Troy Carter in UCLA Newsroom: ‘Surfing’ particles: Physicists solve a mystery surrounding aurora borealis

Scientists know that electrons and other energized particles that emanate from the sun as part of the “solar wind” speed down Earth’s magnetic field lines and into the upper atmosphere, where they collide with oxygen and nitrogen molecules, kicking them into an excited state. These molecules then relax by emitting light, producing the beautiful green and red hues of the aurora. What has not been well understood is precisely how groups of electrons accelerate through the magnetic field on the last leg of their journey, reaching speeds of up to 45 million mph.  “This challenging experiment required a measurement of the very small population of electrons moving down the chamber at nearly the same speed as the Alfvén waves, numbering less than one in a thousand of the electrons in the plasma,” said Troy Carter, a professor of physics and director of the UCLA Plasma Science and Technology Institute.