Step outside on a clear night, and the sky above you holds eight planets, more than 200 known moons, five dwarf planets, millions of asteroids, and countless comets, all orbiting the same star. Our solar system is one of the best-studied corners of the universe, yet it still surprises scientists every year. For children working through KS2 science and geography in UK primary schools, understanding how the solar system works is a foundation for almost everything else in space science.
This guide covers everything primary-aged learners need to know: what the solar system is and why it formed the way it did, a planet-by-planet journey from Mercury to Neptune, the difference between terrestrial and gas giant planets, moons that might harbour life, dwarf planets including Pluto, and the asteroids and comets that travel through our neighbourhood. Every section connects to the UK National Curriculum, so teachers and parents can use it with confidence.
LearningMole has produced this guide to give KS2 teachers, home educators, and curious children a single, trustworthy resource for solar system learning. Whether you are planning a lesson, supporting homework, or simply feeding a child’s curiosity about space, you will find accurate, curriculum-aligned information alongside practical teaching ideas throughout.
The solar system is the collection of the Sun and everything held in orbit by its gravity. Eight planets, their moons, five recognised dwarf planets, the asteroid belt, the Kuiper Belt, and billions of smaller objects all form part of this gravitational family. The word “solar” comes from Sol, the Latin name for the Sun, making “solar system” simply mean “the Sun’s system.”
Our solar system sits inside the Milky Way galaxy, which contains hundreds of billions of stars. The solar system itself takes approximately 225 million years to orbit the centre of the Milky Way, a journey sometimes called a cosmic year. At the scale of the universe, our solar system is a relatively small neighbourhood, but it contains enough variety to fill a lifetime of scientific study.
The solar system formed approximately 4.5 billion years ago from a rotating cloud of gas and dust. As gravity pulled this cloud together, the Sun ignited at the centre and the remaining material clumped into the planets, moons, and smaller bodies we recognise today. Understanding this formation process helps children grasp why rocky planets sit closer to the Sun while gas giants form further out.
| Planet | Type | Distance from Sun | Moons | Day Length |
|---|---|---|---|---|
| Mercury | Terrestrial | Closest | 0 | 59 Earth days |
| Venus | Terrestrial | 2nd | 0 | 243 Earth days |
| Earth | Terrestrial | 3rd | 1 | 24 hours |
| Mars | Terrestrial | 4th | 2 | 24.6 hours |
| Jupiter | Gas giant | 5th | 95+ | 10 hours |
| Saturn | Gas giant | 6th | 146+ | 10.7 hours |
| Uranus | Ice giant | 7th | 27 | 17 hours |
| Neptune | Ice giant | Farthest | 14 | 16 hours |
The eight planets divide into two clear groups based on what they are made of. Knowing which group each planet belongs to makes the solar system much easier to remember and understand.
The four inner planets — Mercury, Venus, Earth, and Mars — are terrestrial planets. Terrestrial means Earth-like: they have solid, rocky surfaces and metal cores. You could stand on the surface of any of them (if the conditions were survivable). These planets are smaller and denser than the outer planets.
The four outer planets divide further into gas giants and ice giants. Jupiter and Saturn are gas giants, composed almost entirely of hydrogen and helium with no solid surface to land on. Uranus and Neptune are ice giants, made primarily of water, ammonia, and methane in hot, dense fluid form above small rocky cores. All four outer planets have ring systems, though Saturn’s are by far the most spectacular.
Everything in the solar system orbits the Sun, which contains 99.8% of the system’s total mass. It is a medium-sized star that has been burning for approximately 4.5 billion years and has roughly another 5 billion years of fuel remaining. Its surface temperature is about 5,500 degrees Celsius, while its core reaches around 15 million degrees Celsius.
The Sun’s energy comes from nuclear fusion: hydrogen atoms fuse into helium, releasing enormous amounts of light and heat. This energy travels 93 million miles to reach Earth, taking approximately 8 minutes to make the journey. Without the Sun’s warmth and light, life on Earth would be impossible.
When the Sun eventually exhausts its hydrogen fuel, it will expand into a red giant large enough to swallow Mercury, Venus, and possibly Earth. It will then collapse into a white dwarf — a dense, cooling remnant about the size of our planet. This will happen in around 5 billion years, giving children something reassuringly distant to think about.
Mercury is the smallest planet in the solar system and the closest to the Sun. Despite this proximity, it is not the hottest planet, that distinction belongs to Venus. Mercury has almost no atmosphere to trap heat, so temperatures swing wildly between 430 degrees Celsius in direct sunlight and -180 degrees Celsius in darkness.
