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 study of the relative abundances of hydrogen and heavy hydrogen (or deuterium) – the very first atoms created together with helium - provides an important way to understand the nature and density of the matter that came into existence shortly (from 1 second to a few minutes) after the Big Bang.
This knowledge is key to understanding whether the amount of matter (and energy) present in the Universe is enough for the Universe to collapse or to expand indefinitely (‘closed’ or ‘open’ Universe).