Our Amazing Solar System!
Our Solar System is a vast and dynamic collection of celestial bodies revolving around a central star—the Sun. Formed approximately 4.6 billion years ago from a collapsing cloud of gas and dust, it encompasses a diverse array of objects including eight planets, five recognized dwarf planets, moons, asteroids, and comets. These objects are arranged in distinct zones characterized by their compositions and distances from the Sun. The inner Solar System is dominated by rocky terrestrial planets with solid surfaces, whilst the outer Solar System consists of massive gas and ice giants. Beyond the planets lie regions such as the asteroid belt, Kuiper Belt, and the distant Oort Cloud, each containing relics from the system’s formation, providing valuable insight into its history and evolution. This guide explores the fascinating features of the Solar System—from the blazing Sun to the icy edges at its very depths.
THE SUN
At the centre of the Solar System lies the Sun, a massive ball of burning gas that accounts for 99% of the total mass of the Solar System. Our star, the Sun, is about 4.6 billion years old, halfway through its 10 billion year phase, where it fuses hydrogen into helium. It is a G type main sequence star, otherwise known as a yellow dwarf. The core temperature of the Sun reaches temperatures of 15 million °C, whilst the surface of the Sun reaches temperatures of 5,500 °C. The Sun holds 99% of the total mass of the solar system, and the light from it takes 8 minutes to reach the Earth, travelling at the speed of light, (299 792 458 metres per second). The speed of light is the maximum speed that light, energy and matter can travel through the vacuum of space. The Sun provides the light and warmth that we need to sustain life on Earth.
THE TERRESTRIAL PLANETS
The first four planets closest to the Sun are the terrestrial planets, defined as a planet composed primarily of silicate rocks or metals, with a solid, hard surface.
MERCURY
Mercury is the smallest and closest planet to the Sun. Mercury is a rocky planet, with a radius of 2440 kilometres, making it about ⅓ the width of the Earth and similar in size to the Earth's moon, (which has a radius of 1737km). Without an atmosphere to retain heat, the planet experiences wild temperature fluctuations, ranging from highs of 430°C during the day, to temperatures as low as -180°C during the night. Mercury completes one orbit (the time it takes to make one full revolution around the Sun) every 88 Earth days, making it the fastest orbit in the Solar System. As Mercury does not have an atmosphere, it experiences intense Solar radiation, making it unlikely to be conducive to life as we know it. It has a heavily cratered surface and does not have any Moons of its own. Mercury spins slowly on its axis, completing one rotation every 59 Earth days. Mercury has an axis of rotation tilted to 2 degrees, meaning that it spins almost perfectly upright. Because of this, the planet does not experience seasons. Mercury is located at a distance of 58 million kilometres from the Sun, which makes it 0.39 Astronomical Units (AU) away. One astronomical unit (AU), is the distance from the Sun to Earth.
Distance from Sun: 0.39 AU (58 million km)
Diameter: 4,880 km
Moons: 0
Temperature: -180°C to 430°C
Orbit around the Sun: 88 days
Axial rotation: 59 days
Axial tilt: 2 degrees
Rings: No
Named after: Roman messenger God
VENUS
Venus is the second planet out from the Sun, often referred to as Earth’s sister planet. It is the only planet named after a female god- named after the ancient Roman goddess of love and beauty. Venus is a rocky planet, with a diameter of 12,104 km. In comparison, the Earth has a diameter of 12,756 km. Although similar in size to Earth, Venus is cloaked in a thick, toxic atmosphere primarily composed of carbon dioxide. This creates a greenhouse effect so strong that surface temperatures soar to around 465°C, making Venus the hottest planet in the Solar System. The surface pressure on Venus is incredibly intense, approximately 92 times greater than Earth's atmospheric pressure at sea level. This immense pressure is equivalent to what would be experienced nearly 1 kilometre underwater on Earth. The clouds of Venus are also made of sulfuric acid, causing acid rain. This extreme pressure, combined with its surface temperature, makes Venus an extremely hostile environment. Because Venus rotates extremely slowly on its axis, a single day on Venus is 243 days, which is longer than its year of 225 days. In addition to this, Venus spins backwards relative to its orbit, making it different to most planets. It spins in the opposite direction to the Earth. Venus orbits the Sun from an average distance of 108 million kilometres, or 0.72 astronomical units. From this distance, it takes sunlight about six minutes to travel to Venus from the Sun. As Venus is the third brightest object in the sky after the Sun and the Moon, it is famously referred to as the morning or the evening star.
