(this is doublet of my previous question, so I did a little improvement on it)

-my exomoon is around size of venus, but a little bit smaller.

  • is very windy, so windy in fact filter feeders thrives in it air.
  • have a day and night cycle around 1 year long. -however it have almost zero axial tilt
  • the plant life obtained blue leaves
  • very tectonicaly active, so much so the sea in this planet resemble a connected mega lakes.
  • 1
    $\begingroup$ There are too many questions here. The more questions should be rewritten into their own questions. $\endgroup$ Feb 25 at 0:47
  • $\begingroup$ Indeed.. and suggest to remove the second one :) A picture can be nice, nicer, nicest.. for someone.. and for another one, some other picture would look more realistic (you ask reality-check) so it would become opinion-based and you'd never have ONE answer that is best. The first question is more appropriate for WB ! put the plant-life question in the title.. your tag reality-check is enough to get plausible answers. $\endgroup$
    – Goodies
    Feb 25 at 1:29
  • $\begingroup$ thanks for suggestion $\endgroup$
    – faddllz
    Feb 25 at 1:53
  • 2
    $\begingroup$ Related but not a duplicate worldbuilding.stackexchange.com/questions/720/… $\endgroup$ Feb 25 at 2:14
  • $\begingroup$ Nice find ! Keltshk's answer is a great opportunity, to change just a little thing.. magnesium deficit $\endgroup$
    – Goodies
    Feb 25 at 18:36

3 Answers 3


Simple answer is "not very plausible," but in an infinite universe, the improbable becomes the inevitable.

For a moon to be that volcanically active, it would need to either be very young (<100M years), or regularly squished by tidal forces of other moons (like Io). Both of these would make it difficult for it to have a thick atmosphere, but would make for strong winds.

This is a moon, not a planet, so a 1 year day/night cycle suggests that it rotates that much compared to the star its planet orbits. If its body is wracked by tidal forces, then you can guarantee that it's tide-locked to its planet, so it would have to orbit the planet once per earth year. There are moons of Saturn with an orbital period that long, but they're all airless rocks, and absolutely NONE of them are close enough to other moons to cause tidal force heating.

Let's go outside the realm of probability and say that we once had a planet with thriving life that got destroyed, and a huge chunk of the planet's ocean spun off as an ice moon/asteroid/comet. The ice froze before all of the elemental bits of life could decay. A billion years later, it enters a new star system and hits this other moon, maybe only 2-4x its size. This melts much of the moon's crust and covers it with a thick layer of water vapor atmosphere, and provides panspermia style fertilization.

Let's further posit that the planet it revolves around is a few times larger than Jupiter, generating enough heat to keep this planet warm while life evolves. The impact could adjust the rotation and orbit of the moon so that it has counter-rotation: it's nearly stable pointed at the star, but orbits the planet once every 60 hours or so. Thus, the planet would rise and set every 60 hours, but the star would stay stable in the sky for a long time. This would also explain a lot of the tidal heating.

Blue leaves is the easy part. Just presume that this planet's equivalent to chlorophyl absorbs red and green instead of red and blue. Chemically speaking, there's nothing magical about that.

Overall, highly improbable, but only the panspermia part is more improbable than the hypothesized Theia/Earth impact a few hundred million years after Earth's birth.


One massive hurdle here is the year-long night cycle. Back in the year 536 AD, cultures around the world recorded what turned out to be the longest night in recorded history; around a year and a half, during which an estimated 80% of the population died, people resorted to cannabilism, and in general, this paradise of a world became a cold hell. It's impossible to know how many species of living organisms went extinct during that time period, though apparently everything we see today was able to survive.

The plants would have to be well-equipped to deal with both the extreme heat built up during the summer(day) and the extreme cold built up over the winter (night). The animals here on Earth are already equipped for that, as are many of the plants, but anywhere near the equator the plants are rather unable to survive the cold, and only a few species of tree and moss are able to survive the long nights of our northern and southern extremities. With the nightly plant die-off/dormancy, the animals will have a hard time foraging and likely will almost entirely have to be omnivores. Just some things to consider.

Your other questions are covered nicely by these other answers, so I'll leave them alone.


I find it hard to even start thinking about this scenario, as even some definitions are vague and stand in the way of modelling it. But let me try to disassemble some of it and maybe it will answer your question.

First Venus sized exomoon. It surprised me, but at the moment there is not an universally accepted definition on moon - planet system and binary planet system. In fact by some definitions even Earth-Moon system is in fact binary planet system, but I digress. One that seems to be fairly popular and makes an intuitive sense is the definition by barycenter, I.E. if the barycenter in within the radius of the planet, the other object is a moon, if it is outside, it is a binary planet system. This means that for a Venus like planet you need a fairly big primary planet my napkin math points to some gas giants or similarly massive rock planets.

One thing that will cause most troubles I think, is your 2nd condition. IF we use the Sun for our solar system, AND we need to stay within Goldilocks zone, then for a year log day night cycle, we will need our planet moon combo to be essentially tidally locked with sun. And tidally locked Goldilocks planet is not a great place of life to evolve. Any thriving takes place at the twilight zone which moves around the planet around the year.

Good news is, that you will have plenty of wind, as the air at the sunlit side gets heated up and rises, which pull the cold air from the sunset side giving you ever-present low altitude extreme winds towards the point of the moon that experiences high noon and at the same time high altitude winds towards the cold side of the planet.

In general tidal locking takes place AFTER the molten core of the planet solidifies, so this might be a problem, but it is apparently not a rule, so there can be some plate tectonics.

As with sees, the tidal locking would make the ocean situation very stable, and depending on your crust shape, I don't see why you couldn't have mega lakes. They would however be shifting quite a lot depending on whether they are facing the sun and evaporating rapidly or point away from sun and are frozen solid.

As for blue colored plant live, I honestly don't know hot to even guess. I would assume some fast growing weed/moss just might grow fast enough to stay within the twilight zone and keep shifting around the year, but ... this it too theoretical even for me

TLDR: Venus like exomoon- Plausible, windy- very plausible, year day night cycle - plausible, blue plant life - no idea, tectonic activity - plausible, giant lake-like oceans - no idea.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .