The European Space Agency (ESA) is Europe’s gateway to space. Its mission is to shape the development of Europe’s space capability and ensure that investment in space continues to deliver benefits to the citizens of Europe and the world.
Find out more about space activities in our 23 Member States, and understand how ESA works together with their national agencies, institutions and organisations.
Exploring our Solar System and unlocking the secrets of the Universe
Go to topicProtecting life and infrastructure on Earth and in orbit
Go to topicUsing space to benefit citizens and meet future challenges on Earth
Go to topicMaking space accessible and developing the technologies for the future
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The Solar System consists of more than just the Sun and the planets. Dwarf planets and so-called ‘small Solar System bodies’ — a term that includes comets and asteroids — also orbit the Sun. This illustration shows three of the best places to go looking for them.
Closest to home, between the orbits of Mars and Jupiter, lies the asteroid belt. As the name implies, the main asteroid belt is a doughnut-shaped ring consisting mostly of asteroids. These orbit the Sun at a distance of 2.1–3.3 AU, where 1 AU is the Earth-Sun distance of around 150 million km. The total mass of objects in the asteroid belt is estimated to be around 3% of the mass of the Moon.
30–50 AU from the Sun, beyond the orbit of Neptune, lies the Kuiper Belt. The Kuiper Belt is home to dwarf planet Pluto and thought to be an important refuge of comets. It is similar in shape to the asteroid belt, but 20 times as wide and 20–200 times as massive.
So distant that it’s never been seen directly, the Oort Cloud is a shell of icy objects thought to surround the entire Solar System. The region can be subdivided into a spherical outer Oort Cloud with a radius of some 20 000–200 000 AU and a doughnut-shaped inner Oort Cloud with a radius of 2000–20 000 AU. The Oort Cloud is home to billions of comets, some of which we have seen passing through the inner Solar System on orbits that take thousands or even millions of years to complete.