Planetary Phenomena - Saturn & Titan

In February 2005 our guest speaker was Dr Andrew Coates from the Mullard Space Science Laboratory which is the largest university-based space research group in the UK and part of University College London. The Laboratory is subdivided into five research groups, all studying various types of physics, and Dr Coates heads the Space Plasma Physics Group.

A plasma is a very hot gas, where some or all of the atoms are separated into ions & electrons. As the negative and positive charges are free to move, plasma is an excellent conductor and is influenced by magnetic and electric fields. At the moment the Group are very busy working on the current mission to Saturn called Cassini-Huygens. They have designed a special instrument called a "Cassini Plasma Spectrometer-Electron Spectrometer"; shortened to CAPS-ELS.

This instrument is designed to study Saturn's magnetic field, which is thought to be the most complex in our Solar System. It is twenty times the size of Earth's magnetic field and, unlike the other planets, the magnetic north and south poles align with Saturn's geographical poles.

On Earth, the geographic and magnetic poles are not coincident, with the north magnetic pole in the Canadian arctic and the south pole off the coast of Antarctica. At present the estimated position of the north magnetic pole is thought to be at 82N 114W but this in fact is an average as the pole can wander as much as 85km in a single day. Earth's magnetic field is thought to be generated by the chaotic motions of the outer core which is some sort of metallic liquid. However, it is not known where Saturn's magnetic field comes from. It could, like Earth, originate deep in its core or it may be generated by processes further out. Saturn's magnetic field, or magnetosphere, is large enough to contain its numerous orbiting moons, protecting them from the worst effects of the solar wind. The field is not spherical but shaped like a teardrop with its sunward-facing side being compressed by the solar wind and its opposite side being drawn out into a long tail that stretches far behind the planet.

Just like on Earth, when the solar wind penetrates the Earth's magnetic field at the poles to produce aurorae, Saturn also has its dazzling light shows. But these enigmatic displays are quite different from those on Earth. On Saturn they can last for days instead of hours. Sometimes they rotate with the planet and sometimes they remain fixed. When they brighten they head towards the pole instead of away from it, and sometimes they do not form a ring but a spiral shape around the pole.

With all these mysteries the MSSL team will have their work cut out to try and fathom out what is going on. The Cassini mission is scheduled to finish in 2008 but may be extended if budgets allow.