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The Death of the Sun

  1. Mar 26, 2015 #1
    So I am working on making a simulation that shows the habitable zone of our solar system from now until our sun reaches the end of it's red giant phase. The sun will die when it is 10 billion years old and will reach the end of the red giant stage at 5 billion years. I know the habitable zone will be between 50-70 AU at the end of this timeline and the sun will be 256 times bigger than it is now, but how long will Earth to leave a habitable zone? Also, does anyone know how quickly the sun will increase in radius during it's red giant phase? Before it dies, it will be 1.37 it's current size. How will the sun change from now until then in terms of luminosity and temperature?
  2. jcsd
  3. Mar 26, 2015 #2
    The Sun will become a red giant 7.1 billion years from now and a white dwarf 7.8 billion years from now. See this
  4. Mar 26, 2015 #3


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    This movie at the Mesa site has a huge amount of data on the evolution of the sun. You can single step through it and see what happens. The current sun is where log_L crosses zero, about log_star_age = 9.52. I think there is some offset from the current age of the sun, because it takes some time to enter the main sequence. By log_star_age = 9.65 ( about 1.1 billion years from now), log_L will be 0.083, meaning the sun will be about 20% more luminous than today. This may already be enough to make the Earth uninhabitable. In any case, it is clear the Earth will be uninhabitable long before the sun becomes a Red Giant.
  5. Mar 27, 2015 #4
    You might also find this video of interest-

  6. Mar 27, 2015 #5
    Oh wow, I never knew about an eruption that would engulf Mars. Wow this is going to be much more difficult than I thought.
  7. Mar 28, 2015 #6


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    Earth will probably only enjoy bathing in the solar habitable zone for ~1 billion years - with or without human induced 'global warming'. In any case, infrastucture probably deserves more attention than fitting emission control devices on livestock asses and barbeque grills. Pardon my sarcasm.
  8. Apr 6, 2015 #7
    The luminosity of the sun will increase faster than its radius.

    L = 4πr2σT4

    r = The radius of the star, in meters;
    σ = The Stefan-Boltzmann constant, with a value of 5.670373(21) × 10−8 W m−2 K−4; and
    T = Effective surface temperature of the star, in Kelvin.​

    As a result, the habitable zone will gradually be pushed further away from the sun as it ages.

    In another ~1.1 billion years, the sun's luminosity will be 10% greater than it is now, while the sun's radius will only have increased by 5%. According to Kopparapu et al. (2014), that would put Earth right at the inner edge of the conservative habitable zone (0.997 AU).

    To make things even more complicated, as the sun ages it will also lose mass. Which means that the orbits of all the planets will gradually be extended outward, away from the sun.

    Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass - arXiv : 1404.5292v2 [PDF]
    Last edited: Apr 6, 2015
  9. Apr 7, 2015 #8


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    It is widely agreed the earth will become unpleasant for humans in about a billion years. Hopefully, we will learn how to migrate, or adapt by then. Based on our level of advancement thus far, I feel comfortable we will succeed - assuming we manage to avoid self destruction.
  10. Apr 7, 2015 #9
    All complex life with be gone long before a billion years have lapsed. In about a billion years is when the mean surface temperature of the planet reaches ~100°C. When the mean surface temperature reached between 35°C and 40°C 250 million years ago it killed off ~90% of all complex life, so we probably only have another ~500 million years or so. :nb)

    Assuming we eventually get off this rock, one or two of the moons of Saturn or Jupiter might be a nice place to hang out for awhile.
    Last edited: Apr 7, 2015
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