They appear to be more common around F- and G-type stars and less so around K-type stars. Hot Jupiters around red dwarfs are very rare.[14]14 Generalizations about the distribution of these planets must take into account the various observational biases, but in general their prevalence decreases exponentially as a function of the absolute stellar magnitude.[15]
Continued 09-28-2021.
On pages 61 to 63 Dole concludes it should take at least 2 billion to 3 billion years for newly formed planet to become habitable for humans. Since the breathable oxygen rich atmosphere necessary for humans is mostly produced by photosynthisis by plants, a planet can be habitable for some forms of life billions of years before it becomes habitable for humans.
Because more massive stars use up their nucler "fuel" much more rapidly, Dole finds an upper limit to the mass of a star which can shine steadly in the main sequence phase of its existence for long enough.
Dole says on page 68 that only main sequence stars less massive than 1.4 solar mass, F2V stars, can remain on the main sequence for up to 3 billions years and have planets habitable for humans. Of course more massive stars could remain on the main sequence long enough for some of their planets to develop lifeforms which don't need oxygen rich atmospheres.
Dole finds a lower mass limit for stars with planets habitable for humans. Because small changes in stellar mass cause much larger changes in stelalr luminosity, the luminosity of low mass stars is very low and their circumsteller habitable zones (which Dole calls "ecospheres") have to be much deeper into their gravity wells. Thus the gravity and tidal forces which low mass stars exert on any planets which might be in their circumstellar habitable zoens will be much stronger.
Strong enough tidal forces will slow down the rotation of a planet until it becomes tidally locked to its star. It's rotation will slow down until its rotation period equals it's orbital period around the star. One side o fheplanet will always face the star and willhave eternal day, and the other side will always face away from the star and have eternal night.
The day star will get very hot and the night side will get very cold. And it is possible that all the air and water on the planet will eventually feeze solid on the night side leaving the planet waterles, airless, and lifeless.
Dole calculated that a star with about 0.88 solar mass would start to have the the inner part of its habitable zone included in the zone of tidally locking. With less massive strs, the zone of tidal locking would fill mor and more of the circumstellar habitable zone, until with stars of 0.72 stellar mass the zone of tidal locking would fill all of the habitable zone.
On pages 71 to 72 Dole says that only stars with more about than 0.88 soar mass canhave full habitable zones, and stars with less than 0.72 solar mass (spetral class K1V) will have no habitable zone left - at least no habitable zone where the planets would not be tidally locked, and being tidally locked which might make them uninhabitable.
According ot the table mentioned above:
https://astronomy.stackexchange.com/questions/40746/how-would-the-characteristics-of-a-habitable-planet-change-with-stars-of-differe/40758#40758
A G8V star would have a mass about 0.94 solar mass, a K2V star would have a mass of about 0.78 solar mass, and a K5V star would have a mass of about 0.68 solar mass. The the orbital periods and years of planets in their EED orbits would be 280.06, 182.93, and 114.48 Earth days respecively.
Acccording to this article, a G9V star would have a mass of 0.9 solar mass.
https://en.wikipedia.org/wiki/G-type_main-sequence_star
Accoring to this article a K0V star would have a mass of 0.88 solar mass.
https://en.wikipedia.org/wiki/K-type_main-sequence_star
And according to this article a K4V star would have mass of 0.73 solar mass.
Anyway, the shortest years of any habitable planets would be in the range e of about 114 to 280 Earth days, unless it is possible for tidally locked planets to be habitable.
Since the majority of stars are class K and class M stars less massive than spectral type K1V, that would mean that the majority of stars are incapable of having human habitable planets.
So the question of whether most K class orange dwarf stars and all M class red dwarf stars can have planets with life is a big question in discussions of life in the universe.
For many years, it was believed that life on such planets would be limited to a ring-like region known as the terminator, where the star would always appear on or close to the horizon.[further explanation needed] It was also believed that efficient heat transfer between the sides of the planet necessitates atmospheric circulation of an atmosphere so thick as to disallow photosynthesis. Due to differential heating, it was argued, a tidally locked planet would experience fierce winds with permanent torrential rain at the point directly facing the local star,[21] the sub-solar point. In the opinion of one author this makes complex life improbable.[22] Plant life would have to adapt to the constant gale, for example by anchoring securely into the soil and sprouting long flexible leaves that do not snap. Animals would rely on infrared vision, as signaling by calls or scents would be difficult over the din of the planet-wide gale. Underwater life would, however, be protected from fierce winds and flares, and vast blooms of black photosynthetic plankton and algae could support the sea life.[23]
In contrast to the previously bleak picture for life, 1997 studies by Robert Haberle and Manoj Joshi of NASA's Ames Research Center in California have shown that a planet's atmosphere (assuming it included greenhouse gases CO2 and H2O) need only be 100 millibar, or 10% of Earth's atmosphere, for the star's heat to be effectively carried to the night side, a figure well within the bounds of photosynthesis.[24] Research two years later by Martin Heath of Greenwich Community College has shown that seawater, too, could effectively circulate without freezing solid if the ocean basins were deep enough to allow free flow beneath the night side's ice cap. Additionally, a 2010 study concluded that Earth-like water worlds tidally locked to their stars would still have temperatures above 240 K (−33 °C) on the night side.[25] Climate models constructed in 2013 indicate that cloud formation on tidally locked planets would minimize the temperature difference between the day and the night side, greatly improving habitability prospects for red dwarf planets.4 Further research, including a consideration of the amount of photosynthetically active radiation, has suggested that tidally locked planets in red dwarf systems might at least be habitable for higher plants.[26]
https://en.wikipedia.org/wiki/Habitability_of_red_dwarf_systems#Tidal_effects
So it is still an open question whether tidally locked planets can support liquid water using lifeforms.
