A new study suggests that the Sun’s spicules, spike-like geysers of plasma, may not be individual jets but an optical illusion created by complex three-dimensional curtains of plasma, while also identifying giant plasma tornadoes that could help explain why the corona is much hotter than the surface.
A team from the University of Newcastle, Indian Institute of Astrophysics, and University of Sheffield has used computer simulations to propose a new understanding of the Sun’s spicules, potentially millions of which may be present across the Sun at any given time and shoot into the solar atmosphere at tens of kilometres per second before collapsing back down after a few minutes.
Spicules have long been treated as individual, two-dimensional spikes, like miniature plasma tornadoes. The researchers’ model, run with a tool called Pencil Code, suggests they may instead be an optical illusion. The simulations show that acoustic pounding from churning granules of plasma beneath the Sun’s surface launches magnetohydrodynamic waves along magnetic field lines. As these waves travel into thinner gas, they grow into huge bow shocks. When the shock waves break, they blast part of the atmosphere upward, creating giant, rippling curtains of plasma thousands of kilometres into the Sun’s atmosphere.
From a telescope viewing the edge of the Sun, the overlapping folds of these curtains appear as a single line, a spicule. The apparent movement of spicules could simply be the curtains swaying and curling over time.
The team found support for the model in data from the Interface Region Imaging Spectrograph (IRIS) and the Hinode satellite, both of which had recorded spicules undergoing motions that matched the simulated behaviour of a twisting curtain.
A separate but related discovery emerged from the same simulation. Automated vortex-detection algorithms identified giant columns of rotating plasma, hundreds of kilometres across and spinning at up to twenty kilometres per second, which the researchers named Coronal Swirling Conduits, or CoSCos. Two formation pathways appeared in the model: one from snapping and breaking magnetic field lines, a process already suspected to contribute to coronal heating, and another at the edges of the spicule curtains, where large pressure and density differences generate baroclinic vorticity, similar to the way ocean breezes and warm inland air stir coastal weather on Earth.
The model suggests that as the spicule curtains lose energy and drift back to the surface, the tornadoes they kicked up pull the plasma back up into the corona, providing energy that heats the region and powers the solar wind. Observations of rotating bunches of spicules from Hinode and IRIS are consistent with regions where CoSCos should exist.
Many aspects of the process remain unknown. Newer solar observatories such as Solar Orbiter and the Parker Solar Probe may offer further clues.
Analysis
Why This Matters
- The coronal heating problem, why the Sun’s outer atmosphere is millions of degrees hotter than its surface, is one of the longest-standing puzzles in solar physics. This study proposes a new mechanism for how energy is transported into the corona.
- If confirmed, the reinterpretation of spicules as an optical illusion would change how decades of solar observations are analysed.
- Understanding the Sun’s magnetic environment has practical implications for predicting space weather that can affect satellites and power grids on Earth.
Background
Spicules are jets of plasma that shoot up from the Sun’s surface at speeds of tens of kilometres per second, each lasting only a few minutes. They have been observed for decades and were thought to be individual, straw-like structures. The region above the Sun’s surface, the corona, is paradoxically much hotter than the surface itself, a mystery known as the coronal heating problem. Previous research has considered various mechanisms, including nanoflares and magnetic wave heating, but no single explanation has won consensus.
What to Watch
- Observational data from the Parker Solar Probe and Solar Orbiter, which capture the Sun at higher resolution and from different angles, could test whether the predicted curtain structures appear in real images.
- If IRIS or Hinode data can be re-analysed with the new curtain model, additional matches between simulation and observation may strengthen the case.
- Whether the Coronal Swirling Conduits can be directly observed, perhaps as rotating signatures in spectroscopic data, will be a key next step.
Checked
12 claims in this story checked against 1 source: 12 supported.
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- SupportedThe study challenges the view of solar spicules as individual plasma jets.Universe Today: “The paper calls that into question. Instead of two dimensional spikes, it provides evidence that spicules might actually be an optical illusion created by complex three dimension “curtains” of plasma.”
- SupportedThe researchers propose that spicules may be an optical illusion created by plasma curtains.Universe Today: “it provides evidence that spicules might actually be an optical illusion created by complex three dimension “curtains” of plasma.”
- SupportedThe study identifies giant swirling conduits that could help heat the corona.Universe Today: “CoSCos pull spicular sheet plasma back up from the surface into the corona, powering the solar wind and providing energy that heats the area. Or at least that’s how it works in theory.”
- SupportedThe research team is from the University of Newcastle, Indian Institute for Astrophysics and University of Sheffield.Universe Today: “a team of researchers from the University of Newcastle, Indian Institute for Astrophysics, and University of Sheffield”
- SupportedThere may be millions of spicules across the Sun at a time; they travel at tens of kilometres per second and collapse back after a few minutes.Universe Today: “Spicules are spike-like geysers of plasma that shoot up into the solar atmosphere at tens of kilometers per second, eventually collapsing back down towards the surface after a few minutes. [...] potentially millions of them at any given time across the entire surface of the Sun.”
- SupportedThe simulations propose that acoustic pounding from churning solar granules launches magnetohydrodynamic waves along magnetic field lines, which grow into bow shocks and blast atmosphere upward.Universe Today: “That pounding launches the equivalent of sound waves up into the atmosphere itself - though in this case, they are magnetohydrodynamic waves that directly follow magnetic field lines. As they travel higher, the gas surrounding them gets thinner, and they grow into huge bow shocks.”
- SupportedViewed from the Sun’s edge, overlapping folds of the plasma curtains appear as a single spicule.Universe Today: “if a telescope was looking at the edge of the Sun, the integration of those folds made it appear like a single line - a spicule.”
- SupportedIRIS and Hinode data showed spicule motions that matched the simulated curving, twisting curtain.Universe Today: “when the data was lined up with simulated data from the model, those bizarre motions matched well with a curving, twisting curtain.”
- SupportedThe researchers’ algorithms identified CoSCos as rotating plasma columns hundreds of kilometres across, spinning at up to 20 kilometres per second.Universe Today: “these are huge whirlpools hundreds of kilometers across, rotating at up to twenty kilometers per second. The scientists named them Coronal Swirling Conduits, or CoSCos.”
- SupportedOne proposed CoSCo formation pathway is the snapping and breaking of magnetic field lines, which the source calls a primary suspect in coronal heating.Universe Today: “One is created when magnetic field lines snap and break in the solar atmosphere. That snapping and breaking is a primary suspect in the coronal heating mystery”
- SupportedA second proposed pathway is at spicule-curtain edges, where pressure and density differences generate baroclinic vorticity.Universe Today: “A second creation path is tied to the edges of the spicule curtains - they are much denser than the “void” that makes up most of the rest of the corona, causing huge pressure and density differences along their edges. That mismatch generates something called baroclinic vorticity”
- SupportedThe model proposes that tornadoes pull plasma back into the corona, providing heat and powering the solar wind as the curtains lose energy and fall back.Universe Today: “as the spicule curtains themselves begin to lose energy and float back down to the surface, the massive tornadoes they kicked up will actually pull them back up into the corona. [...] powering the solar wind and providing energy that heats the area.”
