A solar flare can unleash enough energy to power the whole earth for 20,000 years in just a few minutes. These solar flares are triggered by an explosive phenomenon known as magnetic reconnection, and physicists have spent the last half-century attempting to figure out how it works.
This visualization shows the Hall effect, which occurs when the motion of the heavier ions (blue) decouple from the lighter electrons (red) as they enter the region with strong electric currents (golden region). Image Credit: Tom Bridgman/NASA's Scientific Visualization Studio.
It is more than scientific curiosity: greater knowledge of magnetic reconnection might lead to new insights into nuclear fusion and improved forecasts of solar particle storms that could disrupt Earth-orbiting technologies.
NASA’s Magnetospheric Multiscale Mission (MMS) scientists believe they have cracked the code. The researchers have devised a theory to explain how the most explosive sort of magnetic reconnection, known as fast reconnection, occurs and why it occurs at a consistent rate. The new theory takes advantage of a common magnetic effect seen in household electronics like sensors that monitor anti-lock braking systems and detect when a mobile phone flip cover is closed.
We finally understand what makes this type of magnetic reconnection so fast. We now have a theory to explain it fully.
Yi-Hsin Liu, Study Lead Author and Physics Professor, Dartmouth College, New Hampshire
Liu is also the deputy leader of MMS’ theoretical and modeling team.
Magnetic reconnection happens in plasma, which is also known as the fourth state of matter. When gas is electrified enough to split apart its atoms, plasma occurs, leaving a mixture of negatively charged electrons and positively charged ions coexisting. Magnetic fields are extremely sensitive to this energetic, fluid-like substance.
Plasmas across the universe experience magnetic reconnection, which rapidly transforms magnetic energy into heat and acceleration, from flares on the Sun to near-Earth space to black holes. While there are various varieties of magnetic reconnection, rapid reconnection, which happens at a predictable rate, is one of the most puzzling.
We have known for a while that fast reconnection happens at a certain rate that seems to be pretty constant. But what really drives that rate has been a mystery, until now.
Barbara Giles, Project Scientist, Magnetospheric Multiscale Mission, NASA
Giles is also a research scientist at the Goddard Space Flight Center.
The new research, which was funded in part by the National Science Foundation and published in Nature’s Communications Physics journal, explains how fast reconnection occurs in collision-less plasmas, which are plasmas in which the particles are spread out enough that they do not collide with one another. Most plasma in space, including plasma in solar flares and space surrounding Earth, is in this collision-less condition where reconnection occurs.
The new theory explains how and why the Hall Effect, which describes the interplay of magnetic fields and electric currents, accelerates rapid reconnection. The Hall Effect is a common magnetic phenomenon that is employed in daily technologies, such as automobile wheel speed sensors and 3D printers, to assess speed, proximity, positioning or electrical currents.
Charged particles in a plasma, such as ions and electrons, cease traveling as a group during rapid magnetic reconnection. As the ions and electrons begin to move apart, the Hall Effect occurs, resulting in an unstable energy vacuum where reconnection occurs. The magnetic fields around the energy vacuum pressurize it, causing it to collapse, releasing massive amounts of energy at a predictable rate.
MMS, which utilizes four spacecraft flown around Earth in a pyramid arrangement to investigate magnetic reconnection in collision-less plasmas, will put the novel theory to the test in the coming years. MMS may research magnetic reconnection at a better resolution than would be possible on Earth in this one-of-a-kind space laboratory.
Ultimately, if we can understand how magnetic reconnection operates, then we can better predict events that can impact us at Earth, like geomagnetic storms and solar flares. And if we can understand how reconnection is initiated, it will also help energy research because researchers could better control magnetic fields in fusion devices.
Barbara Giles, Project Scientist, Magnetospheric Multiscale Mission, NASA
Journal Reference:
Liu, Y-H., et al. (2022) First-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas. Communications Physics. doi.org/10.1038/s42005-022-00854-x.