Imagine a solar system similar to ours that has a star with a similar composition to the Sun and a stellar mass of 1.176 and an Earthlike planet with about 1.18 times the mass of Earth in its habitable zone. Could this planet have a day length of 26 Earth hours, an axial tilt of 0.2 degrees, and a higher eccentricity that will cause planetwide seasons that do not distinguish by hemisphere? If so, what orbital eccentricity is needed to produce this effect?

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    $\begingroup$ Why these very exact decimal values? Where have these come from? $\endgroup$
    – James K
    May 21 at 9:54
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    $\begingroup$ @JamesK They come from PM 2Ring's answer to this question. The OP appears to be playing world-building. $\endgroup$ May 21 at 11:05

1 Answer 1



Such a star would be an F8V star, It would be about twice as bright as the sun and have roughly half the life span (say up to about 4 billion years before becoming unstable.

The habitable zone of a planet would be further out, at about 1.4 AU. It could have planets of various masses, and there is no reason an Earth-sized planet could not exist (1.18 is basically the same size as Earth). It would not be tidally locked, so could have an Earth-like rotation of 26 hours.

Such a planet could have any axial tilt, from 0 to 180. That includes very small values and it could have greater eccentricity, like Mars does. Mars has an eccentricity of about 0.1 which has significant climatic effects.

The only trouble for life is that this star would be finishing its life about a billion years ago. On Earth, this was when life was just emerging from the "anaerobic slime" phase, and the first multicellular life was developing (sponges etc) Nobody knows if 4 billion years is enough time to evolve something like an orangutan or octopus.

  • $\begingroup$ Based on a sample size of one (the Earth), 4 billion years is not enough time to develop intelligent life. That would correspond to the start of the Ediacaran, maybe the start of the Cambrian. To make matters worse, this hypothetical planet would not even have 4 billion years because stars get ever more luminous as they age. I suspect this hypothetical Earth-like planet has only 2 or 3 billion years before it turns into a hypothetical Venus-like planet. $\endgroup$ May 21 at 11:15
  • $\begingroup$ @James K, intelligent life did not evolve on this planet. It was settled by humans using spaceships. I am just trying to see if such a planet could exist that humans could settle. $\endgroup$
    – Galactic
    May 21 at 23:52
  • $\begingroup$ @Galactic I suggest you find a different sized star for your world building, which means a faster orbit rather than a slower one. An Earth-like at the state of the Earth 500 million years ago would not be all that habitable to humans. Life was very primitive and only lived in the oceans back then. $\endgroup$ May 22 at 15:53
  • $\begingroup$ @DavidHammen, plant and animal species from Earth were introduced there. $\endgroup$
    – Galactic
    May 25 at 1:47

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