Scientists in China have demonstrated a laboratory process that could help explain why the Sun's outer atmosphere, or corona, is hundreds of times hotter than its visible surface. The experiment, published in Physical Review Letters, used lasers to create plasma structures that brought magnetic fields together, releasing energy in a way that mimics a possible trigger for the nanoflares thought to heat the corona.
The Sun's visible surface has a temperature of about 5,500 °C, while the corona can exceed a million degrees Celsius. The reason for this discrepancy has puzzled scientists for decades.
Researchers led by Wei Sun at the China Institute of Atomic Energy and Yongli Ping at Beijing Normal University investigated how small energy releases on the Sun might begin. Scientists suspect that countless tiny flares, called nanoflares, could collectively help maintain the corona's temperature.
At the Shenguang-II laser facility in Shanghai, the team fired four overlapping laser pulses, each lasting a billionth of a second, at a plastic target with a finely rippled surface. The pulses turned material from the target into plasma. As the plasma expanded into the surrounding air and slowed down, ripples at the boundary grew into finger-like and mushroom-shaped structures, a behaviour known as the Rayleigh–Taylor instability.
The plasma generated its own magnetic fields around the fingers, with neighbouring structures carrying fields in opposite directions. Computer simulations showed how the expanding fingers brought those fields together, allowing magnetic reconnection to occur and heat the surrounding plasma.
For comparison, the researchers repeated the experiment with a flat plastic target, which produced a smoother plasma flow. By analysing X-rays emitted by the plasma, they estimated the electron temperature. With the rippled target, the peak electron temperature reached the equivalent of roughly 820,000 °C, nearly double the value measured with the flat target.
A separate computer simulation that prevented magnetic fields from forming showed that the extra heating largely disappeared, further supporting the role of magnetic reconnection.
On the Sun, similar conditions could arise where relatively cool, dense plasma falls through the surrounding atmosphere, a phenomenon called coronal rain. This could create boundaries where the instability develops.
The experiment gives scientists a way to investigate processes that are too small and fast to observe clearly on the Sun. The laboratory plasma was much denser, and the process unfolded on a much shorter timescale than in solar nanoflares. The researchers compared key physical ratios to assess which aspects could apply to the corona, but the setup did not recreate the Sun's full buildup of magnetic energy.
The findings support a mechanism that could help heat the corona. Further observations and experiments will be needed to establish how often it operates on the Sun and how much of the heating it supplies.
Analysis
Why This Matters
- The coronal heating problem has been one of the Sun's biggest mysteries for decades. This experiment provides a concrete, testable mechanism that could contribute to the solution.
- Understanding coronal heating has implications for predicting space weather, which can affect satellites, power grids, and communications on Earth.
- The laboratory approach offers a controlled way to study plasma processes that are otherwise too small and fast to observe directly on the Sun.
Background
The Sun's corona, its outermost atmospheric layer, reaches temperatures of over a million degrees Celsius, far hotter than the visible surface below. Scientists have proposed several possible heating mechanisms, including nanoflares, magnetic waves, and magnetic reconnection. Nanoflares are tiny, frequent explosions that could collectively release enough energy to heat the corona. This experiment investigates one potential trigger for such nanoflares involving the Rayleigh–Taylor instability, a process seen when a dense fluid pushes into a less dense one. The same instability occurs in supernova explosions and fusion experiments.
What to Watch
- Whether future solar observatories, such as the Solar Orbiter or the upcoming Solar observatories, can detect direct evidence of Rayleigh–Taylor instability on the Sun associated with coronal rain.
- Follow-up laboratory experiments at different plasma densities and magnetic field strengths to test how efficiently the mechanism heats plasma under solar-like conditions.
- Theoretical models that incorporate this mechanism into coronal heating simulations to estimate its overall contribution.
Checked
10 claims in this story checked against 1 source: 8 supported.
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- Partly supportedThe experiment may reveal how the Sun’s corona stays so hot.ScienceAlert: “Researchers in China have now demonstrated a process in the laboratory that could help explain some of that heat.”
- Partly supportedScientists in China demonstrated a laboratory process that could help explain why the corona is much hotter than the Sun’s visible surface.ScienceAlert: “Researchers in China have now demonstrated a process in the laboratory that could help explain some of that heat.”
- SupportedThe experiment used lasers to create plasma structures that brought magnetic fields together, releasing energy as heat in a way that could trigger nanoflares.ScienceAlert: “Growing structures in laser-produced plasma brought magnetic fields together, allowing magnetic energy to become heat.”
- SupportedThe researchers published the experiment in Physical Review Letters.ScienceAlert: “The research has been published in Physical Review Letters .”
- SupportedThe visible surface is about 5,500 °C and the corona can exceed a million degrees Celsius.ScienceAlert: “The visible surface is around 5,500 °C, while the outer atmosphere, called the corona, can exceed a million degrees Celsius.”
- SupportedScientists suspect countless nanoflares could collectively help maintain the corona’s temperature.ScienceAlert: “Scientists suspect that countless tiny flares , called nanoflares, could collectively help maintain the corona's temperature.”
- SupportedThe researchers fired four overlapping laser pulses, each lasting a billionth of a second, at a finely rippled plastic target.ScienceAlert: “the researchers fired four overlapping laser beams at a plastic target with a finely rippled surface at the Shenguang-II laser facility in Shanghai. The pulses lasted a billionth of a second”
- SupportedWith the rippled target, peak electron temperature reached roughly 820,000 °C, nearly double the value measured with the flat target.ScienceAlert: “With the rippled target, the peak electron temperature reached the equivalent of roughly 820,000 °C. The value measured with the flat target was about half as high.”
- SupportedA simulation that prevented magnetic fields from forming showed that the extra heating largely disappeared.ScienceAlert: “In a separate computer simulation that prevented magnetic fields from forming, the extra heating largely disappeared”
- SupportedSimilar conditions could arise on the Sun where relatively cool, dense plasma falls through the surrounding atmosphere, a phenomenon called coronal rain.ScienceAlert: “On the Sun, similar conditions could arise where relatively cool, dense plasma falls through the surrounding atmosphere. This phenomenon, called coronal rain, could create boundaries where the instability develops.”