Distance from Sun: 0.72 AU (108 million km)
Diameter: 4,880 km
Moons: 0
Temperature: ~465°C (surface)
Orbit around the Sun: 225 days
Axial rotation: 243 days
Axial tilt: 177.4°
Rings: No
Named after: Roman goddess of love and beauty
EARTH
Earth, our home planet, is the largest of the terrestrial planets and uniquely supports a vast diversity of life. Its atmosphere is composed of nitrogen (78%), oxygen (21%), and other elements (argon, carbon dioxide, helium, methane, water vapor) (1%), forming the perfect balance for life as we know it to breathe and live. Earth is the only planet in the Solar System not named after Greek or Roman mythology. Instead, its name was taken from Old English and Germanic, and simply means “The Ground”. Earth is a unique rocky planet with a liquid water surface, a nitrogen-oxygen atmosphere. It has a strong magnetic field which protects life, and helps to maintain relatively stable temperatures, ranging from -88°C to 57°C in extreme cases. Earth orbits the Sun at an average distance of 150 million kilometres, (1 AU), and sunlight takes 8 minutes to reach the Earth. This means that if the Sun were to suddenly disappear, we wouldn’t notice for 8 minutes! The time it takes the Earth to spin once on its axis is 23.9 hours, and it completes one orbit around the Sun every 365.25 days. This orbit led to the development of the leap year- by adding up the .25 days over the course of four years, this allowed the addition of a full day once every four years, hence the leap year. Earth has a Protective Shield around us which is our atmosphere. This atmosphere protects us from incoming meteoroids, most of which break up in the Earth's atmosphere before they can strike the surface. 71% of the surface of the Earth is composed of liquid water, the remaining 29% is made up of land mass.
Earth has one natural satellite, the Moon, which helps to stabilize Earth’s axial tilt of 23.5°, influencing the oceans' tides. As Earth orbits the sun, this axial tilt causes the planet to experience four distinct seasons- Summer, Autumn, Winter & Spring. When the Northern Hemisphere is leaning towards the sun, the region experiences summer, whilst the Southern Hemisphere experiences winter, and vice versa.
In 1994, Carl Sagan made a famous and poignant reflection about the Earth-
“Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives here. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam”.
Distance from Sun: 1 AU (150 million km)
Diameter: 12,756km
Moons: 1
Temperature: -88°C to 57°C
Orbit around the Sun: 365.25 days
Axial rotation: 23.9 hours
Axial tilt: 23.5°
Rings: No
Named after: Old Germanic word, meaning “The ground”
MARS
Mars is the fourth terrestrial planet out from the Sun, famously known as the Red Planet for its iron oxide dust that colours its surface red. Mars was named after the Roman god of War, because the red colour reminded ancient Romans of spilled blood. Similarly, the Egyptians referred to the planet as “Her Desher”, meaning “The Red One”; the Chinese called the planet “Fire Star”; and the Babylonians called the Planet “Nergal”, meaning “God Of War & Fire”. Today, we still refer to Mars as “The Red Planet”, because of the rusting effect on the surface. Mars has two small moons- Phobos and Deimos. In Greek mythology, they were the twin sons of the Roman god of war, Ares (Mars). They translate to the emotions of fear and dread, personifying these emotions which would have accompanied him into battle.
The diameter of Mars is approximately 6,791 kilometres, half the size of the Earth in diameter. Mars orbits the Sun at a distance of 228 million km, making it 1.5AU away from the Sun. From here, sunlight takes 13 minutes to travel to Mars from the Sun. Mars spins once on its axis every 24.6 hours, which is very similar to Earth's 23.9 hours. One Martian day is called “sol”, which is short for “solar day”. It takes Mars 687 Earth days to make a complete orbit around the Sun, which is nearly twice as long as an Earth year. Another similarity between Mars and the Earth are their axial tilts, Mars with a tilt of 25°, and Earth with a tilt of 23.5°. Like the Earth, Mars has distinct seasons, however they last much longer due to the longer time Mars takes to orbit the Sun. They also vary in length due to the elliptical orbit of Mars (oval shaped path around the Sun). Mars has a very thin atmosphere made up mostly of carbon dioxide and nitrogen, however it is so thin it offers no protection from impact objects such as meteoroids. The surface temperature on Mars can range from a high of 20°C, to a low of -153°C, however any heat easily escapes the planet due to the thin atmosphere. Mars experiences strong dust storms which cover most of the planet- these can go on for months at a time. The surface of Mars has many interesting topographical features, such as volcanoes, impact craters, polar ice caps, and dust storms which have altered the landscape of Mars drastically over the years. Mars is home to the tallest volcano in the Solar System- Olympus Mons, which stands three times taller than Mt Everest at approximately 25km tall. Mars also has a vast canyon system called Valles Marineris, which is over 4,800km in length, making it the largest canyon in the Solar System, stretching nearly one quarter of the entire surface of Mars. Valles Marineris is 10 times larger than the grand canyon, and spans 200km in width and 7km in depth.
