When Your Sun Behaves Badly

A future Earth with no Sun in Hodgson’s classic.  This edition published by Pan Books 1973.  Cover design by Robert LoGrippo.

A future Earth with no Sun in Hodgson’s classic. This edition published by Pan Books 1973. Cover design by Robert LoGrippo.

Our Sun is essential for life on Earth – our very existence depends on it.  So if there is any doubt as to whether it is likely to continue to provide its life-giving properties, that should be a matter of considerable concern to us.  These are among the issues we tackle in Odyssey 38, which has just been issued.

We have had some slight nervousness on this score in the past.  Back in the 1960s, Davis and Bahcall’s experiment in the Homestake Mine in South Dakota was measuring the rate of neutrinos coming from the Sun against what was expected from the theory as it then stood.  There were nowhere near enough being detected.

One suggested reason was disturbing – both photons and neutrinos are produced by nuclear fusion reactions at the centre of the Sun but, whereas photons scatter and take thousands of years to escape from the solar surface, neutrinos interact weakly and escape immediately.  Therefore, although we now see photons from nuclear reactions which occurred long ago, the lack of neutrinos could have been evidence that those reactions were running down, or had stopped entirely.  And one day, before too long, the Sun would go out.

Fortunately, there was a happier explanation.  The experiment measured only electron-neutrinos, whereas these particles could change to muon-neutrinos or tau-neutrinos whilst travelling to the Earth, and they wouldn’t be detected by the equipment.  So sighs of relief all round.  The major point of difference was that the theory had previously been based on neutrinos having no mass, and so could not change type, whereas it was subsequently identified that they do have mass and could change.  Progress in science is often very comforting.

But the worrying idea of the Sun failing us runs deep, and has often been used as a basis for fantastic fiction, particularly when written at a time prior to knowledge of nuclear fusion, when it was assumed that the Sun was powered by combustion which could, in due course, run out.  William Hope Hodgson’s 1912 novel The Night Land envisages a far distant Earth where the Sun has gone out and only the remains of geothermal power enable the remnants of the human race to survive in the gigantic Last Redoubt, where they are besieged by unknown beings.  Greg Bear paid homage to Hodgson’s extraordinary story in his 2008 novel City at the End of Time.

In any event, we know that eventually (in around five billion years or so) the supply of hydrogen in the Sun’s core will be depleted by the nuclear fusion reactions occurring there, and it will expand into a red giant before finally collapsing back into a white dwarf, rendering the Earth uninhabitable if it survives at all.  So, sooner or later, changes in the Sun will determine the fate of our planet anyway, though the thought of it turning off anytime soon, whilst extremely unlikely, will always be a rather more disturbing prospect.

So join us in the latest edition of Odyssey in thinking about some of the scenarios, from both fact and fiction, where our Sun might not demonstrate quite the equilibrium we would wish.  Let’s face it, we do rely heavily on it maintaining its nice, stable existence.

Richard Hayes, Assistant Editor (Odyssey)

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