The Basics

Our home planet is the third planet from the Sun, and the only place we know of so far that’s inhabited by living things.

While Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal.

The name Earth is at least 1,000 years old. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”

Credit: NASA

Saturn is the sixth planet from the Sun and the second largest planet in our solar system.

Adorned with thousands of beautiful ringlets, Saturn is unique among the planets. It is not the only planet to have rings—made of chunks of ice and rock—but none are as spectacular or as complicated as Saturn's.

Like fellow gas giant Jupiter, Saturn is a massive ball made mostly of hydrogen and helium.

Credit: NASA

Similar in size and structure to Earth, Venus has been called Earth's twin. These are not identical twins, however – there are radical differences between the two worlds.

Venus has a thick, toxic atmosphere filled with carbon dioxide and it’s perpetually shrouded in thick, yellowish clouds of mostly sulfuric acid that trap heat, causing a runaway greenhouse effect. It’s the hottest planet in our solar system, even though Mercury is closer to the Sun. Venus has crushing air pressure at its surface – more than 90 times that of Earth – similar to the pressure you'd encounter a mile below the ocean on Earth.

Credit: NASA

Jupiter has a long history surprising scientists—all the way back to 1610 when Galileo Galilei found the first moons beyond Earth. That discovery changed the way we see the universe.

Fifth in line from the Sun, Jupiter is, by far, the largest planet in the solar system – more than twice as massive as all the other planets combined.

Jupiter's familiar stripes and swirls are actually cold, windy clouds of ammonia and water, floating in an atmosphere of hydrogen and helium. Jupiter’s iconic Great Red Spot is a giant storm bigger than Earth that has raged for hundreds of years.

Credit: NASA

The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's Moon.

From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere.

Credit: NASA

There are many planetary systems like ours in the universe, with planets orbiting a host star. Our planetary system is named the "solar" system because our Sun is named Sol, after the Latin word for Sun, "solis," and anything related to the Sun we call "solar."

Our planetary system is located in an outer spiral arm of the Milky Way galaxy.

Our solar system consists of our star, the Sun, and everything bound to it by gravity — the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, dwarf planets such as Pluto, dozens of moons and millions of asteroids, comets and meteoroids. Beyond our own solar system, we have discovered thousands of planetary systems orbiting other stars in the Milky Way.

Credit: NASA

Everyone knows that Earth, Mars and Jupiter are planets. But both Pluto and Ceres were once considered planets until new discoveries triggered scientific debate about how to best describe them—a vigorous debate that continues to this day. The most recent definition of a planet was adopted by the International Astronomical Union in 2006. It says a planet must do three things:

How Scientists Use Earth as a Test Lab for Other Worlds

The quest to understand our solar system begins close to home. Earthquake science paves the way for the study of quakes on icy ocean worlds like Jupiter’s moon Europa

Credit: NASA

Once upon a time there lived a poor widow and her son Jack. One day, Jack’s mother told him to sell their only cow. Jack went to the market and on the way he met a man who wanted to buy his cow. Jack asked, “What will you give me in return for my cow?” The man answered, “I will give you five magic beans!” Jack took the magic beans and gave the man the cow. But when he reached home, Jack’s mother was very angry. She said, “You fool! He took away your cow and gave you some beans!” She threw the beans out of the window. Jack was very sad and went to sleep without dinner.

The next day, when Jack woke up in the morning and looked out of the window, he saw that a huge beanstalk had grown from his magic beans! He climbed up the beanstalk and reached a kingdom in the sky. There lived a giant and his wife. Jack went inside the house and found the giant’s wife in the kitchen. Jack said, “Could you please give me something to eat? I am so hungry!” The kind wife gave him bread and some milk.

While he was eating, the giant came home. The giant was very big and looked very fearsome. Jack was terrified and went and hid inside. The giant cried, “Fee-fi-fo-fum, I smell the blood of an Englishman. Be he alive, or be he dead, I’ll grind his bones to make my bread!” The wife said, “There is no boy in here!” So, the giant ate his food and then went to his room. He took out his sacks of gold coins, counted them and kept them aside. Then he went to sleep. In the night, Jack crept out of his hiding place, took one sack of gold coins and climbed down the beanstalk. At home, he gave the coins to his mother. His mother was very happy and they lived well for sometime

Climbed the beanstalk and went to the giant’s house again. Once again, Jack asked the giant’s wife for food, but while he was eating the giant returned. Jack leapt up in fright and went and hid under the bed. The giant cried, “Fee-fifo-fum, I smell the blood of an Englishman. Be he alive, or be he dead, I’ll grind his bones to make my bread!” The wife said, “There is no boy in here!” The giant ate his food and went to his room. There, he took out a hen. He shouted, “Lay!” and the hen laid a golden egg. When the giant fell asleep, Jack took the hen and climbed down the beanstalk. Jack’s mother was very happy with him.

After some days, Jack once again climbed the beanstalk and went to the giant’s castle. For the third time, Jack met the giant’s wife and asked for some food. Once again, the giant’s wife gave him bread and milk. But while Jack was eating, the giant came home. “Fee-fi-fo-fum, I smell the blood of an Englishman. Be he alive, or be he dead, I’ll grind his bones to make my bread!” cried the giant. “Don’t be silly! There is no boy in here!” said his wife.

The giant had a magical harp that could play beautiful songs. While the giant slept, Jack took the harp and was about to leave. Suddenly, the magic harp cried, “Help master! A boy is stealing me!” The giant woke up and saw Jack with the harp. Furious, he ran after Jack. But Jack was too fast for him. He ran down the beanstalk and reached home. The giant followed him down. Jack quickly ran inside his house and fetched an axe. He began to chop the beanstalk. The giant fell and died.

Jack and his mother were now very rich and they lived happily ever after.