I our solar system, the giant planets all orbit much farther from the Sun than the sun's habitable zone, and can be called "cold Jupiters".
And above I have mentioned "hot Jupiters", giant planets that orbit very close to their stars and are super hot.
So it is logical to assume that "warm Jupiters" exist, giant planets which orbit within the habitable zones for liquid water usinglife forms of their stars. And a number of such "warm jupiters" have been found.
Probably almost all giant planets have a lot of moons, varying greatly in size, up to in some cases moons that would be large enough to support lifeforms.
Hypothetical giant exommons orbiting around "warm Jupiters" in their star's circumstellar habitable zones could be habitable for liquid water using life. Since most moons would be tidally locked to their planets, the hypothetical giant moons of hypothetical giant planets in the habitable zones of low mass class K and class M stars would be locked to their planets and not to their stars.
So those hypothetical giant exomoons orbiting giant exoplanets in the habitable zones of low mass stars would have rotational periods which were as long as their orbital periods around the planet. Thus they would have alterations of night and day every few Earth hours or Earth days, instead of having eternal day on one side and eternal night on the other side.
So the potential habitability of exomoons in the circumstellar habitable zones of dim K and M type stars has been studied as a factor which might have a big effect on how common worlds with life are.
How long would the days of such habitable exomoons be?
Dole claims on page 60 estimated that if a planet rotated slower than once every 96 hours (4 Earth days), hte alternations of heat and cold would be too much, and the plants owuld not e able to survive thelong lightness nights.
I don't know how accurate that four day limit is, and I suppose that some lifeforms could survive longer days and nights.
"Exomoon habitabitiy Constrained by illumination and tidal heating" Rene Heller and Roy Barnes, Astrobiology, Volume 13,number 1, 2013 discusses many factors relating to potential habitability of exomoons.
https://search.yahoo.com/search;_ylt=A0geKLmXz1NhfFgAky1XNyoA;_ylc=X1MDMjc2NjY3OQRfcgMyBGZyA21jYWZlZQRmcjIDc2EtZ3Atc2VhcmNoBGdwcmlkA0g5Q0tmZUhjVFUucFpZNEdicmFKMEEEbl9yc2x0AzAEbl9zdWdnAzEEb3JpZ2luA3NlYXJjaC55YWhvby5jb20EcG9zAzEEcHFzdHIDZXhvbW9vbiBoYWJpdGFiaWl0eSBjb25zdHJhaWluZWQgYnkgaWxsdW1pbmF0aW9uIGFuZCB0aWRhbCBoZWF0aW5nBHBxc3RybAM2NgRxc3RybAM2NgRxdWVyeQNleG9tb29uJTIwaGFiaXRhYmlsaXR5JTIwY29uc3RyYWluZWQlMjBieSUyMGlsbHVtaW5hdGlvbiUyMGFuZCUyMHRpZGFsJTIwaGVhdGluZwR0X3N0bXADMTYzMjg4Mjc0MgR1c2VfY2FzZQM-?p=exomoon+habitability+constrained+by+illumination+and+tidal+heating&fr2=sa-gp-search&fr=mcafee&type=E211US105G0
In section 2. Habitability of exomoons, they say on page 3:
The synchronized rotation periods of
putative Earth-mass exomoons around giant planets could be in the same range as the orbital periods of the Galilean moons
around Jupiter (1.7d 16.7d) and as Titan’s orbital period around Saturn ("16d) (NASA/JPL planetary satellite ephemerides)4.
So they think that the orbital periods, and thus days, of the hypothetical habitable exomoons might be between 1.7 and 16.7 Earth days.
And that has some relevance to the types of star systems which such hypothetical habitable exomoons could be found in.
The next statement they make is:
The longest possible length of a satellite’s day compatible with Hill stability has been shown to be about P"p/9, P"p being the
planet’s orbital period about the star (Kipping 2009a)
So that means that the orbital period of the planet around the star has to be at least nine times as long as the orbital period of the moon around the planet, for the moon to have an orbit stable in the long term.
So the minimum orbital period for an exoplanet which has a habitable exomoon should be at least about - times 1.7 to 16.7 Earth days, or at least about 15.3 to 150.3 Earth Days.
If an exoplanet with a year 15.3 days long has to orbit in the EED of its star, the star would have to be somewhere between an M5V with an EED of 11.68 Earth days and a M2V with an EED of 36.5 Earth days
If an exoplanet with a year 150.3 days long has to orbit in the EED of its star, the star would have to be somewhere between an K5V with an EED of 114.84 Earth days and a K2V with an EED of 182.93 Earth days.
And of course a planet with a habitable exomoon could have a year much more than 9 times as long as the orbital period of the moon.
This indicates that some but not all sub classes of class M red dwarf stars could have habitable exomoons orbiting giant exoplanets in their habitable zones.
