For the first time, physicists have observed a mysterious process called magnetic reconnection — wherein opposing magnetic field lines join up, releasing a tremendous burst of energy. The discovery, published in Science, may help us unlock the secrets of space weather and learn about some of the weirdest, most magnetic objects in the universe.
Artist's rendition of Earth's magnetosphere and NASA's four MMS satellites. Image: University of Maryland
The magnetosphere, an invisible magnetic field surrounding our planet, is a critical shield for life on Earth. It protects us from all sorts of high energy particles emitted by the sun on a daily basis. When a particularly large burst of solar energy hits the edge of the magnetosphere (called the magnetopause), it can trigger space weather. This includes geomagnetic storms that light up the northern and southern skies with auroras, occasionally knocking out our satellites and power grids.
A better understanding of space weather is key to helping us prepare for the next massive geomagnetic storm — a once-in-a-century event that could quite literally cause a global power surge. Magnetic reconnection is at the heart of the mystery, underlying both the formation of solar eruptions and how they interact with our planet.
"The process of space weather starts on the sun — reconnection there produces coronal mass ejections and solar flares, both of which lead to space weather at the Earth," James Burch, a space weather scientist at the Southwest Research Institute told Gizmodo. "When the solar wind and its embedded magnetic field lines collide with Earth's magnetosphere at a high angle, then you have a direct connection between the sun and the Earth."
Now, for the first time, Burch and his colleagues have observed that sun-Earth connection at the subatomic scale, using data collected by NASA's Magnetospheric Multiscale (MMS) mission. This high-resolution physics laboratory consists of four identical spacecraft that fly in pyramid formation around Earth's magnetopause, collecting precise information on tiny charged particles every 30 milliseconds.
Artist's concept of the four MMS satellites flying in formation. Image: University of Maryland
Almost as soon as the mission launched in March of 2015, researchers started observing magnetic reconnection at unprecedented resolution. The most detailed of those is the subject of the new paper. "We hit the jackpot," Roy Torbert, MMS deputy principal investigator said in a statement. "The spacecraft passed directly through the electron dissipation region and we were able to perform the first-ever physics experiment in this environment."
The features of reconnection recorded in the data include a drop in the magnetic field to near zero, and a power spike generated by accelerating electrons. "We realised that the process of reconnection is really driven by electrons," Burch said. "Before, all measurements had been made at much larger scales. People could see dramatic effects, but these are the result of reconnection, not the cause."
Burch and his colleagues are continuing to study five other instances of magnetic reconnection recently observed by the MMS, and they're hopeful the mission will yield more events for years to come. In addition to shedding light on space weather, magnetic reconnection can help us understand exotic astronomical objects like magnetars, as well as the strong magnetic environments created by fusion reactors.
"The quality of the MMS data is absolutely inspiring," said James Drake, a physicist at the University of Maryland and a co-author on the study. "It's not clear that there will ever be another mission quite like this one."