Six successful rovers have successfully landed on the surface of Mars: NASA's Sojourner, Spirit, Opportunity, Curiosity, and Perseverance, along with China's Zhurong. From these missions, we have found evidence that billions of years ago, Mars was wetter, and warmer, with a thicker atmosphere and liquid water.
Distance from Sun: 1.52 AU (228 million km)
Diameter: 6791 km
Moons: 2
Temperature: 20°C to -153°C
Orbit around the Sun: 687 days
Axial Rotation: 24.6 hours
Axial tilt: 25°
Rings: No
Named after: Roman god of war
THE ASTEROID BELT
Located between the terrestrial inner rocky planets, and the gas and ice giants of the outer solar system lies a distinct region known as the asteroid belt. In total, the Solar System is home to a current total of 1,477,736 asteroids (as of November 2025), which are rocky remnants left over from the early formation of the Solar System 4.6 billion years ago. The large majority of asteroids in the Solar System are found orbiting in the asteroid Belt, and range in size from 10 metres to 530 kilometres in diameter, including the dwarf planet Ceres. It is believed that the asteroid belt never formed into a planet due to the gravitational pull of Jupiter. Despite many movies and pop culture depicting the asteroid belt as a region filled with rocks that would be impossible to fly through, in reality the asteroid belt is mostly empty space and the objects are very far apart, averaging 1 million kilometres apart. It would actually be very easy to fly through the asteroid belt without being hit. The total mass of all of the asteroids combined only equates to about 4% of the total mass of the Earth's moon.
THE GAS GIANT PLANETS
The four outer planets furthest from the Sun are the gas/ice giant planets, defined as a planet composed primarily of hydrogen and helium (gas giants) or water, methane, and ammonia (ice giants). These planets are much larger and less dense, with no solid surface, unlike the inner terrestrial planets.
JUPITER
Jupiter is the largest and oldest planet in our solar system, named after the king of the gods in Roman Mythology. It currently has 95 recognised moons, with the four largest moons known as the Galilean Moons/Satellites, as they were first observed by the astronomer Galileo Galilei in the early 1600’s. Most of Jupiter's moons are also named for mythological characters and figures associated with Jupiter or his Greek counterpart, Zeus. The four Galilean satellites are some of the most fascinating objects in the Solar System. Europa is thought to host a liquid water ocean with conditions hospitable for some life forms beneath its frozen crust. Io is the most volcanically active object in the entire Solar System. Ganymede is the largest moon in the Solar System, being even larger than Mercury, whilst the icy surface of Callisto is smooth and features very few craters, indicating current surface activity. All four of these moons can be viewed through a telescope or a small pair of binoculars- they appear as tiny points of light similar to stars which appear to move if observed over a period of time (days-weeks).
Jupiter is located at a distance of 778 million kilometres from the Sun, making it 5.2 AU away. From here, it takes 43 minutes for sunlight to travel to Jupiter.
As Jupiter is a gas giant, it has a composition similar to the Sun, with mostly hydrogen and helium. Interestingly, if Jupiter was 80 times heavier, it would have formed into a second star in the Solar System, allowing its core to start fusing hydrogen into helium. Jupiter does not have a true solid surface. The further down into the atmosphere towards the core, pressures and temperatures increase, effectively compressing hydrogen gas into liquid- forming an ocean of hydrogen. These extreme pressures and temperatures at these depths would crush, melt and vaporize any spacecraft, making any missions almost impossible. NASA’s Juno spacecraft found that the core of Jupiter is partially dissolved with no separation from the metallic hydrogen around it, and is not solid. Jupiter's temperature varies significantly with depth, with the cloud tops around -110°C, whilst the core reaches 24,000°C. This temperature makes the core far hotter than the Sun's surface.
Jupiter is so large that 11 Earths could fit side by side along its diameter, whilst over 1000 Earths could fit inside! Jupiter has the strongest magnetic field of any planet in the solar system, which is over 20,000 times stronger than Earth's, and it exhibits the shortest day in the Solar System, taking 9.9 hours to spin once on its axis, whilst it takes 12 Earth years to make a complete orbit around the Sun.
