Electrons ‘surf’ across space to create the northern lights
Physicists have definitive evidence that the aurora borealis is the result of electrons ‘surfing’ across the cosmos on powerful party waves. Scientists have known for a while that aurorae occur when energised particles from the Sun soar across space and crash into Earth’s magnetosphere. Those energised particles ride our planet’s magnetic field lines into the upper atmosphere, where they collide with oxygen and nitrogen molecules, releasing dazzlingly coloured light in the process. But there’s still a big lingering question about the aurora process: How do those solar particles pick up enough speed and energy to crash into Earth’s atmosphere with such force?
One popular explanation involves Alfvén waves, powerful geomagnetic waves that propagate through plasma, a charged gas that makes up the solar wind. These waves can pick up electrons in plasma and accelerate them to extremely high speeds without knocking them off course. Spacebased instruments have detected Alfvén waves travelling towards Earth above aurorae, but scientists lacked a definitive way of proving these waves were accelerating electrons – until now.
In a recent study, researchers used an instrument called the Large Plasma Device, a 20-metre-long vacuum chamber at UCLA that’s capable of holding a magnetic field, to recreate Alfvén waves under conditions similar to those in the solar wind. The team measured the velocity of electrons moving through the plasma chamber, finding that a small number of electrons were indeed being accelerated to great speeds by the waves. BRANDON SPECKTOR