Importance of the Magnetic Field

The magnetic field is a fundamental parameter in any plasma:

  • The magnetic field controls the motion of all the particles within the plasma
  • The magnetic field is key to wave-particle interactions, which cause plasma heating, for example in the corona
  • The magnetic field determines the connectivity between different regions, such as the corona and the solar wind, and hence how energy is transported
  • Energy can be stored in and released from the magnetic field, such as in flares
  • The magnetic field plays the key role in dynamos, in both stars and planets

Accurate measurement of the magnetic field is therefore key to all plasma science.

Science Objectives

How does the Sun's internal magnetic field change over time?

Solar Orbiter will remotely measure the polar magnetic fields of the Sun for the first time. The magnetometer will play a key role in understanding how this field links into the interplanetary medium and hence how long term proxy records are signatures for changes in solar conditions. Our science team contains experts on the solar field and dynamo (T. Hoeksema, Stanford; M. Thompson, Sheffield) as well as M. Lockwood (RAL) who has led efforts to understand long term changes in the Sun and their effects on climate.

How is the corona heated?

The continuing enigma of coronal heating will be addressed by Solar Orbiter with both remote sensing and in-situ instruments. Whether nano-flares or wave-particle interactions play the lead role in the heating, we know from Helios measurements that the solar wind ions are not fully thermalised by 0.3 AU. Solar Orbiter will be able to measure the particles, and their interactions with the field, to reveal the signatures of nano-flares or wave-particle interactions. Our team includes experts on wave-particle interactions, including some with Helios experience (E. Marsch, Lindau; B. Bavassano, Rome; S. Bale, Berkeley). It also includes experts on coronal heating (R. Walsh, U. Central Lancashire)

How does the solar wind originate in the corona?

Only by travelling close to the Sun can we remove the complications of interplanetary dynamics and directly link coronal regions to the outflowing solar wind. Hence we can determine how different coronal conditions affect outflowing solar wind conditions. The magnetic field is the path along which the particles travel. Our science team includes experts on coronal dynamics and flare s (P. Cargill, Imperial) as well as modellers of the global solar field and solar wind (P. Riley, SAIC) and we will study the dynamic links between the lower corona and interplanetary space.

How does energy flow from the Sun to the Earth?

The interplanetary manifestations of coronal mass ejections (ICMEs) are key triggers of energy transfer into the Earth's magnetosphere and magnetospheric storms. Many aspects of their triggering and subsequent propagation are not well understood. We will study ICMEs close to the Sun, before they are affected by their interactions with the solar wind, the better to link them to solar phenomena. Our team includes the world leaders in ICME analysis (N. Crooker, Boston; C. Russell, UCLA; R. Forsyth, Imperial) and modelling (P. Riley, SAIC).

How are particles accelerated near the Sun and how do they travel through space?

Flares and shocks can accelerate particles to high energies; these particles then propagate through the complex, turbulent interplanetary magnetic field to the spacecraft, or the Earth. Many questions remain about the details of both their acceleration and propagation. Our team of particle theorists (J. Giacalone, LPL; R. Vainio, Helsinki) and turbulence experts (W. Matthaeus, Bartol; T. Horbury, Imperial) will study these linked problems, helping to explain the acceleration of particles such as cosmic rays through the Universe.

How do plasmas work?

Solar Orbiter will allow us to take extremely detailed measurements of fundamental plasma processes such as shocks and turbulence in a more extreme environment than has previously been possible. Our team includes world leaders in turbulence research, both analysis and theory (W. Matthaeus, Bartol; M. Goldstein, GSFC; T. Horbury, Imperial; M. Velli, Firenze) and shock physics (S. Schwartz, Imperial; A. Szabo, GSFC; W. Baumjohann, Graz).