I am writing a novel about what it will be like on earth 500 or so years before the death of our Sun. The Sun is heating up gradually and one day that will negatively affect life on Earth. I know that we are a long ways away from the heat being to much to permit life though. That being said, the novel is more about the social/political/religious ramifications of living in such a time. I still am very interested in making it as relatable and understandable as possible.

Is there any causal mechanism (hypothetically or imaginatively possible) that could cause the sun to heat up faster than it is at present? This could be internal (something collapses and the increase in core pressure speeds up the reaction rate of hydrogen fusion) or external (something impacts the sun with enough extra mass to increase net g, thus increasing pressure in the core).

If not a causal mechanism, maybe something you can think of that current science/ scientists could have missed/ aren't taking into account in their models that, if true, would mean the sun is going to be much hotter, much sooner than we thought.

Thank you so much for your help! I am pretty passionate about writing and I am only an amateur in the subject of astronomy. I'm hoping some brilliant minds can help me flesh out this idea to make it more concrete.

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    $\begingroup$ I'm voting to close this question as off-topic because this question seems more suited to Worldbuilding SE. $\endgroup$ – StephenG Feb 8 '19 at 7:12
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    $\begingroup$ The Sun will become too hot for life on Earth long before it turns into a red giant. And it will survive as a red giant for billions of years before it "dies" as a white dwarf. See en.wikipedia.org/wiki/… $\endgroup$ – PM 2Ring Feb 8 '19 at 7:44
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    $\begingroup$ I'm voting to close this question as off-topic because the Help Centre says off-topic includes "Questions that are purely hypothetical, for example a question such as 'Could a black hole destroy the universe' or 'What if our solar system had two suns' (however, feel free to visit World Building)." $\endgroup$ – Chappo Hasn't Forgotten Monica Feb 8 '19 at 11:29
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    $\begingroup$ @peterh read the question! It's off-topic to ask "what it will be like [living] on earth 500 or so years before the death of our Sun", and your answer, while a good summary of recent science about neutrinos, doesn't actually explain how neutrinos could represent a "causal mechanism [that] would mean the sun is going to be much hotter, much sooner than we thought." Are you seriously suggesting that a neutrino discovery could change the timeframe for evolution to a white dwarf from 8 billion years to, say, one billion years from now? [Noting that even this wouldn't fit the OP's story plot.] $\endgroup$ – Chappo Hasn't Forgotten Monica Feb 8 '19 at 12:16
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    $\begingroup$ OP- Thank you all for the feedback! I agree, this Q is off topic for this stack exchange. I'm new to this community and was looking for a place where I thought the science experts would be. After exploring, I found world building and have moved the Q there. However this answer was very helpful. Exactly what I was looking for. It gave me a time period at which the story could take place and a different outcome could occur based on real uncertainties. Thank you @peterh. $\endgroup$ – Dan Feb 8 '19 at 13:34

The Solar Neutrino Problem

The solar neutrino problem concerned a large discrepancy between the flux of solar neutrinos as predicted from the Sun's luminosity and measured directly. The discrepancy was first observed in the mid-1960s and finally resolved around 2002.

The flux of neutrinos at Earth is several tens of billions per square centimetre per second, mostly from the Sun's core. They are nevertheless hard to detect, because they interact very weakly with matter, traversing the whole Earth as light does thin air. Of the three types (flavors) of neutrinos known in the Standard Model of particle physics, the Sun produces only electron neutrinos. When neutrino detectors became sensitive enough to measure the flow of electron neutrinos from the Sun, the number detected was much lower than predicted. In various experiments, the number deficit was between one half and two thirds.

The problem is practically solved today. It wasn't so until $\approx$ 2002. However, a little chance that we know something not enough well, still exists, but it is little.

The currently accepted solution of the problem is this: yes, we know the Sun enough well, but the neutrinos can change flavor on the way they reach us. Thus, for example, if an electron-neutrino becomes muon-neutrino, then the detectors capable to see only electron-neutrinos, won't detect it.

It is today a hot research topic in the particle physics, thus some surprising result in the future isn't yet closed out. The main problem is that the neutrino practically don't interact with anything (a light year of lead would stop half of them), so there are only very little possibilities to measure their properties.

The KATRIN neutrino experiment

KATRIN is a German acronym (Karlsruhe Tritium Neutrino Experiment) for an undertaking to measure the mass of the electron antineutrino with sub-eV precision by examining the spectrum of electrons emitted from the beta decay of tritium. The core of the apparatus is a 200-ton spectrometer. In 2015, the commissioning measurements on this spectrometer were completed, successfully verifying its basic vacuum, transmission and background properties. The experiment began running tests in October 2016. Regular measurements started 2018-06-11, with a projected duration of 5 years.

As far I know, too much surprising results aren't expected from this - most likely, the electron neutrino mass of some tenths of eV will be found, or possible the result will be that the experiment is not enough precise to find anything. (In this case, we will still get an "upper limit").

However, there is a little chance that some surprising result will happen.

For example, such a neutrino mass could be found, which can be explained only by some hyphotetical effect (like sterile neutrinos, which might also contribute to the solution of the dark matter problem).

The idea

Go back to the 80ties, where a possible solution to the solar neutrino problem was a different working and internal structure of the Sun, which looks the same for us, but generates lesser neutrinos. By analogy, a similarly different Sun should be expected, which goes into a red giant phase soon. (Or, at least its luminosity will increase enough in the near future to make the Earth inhabitable).

Note, we also know a lot of other stars today, there are very good models running on big computers, and these are enough sophisticated to close this possibility out with a good probability. Thus, the Sun should be somehow exceptional on these results.

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    $\begingroup$ How this is supposed to answer the Q? $\endgroup$ – Alchimista Feb 8 '19 at 11:00
  • $\begingroup$ @Alchimista The question asks for the most reasonable causal mechanism (on our current knowledge), which could cause a serious heating up of the Sun in the near future. After some thinking, I think this is that. I am surprised on your comment, I think it is well comprehensible in the answer. How is it unclear? I am fully open to clarify/extend/improve it. $\endgroup$ – peterh - Reinstate Monica Feb 8 '19 at 11:15
  • $\begingroup$ Why would you try to improve an answer on an off-topic question? $\endgroup$ – Chappo Hasn't Forgotten Monica Feb 8 '19 at 11:27
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    $\begingroup$ I really don't understand. Perhaps you wanted to say that we don't know Sun very well so that it could get hotter or go red giant even before than somehow expected? Something like "we currently aren't sure of the timescale future evolution of Sun and as such a fictional novel can pose it warmer or bigger without much problems"? $\endgroup$ – Alchimista Feb 8 '19 at 13:31
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    $\begingroup$ This answer is signifcantly less plausible than, say, "Romulans planted a gold-pressed dilithium bomb in the center of our sun." $\endgroup$ – Carl Witthoft Feb 8 '19 at 15:14

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