The Path of the Planets

About 4.6 billion years ago, there was an enormous cloud of gas and dust in space. This cloud contracted and started to spin. In the centre, the Sun formed. From the rest of the cloud, planets, moons, and other celestial bodies came into being. Gradually, the planets settled into orderly orbits, creating the solar system as we know it today, which revolves around the centre of the Milky Way.

Since Pluto is no longer considered a planet, Neptune is the outermost of all planets! The eighth planet seen from the Sun is very far away from us. From there, the Sun looks like a small, twinkling star.
Johann Gottfried Galle and Heinrich Louis d’Arrest discovered the planet on 23rd September 1846. Neptune was the first planet to be discovered not through direct observation, but by calculations. Galileo Galilei had observed it through his telescope but did not recognize it as a planet. Unlike Earth, Neptune has no solid surface. Its colour is a deep blue due to the abundance of methane. Triton, one of its 16 moons, is covered with ice, and ice volcanoes eject nitrogen at a frigid -220 degrees Celsius.

The third largest planet in our solar system, where summer lasts for 40 years at the North Pole! Uranus was discovered by William Herschel with a telescope on March 13, 1781. At first, he thought it was a comet or a star. Due to the methane gas in its atmosphere, Uranus appears bluish-green, similar to Pluto. The most fascinating thing about Uranus is that it rotates differently from the other planets. Most planets spin like a top, but Uranus lies on its side and rolls like a barrel. This results in particularly long seasons. As a gas planet, it has no solid surface, only an icy core. Uranus also has rings around it, which are very thin and hard to see. Its moons are named after characters from Shakespeare’s and Pope’s works.

The impressive rings make Saturn the most striking object in the solar system. In 1610, Galileo Galilei was the first to observe the sixth planet in the solar system through a telescope. At that time, he did not know that its rings consist of billions of ice and dust particles. Some are tiny, others as large as a house! These are influenced by more than 146 moons. Some of them even help keep the rings in shape. One of the best-known moons is Titan – it even has lakes and rivers of liquid methane! On Saturn itself, strong storms sometimes rage for many years. As a gas giant composed of hydrogen and helium, it has no solid surface. More than 700 Earths could fit inside Saturn!

Jupiter is the largest planet in the solar system and has changed our view of the world. Jupiter is the fifth planet in the solar system. It consists of layers of clouds and gas, which become increasingly dense toward the core. Its core is probably solid and about the size of Earth. These clouds move at varying speed around the planet. The surface displays turbulent bands of clouds. The most notable feature being the “Great Red Spot” – a massive storm. In 1610, the polymath Galileo Galilei discovered four moons orbiting Jupiter through his telescope. This observation significantly contributed to the corroboration of the Copernican model, which had been debated since 1543: not the Earth but the Sun is at the centre of our planetary system.

1-2 million asteroids orbit the Sun between the gas and the rocky planets. Most asteroids are small rocks, though some are several kilometres in size. Astronomers believe that the asteroid belt consists of material that could never form a planet. Alternatively, it may be the remnants of a planet that broke apart long ago. Occasionally, Asteroids are deflected from their path und then crash onto the planets and moons of our solar system. This is how the striking craters on many celestial bodies are formed. In the distant future, asteroids might be of interest as “providers of rescources”. NASA is already planning a mission for research purposes in which a house-sized asteroid will be “captured”.

Mars is the fourth planet and, together with Venus, one of our two neighbouring planets. No other planet has been studied so intensively and for good reason. Mars is considered a possible candidate for extraterrestrial life. The dried-up river courses show that there must have been large water deposits - the prerequisite for life. The Martian sand contains iron oxide, i.e. rust, which gives the planet its colour. In addition to the highest mountain (Olympus Mons, height: 21 km), there is also the deepest valley (Valles Marineris, depth: 11 km) in the solar system. The planet is constantly being explored with space probes and automatic vehicles (Mars rovers) such as “Curiosity”. A manned mission to Mars is currently still a vision and will not take place for several decades.

The only celestial body in the solar system on which life exists. Earth is approximately 4.6 billion years old and the third planet in the solar system. It consists of the core, mantle, and crust. For life to exist on Earth, the distance from the Sun must be just right. Other essential factors include the presence of liquid water, a protective magnetic field against harmful radiation, a suitable atmosphere, and much more. Our Moon plays an important role in stabilising Earth’s axis. The tilt of Earth’s axis, in turn, is responsible for the diverse seasons. The first life forms developed around 3.9 to 3.5 billion years ago, but the development of humans began only about 7 million years ago.

Venus is probably the most hellish planet, due to the carbon dioxide content in its atmosphere. Venus is the second planet from the Sun and our closest neighbour. Its proximity to the Sun and a strong greenhouse effect would even melt lead! Its atmosphere, composed of carbon dioxide and clouds of sulphuric acid, is hostile to life. Due to the high pressure – comparable to a depth of 900 metres underwater – many unmanned probes have been crushed. The surface is marked by lowlands, high plateaus, volcanoes, solidified lava flows, craters, and trenches. Venus can be seen in the sky shortly after sunset or just before sunrise, often as the brightest object in the sky.

Besides lacking seasons, Mercury has several characteristics that make it unique. Named after the swift messenger god, it is the smallest planet and the closest to the Sun. It was observed as early as 265 BC. During two rapid orbits around the Sun, it rotates exactly three times on its axis, which is very slow. As a result, it heats up significantly on the sunlit side and cools dramatically without sunlight. These extremes and its proximity to the Sun make it a hostile environment for life. Due to the lack of an atmosphere, meteors can impact the surface unimpeded. The resulting craters remain visible for long periods due to the absence of erosion. NASA has already detected ice on Mercury.

The Sun is a fairly average star, but compared to Earth it is enormous. The Sun is a ball of gas at the centre of our solar system, providing light and warmth. In its core, pressure and heat convert hydrogen into helium, which makes life on Earth possible. It is 750 times heavier than all the planets combined and could hold Earth over a million times within it. Here in the solar observatory, phenomena such as sunspots and solar storms are observed. The data is made available to the ESA and all scientists, to assist them in studying their effects on Earth. In 1543, Copernicus proposed the theory that the Sun is at the centre of the universe; later, after his death, Kepler was able to confirm this fact.