Understanding why the Sun’s corona—the outer layer of its atmosphere—reaches temperatures of millions of degrees Celsius while its surface remains relatively cool has puzzled scientists for over seven decades. Now, an international team of researchers has made significant strides in solving this long-standing mystery, providing crucial insights into solar dynamics.
The new study, published in Nature Astronomy in March 2024, presents the first clear evidence of small-scale torsional Alfvén waves across the corona. These waves twist through magnetic fields and play a vital role in transporting plasma upward from the Sun’s surface, where temperatures hover around 5,500 °C (approximately 10,000 °F), to the superheated corona.
Until now, researchers had only detected larger, isolated Alfvén waves associated with solar flares. The existence of smaller Alfvén waves had been theorized but not directly observed. This groundbreaking discovery was facilitated by advanced imaging techniques from the US National Science Foundation’s Daniel K. Inouye Solar Telescope in Hawaii, renowned for its ability to capture high-resolution images of solar activity.
High-Resolution Imaging Reveals New Insights
The telescope’s instruments allow scientists to track the motion of solar plasma, which consists of charged particles, with remarkable precision. By observing the movement of superheated iron, which emits bluer light as it approaches Earth and redder light as it moves away, the researchers successfully isolated the torsional motions of the Alfvén waves.
physicist Richard Morton from Northumbria University in the UK emphasized the significance of this breakthrough: “This discovery ends a protracted search for these waves that has its origins in the 1940s. We have finally been able to directly observe these torsional motions twisting the magnetic field lines back and forth in the corona.”
Morton explained that the prevailing motion of plasma in the Sun’s corona had previously obscured these torsional movements. He developed a method to filter out the swaying motions, allowing the team to reveal the twisting dynamics that are critical to understanding the corona’s temperature and behavior.
Implications for Solar Research and Space Weather Forecasts
These findings not only illuminate the mechanisms that heat the corona but also provide insights into solar winds that can affect Earth, potentially disrupting satellite networks and power systems. The small-scale torsional Alfvén waves could contribute to the forces necessary for these solar winds to escape the Sun’s gravitational influence, as well as help maintain the extremely high temperatures of the corona.
Being able to visualize and accurately model these processes enhances the ability to forecast space weather. Improved predictions of geomagnetic storms could offer advanced warnings for events that might impact technology on Earth.
As future research delves deeper into the mechanisms and distributions of these small Alfvén waves across the corona, scientists aim to rigorously test other theories about solar dynamics. Morton noted, “This research provides essential validation for the range of theoretical models that describe how Alfvén wave turbulence powers the solar atmosphere. Having direct observations finally allows us to test these models against reality.”
This culmination of decades of inquiry marks a pivotal moment in solar science, offering new tools and perspectives for understanding one of the most powerful forces in our solar system.
