Our Solar System

Planets

A planet is a large ball of rock or gas that revolves around a central star. The Earth, the planet we live on, is the only known planet to contain life. The central star that the Earth orbits is the Sun. In all, there are eight planets orbiting the Sun.

These planets, their moons and other objects orbiting the Sun make up our solar system. In order of their distance from the Sun, the four closest planets are Mercury, Venus, Earth and Mars. These planets are called the inner planets. They are made up mostly of rock. Due to their close distance to the Sun, the inner planets are also much warmer than the planets further from the Sun.

Mercury Venus

Earth Mars

Jupiter

The outer planets are the four furthest planets from the Sun – Jupiter, Saturn, Uranus and Neptune. These planets are much larger than the inner planets. They are not rocky like the inner planets. Instead, they are made up mostly of gases. They are often referred to gas giants.

Besides Mercury and Venus, all of the planets in the solar system have one or more moons. Our planet, Earth, has just one moon. Mars has two moons. The planet with the most moons is Jupiter. It has 79 moons. Its largest moon, Ganymede, is larger than the planet Mercury!

Amazing Fact!

Although Mercury is the Although Mercury is the closest planet to the Sun, closest planet to the Sun, Venus is the hottest planet Venus is the hottest planet in our solar system! This is in our solar system! This is because of the make up because of the make up of its thick atmosphere. of its thick atmosphere. During the day, the During the day, the temperature on its surface temperature on its surface can reach more than 440 can reach more than 440 degrees Celsius! degrees Celsius!

Uranus

Saturn

Earth is the only planet in the solar system known to contain life. Why is this so?

AB Activity 7.5

Neptune

Did You Know?

Scientists once considered there to be nine planets in the solar system. This included a small icy planet beyond Neptune, called Pluto. In 2006, scientists decided that Pluto was too small to be considered a planet and classified it as a dwarf planet.

asteroids

Did You Know?

Beyond Neptune is a large belt of ice rocks called the Kuiper belt. The belt is around 2,000 times larger than the the asteroid belt and is also home to the dwarf planet Pluto.

Other Objects in the Solar System

Besides the Sun, planets and their moons, what other objects can be found in the solar system?

There are many different objects in the solar system. Some, such as space rocks, are natural. Others objects, such as communication satellites, have been sent into space by people. One of the most commonly found objects in space are asteroids. Asteroids are large rocks that can range in size from just a few centimeters up to thousands of kilometers. Most asteroids orbit the Sun in an asteroid belt between the planets Mars and Jupiter.

Like asteroids, comets are made up of large chunks of rock. However, comets are also composed of ice, water and dust. Comets are often seen with a long tail which is mostly due to the dust that is left behind by the comet. The size of most comets ranges from around 700 meters to 20 kilometers.

Asteroids and comets often break up into smaller pieces and form meteoroids. Meteoroids have a size ranging from a grain of sand to one meter.

If a meteoroid enters Earth’s atmosphere, it becomes known as a meteor. Most meteors burn up completely before reaching the Earth’s surface. Have you ever seen a shooting star? It was most likely a meteor burning up in the Earth’s atmosphere. Occasionally, a meteor doesn’t burn up completely as it enters the atmosphere. A meteor that reaches the Earth’s surface is called a meteorite.

meteor

Amazing Fact!

About two billion years ago, a giant meteorite hit the surface of the Earth. It created the largest crater on Earth – the Vredefort Crater. It is more than 300 kilometers wide!

Did You Know?

The Soviet Union launched Sputnik 1, the first man-made satellite, into space on October 4, 1957. Sputnik 1 completed a full orbit of the Earth every 98 minutes. After three months of orbiting the Earth, Sputnik 1 burned up on re-entry into the Earth’s atmosphere.

Sputnik 1 Some satellites in the solar system are manmade and have been launched into space by people. They are used for communication, weather forecasting and can provide us with accurate information about locations on Earth.

Some satellites are used to observe and gather data about other objects in the solar system, such as planets, moons and the Sun. Space telescopes are man-made satellites in space. They are used to see things further away and more clearly than telescopes on Earth.

communication satellite

One of the largest is the Hubble Space Telescope. It has been observing objects in the solar system and beyond since 1990. It has helped scientists learn many things about space. People often go on missions aboard space crafts launched into space by powerful rockets. The International Space Station (ISS) is the largest man-made object in space. The ISS is a giant space laboratory that orbits the Earth with up to nine astronauts on board. The astronauts carry out experiments about living in space in a hope to one day make living in space or even on other planets possible.

