The SOHO satellite is one of the European Space Agency’s most ambitious projects from the 1990s. Launched in 1995, it is still operating with its instruments pointed permanently at the Sun.

The SOHO satellite (SOlar Heliospheric Observatory) was designed to study the Sun’s interior structure (helioseismology), its outer atmosphere (heliosphere) and the origin of the solar wind. Its observations have helped scientists to better understand the interactions between the Sun and Earth’s environment and to gain new insights into some of our star’s best-kept secrets, such as how its corona is heated. SOHO has an uninterrupted view from its vantage point in a halo orbit around the L1 Lagrange point 1.5 million kilometres from Earth in the direction of the Sun.

The first cornerstone, along with the CLUSTER mission, of the European Space Agency’s Horizon 2000 programme, SOHO has revealed the Sun’s dynamic variations over a range of timescales and in this respect it can be considered the forerunner of the new field of science known as space weather and meteorology.

France helped to fund SOHO through its contribution to ESA’s mandatory science programme and built three of the satellite’s 12 instruments. It also worked on the design of three other instruments and is playing a key role in exploiting the mission’s science data through the MEDOC data centre at the IAS space astrophysics institute in Orsay.