A SOUTHAMPTON researcher has helped solve a long-standing space mystery - the origin of one of the colourful displays seen in the night sky.

Experts understand where many auroras, such as the Northern and Sothern Lights, come from, but the origin of the theta aurora has been unclear until now.

The well-known Northern Lights - the Aurora Borealis - are caused by the Earth's magnetic field interacting with the solar wind caused by the sun.

However, while the charged particles in these are cold, those in the theta aura are relatively hot.

But the mystery of why this is has finally been solved by studying data collected by the European Space Agency's Cluster and NASA's IMAGE satellites.

It is thought it is because the theta aurora occurs closer to the poles, where hotter particles seem to get trapped.

Dr Robert Fear, from the University of Southampton and lead author of the paper, said: “This is the first time that the origin of the theta aurora phenomenon has been revealed, and it is thanks to localised measurements from Cluster combined with the wide-field view of IMAGE that we can better understand another aspect of the Sun-Earth connection.”