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Solar probe sheds new light on the sun

SOHO celebrates 15 years in orbit!

On 2 December 1995, the scientific solar observatory spacecraft SOHO (SOlar and Heliospheric Observatory), designed and built under Airbus Defence and Space’s prime contractorship for European Space Agency (ESA), was launched by an Atlas II rocket. It continuously monitors the sun, the heliosphere, and the solar wind particles that stream towards the Earth. Its mission is to help achieve a clearer understanding of the structure and dynamics of the solar interior, to gain better insight into the physical processes that form and heat the sun’s corona, and to investigate solar wind.

It now ranks among the most successful space observatories ever and is one of Airbus Defence and Space’s masterpieces in scientific missions. SOHO has provided a wealth of data of incalculable value to science, which has revolutionised our understanding of the workings of our sun.

SOHO operates in a ‘halo’ orbit around the first Lagrange point (L1), 1.5 million km from Earth, where the gravity of the sun and the Earth neutralise each other. A joint ESA–NASA project, its 12 instruments were provided by more than 500 European and American scientists.

It is a remarkable success story: the SOHO mission, originally designed for a two-year lifetime, has been extended several times and is now beginning its fifteenth year of operation. However, there was a moment when all seemed lost – and the extraordinary adventure of how SOHO was rescued figures in the annals of space history.



Helioseismology instruments measure the oscillations on the surface of the sun. Using these measurements, scientists have mapped the convection currents of hot gas beneath the surface and identified how twists in the magnetic fields cause them to break through the surface, forming sunspots. SOHO’s instruments can even look right through the sun to the active surface zones on the other side – zones that are invisible from the Earth. This makes it possible to predict solar flares several days in advance. These massive eruptions of gas have a noticeable effect on the Earth’s outer reaches, causing magnetic storms, the aurora borealis and sometimes even triggering power blackouts in the electricity grid.
Another of the satellite’s instruments is capable of detecting an area of activity on the hidden face of the sun by detecting the emission of hydrogen atoms in space beyond the sun’s surface – in the same way as the shaft of light from a lighthouse becomes visible when it strikes the clouds.
Instruments designed to observe the sun’s ‘atmosphere’ or corona have enabled scientists to analyse the mighty flares known as coronal mass ejections. These occur almost daily as the sun spits out millions or occasionally billions of tonnes of gas at a velocity of several hundred kilometres per second.
SOHO is also the greatest comet hunter of all time. Its data has led to the discovery of more than 1,800 comets, the majority by amateur astronomers in places all over the world who look for bright spots in the images taken by SOHO that are moving relative to the sun. Enormous patience and dedication are needed to analyse the images down to the very last detail – illustrating the passionate enthusiasm that news and images from the SOHO mission invoke among Internet users.