Magnetic waves explain mystery of Sun’s outer layer

A theory as to why the Sun's outer atmosphere differs in its chemical make-up from its inner layers has been confirmed by direct observation for the first time by scientists at UCL and the Italian Space Agency. The Sun's extremely hot outer layer, the corona, has a very different chemical composition from the cooler inner layers, but the reason for this has puzzled scientists for decades. One explanation is that, in the middle layer (the chromosphere), magnetic waves exert a force that separates the Sun's plasma into different components, so that only the ion particles are transported into the corona, while leaving neutral particles behind (thus leading to a build-up of elements such as iron, silicon and magnesium in the outer atmosphere). Now, in a new study published in The Astrophysical Journal , researchers combined observations from a telescope in New Mexico, the United States, with satellites located near Earth to identify a link between magnetic waves in the chromosphere and areas of abundant ionised particles in the hot outer atmosphere. Lead author Dr Deborah Baker (UCL Space & Climate Physics) said: "The different chemical compositions of the Sun's inner and outer layers were first noted more than 50 years ago. This discovery generated what is one of the long-standing open questions in astrophysics. "The difference in composition is surprising, given that the layers are physically linked, and that matter in the corona originates in the innermost layer, the photosphere.