Monday, May 16, 2022

60-years old mystery of Fast Magnetic Explosions solved

It’s not just a scientific curiosity.

Solar flares can generate enough energy that can power the whole world for 20,000 years. They result from the most dramatic events of significance released by magnetic reconnection on the Sun. However, what causes magnetic explosions remains elusive.

A complete understanding of this process could help scientists get insights into nuclear fusion and provide better predictions of particle storms from the Sun that can affect Earth-orbiting technology.

Scientists with NASA’s Magnetospheric Multiscale Mission, or MMS, have developed a new hypothesis that explains how the most explosive type of magnetic reconnection – called fast reconnection – occurs. It also describes why it happens at a consistent speed.

The lead author of the new study Yi-Hsin Liu, a physics professor at Dartmouth College in New Hampshire and the deputy lead of MMS’ theory and modeling team, said, “We finally understand what makes this type of magnetic reconnection so fast. We now have a theory to explain it fully.”

Magnetic reconnection is a multi-faceted process of energy conversion that occurs in plasma. The plasma immediately converts magnetic energy into heat and acceleration. Throughout the Universe, the plasma gets While there are several types of magnetic reconnection, one particularly puzzling variant is known as fast reconnection, which occurs at a predictable rate.

Barbara Giles, project scientist for MMS and research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said, “We have known that fast reconnection happens at a certain rate that seems to be pretty constant. But what drives that rate has been a mystery until now.”

A new study explains how fast reconnection occurs, specifically in collisionless plasmas. Collisionless plasmas are plasma whose particles are spread out enough that the individual particles don’t collide with one another. Where reconnection happens in space, most plasma is in this collisionless state, including the plasma in solar flares and the space around Earth.

Charged particles in plasma stop moving as a group during fast magnetic reconnection. They start moving independently, giving rise to the Hall effect and thus creating an unstable energy vacuum where reconnection happens. Pressure from the magnetic fields around the energy vacuum causes the vacuum to implode, quickly releasing immense amounts of energy at a predictable rate.

The new theory will be tested in the coming years with MMS, which uses four spacecraft flown around Earth in a pyramid formation to study magnetic reconnection in collisionless plasmas. In this unique space laboratory, MMS can study magnetic reconnection at a higher resolution than would be possible on Earth.

Giles said“Ultimately, if we can understand how magnetic reconnection operates, we can better predict events that can impact us on 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.”

Journal Reference:

  1. Liu, YH., Cassak, P., Li, X. et al. First-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas. Commun Phys 5, 97 (2022). DOI: 10.1038/s42005-022-00854-x

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