A year on Mercury lasts just 88 Earth days because it moves so quickly around the Sun. Its day, however, is surprisingly long: Mercury takes 59 Earth days to rotate once on its axis. It has no moons and no rings. Its heavily cratered surface resembles our own Moon, covered in grey-brown rock with bright streaks called crater rays.
Mercury was named after the Roman messenger god, known for the winged sandals that let him travel faster than any other deity, a fitting choice for the fastest planet in the solar system.
Venus is the second planet from the Sun and the hottest in the solar system, with surface temperatures reaching around 465 degrees Celsius — hot enough to melt lead. Its thick atmosphere of carbon dioxide traps heat in a runaway greenhouse effect, making Venus significantly hotter than Mercury despite being further from the Sun.
Venus is similar in size and mass to Earth, which is why it is sometimes called Earth’s twin. In nearly every other way, the two planets are opposites. Venus has no liquid water, a toxic atmosphere to humans, volcanic plains, and it rotates in the opposite direction to most planets. A day on Venus lasts 243 Earth days, which is longer than its year of 225 Earth days.
One curious consequence of Venus’s reversed rotation: if you were standing on its surface, the Sun would rise in the west and set in the east. Venus was named after the Roman goddess of love and beauty, the planet is striking enough from Earth that ancient astronomers considered it worthy of the name.
Earth is the third planet from the Sun and the only world where we know life exists. It is the largest of the four terrestrial planets. About 71% of Earth’s surface is covered by water, earning it the nickname “the Blue Planet.” That water exists in liquid form because Earth sits at just the right distance from the Sun — what scientists call the habitable zone.
Earth’s atmosphere is 78% nitrogen and 21% oxygen, with the remainder made up of other gases, including carbon dioxide and argon. This atmosphere shields us from harmful solar radiation, burns up incoming meteoroids, and regulates temperature. Earth takes 24 hours to rotate on its axis (one day) and 365.25 days to orbit the Sun (one year). That extra quarter day is why we add a leap day every four years.
Earth is the only planet not named after a Roman or Greek god. Its name comes from the Old English word “ertha” and the Germanic word “erde”, both meaning ground. It is also the only planet with one single natural moon, which plays a key role in stabilising Earth’s axial tilt and driving the ocean tides.
Mars is the fourth planet from the Sun and the second smallest in the solar system. Its red colour comes from iron oxide, rust, in its soil, making it easy to spot as a bright reddish dot in the night sky. A Martian day lasts 24.6 hours, close enough to an Earth day that scientists call Martian days “sols.” A Martian year lasts 687 Earth days.
Mars is home to Olympus Mons, the largest volcano in the solar system, standing three times taller than Mount Everest. Evidence suggests Mars once had liquid water flowing across its surface. Today it is cold, dry, and dusty, with surface temperatures ranging from 20 degrees Celsius at the equator in summer to -153 degrees Celsius at the poles in winter. Dust storms can engulf the entire planet for months at a time.
Mars has two small moons, Phobos and Deimos, both irregularly shaped and heavily cratered. Mars is the most explored planet beyond Earth: NASA currently operates the Perseverance and Curiosity rovers on its surface, searching for signs of past microbial life. NASA aims to send human explorers to Mars in the 2030s.
Jupiter is the largest planet in the solar system, so massive that all the other planets combined would fit inside it twice over. It is a gas giant made primarily of hydrogen and helium, with no solid surface. Jupiter’s core may be solid rock or a dense mixture of metals, roughly the size of Earth.
The most recognisable feature of Jupiter is the Great Red Spot, a storm wider than Earth that has been raging for hundreds of years. The horizontal stripes visible in photographs are bands of clouds made from ammonia and water at different altitudes moving in opposite directions. Jupiter also has a faint ring system.
Jupiter has 95 confirmed moons as of 2024, more than any other planet. Four large moons, Io, Europa, Ganymede, and Callisto, were first spotted by the astronomer Galileo Galilei in 1610 and are known collectively as the Galilean moons. Europa is of particular interest to scientists because evidence suggests it has a liquid water ocean beneath its icy surface, a potential environment for life.
Saturn is the second-largest planet in the solar system and the most visually striking. Its magnificent ring system is made of billions of pieces of ice and rock, ranging from tiny grains to chunks as large as a house, all orbiting Saturn at different speeds. The rings are vast in width but remarkably thin — in places only about 10 metres deep.
