Imaging Earth’s plasma ducts

For many decades, researchers have known that the Sun’s light ionizes the upper reaches of Earth’s atmosphere. The resulting charged particles in the ionosphere—and the even more rarefied plasmasphere above it—have a noticeable effect on impinging electromagnetic signals. Additionally, waves of plasma known as “whistler modes” have been observed for the past 50 years or so as they bounce back-and-forth between Earth’s hemispheres; thus have researchers recognized that the plasma supporting those waves is in cylindrical structures aligned with Earth’s magnetic field lines. And now the inferred “plasma ducts” have been imaged in real time, in three dimensions, and over a large swath of sky. University of Sydney undergraduate Cleo Loi, her adviser Tara Murphy, and a host of colleagues used the Murchison Widefield Array (MWA) radio telescope in Western Australia to monitor cosmically distant radio sources that backlight the fluctuating plasma. As myriad sources shifted their apparent positions due...