For the first time, NASA spacecraft have measured the strange interactions between the Sun’s and Earth’s magnetic fields that are linked to explosive space weather events high above our planet’s surface. The phenomenon, known as magnetic reconnection, can disrupt satellites and telecommunications systems on our planet. Understanding how it works can potentially help researchers predict such space weather episodes and reduce their destructive side effects.
Magnetic reconnection occurs when the magnetic fields of the Earth and the Sun connect and release intense bursts of energy toward our planet. Scientists have known about these interactions for decades and have linked them to geomagnetic storms, which trigger brilliant aurorae near the Earth's poles. But because such storms can also impact our technology, scientists have been interested in figuring out the underlying physics of magnetic reconnection in space. Today's study, published in the journal Science, confirms a lot of what researchers suspected about the process, but also revealed data the researchers did not expect.
The magnetic fields of the Earth and the Sun connect and release intense bursts of energy
Reconnection takes place at the outer edges of the Earth's magnetic field, which is known as the magnetosphere. This field is thought to be generated by liquid iron flowing deep within the Earth’s core. The twisting and turning of this hot metal creates an electrical current, which ultimately produces a charged magnetic field that extends between 40,000 and 370,000 miles around Earth.
The magnetosphere acts like a protective barrier and shields our planet from high-energy solar winds, which would otherwise strip away the gases in our atmosphere and kill life on Earth. The solar winds are created by the Sun's outer atmosphere, which is so heated that it's constantly sending out streams of highly energized, fast-moving particles toward Earth. These charged winds create their own magnetic fields, which clash against our planet's magnetosphere.
Normally, the two magnetic fields oppose each other and move in different directions. But every so often the magnetic field lines switch and connect with each other. That’s called a magnetic reconnection event. "When the two magnetic fields link up, then that allows the solar energy to flow straight into the magnetosphere," said study author Jim Burch, vice president of the space science and engineering at the Southwest Research Institute. "It sets the entire field in motion." The excited particles from the Sun stream into the magnetic field lines of Earth, transferring energy into the magnetosphere.
To study these explosive reconnections directly, NASA launched the Magnetospheric Multiscale, or MMS, mission in March of 2015. The project involved sending four identical spacecraft into orbit around Earth. In space, the probes are situated in a pyramid formation, so that they can study magnetic reconnection in three dimensions.
Instruments onboard the MMS spacecraft were able to precisely detect the movement of electrons during a reconnection event on October 16th, 2015, taking measurements once every 30 milliseconds. This way, the researchers were able to observe how energy was transferred. The data also revealed the behavior of the electrons during magnetic reconnection, showing how fast the particles moved and the directions in which they flowed. The electrons mostly followed the same patterns that researchers predicted.
"This is valuable insight," said Amitava Bhattacharjee, a professor of astrophysical sciences at Princeton University, who was not involved in the study. "It's testing past theory and is certainly bringing to light that certain features were in fact predicted by theory."
Learning more about magnetic reconnection means scientists can potentially know when it is going to happen
But during their observations, the researchers also found that the electrons behaved in unexpected ways they had not theorized. That provides more incentive to keep studying magnetic reconnection, the authors write. And by understanding more about the process, scientists can potentially know when magnetic reconnection is going to happen. "If you understand the underlying physics that drives space weather, I expect you can do a better job of predicting storms," said Burch.
That means we could someday know when geomagnetic storms are going to occur, allowing us to take the necessary steps to minimize space weather's effects on our technology.