27th January 2015
This talk, prompted by Voyager 1 leaving the solar system, was given by the Lucie Green, a well-known astronomer and broadcaster.
The heliosphere is the volume within which the Sun’s magnetic field and the solar wind dominate the interplanetary medium. Lucie talked about many of the features on and near the Sun’s surface, including sun spots, the corona and magnetic field lines. We have a number of spacecraft studying the Sun, including in particular the ESO’s Ulysses, which has a polar orbit, and the STEREO pair of spacecraft. These give us unprecedented views of what’s going on there.
We had many video clips of activity, with explanations of how that fits with what’s going on in the Sun’s magnetic field. For example, the differences in outflow characteristics between solar minimum and solar maximum can be explained by looking at the magnetic field has increased complexity at maximum.
There has been lack of understanding of how charged particles can leave the Sun’s surface when they are following magnetic field lines which loop up and back down to the surface. Models explained how the magnetic field can make “chimneys” that the particles can flow up.
Further out, the heliosphere is shaped a bit like a wind sock as the Sun moves through then interstellar medium. Contrary to expectation there are a large number of magnetic field “bubbles” near the heliopause, which are explained by twisty bundles being forced up from the Sun and moving to the edge of the solar system. The field structure is so complex the field lines look rather like a ballerina’s fluffy tutu!
Lastly Lucie talked about the ESA Solar Orbiter which will be launched later this decade. It has 10 instruments on board, and its orbit will move out of the ecliptic to give some polar observations, as well as approaching the Sun inside Mercury’s orbit: at 600⁰C heat shielding is of paramount importance. It has been in development for many years, and we have high hopes for what it will tell us.
An excellent and well-attended lecture: a very technical subject that Lucie explained with great clarity.