Like Jupiter, Saturn is a gas giant composed primarily of hydrogen and helium. It has the lowest density of any planet in the solar system — if you could find a bathtub large enough, Saturn would float. A day on Saturn lasts just 10.7 hours, but a year takes 29.4 Earth years to complete.
Saturn has 146 confirmed moons, the most of any planet in the solar system. Titan is the largest and the only moon in the solar system with a dense atmosphere. Its atmosphere is mostly nitrogen, like Earth’s, and scientists believe it has lakes and rivers of liquid methane on its surface. Enceladus, another of Saturn’s moons, sprays icy particles into space and is thought to have a subsurface ocean.
Uranus is an ice giant, the seventh planet from the Sun, and the coldest in the solar system, with the lowest recorded temperature of -224 degrees Celsius. It is made of a hot, dense fluid of water, ammonia, and methane above a small rocky core. Methane in its atmosphere absorbs red light and reflects blue, giving Uranus its distinctive blue-green colour.
The most unusual thing about Uranus is its extreme axial tilt of 98 degrees. Scientists believe a large object collided with Uranus billions of years ago, knocking it onto its side. As a result, Uranus essentially rolls around the Sun like a ball rather than spinning upright like the other planets. One pole faces the Sun for 42 years at a time, then the other takes over.
Uranus takes 84 Earth years to complete one orbit of the Sun and 17 hours to rotate once. It has 27 known moons, all named after characters from the works of Shakespeare and the poet Alexander Pope — the only planet whose moons do not take their names from Greek or Roman mythology. Uranus also has 13 faint rings.
Neptune is the eighth and most distant planet from the Sun, an ice giant similar in composition to Uranus. Its deep blue colour, caused by methane in its atmosphere absorbing red light, reminded astronomers of the sea — which is why it was named after the Roman god of the oceans. Neptune takes 165 Earth years to complete one orbit of the Sun. In 2011, it completed its first full orbit since its discovery in 1846.
Neptune has the strongest winds in the solar system, with gusts recorded at over 2,000 kilometres per hour. A large storm system known as the Great Dark Spot was observed by the Voyager 2 spacecraft in 1989; later observations found it had disappeared, unlike Jupiter’s enduring Great Red Spot. Neptune’s day lasts 16 hours.
Neptune has 14 known moons. The largest, Triton, orbits in the opposite direction to Neptune’s rotation — a retrograde orbit that suggests Triton was captured from the Kuiper Belt by Neptune’s gravity rather than forming alongside the planet. Triton is slowly spiralling inward and is expected to break apart in around 3.6 billion years.
A moon is a natural satellite: a body that orbits a planet due to gravity. The solar system contains more than 200 known moons orbiting six of the eight planets — Mercury and Venus have none. Moons vary enormously in size, from tiny irregular rocks a few kilometres across to Ganymede, which is larger than the planet Mercury.
| Moon | Planet | Notable Feature |
|---|---|---|
| Moon | Earth | Only humans have visited beyond Earth |
| Io | Jupiter | Most volcanically active body in the solar system |
| Europa | Jupiter | Possible subsurface ocean; candidate for life |
| Ganymede | Jupiter | Largest moon in the solar system |
| Titan | Saturn | Only the moon with a dense atmosphere and weather |
| Enceladus | Saturn | Icy geysers; possible subsurface ocean |
| Triton | Neptune | Only a large moon with a retrograde orbit |
Our Moon is the fifth largest in the solar system and the only place beyond Earth where humans have walked. Twelve astronauts set foot on the Moon between 1969 and 1972 during NASA’s Apollo programme. The Moon takes 27.3 days to orbit Earth and the same time to rotate once, which is why we always see the same side. Its gravitational pull creates the ocean tides on Earth.
Jupiter’s four largest moons, Io, Europa, Ganymede, and Callisto, were named the Galilean moons after Galileo Galilei. Io is the most volcanically active body in the solar system. Europa has a smooth icy surface beneath which scientists believe a saltwater ocean may contain twice as much water as all of Earth’s oceans combined. Ganymede is the solar system’s largest moon and has its own magnetic field. Callisto is the most heavily cratered body known.
Titan is Saturn’s largest moon and uniquely has a thick nitrogen atmosphere with weather patterns, clouds, and rain, though the rain is liquid methane rather than water. Enceladus actively sprays icy geysers into space; samples collected by the Cassini spacecraft contained water, carbon dioxide, and organic compounds, placing Enceladus on the short list of worlds that might support microbial life.
