Magnetic fields around the Earth release strong bursts of energy, accelerating particles and feeding the auroras that glow in the polar skies. On July 11, 2017, four NASA spacecrafts were there to watch one of these explosions happen.
The process that produces these bursts is called magnetic reconnection, in which different plasmas and their associated magnetic fields interact, releasing energy. The Magnetospehric Multiscale Mission (MMS) satellites launched in 2015 to study the places where this reconnection process occurs. This newly released research shows for the first time that the mission encountered one of these reconnection sites in the night side of the Earth's magnetic field, which extends behind the planet as a long "magnetotail."
"It's a long-standing mystery, this process called reconnection," study author Roy Torbert from the University of New Hampshire told Gizmodo. "The mission studies a fundamental and universal process out in space."
The reconnection process occurs because the Sun beams plasma, or a gas of charged particles, at the Earth and its magnetic field. The Sun's plasma contains a magnetic field represented as lines running through it, but these lines could be in a different or opposite orientation from Earth's own magnetic field. The magnetic field lines connect with new lines, causing a release of energy.
The MMS spacecraft have previously witnessed asymmetric reconnection events, which occur at the sunlit side of the Earth where the solar wind interacts with the Earth's magnetic field. But the July 11, 2017 event was the first MMS observations of reconnection in the magnetotail where symmetric reconnection occurs — where the tail pinches in and interacts with itself. The event produced a jet of electrons travelling at 20,000km/h, according to the paper published in Science.
You wouldn't be able to see these explosions directly, but they provide some of the energy that powers the aurora, explained Torbert. And understanding this process is important. This phenomenon only occurs in plasma, but plasma makes up most of the universe's visible matter.
But, while one event is exciting, multiple events is science. "You don't just want to understand a singular event," he said. "You want to put that in the context of many events. Synthesising it all, you can understand the process better."