In a lot of science fiction, including Star Wars and Star Trek, the many alien worlds which have life and often are habitable by human beings, include some which are described as 'moons", presumably meaning natural instead of man made satellites of planets.
And maybe that is because many people might feel disappointed that Earth's moon is airless, waterless, and lifeless, and so like to imagine that some moons might be habitable.
Scientists who theorize about life on other worlds are also interested in the possibility of habitable moons.
Because a small change in the mass of a main sequence star causes a much bigger change in its luminosity, the habitable zones where planets can have liquid water around small stars is very close to those stars, and so any planets in the habitable zones of thsoes stars would experience very strong gravity and tidal forces from their stars.
The most common type of stars, red dwarf stars, are so dim that planets in their habitable zones would have to be so close and experience so strong stellar tides that they would become tidally locked to their stars, with one side always facing the star and having eternal day and the other side always facing away from the star and having eternal night.
And there is considerable uncertainty and controversy whether such tidally locked planets could be habitabel.
But if a giant planet and its moons happen to be within the habitable zone of a dime red star, each of the moons would be tidally locked to the much closer planet instead of the star. So each side of the moon would have alternations of day and night as the moon orbited the planet, avoiding the eternal day and night of a world tidally locked to its star. And so a large enough moon of a giant planet inside the habitable zone of their star could possibly be habitable, making it possible for the most common type of stars to have habitable worlds.
Any moon large enough to be habitable for life on its surface, let alone for humans and other lifeforms that need oxygen rich atmospheres, would be a planetary mass object, or a planemo.
Most astronomical objects, asteroids, comets, and smaller moons, are not massive enough for their gravity to pull them into rounded, roughly spherical shapes. Those objects massive enough to be pulled into spheroidal shapes are planetary mass objects.
In our solar system planetary mass objects include the 8 planets, and the objects classified as dwarf planets, and a dozen or two of the moons.
Planets and thus planetary mass objects, can only get up to about 13 times the mass of Jupiter, (which is 317.8 times the mass of Earth) or about 4,131.4 times the mass of Earth, give or take tens or hundreds of Earth masses. Objects between about 13 Jupiter masses and about 75-80 Jupiter masses are classified as brown dwarfs. Objects more than about 75 or 80 Jupiter masses are classified as stars.
It is uncertain whether brown dwarfs form the way that planets do or the way that stars do,or both ways.. Brown dwarfs have been found in star systems with stars, and also floating by themselves in interstellar space.
If brown dwarfs form the same way that planets, including giant planets with moons, form, many borwn dwarfs should have objects orbiting them, formed the same way the moons of giant planets form. If brown dwarfs form the same way that stars form, including stars with planets, many brown dwarfs should have objects orbiting them, formed the way planets form.
If planets orbit stars, and moons orbit planets, what should objects that orbit browndwarfs be callled? If orbjects which orbit brown dwarfs are classified as moons, that would greatly increase the number of objects classified as moons, and thus greatly increase the number of habitable worlds classified as moons.
I have seen estimates that the number of habitable exomoons in the Milky Way Galaxy might equal the number of habitable planets. And if hypothetical habitable worlds orbiting brown dwarfs are not counted in those estimates, it is possible that there might b emany more habitable "moons"if satellites of brown dwarfs are counted as "moons".
So a series like Star Trek, where some of the habitable worlds are moons instead of planets, is not using using bad science or aviolating any laws of nature, so long as those habitable moons are depicteding with scientific realism.
And maybe that is because many people might feel disappointed that Earth's moon is airless, waterless, and lifeless, and so like to imagine that some moons might be habitable.
Scientists who theorize about life on other worlds are also interested in the possibility of habitable moons.
Because a small change in the mass of a main sequence star causes a much bigger change in its luminosity, the habitable zones where planets can have liquid water around small stars is very close to those stars, and so any planets in the habitable zones of thsoes stars would experience very strong gravity and tidal forces from their stars.
The most common type of stars, red dwarf stars, are so dim that planets in their habitable zones would have to be so close and experience so strong stellar tides that they would become tidally locked to their stars, with one side always facing the star and having eternal day and the other side always facing away from the star and having eternal night.
And there is considerable uncertainty and controversy whether such tidally locked planets could be habitabel.
But if a giant planet and its moons happen to be within the habitable zone of a dime red star, each of the moons would be tidally locked to the much closer planet instead of the star. So each side of the moon would have alternations of day and night as the moon orbited the planet, avoiding the eternal day and night of a world tidally locked to its star. And so a large enough moon of a giant planet inside the habitable zone of their star could possibly be habitable, making it possible for the most common type of stars to have habitable worlds.
Any moon large enough to be habitable for life on its surface, let alone for humans and other lifeforms that need oxygen rich atmospheres, would be a planetary mass object, or a planemo.
Most astronomical objects, asteroids, comets, and smaller moons, are not massive enough for their gravity to pull them into rounded, roughly spherical shapes. Those objects massive enough to be pulled into spheroidal shapes are planetary mass objects.
In our solar system planetary mass objects include the 8 planets, and the objects classified as dwarf planets, and a dozen or two of the moons.
Planets and thus planetary mass objects, can only get up to about 13 times the mass of Jupiter, (which is 317.8 times the mass of Earth) or about 4,131.4 times the mass of Earth, give or take tens or hundreds of Earth masses. Objects between about 13 Jupiter masses and about 75-80 Jupiter masses are classified as brown dwarfs. Objects more than about 75 or 80 Jupiter masses are classified as stars.
It is uncertain whether brown dwarfs form the way that planets do or the way that stars do,or both ways.. Brown dwarfs have been found in star systems with stars, and also floating by themselves in interstellar space.
If brown dwarfs form the same way that planets, including giant planets with moons, form, many borwn dwarfs should have objects orbiting them, formed the same way the moons of giant planets form. If brown dwarfs form the same way that stars form, including stars with planets, many brown dwarfs should have objects orbiting them, formed the way planets form.
If planets orbit stars, and moons orbit planets, what should objects that orbit browndwarfs be callled? If orbjects which orbit brown dwarfs are classified as moons, that would greatly increase the number of objects classified as moons, and thus greatly increase the number of habitable worlds classified as moons.
I have seen estimates that the number of habitable exomoons in the Milky Way Galaxy might equal the number of habitable planets. And if hypothetical habitable worlds orbiting brown dwarfs are not counted in those estimates, it is possible that there might b emany more habitable "moons"if satellites of brown dwarfs are counted as "moons".
So a series like Star Trek, where some of the habitable worlds are moons instead of planets, is not using using bad science or aviolating any laws of nature, so long as those habitable moons are depicteding with scientific realism.