A dwarf planet is a body that orbits the Sun and has enough mass for its gravity to pull it into a roughly spherical shape, but has not cleared its orbital neighbourhood of other objects the way the eight main planets have. The International Astronomical Union currently recognises five dwarf planets in our solar system.
Pluto is the most famous dwarf planet. It was classified as the ninth planet from 1930 until 2006, when the discovery of similarly sized objects in the Kuiper Belt prompted the IAU to reclassify it. Pluto is smaller than Earth’s Moon. A day on Pluto lasts about 153 hours, and a year lasts 248 Earth years. It has five moons, the largest of which is Charon.
Ceres is the smallest recognised dwarf planet and the only one that orbits in the asteroid belt between Mars and Jupiter. Eris, discovered in 2005, is roughly the same size as Pluto and was a key factor in triggering the reclassification debate. Makemake and Haumea are two further dwarf planets in the Kuiper Belt.
The solar system contains an enormous number of smaller objects that are not planets or moons. The asteroid belt between Mars and Jupiter holds over a million known asteroids, rocky remnants from the solar system’s formation. Most asteroids are made of carbon, silicate rock, or metal. The largest, Ceres, is now classified as a dwarf planet; others include Vesta, Pallas, and Hygiea.
Comets are icy bodies that develop spectacular tails when they travel close to the Sun. Heat causes their frozen nucleus to release gas and dust, which stream away from the Sun to form a glowing tail that can stretch millions of kilometres. Short-period comets originate in the Kuiper Belt beyond Neptune; long-period comets come from the distant Oort Cloud at the very edge of the solar system.
Meteoroids are smaller rocky or metallic objects. When a meteoroid enters Earth’s atmosphere and burns up, we see it as a meteor or shooting star. If a fragment survives and lands on Earth, it becomes a meteorite. Meteor showers occur when Earth passes through trails of debris left by comets — the Perseids in August and the Lyrids in April are among the most reliable annual events.
The solar system appears explicitly in the KS2 Science curriculum under Earth and Space (Year 5), where children are expected to describe the movement of Earth and other planets relative to the Sun, describe the movement of the Moon relative to Earth, and use models to explain night and day. It also links to KS2 Geography content on the Earth’s layers and weather patterns.
“Space captures children’s imaginations like almost nothing else in primary science. The solar system gives teachers a genuine opportunity to connect abstract concepts — gravity, scale, rotation — to something children already have feelings and questions about. That emotional engagement is what makes the learning stick.” — Michelle Connolly, Founder of LearningMole and former teacher with over 15 years of classroom experience
LearningMole provides curriculum-aligned video resources covering the solar system, Earth and Space, and the wider science programme for KS2. Our educational videos explain the movements of planets and moons using clear animations and child-friendly language, directly supporting the Year 5 Science objectives.
A practical classroom activity for teaching scale: have children create a scale model of the solar system using different sizes of balls or circles of paper. Because the distances in the solar system are so vast, you will need either a very long corridor or a simplified distance scale that preserves relative sizes. This kind of hands-on work with proportional reasoning also supports KS2 maths objectives.
Parents can reinforce solar system learning at home without specialist equipment. Stargazing apps are freely available and help children identify planets visible with the naked eye; Venus, Mars, Jupiter, and Saturn are often visible and dramatically brighter than surrounding stars. Drawing and labelling the planets in order from the Sun is a classic home activity that consolidates both order and relative size.
LearningMole’s educational videos work well for homework support and for children who want to go deeper than the classroom allows. Our space and astronomy topic page brings together videos, activities, and explanations across all aspects of the KS2 space curriculum.
There are eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was counted as the ninth planet until 2006, when the International Astronomical Union reclassified it as a dwarf planet. This happened because scientists discovered other similarly sized objects in the Kuiper Belt and needed a consistent definition. The eight remaining planets are divided into four rocky terrestrial planets closer to the Sun and four larger outer planets (two gas giants and two ice giants). The order from the Sun can be remembered with the mnemonic: My Very Eager Mother Just Served Us Nachos.
Jupiter is the biggest planet in the solar system by a significant margin. It is so large that all seven other planets could fit inside it with room to spare. Jupiter’s diameter is approximately 143,000 kilometres, compared to Earth’s diameter of about 12,750 kilometres. Jupiter is classified as a gas giant and is made mostly of hydrogen and helium. It does not have a solid surface. Its Great Red Spot, a storm that has persisted for hundreds of years, is itself wider than the entire Earth.
