From Robert Nield
Recent measurements of the solar wind, which seem to show a strong correlation with the solar neutrino flux, suggest that a revolution in astrophysics may be at hand (New Scientist, Science, 12 August).
Fusion in the solar core cannot fluctuate as rapidly as the putative variations in neutrino flux and solar wind unless the fusion reactions are driven by an altogether different process – perhaps an electromagnetic mechanism such as chaotic rotation of magnetic fields in the core.
The hypothesis that fusion is not, and has never been, the main source of solar energy could be tested by comparing the present abundance of helium-4 in the Sun with the initial abundance five billion years ago, known to be about 25 per cent by mass.
The Sun has been shining steadily for at least four billion years (enabling life on Earth). It is therefore easy to show that, if fusion alone has been responsible for the solar energy output up to the present time, the helium-4 enhancement must now be at least 4.5 per cent by mass. The current abundance therefore cannot be less than 29 to 30 per cent.
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The amount of helium-4 in the core could be estimated, using solar seismology, from acoustic wave velocities. The big question is whether such measurements agree with the expected 20 to 30 per cent mass fraction. Clearly, if a significant discrepancy exists, fusion cannot be the only or even the main source of solar energy.
