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 nucleus is presumed to be a body of a few kilometres in diameter (not necessarily round) consisting mostly of water ice mixed with dust. On approaching the Sun, the nucleus is heated up and releases enormous amounts of dust and gas (a few tons per second), preferentially from the sunward side.