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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Artist’s impression of the Cheops satellite observing an exoplanet transiting its parent star.
ESA’s Characterising Exoplanet Satellite, Cheops, will observe bright stars that are already known to host planets, measuring minuscule brightness changes due to the planet’s transit across the star’s disc.
Cheops makes use of the technique of ‘ultra-high-precision transit photometry’ to measure very precisely the sizes of exoplanets. The size of the dip in the light due to the exoplanet transit is known as the ‘depth’ of the transit, and relates directly to the size of the planet relative to the star: a large planet will block a larger fraction of the light from the star than would a small one.
By knowing when and where to point in order to catch planetary transits, Cheops will maximise the time it spends monitoring actual transit events. It will point at stars over most of the sky, returning to the same stars to observe multiple transits over the course of the mission, thus building up the accuracy of measurement of planet sizes.
Relative sizes and distances are not to scale.