Astronomers have made a major breakthrough in understanding how Earth’s magnetic field interacts with that of the Sun. For the first time, the process of the two fields combining – known as magnetic reconnection – has been observed, opening up the door to understanding how this important process takes place.

The discovery was made by NASA’s Earth-orbiting Magnetospheric Multiscale (MMS) mission. This involves four identical spacecraft, launched in 2015, flying in a tight pyramid formation and separated by just a few kilometers. Over the past six months, they have observed six of these reconnection events taking place, and the best studied of these has now been described in the journal Science.

“The main thing that people are most excited about is that we’re able to see reconnection actually happening,” lead author James Burch from the Southwest Research Institute (SwRI) told IFLScience. “There are tremendous implications, and it’s going to yield a lot of work in the future.”

So, what is reconnection exactly? Well, as mentioned, it’s the moment that magnetic field loops from the Sun meet Earth’s magnetic field, or its magnetosphere. When the two combine, they break and reconnect with each other, releasing a large amount of energy

The major finding from this research is that the magnetic field dropped to near zero at the moment of reconnection, known as a magnetic “null,” according to Burch. This then caused a spike in power generated by the electrons, confirming a previous theory that the electrons were responsible for the energy produced in the process. These electrons then streamed away along the magnetic field lines caused by the reconnection.

^{Above, a diagram of the moment of reconnection. James Burch}

“What we found was the situation was much simpler than we thought,” said Burch. “We thought it might be turbulent and we couldn’t make sense of it, but it turns out the electron motion is very similar to what was predicted in simulations.”

The finding was made possible by the capabilities of the MMS spacecraft. They were able to image electrons within their pyramid formation once every 30 milliseconds. This allowed for about 100 measurements over three seconds, important as each reconnection event (measuring a few kilometers across) lasts only one to two seconds.

Although we can’t see the process of reconnection itself in visible light, we can see the results of it in the form of aurorae on Earth. Occurring near the poles, aurorae involve electrons passing down Earth’s magnetic field lines and exciting atoms in the atmosphere, producing the iconic curtains of light we can see from the ground.

^{You can thank magnetic reconnection for beautiful views like this. NASA}

But reconnection is not limited only to Earth. It is prevalent throughout the universe, and indeed occurs at all planets in our Solar System that have their own atmosphere. Importantly, it also has important connotations for Earth-based research, most notably nuclear fusion.

“One of the ways of doing sustained nuclear fusion is to trap particles in a toroidal magnetic field, heat them up, and if the temperature is high enough, nuclear fusion gets triggered where the energy output is greater than the energy put in,” Burch explained. But reconnection allows the trapped atoms to escape, causing the temperature to drop, known as “sawtooth crashes.” Better understanding of how reconnection occurs could help us overcome this impediment.

Another useful area is in space weather prediction. Large solar flares, blasting off charged particles towards Earth, can cause havoc for satellites in orbit if safety measures are not taken. If we know how and when reconnection takes place, we can better prepare for potentially debilitating solar flares.

The MMS mission will continue for another year and a half, observing more events on the day side of Earth, and then other events on the night side, although the team is hopeful of a mission extension if the spacecraft remain in working order. But for now, thanks to the initial results, we can better understand this intriguing phenomena.