AB Activity 7.6

Powerful rockets are used to launch man-made objects and people into space. Hubble Space Telescope

Amazing Fact!

Shortly after its launch in 1990, scientists noticed that the Hubble Space Telescope had trouble focusing on distant objects. Astronauts were sent into space to fit a new set of focal mirrors to the telescope. Much like putting on a pair of glasses.

Go Online!

On July 20, 1969, pilot Buzz Aldrin landed the lunar module ‘Eagle’ on the surface of the Earth’s moon. On July 21 at 2:56 a.m. Commander Neil Armstrong stepped off the ‘Eagle’, becoming the first human to walk on the surface of the moon. Watch this amazing and historic event on the NGScience website. QuickCode: T4P3

Space Exploration

People have long been fascinated with space. The searching, observing and collecting of data in space is called space exploration. Through space exploration, people are able to learn more about the objects in space, their properties and the patterns in which they move. Space exploration can be done using observation and monitoring instruments on Earth. It can also be done by sending objects or people into space. To observe objects in space from Earth, scientists use powerful telescopes. A telescope is an instrument that makes objects that are far away look closer and clearer. This allows scientists to observe distant objects in greater detail.

The Gran Telescopio Canarias is one of the largest telescopes on Earth. It has been exploring space since 2009.

Another way that scientists explore space is by sending objects into space to make observations and collect data. These objects, called space probes, include space telescopes, robots and satellites.

Space probes collect data about space objects and conditions. They may also collect and analyze samples of objects or take photographs and videos. The data collected by space probes is sent back to Earth where scientists study and interpret the data.

People also explore space by venturing into space in space crafts. Scientists that travel into space, called astronauts, are highly trained in operating space crafts and living in space. In space, astronauts collect data and do experiments that cannot be done on Earth.

Large rockets are needed to get objects and people into space.

Amazing Fact!

The National Aeronautics and Space Administration (NASA) have sent five space robots, called rovers, to the planet Mars. They collect data about the planet’s surface and send the data back to Earth for analysis. The latest rover to land on Mars, called Perseverance, left Earth on July 30, 2020 and touched down on February 18, 2021. On board the rover is a small robotic helicopter called Ingenuity.

Engineer It!

Design and build your own model of an exploration robot to explore the surface of Mars. What data will it collect? What features will it have to collect the data?

What types of experiments might astronauts carry out in space?

A Closer Look The International Space Station

There are about eight billion people living on Earth. That’s a lot of people! Did you know that at this moment, there are a small group of people that don’t live on Earth – they live in space aboard the International Space Station. The International Space Station (ISS), is a large satellite that orbits the Earth. It’s the biggest man-made object in space and travels at a speed of about 27,000 kilometers per hour. In just one day, it orbits the Earth 16 times. Since the year 2000, up to nine astronauts and cosmonauts have been on board the ISS at any one time. They are highly-trained to live and work in space.

Go Online!

Learn more about the International Space Station in a video on the NGScience website. QuickCode: P4S6

International Space Station (ISS)

You can think of the ISS as a giant science laboratory in space. Each day, the people on board carry out investigations about living in space for long periods of time. The data collected on board the ISS is sent back to Earth and shared with many different countries.

In what ways is living in space different from living on Earth?

Science Words

Use the words to complete the sentences.

axis rotation orbit

Northern Hemisphere

Southern Hemisphere seasons solar system revolution planet satellite phases of the moon asteroids comets meteoroids star meteor meteorite space exploration telescope space probes

1. A is a very large, hot ball of glowing gases. 2. The Earth spins on its . It completes one every 24 hours. 3. Any object that orbits another object is called a .

4. The changing shape of the moon’s directly sunlit portion, as viewed from Earth, is called the .

5. The Earth is divided into two parts. The upper part of the Earth is called the . The lower part is called the .

6. are chunks of rock, ice, water and dust.

7. Asteroids and comets often break up into smaller pieces and form .

8. The Earth moves in a curved path, called an

Sun. It takes the Earth 365 days to complete one , around the of the Sun.

9. The revolution of the Earth around the Sun causes changes in weather patterns called .

10. A central star. is a large ball of rock or gas that revolves around a