Our sun is in a small part of the Milky Way galaxy, within the Orion Arm.
As the closest network of planets to Earth, we know more about the planets of the solar system than other planets further afield. Here we’ll share some of what we know about those planets that make up our solar system.
How the solar system was formed
The solar system was created around 5 billion years ago. Nebulae – clouds consisting of dust and gas – were drawn together by gravity, eventually forming the Sun.
Because distances in space are so big, we use units like AU (Astronomical Units), Light Year, and Parsec as measures of distances. 1AU is the distance from the Earth to the Sun, which equates to 93 million miles. We use AU to measure distances within the solar system and all distances given are from the Sun.
The Solar System
There is more to our solar system than just the planets. It is made up of a star—the Sun—eight planets, several hundred moons (more are regularly found), a bunch of comets, asteroids and space rocks, ice, and several dwarf planets, such as Pluto. The first four planets closest to the sun are called The Inner Planets and are all rocky. The other four consist of two gas giants and two icy planets.
The Asteroid Belt sits between Mars and Jupiter and consists of millions of asteroids, rocks, dust, and smaller debris left over from the formation of the planets. We also have other wandering bodies that come our way, some of them in regular orbits. Some comets are regular visitors, and some, like the peanut-shaped large asteroid called Oumuamua, which means “A messenger from afar visiting first” are from interstellar space (i.e. the area between stars in a galaxy).
The Sun is about halfway through its life of 10 Billion years. At approx. 865.000 miles, or 1.4 million km in diameter, it makes up more than 98% of the total mass of our solar system. Its average surface temperature is nearly 6,000 degrees Celsius, whereas its temperature in the centre is 27,000,000°F or 15,000,000°C, and the corona (the sun’s outer atmosphere) measures about 6,000,000°C.
Mercury 0.4AU
The nearest planet, Mercury, is the smallest planet now that Pluto has been reclassified as a Dwarf Planet. With a diameter of 3,030 miles (4,878 km), it is only slightly larger than the Earth’s moon.
However, despite being the nearest to the sun, it is not the hottest. It is 430°C on the side facing the sun and -180°C on the night side.
It revolves so slowly that one day on Mercury is 176 Earth days and it takes 88 days to complete an orbit around the sun, which means that one day on Mercury is more than twice the length of its year!!
It’s named after the god Mercury, the winged messenger, because it moves so quickly around the sun.
Mercury can only be seen from the Earth when it is passing in front of the sun, and then only with a telescope with a special filter.
Venus 0.7AU
Sometimes called Earth’s sister, Venus has a slightly smaller diameter at 7,520.8 miles (12,104 km)
It rotates clockwise whereas all the others, including the Sun, rotate anti-clockwise (except Uranus, which rotates on its side). It has an atmosphere of over 95% carbon dioxide, with the remainder mostly nitrogen. It is hot enough at the surface to melt lead at 464°C, and the atmospheric pressure is over 90 times (1350 psi – 95 kg sq cm) that of the Earth at sea level.
These atmospheric conditions would crush us to a pancake and burn us to ash in minutes. It is the hottest planet in the solar system, with clouds mostly consisting of sulphuric acid, so when it rains, it rains sulfuric acid. Very Nasty!
Earth 1AU
The Earth’s diameter is 7,926 miles (12,756 km). It is in what is called The Goldilocks Zone, which means that it is just the right temperature and climate to have liquid water on the surface, and an overall climate ideal for life.
97% of the water on the earth is salty, with only 3% being fresh water. One-third of the Earth’s surface is either partially or completely desert. In total, 70% is water, one-third of the rest is desert, and 50% of what remains is either uninhabitable or has not yet been developed.
Did you know that Earth is struck by lightning 8.6 million times per day – that’s 100 times per second!! The higher frequency of lightning is over land mass, and because solid earth absorbs sunlight and heats up faster than water, this means there is greater atmospheric instability, leading to the formation of thunder and lightning-producing storms.
Mars 1.55AU
The diameter of Mars is 4,222 miles (6,794 km), which makes it around 55% the size of Earth. The fourth and last of the inner rocky planets from the Sun.
