The SOHO Mission

Image 1: A Poster illustrating the SOHO Mission

Solar & Heliospheric Observatory (SOHO)

SOHO is a scientific mission in cooperation with ESA and NASA. The space probe was built in Toulouse, France from Matra. The launch was on October 2, 1995 from Kennedy Space Center, Florida, with an AtlasII/AS rocket combination to transfer to liberation point L1 between the sun and the earth (a distance of 1.5 million km from earth). Here the centrifugal force of its orbit and the gravitational pull of the sun and the earth offset.

Since May 1996, SOHO has been examining the sun, including the inside, with optical instruments (helioseismology), observing the sun’s atmosphere with optical instruments in visible and extreme UV light, and measuring in-situ the high energy charged particles of the interplanetary plasma locally from SOHO in the proximity of earth’s orbit. The most important goal of the mission is the correlated analysis of all the information from 10 experiments in order to gain as much information as possible about the sun’s “weather” (the state of the sun’s atmosphere) at the moment when packets of solar wind or high energy particles on the sun are so accelerated that they leave the sun and reach the earth’s atmosphere.

In the meantime the mission has been extended several times and had its 20th anniversary on 12/02/2015.

The scientific goals and results from SOHO

The sun body: structure und dynamics?
The sun is the central star in our galaxy. All life on this earth is dependent on it. On its surface, the visible part of the solar disk, it has a temperature of 6400 K which accounts for most of the visible and thermal radiation from the sun. With optical methods, vibrations on the sun’s surface can be observed in large frequency ranges of extremely slow periods (minutes to hundreds of days). These can be traced back to oscillations in the body of the sun. As with seismologic examinations of the earth, conclusions can be drawn about the sun’s inside that allow the scientists to see inside the sun and explore its inner structure

Corona: Why does it exist and how is it heated?
The atmosphere of the sun is considerable higher and more complex than the earth’s. Of special interest is the outer laver of the atmosphere, the corona, that is visible during solar eclipses, glowing weakly with its often frayed structure. The extraordinary thing about the corona is the temperature, which can reach several million K. For a long time, one of the biggest riddles of the solar system was how it could reach such high temperatures when the sun’s surface is only 6400 K. SOHO has contributed significant data for the solving of this problem.

Solar wind and energetic particles: accelerating where and how?
Every second, millions of tons of hot plasma (ionized hydrogen and helium gas) are spewed into interplanetary space at speeds from 300 to 800 km/s. This flow of plasma is called solar wind. Magnetic field lines from the sun are also carried out with the solar wind. Because the sun rotates with a period of 27 days, the magnetic field lines form Archimedean spirals in interplanetary space. High energy particles move along these magnetic field lines. Therefore, magnetic field lines are the most important structural element in the heliosphere. They can be considered as the long arms of the sun that it uses to extend its sovereignty to at least 130 billion km away. The sun is extremely variable with time and place. Sunspots, coronal holes and the 11-season cycle of solar activity, which really takes 22 years, are the most well-known variable aspects of the sun, which also affects the heliosphere

Kiel’s contribution

Measuring of suprathermal and high energy particles for the research of:

  • Energy-release and acceleration in the solar atmosphere
  • Samples of solar atmospheric material
  • Dispersion, acceleration, and modulation in the interplanetary medium


COSTEP: particle sensors from half-life detectors, scintillators and magnets consist of the LION and EPHIN instruments
CELIAS: measuring systems for the determination of charge, elemental and isotopic composition of suprathermal particles and plasma