bubble

This image shows a truly miniature, magnetosphere recreated in the laboratory. The plasma “bubble” shown here is a mere inch across in total. The purple glow, seen in the photograph, is the stream of super-heated hot gas particles (plasma) of the Solar Wind Tunnel. You'd expect this stream to scorch the metal target. Without a magnetic field it would. But the experiment shows how instead what happens is a thin barrier or “skin” is formed of the plasma itself, within which a tiny cavity in the pseudo- solar wind is formed, which holds back the hazardous particles, so protecting the target except for at the magnetic poles. On the moon this cavity formation prevents the bombarding particles of the solar wind from weathering or darkening the surface color, keeping it white. The barrier width is about 100th the width that such a weak magnetic field (known to exist on the Moon’s surface) could possibly bend a heavy, fast moving, positively charged proton ion out of the way. So something else must be deflecting the ions into such a narrow "skin". That is an electric field the origin of which although complicated has been theoretically determined by the team and found to match the values seen in space by spacecraft and in the laboratory recreation. (Credit: RAL Space & Uni. of York)