It is the most explored planet after Earth and was believed to have had some form of life on it a long time ago. However, now it has only a very thin atmosphere, mostly consisting of 95% carbon dioxide and 1.5% nitrogen.
Mars takes 6,876 Earth days or 1.88 years to orbit the Sun. As of September 2024, there are several rovers on the surface, of which only 3 are still in operation:: Curiosity, Perseverance and Zhurong.
Mars is subject to the worst dust storms in the solar system. It also has the largest mountain/volcano called Olympus Mons, which is so high that it would dwarf Everest at 16 miles (25 km) high, 374 miles (601 km) wide which is roughly the size of Arizona. However, it is extinct. It also has the Valles Marineris which is similar to the Grand Canyon on a much larger scale, as it would stretch across the USA from the east to west coast.
Jupiter 5.2AU
The largest of all the planets with a diameter of 88,695 miles (142,800 km). A giant planet made of gas, Jupiter is 2.5 times bigger than all the other planets in the solar system combined! NASA calculated that if Jupiter were the size of a football, the Earth would be less than the size of a pea!
Jupiter is sometimes called The Vacuum Cleaner of the solar system because its huge gravitational pull attracts objects coming into the solar system. The most recent recorded event was in July 1992, when the comet Shoemaker-Levy9 was broken up by Jupiter’s gravity and absorbed into its atmosphere.
It is unique, in that its cloud cover consists of bands of many colours. Spinning so fast that its day is only 9.55 hours long, it has the shortest day of any planet in the solar system.
The Great Red Spot is a storm on Jupiter that has been happening for at least 350 years. This storm has been observed to be getting gradually smaller, although it is still large enough to engulf the Earth.
Jupiter is so large that you could fit the Earth inside it more than 1,300 times. It has the largest moon in the solar system – Ganymede, which has a diameter of 3,270 miles (5,270 km). This is also the only moon in our solar system to have its own magnetic field.
Saturn 9.2AU
Saturn is another gas giant made mostly of hydrogen and helium. With a diameter of 74,898 miles (120,536 km), it is nine times wider than Earth. At this distance from the Sun, it takes sunlight 80 minutes to travel from the Sun to Saturn.
Saturn is considered the most visually impressive planet in the solar system due to its rings. The material in its rings ranges in size from small particles to much larger rocks made up of ice and dust. Some particles are up to a kilometre (more than half a mile) across. The rings are only up to 200 metres thick but thousands of miles wide. Saturn is not the only planet to have rings – Jupiter, Neptune and Uranus also have this feature, but theirs are not visible to the naked eye.
Saturn is also the furthest planet from the sun which can be seen by the naked eye. Winds around its equator can reach 1,800 kilometres per hour. That’s 1,118 miles per hour!
Uranus 19.8AU
This ice giant was discovered in 1781 by astronomer William Herschel, who initially thought it was a comet or a star. As the third-largest in our solar system, it has a diameter of 31,763 miles (51,118 km).
Uranus has an atmosphere made mostly of molecular hydrogen and atomic helium, with a small amount of methane and a rocky core. It is the only planet whose equator is nearly at right angles to its orbit, (possibly due to a collision with an Earth-sized object in the distant past), and is unique in that it rotates on its side.
It is the coldest and windiest planet in the solar system, with wind speeds of up to 900 km per hour and a temperature of -372°F or -224°C. Whilst it takes 84 Earth years to orbit the Sun, one day on Uranus only lasts 17 hours and 14 minutes.
Neptune 30AU
Neptune is nearly as big as its inner neighbour, Uranus. Neptune’s diameter is about 31,000 miles (50,000 km).
Like Uranus, Neptune is a kind of planet called an ice giant. It is made up mostly of gasses, predominantly hydrogen and helium.
In 2011 Neptune completed its first 165-year orbit since it was first discovered in 1846. It takes sunlight 4 hours to travel from the Sun to Neptune (compared to 8 minutes from the Sun to Earth).
One day on Neptune lasts around 16 hours. Scientists believe that there may be an ocean of superhot water under Neptune’s cold clouds. The water does not boil away because the planet’s incredibly high pressure keeps it locked inside.
Author – Jon Cross
Find out more about the Sun and its planets on your visit to Sherwood Observatory.