Jupiter is tilted on its axis by 3°. As a result, it spins almost completely upright, and does not have extreme seasons. It also has a very faint ring system made from dust and rocks. Jupiter has a spectacular storm system known as “The Great Red Spot”, which has persisted for over 400 years so far!
Distance from Sun: 5.2 AU (778 million km)
Diameter: 139,820 km
Moons: 95+
Temperature: -110°C, to 24,000°C (clouds to core)
Orbit around the Sun: 12 years
Axial Rotation: 9.9 hours
Axial tilt: 3°
Rings: Yes
Named after: Roman god of Sky & Thunder / Greek god Zeus
SATURN
Saturn is the 6th planet from the Sun, and the second largest in the solar system next to Jupiter. It is another gas giant, distinguished by its extraordinary rings, made mostly of ice and rock particles. Like Jupiter, Saturn is made mostly of hydrogen and helium, with a small rocky core which is enveloped by liquid metallic hydrogen similar to the core of Jupiter, albeit smaller.
Interestingly, as Saturn has an average density less than water, if there were a pool large enough, Saturn would float in it!
Saturn is named after the Roman god of agriculture and wealth, and to date has 274 confirmed moons, far more than any other planet in the Solar system. Some of Saturn's moons are of great scientific interest. Its largest moon Titan has a thick nitrogen rich atmosphere making it the only known moon in the solar system to have a substantial atmosphere with liquid on its surface. Like the Earth, Titan has rivers, lakes, seas, clouds and rain, though unlike Earth, these are made of liquid hydrocarbons including methane and ethane. Another moon, Enceladus features large geysers expelling water vapor and ice particles into space, indicative of a global ocean underneath its icy shell.
Saturn is located 1.4 billion kilometres from the Earth (9.5AU), and light takes 80 minutes to reach Saturn from the Sun. Saturn has a diameter 9 times wider than that of the Earth, with a diameter at the equator of 120,500 kilometres. Despite its colossal size, Saturn has the second shortest day of all objects in the Solar System. One day on Saturn takes 10.7 hours to make a complete rotation on its axis. In contrast, Saturn makes one complete orbit around the Sun once every 29.4 Earth years (10,756 days). Similar to the Earth's axis of 23.5 degrees, Saturn has an axis tilted at 26.73 degrees, which means that it also experiences seasons.
Perhaps the most impressive part of Saturn are its impressive ring systems, which extend nearly 300,000 kilometres in diameter, yet the vertical height of the rings is just 10 metres! The rings are made from billions of chunks of comets, asteroids, or moons that were torn apart from Saturn's powerful gravity and captured in its orbit, along with ice, rock and dust.
Distance from Sun: 9.5 AU (1.4 billion km)
Diameter: 120,500 km
Moons: 274
Temperature: -178°C, to 11,700°C (clouds to core)
Orbit around the Sun: 29.4 years
Axial Rotation: 10.7 hours
Axial tilt: 26.73°
Rings: Yes
Named after: Roman god of agriculture and wealth
URANUS
Uranus is the 7th planet from the Sun, and the first ice giant in the Solar System. First discovered by telescope in 1781 by astronomer William Herschel, it was named after the Greek god of the sky. Located at a distance of 2.9 billion kilometres from the Sun, this makes Uranus 19 AU from the Sun, meaning that light from the Sun would take 2 hours 40 minutes to reach it. Uranus spins on its axis once every 17 hours, and makes a complete orbit around the Sun in a human lifetime- 84 years (30,687 years). Spanning just over 51,000 kilometres in diameter, Uranus is four times wider than the Earth, and has a methane rich atmosphere which exhibits a beautiful blue-green hue to it. Uranus is the coldest planet in the Solar System, with temperatures plummeting to -224°C, and it has 13 faint rings surrounding it, along with 28 small moons. Whilst most celestial bodies in the Solar System are named after Greek or Roman mythology, the moons of Uranus are named for characters from the works of William Shakespeare and Alexander Pope.
Uranus is famously known for its extreme axial tilt, where its equator is almost at a right angle to its orbit, at an axial tilt of 97.7 degrees. This tilt makes Uranus appear to spin sideways, and have the most extreme seasons in all of the Solar System. Uranus also rotates in the opposite direction to the other planets, aside for Venus. It is believed that this tilt is due to a collision with an Earth sized object a long time ago. Every 21 years, the Sun shines directly over each pole, plunging the other half of Uranus into a 21 year long winter. Uranus experiences extreme winds, with speeds up to 900 km/h.
