Our Sun is a dynamic star, constantly bombarding Earth with charged particles that cause auroras and geomagnetic storms. Now, a team of researchers has discovered that an energetic burst from the Sun disrupted Earth’s magnetic field for two hours in 2023.
The event occurred on April 24, 2023, when a coronal mass ejection (CME), an explosion of solar radiation from the Sun, struck the Earth. CMEs typically travel faster than the Alfvén speed, i.e. the speed of magnetic field lines in the plasma.
But that wasn’t the case late last April, when NASA’s Magnetospheric Multiscale Mission observed an Alfvén speed faster than a CME heading toward Earth. The mission detected the energy flow of electrons and ions, as well as changes in electron density, as the solar phenomenon passed by. The CME caused Earth’s bow shock, a shock wave that normally forms when it strikes Earth’s magnetic field, to disappear over a two-hour period between 8:30 a.m. and 10:30 a.m. EST. The team’s analysis of this surprising solar phenomenon was published last week. Geophysical Research Letters.
“Earth’s bow shock disappears, leaving the magnetosphere directly exposed to the cold CME plasma and the powerful magnetic fields from the solar corona,” the study authors wrote in the paper. “Our results show that the magnetosphere changes from a typical windsock-like shape to one with wings that magnetically couples Earth to the Sun.”
These structures, called Alfvén wing auroras, acted as highways transporting plasma between the Sun and Earth’s magnetosphere, according to a statement from the American Geophysical Union. The team noted that Alfvén wing auroras could occur on Earth and could be observed in future studies.
“The wing is a highway for Earth’s plasma to escape to the Sun, and also for plasma emanating from the ends of the Sun’s erupted magnetic flux ropes to reach the Earth’s ionosphere,” the team added. “Our study shows the highly dynamic generation and interaction of the wing filaments and sheds new light on how sub-Alfvén plasma winds affect astrophysical objects in the Solar System and other stellar systems.”
CMEs should not be confused with solar flares, which are brilliant phenomena that can cause geomagnetic storms on Earth. As EarthSky explains, both solar flares and CMEs are caused by a rearrangement of the Sun’s magnetic field, which releases energy into space. While solar flares are bright flashes of light on the Sun’s surface, CMEs release magnetized particles into space, sometimes towards Earth.
“The connection between the Sun and Earth through the Alfvén wing is similar to that between Jupiter and Ganymede,” the team added, suggesting that the auroras on Jupiter’s moon Ganymede could be formed by a similar Alfvén wing path.
Further observations may reveal how the Sun’s powerful outburst affects other objects in its cosmic neighborhood, but as far as the Earth’s magnetic field is concerned, for now everything is back to normal.
