I want ten Earth-years long day on my planet. Can I have it?

I need ten Earth years long day-night cycle on my planet.

Hemera is a world I am creating as a setting for my story. Name comes from Greek deity - personification of Day. Needs of storytelling have precedence, but I would like my world to be more or less plausible.

Hemera is a very slowly rotating planet. So slow that people and animals can migrate without haste and keep the local sun in one point above their head. It's a bit smaller than Earth "“ 12 000 km diameter, that gives 37 680 km on the equator. Axial tilt is close to zero to keep things simple (it may change).

The most important point: nomads living on Hemera's mid latitudes (around latitude 45°) have to move around 5 km per 24 hours in east-west direction to stay in one time zone. 45th parallel is 18 840 km long, so I need planetary day to have 3768 Earth-days. In other words one Hemera day is more than 10 Earth years long.

How long should I make planetary year? It cannot be as long as hemerian day "“ it would make my world tidally locked. I don't' want that. Not to mention so long or longer orbital year would put Hemera somewhere around Jupiter in terms of distance from the local sun and everything would froze. So it must be shorter.

Are there any interactions between planetary rotation and orbital period that can change the length of daylight (for example as it is in case of Venus and Mercury)?

Other things:

The planet started slowly rotating and is obviously rather old and on its way to be tidally locked in future. That would mean local star is also rather older and hotter. So the world can be further away than Earth. Actually it can mean that Hemera is just only now moving into its biological prime time. Because of very slow spin oceans have migrated toward poles. Equatorial bulge is slowly sinking and the whole planet is returning to more spherical shape but it's a very slow process. There's a wide belt of high desert land around the equator and there are two big polar oceans which transport heat around the planet making mid-latitudes liveable. Maybe even nice place to live. It looks a bit like this, but Hemera has more land: https://www.reddit.com/r/MapPorn/comments/10dbw6/a_map_of_the_worldif_the_earth_did_not_spin/

Climate: there will be hotspot that moves from east to west and it will be unpleasantly hot. But there will be long Afternoon and Morning, each longer than two Earth-years with climate. Life has adjusted and there are be two big groups: migrators travelling around the world and stay-at-homes: fast grass like growers that manage to grow again between waves of migrating grazers, armored trees that can withstand five year nights, burrowers and hibernators in case of animals.

Equatorial desert belt cuts planet in two and creates two different environments. Animals and plants on northern and southern hemisphere can be very different.

Can such slowly rotating planet has a moon? It would stabilize climate. If not a pair of captured asteroids will do for making sky interesting during long night.

posted almost 4 years ago

Zjerzy‭

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