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For story reasons, I'd like one planet habitable, plausible, but in some noticeable way older than Earth. Just not all planets are 4,5 bilion years. Tidally locked planet that orbit red dwarf, saves me from problem of stellar evolution and shifting habitable zones.

1) I should give it less fissile isotopes, there would be clearly less U-235 in relation to U-238 what would affect local nuclear sector.

2) Less radioactive isotopes -> colder core -> weaker magnetic field.

3) colder core -> less active surface, avoid any really high, recently formed mountains

4) Adjust for atmospheric loss, which can be measurable by assessing ration of hydrogen and deuterium

What else should I realistically adjust? How old I can make this planet not to have to worry about early metal-poor universe?

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  • $\begingroup$ What does the age have to do with the amount of metal? $\endgroup$
    – Xandar The Zenon
    Dec 22, 2016 at 3:14
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    $\begingroup$ @XandarTheZenon in astronomy, all elements aside from hydrogen and helium are referred to as "metals". These elements were all originally formed in the core of early stars (everything up to iron) or in the supernovae of said early stars (up to uranium). The first generation of stars, and thus the first generation of stellar systems, would have been formed from just hydrogen, so there would have been no heavier elements to form rocky planets with. Rocky planets require heavier elements, and thus at least one generation of earlier stars has to have exploded. $\endgroup$
    – Salda007
    Dec 22, 2016 at 7:21

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Without a magnetic field, it's hard to have nice things.

  • As the strength of the planet's magnetic field decreases, the amount of solar radiation and charged particles that reach the surface will increase. Global temperatures will rise as the magnetic field dies.
  • Radiation powers the evaporation of water, driving the water cycle. Weather will be more erratic and severe due to this.
  • The water cycle is responsible for erosion. Therefore, as solar radiation increases, the rate of erosion on the planet will increase. With no tectonic forces to build the land back up as a result of the dying core, the world will begin to smooth out into a hot, steamy, marshy environment.
  • In the long term, the planet is doomed. Some speculate that in addition to having low gravity, Mars lost its atmosphere and oceans due to solar winds. It couldn't keep out charged particles because it did not have a strong magnetic field, so the atmosphere was stripped, and water slowly evaporated into space. Expect something like this to happen after a billion years or so.
  • Organisms will evolve or perish in response to the above factors / climate change.
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  • $\begingroup$ @Christoph What makes you think humans will still be around in millions of years, let alone billions of years? $\endgroup$
    – user
    Dec 22, 2016 at 8:59
  • $\begingroup$ @Zxyrra When the magnetic fields deflects particles, one of two things happen: they are attracted to and hit the poles or they are deflected out into space and a equal and opposite force is applied to the iron dynamo in Earth's core. The energy of those particles is still getting to the Earth. I don't think your first assumption is correct without further evidence. $\endgroup$
    – kingledion
    Dec 22, 2016 at 14:16
  • $\begingroup$ @kingledion Energy on the surface will be more consequential in this situation that in the core $\endgroup$
    – Zxyrra
    Dec 22, 2016 at 15:57
  • $\begingroup$ @kingledion To elaborate, the net force does not change, but warming the surface as opposed to the core will have these effects. $\endgroup$
    – Zxyrra
    Dec 22, 2016 at 17:48

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