest planet by far: more than 1,300 Earths would fit inside it. It is a giant ball of gas with colorful stripes of clouds and a storm wider than Earth – the Great Red Spot, which has been swirling for at least 150 years. Jupiter also spins the fastest: a day there lasts less than 10 hours.
The lord of the rings: Saturn wears the most beautiful rings in the solar system. They are made of countless chunks of ice and rock – some as small as grains of sand, others as big as a house. Saturn is so light for its size that it would float in water – if you could find a bathtub big enough!
The roller: Uranus is tipped over on its side, so it rolls around the sun like a ball. That's why each of its poles gets 42 years of sunshine in a row, followed by 42 years of darkness. Its blue-green color comes from a gas called methane. In 1781, Uranus became the first planet ever discovered with a telescope.
The stormy one: Neptune is the planet farthest from the sun – so far away that sunlight needs more than four hours to get there. It has the strongest winds in the solar system, over 1,200 miles per hour, faster than a jet plane. One Neptune year lasts 165 Earth years: since it was discovered in 1846, it has gone around the sun only once.
Planet records
on Venus (464 °C): the hottest planet – hotter than Mercury, which is closer to the sun.
was measured high in the air of Uranus (−224 °C): the coldest planet.
known moons circle Saturn – more than any other planet.
is all Mercury needs to race once around the sun.
is how long Venus takes to turn around once – longer than its whole year!
How heavy would you be on other worlds?
Your body stays exactly the same everywhere – but every world pulls on you with a different strength. A bathroom scale would show these numbers:
Jupiter, Saturn, Uranus and Neptune have no solid ground – this is how heavy you would feel at the top of their clouds.
Nobody could ever stand on the sun – but it pulls about 28 times as hard as Earth.
How old would you be on other planets?
A year is one trip around the sun. Planets close to the sun go around fast, planets far away are slow – so you have a different age on every planet. Enter your birthday:
Pick a day in the past – the day you were born.
How far away are the planets?
Space is mostly empty – so empty that no picture in a book can show it properly. Shrink the sun to a ball and see where the planets would be.
Build a planet walk
Take a ping-pong ball outside as your sun and pace out the planets – the kid steps are in the table. The trip to Neptune is about 130 meters (140 yards) long, a bit longer than a soccer field. Put down a grain of sand for the Earth, and you'll see how tiny our world is!
Which planets can you see tonight?
Five planets are bright enough to see without a telescope: Mercury, Venus, Mars, Jupiter and Saturn. They look like bright stars – but they don't twinkle, and they slowly wander among the stars from week to week.
What else travels around the sun?
Dwarf planets: For 76 years, Pluto was called the ninth planet. In 2006, astronomers decided it is a dwarf planet: it is smaller than our moon and shares its path with lots of other icy bodies. Other dwarf planets are called Eris, Ceres, Makemake and Haumea.
Asteroids: Between Mars and Jupiter, millions of rocks circle the sun in the asteroid belt. Most of them are small, but the biggest, Ceres, is almost 600 miles wide – so big and round that it counts as a dwarf planet.
Comets: Comets are giant, dirty snowballs from the far edge of the solar system. When one comes close to the sun, its ice turns into gas and it grows a long, glowing tail – which always points away from the sun.
Moons: More than 400 moons circle the planets of our solar system. Jupiter's moon Io has hundreds of volcanoes, Saturn's moon Titan has lakes of liquid gas, and under the icy crust of Jupiter's moon Europa there is probably a huge ocean.
Questions about the planets
How many planets are there? Eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto was counted as the ninth planet until 2006. Today it is called a dwarf planet, because it is small and shares its path with many other icy bodies.
Which planet is the biggest? Jupiter. It is 11 times as wide as Earth, and more than 1,300 Earths would fit inside it. But even Jupiter is small next to the sun: about 1,000 Jupiters would fit inside the sun.
Which planet is the hottest? Venus, at about 867 °F (464 °C). Mercury is closer to the sun, but the thick clouds of Venus trap the heat like a greenhouse – day and night, at the poles and at the equator.
Could people live on Mars? Not without a lot of help. The air on Mars is far too thin to breathe, it is colder on average than any freezer, and nothing shields you from the sun's harmful rays. Astronauts would need space suits, sealed homes and greenhouses to grow food. Space agencies hope to send the first people to Mars in the 2030s or later.
Why are planets round? Because of gravity. Every bit of a planet pulls on every other bit, and together they squeeze it into the roundest shape there is: a ball. Small asteroids don't pull hard enough – that's why many of them look like potatoes.