Scientists have unlocked a vital clue in a solar mystery that has intrigued astronomers, including the great Galileo, for some 400 years.
Research suggests that the process that generates the sun's magnetic field - known as the solar dynamo - begins much nearer the star's surface than previously thought, and happens for unexpected reasons.
Pinpointing the process's starting location and understanding its evolution could help improve solar storm forecasting, researchers say.
These explosive eruptions from the magnetic field can trigger auroral displays - such as the northern lights - and, on rare occasions, damage satellites and electricity grids.
Centuries-old mystery
Astronomers have for centuries studied tell-tale signs of the sun's magnetic activity. The Renaissance polymath Galileo Galilei made the first detailed observations of sunspots - dark patches caused by changes in the sun's magnetic field - in 1612 using early astronomical telescopes of his invention.
The solar dynamo converts energy from the sun's roiling, super-hot plasma into a powerful magnetic field. While the sun is known to go through 11-year cycles during which solar activity grows increasingly intense, nearly all the detail about what happens below the surface - including the starting point of the solar dynamo - has remained unclear for centuries.
Previous research suggested the dynamo process begins at the bottom of a deep ocean of churning gasses more than 130,000 miles below the surface. Now, mathematical modelling using a NASA supercomputer by a team led by the University of Edinburgh indicates the process originates relatively nearer to the surface, some 20,000 miles below.
They found that strong winds near the solar surface drive the creation of magnetic fields through a process that previous theories had overlooked, called the magnetorotational instability, which also occurs around black holes and young planetary star systems.
Impact on Earth
The most powerful solar storm known to have hit Earth was the so-called Carrington Event in 1859, which damaged the fledgling telegraph system and caused striking worldwide auroral displays. A storm of similar intensity would wreak havoc on Earth today, the team says, given that so many aspects of modern life depend on electricity. A similar storm in 2012 missed Earth by only nine days.
However, with enough warning about incoming solar storms - which can reach Earth in as little as 15 hours - engineers could take steps to prevent catastrophic damage to electronics networks, they add.
The solar dynamo is the oldest unsolved problem in theoretical physics; it's absolutely fascinating. We know the dynamo acts like a giant clock with many complex interacting parts, but we don't know all the pieces or how they fit together.
Knowing how something starts is essential to understanding and predicting it. My colleagues and I have been working out the details of these ideas for 20 years, it's very satisfying to see the model fit nicely with observational data.
We found a new idea about how the sun's dynamo happens, which was quite unexpected but makes a lot of sense in the context.
The team paid tribute to Professor Keith Julien of the University of Colorado Boulder, who was part of the study for many years and passed away after its completion.
The research, published in the journal Nature, was funded by NASA. It involved the University of Colorado Boulder, Massachusetts Institute of Technology, Northwestern University, University of California Santa Cruz, Bates College, and the Flatiron Institute, in the US.
