Three Dimensions, No New Telescope

There is a particular frustration in knowing that the answer is there, encoded in the light, and being unable to read it. For decades, solar physicists have understood that the Sun's corona—the million-degree atmosphere that produces solar wind, flares, and coronal mass ejections—is shaped by magnetic fields. They have known that these eruptions, when they reach Earth, can disrupt satellites, radio communications, and power grids. But measuring those fields directly has remained out of reach. Until now, a team has found a way to extract a three-dimensional picture of the coronal magnetic field from observations that were already sitting in the archive.

The research, led by Alin Paraschiv of the National Solar Observatory and involving the National Science Foundation's National Center for Atmospheric Research and the Southwest Research Institute, used data from the Mauna Loa Solar Observatory in Hawaii. Rather than building a new instrument, the team applied a novel mathematical technique called IQUD inversion to observations from two generations of coronagraphs, CoMP and UCoMP . The method combines information about the polarization of infrared iron lines, which reveals the orientation of the magnetic field, with the motion of Alfvén waves—plasma oscillations whose speed depends on the field's strength—to reconstruct the field's missing component along the line of sight .

The result is the first global three-dimensional estimate of the coronal magnetic field, including regions beyond the Sun's visible edge. Daniela Lacatus of NSF NCAR described it as overcoming a bottleneck that had persisted for decades: the strength and direction of the field in the corona can now be determined wherever MLSO observations are available . Paraschiv framed the achievement in terms of what it does not require. For the first time, he said, we can begin to see the Sun's hidden magnetic structure in three dimensions not by building a new ground-based or space-based instrument, but by deciphering the light and waves the corona already emits .

The maps are not yet a routine product. For each pixel, the inversion returns four possible solutions, with ambiguities in the sign of the field components along the line of sight and vertical direction. For visualization, the team resolved this ambiguity qualitatively, using an algorithm that favors spatial consistency with neighboring pixels, but they are explicit that this does not replace a full physical disambiguation method . The temporal resolution is also limited, requiring roughly an hour of observations to analyze the wave motions . These are limitations, not failures. They are the normal boundaries of a new technique.

What makes the work significant is not only what it reveals but what it enables. The coronal magnetic field is the driver of space weather, and understanding its structure is essential for improving predictions of when and where eruptions will occur. Until now, models of the coronal field have relied primarily on extrapolating from measurements of the Sun's surface, a process that carries assumptions and uncertainties. Direct estimates, even preliminary ones, offer a way to test and refine those models .

The team has released the software and datasets, hoping the community will test the method, find its weaknesses, and improve it. The next step is integration into operational pipelines, particularly the future COSMO network of coronagraphs that will replace the current MLSO . Tom Berger, director of MLSO, noted that the observatory's data are pioneering the development of solar eruption forecasting capabilities, and that COSMO's coronagraphs will fill a critical gap in observations of the Sun's magnetic field .

There is something fitting about the way this discovery arrived. The Sun has been emitting the information all along. The waves have been moving through the corona, the polarized light has been traveling to Earth, and the instruments have been recording it for years. What was missing was the method to read it. That method now exists, and the Sun's hidden structure is beginning to come into view.

Image note: The visuals in this article were generated using artificial intelligence and do not represent actual solar observatory data or imagery.

Sources: NSF National Center for Atmospheric Research, National Solar Observatory, Phys.org, Scinexx, NV Techno