Both planets and dwarf planets orbit the Sun and have sufficient mass to be pulled into roughly spherical shapes by gravity. The key difference is that a planet has “cleared the neighbourhood” of its orbit — meaning its gravity has either absorbed or ejected other objects in its orbital path over time. Dwarf planets have not done this. Pluto, for example, shares its orbital region with many other Kuiper Belt objects. There are currently five recognised dwarf planets: Pluto, Eris, Ceres, Makemake, and Haumea.
Saturn’s rings are made of billions of pieces of ice and rock, ranging from tiny grains to chunks several metres across. Scientists believe the rings formed from the remains of moons, comets, or asteroids that were pulled apart by Saturn’s powerful gravity. The rings orbit Saturn at different speeds depending on their distance from the planet. While Saturn has the most spectacular rings, all four outer planets — Jupiter, Saturn, Uranus, and Neptune — have ring systems. Saturns are simply far more visible because they are larger, more extensive, and made of highly reflective ice.
No other planet in our solar system is currently suitable for human life without significant engineering support. Mars is the most frequently discussed candidate: it has a 24.6-hour day, evidence of ancient water, and polar ice caps, but its atmosphere is too thin to breathe, temperatures drop to -153 degrees Celsius, and radiation levels are dangerous. Venus has surface temperatures hot enough to melt lead and a toxic atmosphere. Jupiter, Saturn, Uranus, and Neptune have no solid surfaces. Mercury has no atmosphere and extreme temperature swings. Scientists are more interested in potential microbial life on Europa and Enceladus than in human habitation.
Yes. This guide maps directly to the KS2 Science curriculum for Year 5 (Earth and Space), covering the motion of planets relative to the Sun, the motion of the Moon relative to Earth, and the differences between terrestrial and gas giant planets. It also supports KS2 Geography content on climate, weather, and Earth’s structure. The FAQ sections and structured tables are suitable for use as classroom reference materials. LearningMole’s accompanying video resources align with specific National Curriculum objectives and can be used for whole-class teaching or independent learning.
These three terms describe the same type of object at different stages of its journey. A meteoroid is a small rocky or metallic object travelling through space. When it enters Earth’s atmosphere, friction heats it up and makes it glow; it becomes a meteor, also called a shooting star. Most meteors burn up completely before reaching the ground. If a fragment survives the journey through the atmosphere and lands on Earth’s surface, it is called a meteorite. Meteorites have been found on every continent, including Antarctica, where they are easier to spot against the ice.
LearningMole produces curriculum-aligned educational videos covering the solar system, individual planets, Earth and Space science, and related KS2 topics. You can find our solar system videos at [URL: KS2 science resources — confirm with Ciaran] or by visiting LearningMole’s YouTube channel, which has over 260,000 subscribers and more than 800 educational videos for primary-aged children. Our space videos explain key concepts using clear animations designed to support classroom teaching and home learning.
The solar system is one of those topics that starts with simple facts and opens up into something genuinely vast. Eight planets with entirely different characters, more than 200 moons with their own stories, dwarf planets, asteroid belts, icy comets arriving from the edges of the Sun’s reach — there is always more to discover. For KS2 children, understanding the solar system builds a mental model of how gravity, scale, and scientific classification work, skills that carry through to secondary science and beyond.
Teachers and parents looking for classroom resources, video explanations, and home learning activities can explore LearningMole’s full range of KS2 science content at [URL: KS2 science resources — confirm with Ciaran]. Our educational videos cover the Year 5 Earth and Space curriculum in detail, with clear explanations of why planets move, what moons are, and how scientists have explored the solar system over centuries of observation. LearningMole’s resources are designed by experienced educators to make complex science accessible without oversimplifying.
Space remains one of the most powerful ways to capture a child’s imagination in the classroom. The solar system in particular offers something rare: a subject where the facts are stranger and more dramatic than anything invented. Mercury, smaller than Earth’s Moon and roasting in sunlight. Venus is hotter than Mercury despite being farther from the Sun. Jupiter has 95 moons and a storm that has persisted for centuries. Every planet is worth exploring — and so is every question a child asks about them.
LearningMole provides free and subscription-based educational videos and resources aligned with the UK National Curriculum. Our Earth and Space content for Year 5 covers solar system movement, planets, moons, and the differences between celestial bodies. Whether you are a KS2 teacher planning lessons or a parent supporting homework, our library is designed to make primary science engaging and accurate. Visit learningmole.com to explore our teaching resources and watch free videos on our YouTube channel
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