3 Minutes
A recent theoretical analysis indicates that ions expelled in solar flares may be heated to far higher temperatures than previously estimated, potentially reaching about 60 million Kelvin (60 million ºC, or 108 million ºF). If confirmed, this result would revise how researchers interpret flare energy budgets and remote observations of the Sun.
A massive solar flare captured by the Solar Dynamics Observatory in May 2024, with a superimposed Earth for scale. Earth is not actually that close to the Sun. (NASA/SDO)
Scientific background: why temperatures might differ
Solar flares arise when twisted magnetic field lines in the Sun's atmosphere suddenly reconnect and release large amounts of magnetic energy. That energy accelerates particles and heats plasma in the solar atmosphere, producing temperatures far above the Sun's photospheric surface (≈5,500 ºC) and even the hot corona (≈2 million ºC).
Traditional flare diagnostics infer temperature primarily from electron-driven signals, such as X-ray emission and spectral line ratios. Historically, solar physicists assumed electrons and ions equilibrate quickly and share the same temperature. The new analysis revisits that assumption by combining modern measurements, computational results, and recent findings from near-Earth space and the solar wind.
Lead author Alexander Russell and collaborators applied updated reconnection heating scalings showing that magnetic reconnection can preferentially transfer more energy to ions than to electrons. Their calculations indicate ions may be heated roughly 6.5 times more efficiently, allowing ion temperatures in flare plasma to climb to tens of millions of kelvin—potentially as high as 60 million K in some regions.
Implications for observations and space weather
If flare ions are substantially hotter than electrons, several consequences follow. First, spectral features attributed to a single temperature component could be misinterpreted, explaining long-standing anomalies in flare spectra. Second, estimates of the total flare energy and particle acceleration efficiency would need revision. Third, hotter ions could change how energetic particles escape into the heliosphere, with downstream impacts on space weather forecasting and radiation risk for satellites and astronauts.
The finding remains theoretical. The authors note that targeted observations and instrument strategies can test the prediction: high-resolution spectral imaging (from instruments like SDO, Solar Orbiter, Parker Solar Probe, and ground-based facilities such as DKIST) combined with tailored modeling can search for signatures of ion-electron temperature separation during reconnection-driven flares.
Future prospects and next steps
Confirming super-hot ions will require coordinated observations and detailed modeling linking reconnection physics to spectral diagnostics. If validated, the result will refine models of energy partition in flares and improve interpretation of remote sensing of high-energy solar phenomena. The analysis has been published in The Astrophysical Journal Letters.
Conclusion
New reconnection-based calculations suggest ions in solar flares could reach temperatures up to ~60 million ºC, significantly higher than electron-based estimates. This challenges long-held assumptions about thermal equilibration in flare plasma and motivates targeted observations to detect ion-electron temperature differences and reassess flare energy budgets.
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