Distance from Sun: 19 AU (2.9 billion km)
Diameter: 51,000 km
Moons: 28
Temperature: -224.2°C
Orbit around the Sun: 84 years
Axial Rotation: 17 hours
Axial tilt: 97.7°
Rings: Yes
Named after: Greek god of the sky
NEPTUNE
Neptune, the furthest and 8th planet from the Sun, is known for its incredibly strong winds and storms, including the fastest winds in the Solar System, with clouds of frozen methane reaching speeds of up to 1200km/h. Neptune is an ice giant, located 30 times further from the Sun than the Earth, at a distance of 4.5 billion kilometres (30 AU). From this distance, sunlight takes 4 hours to reach Neptune. Named after the Roman god of the Sea, Neptune is four times wider than the Earth, with a diameter just under 50,000 kilometres, and very similar in size to Uranus. More than 80% of Neptune's mass is composed of a hot dense fluid of icy materials, including water, methane and ammonia, making it the densest giant planet. It is theorized that Neptune might harbour an ocean under its clouds, due to the high pressures. A single day on Neptune takes 16 hours for it to spin on its axis, whilst it takes 165 Earth years to make a complete orbit around the Sun. Neptune has a similar axis of rotation to Mars and Earth, of 28 degrees, causing the planet to experience seasons which last for over 40 years each! Currently Neptune has 16 known moons, with its largest moon Triton exhibiting a thin atmosphere, along with geysers that eject icy material up more than 8 kilometres upwards. These cryovolcanoes are of great scientific interest. Triton also orbits Neptune in a direction opposite to Neptune's rotation. Like the other giant planets, Neptune does not have a solid surface, and instead has an atmosphere composed of hydrogen, helium and methane.
Distance from Sun: 30 AU (4.5 billion km)
Diameter: 49,528 km
Moons: 16
Temperature: -223°C
Orbit around the Sun: 165
Axial Rotation: 16 hours
Axial tilt: 28°
Rings: Yes- faint
Named after: Roman god of the Sea
DWARF PLANETS
In addition to the eight major planets, there are five recognized dwarf planets in the Solar System. These include Ceres, Pluto, Haumea, Makemake, and Eris. Ceres is the largest object in the asteroid belt, followed by Pluto, which is located beyond the orbit of Neptune. Pluto has five moons and a cold, icy surface. Beyond this, Eris, Haumea and Makemake reside far beyond Neptune. There was great debate about whether Pluto should remain as a planet or be de-classified as a dwarf planet. In 2006 the International Astronomical Union (IAU) created new parameters to define a planet. These include three criteria- firstly, the object needs to orbit the Sun. Secondly, the object needs to be (mostly) round in shape. Finally, the object needs to have cleared its orbital path of other debris. Pluto is not large enough to exert orbital dominance in its orbit, and therefore was reclassified to a dwarf planet in 2006.
KUIPER BELT & OORT CLOUD
Beyond the reaches of Neptune lies the Kuiper Belt & Oort Cloud. The Kuiper belt is filled with millions of small icy objects in the region, including many objects larger than 100 kilometres in width. Pluto, and some of the other dwarf planets are located within this region, along with frozen compounds such as ammonia and methane, rocks & ice. The Kuiper Belt is considered an area filled with ‘leftovers’ from the formation of the Solar System 4.6 billion years ago. The inner edge of the Kuiper Belt begins at a distance of 30 AU from the Sun, the same distance where Neptune orbits the Sun. The inner Kuiper Belt spans a distance out to 50 AU from the Sun, followed by a secondary region called the scattered disk. This region continues to a distance of 1000 AU. Beyond this, the Oort cloud is the most distant region in the Solar System, extending up to halfway from our Sun to the next nearest star. The Oort cloud is filled with icy bodies, including comets. To consider that 1 AU (the distance between the Sun & the Earth) is 150 million kilometres, the inner edge of the Oort cloud is located about 3000 AU from the Sun, and the outer edge of the Oort Cloud spans a far distance up to 100,000 AU from the Sun. That is 100,000 times further than the distance from the Sun to the Earth! At the edge of the Oort cloud, the Sun's gravitational influence ceases, and the edge of the Solar System ends. The Voyager 1 spacecraft is travelling at a speed of over 1.5 million kilometres a day, and it won’t reach the edge of the Oort cloud for approximately 30,000 years.