Yang et al. 2020
The outermost layer of the sun, called the corona, is extraordinarily difficult to study, but now researchers have made the first map of its magnetic field. This will help us predict solar flares that potentially threaten Earth.
The plasma – a hot, ionised state of matter – that makes up the corona is incredibly tenuous, which is why it isn’t visible with the naked eye except during a total solar eclipse. That tenuousness, along with the brightness of the disk of the sun, also makes it tough to measure.
Steven Tomczyk at the US National Center for Atmospheric Research in Colorado and his colleagues used a ground-based instrument called the Coronal Multi-channel Polarimeter to block out the light from the sun’s disk so the fainter corona wasn’t lost in its glare. This allowed the team to measure the density of its plasma. They also measured the speed of waves that move through the corona like ripples on the ocean.
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The waves are caused by magnetic fields, and their speed is dependent on the plasma density and the magnetic field strengths, so those measurements allowed the researchers to calculate the magnetic field strength across the corona. They found it was between 1 and 4 gauss, which is more than 10 times weaker than the magnetic field of a typical refrigerator magnet.
“These are very small magnetic fields, but they’re important nonetheless,” says Tomczyk. “The magnetic fields can get twisted and tangled and they can cause eruptions, which can be impactful to Earth, to satellites, GPS systems, power grids.”
The researchers hope that now that we can map the corona’s magnetic field, we can work on understanding the processes that lead to eruptions which blast charged particles towards Earth that can damage our satellites and power grids. Once we understand those processes, we may be able to predict the eruptions, which will help us protect our technology.
Journal reference: Science, DOI: 10.1126/science.abb4462
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