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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A time series of six images of Comet Hale-Bopp taken by the SWAN instrument onboard ESA's Soho satellite in ultraviolet light (110-180 nm), on January 4, February 2 and 18, March 4 and 16, and April 3, 1997, as the comet slowly approaches the Sun, increasing in brightness. Hale-Bopp is clearly visible because of its huge hydrogen cloud produced by photodissociation of water vapour molecules evaporated from the solid nucleus. This nucleus is composed of ice and dust and has an estimated diameter of about 40 km. In contrast, the hydrogen cloud is more than 100 million km across, which makes it the largest object in the Solar System. The analysis of SWAN data of the hydrogen cloud indicates that about 600 tonnes of ice are vaporised and ejected in space each second during closest approach, forming its brilliant tail. [Image Date: 01-04-97] [97.04.011-001]