# life on a gas giant moon in the habitable zone? **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2012, 4:27pm UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206 "2012-11-16T16:27:16Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [November 16, 2012, 4:27pm UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/1 "2012-11-16T16:27:16Z")
So we’re now finding an awful of of exoplanets, most of which are gas giants. Quite a few of those are in the goldilocks zone that could allow liquid water. So whats the implications for life on moons of gas giants in the habitable zone? Especially for it being a stable enough long term environment for intelligent life and a civilization to evolve? Am I right that a moon needs to be pretty close to earths size in order to maintain a dense atmosphere? Could intelligent life evolve and survive in a much less dense atmosphere on a small moon? Whats the chance’s of earth size moons being around gas giants in the HZ? How bad is the radiation from gas giants for the chances of life evolving and surviving long term? Is a moon around a gas giant in the HZ likely to be more or less protected from cataclysmic asteroid or comet impacts than the earth is? What about plate tectonics / tidal forces on the moon from the gas giant? Bonus question, how would evolving on a gas giant moon effect any civilization that did arise? I imagine that assuming the gas giant has lots of moons like ours do, that astrology and astronomy would be even more important in religion and culture. Lots of questions… anyone? ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [November 16, 2012, 9:34pm UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/2 "2012-11-16T21:34:19Z")
> [@coremelt](#): > > Bonus question, how would evolving on a gas giant moon effect any civilization that did arise? I imagine that assuming the gas giant has lots of moons like ours do, that astrology and astronomy would be even more important in religion and culture. I suspect their Copernicus would have an easier time of it. It would likely be easier to deduce and confirm (and convince the powers that be if needed) that the other moons were orbiting the planet while therefore the other planets were orbiting the sun. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 16, 2012, 10:30pm UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/3 "2012-11-16T22:30:59Z")
Find Stephen Dole’s “Habitable Planets for Man” from the Rand Corp, about late 1960’s. The thought would be: (a) the moon would be tidally locked to the planet, so it would perpetually hand in the sky in pretty much one place. (b) the implication then is very long days, but it beats being tidally locked to the sun, where probably the atmosphere would freeze on the dark side and the front would bake. © Are these planets gas giants? The thought is that the gas giants are in the zone where the sun was not providing enough warmth to boil off the more volatile hydrogen and helium over the billenia. (d) would the side facing the planet, which gets an eclipse every “day”, be significantly cooler? Take note from Mars - it either lost or never got an atmosphere - IIRC about 1/100th Earth sea level pressure - due to size, since its gravity is 40% of earth. OTOH, maybe a moon would have a decent amount of extra atmosphere catching some of the blow-off from the mother planet. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [November 17, 2012, 1:02am UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/4 "2012-11-17T01:02:41Z")
> [@md2000](#): > > Find Stephen Dole’s “Habitable Planets for Man” > (c) Are these planets gas giants? The thought is that the gas giants are in the zone where the sun was not providing enough warmth to boil off the more volatile hydrogen and helium over the billenia. Thanks, the ebook is available for free here: [http://www.rand.org/pubs/commercial\_books/CB179-1.html](http://www.rand.org/pubs/commercial_books/CB179-1.html) Are they Gas giants? Well here’s an example HD10180 g is a neptune sized exoplanet smack straight in the habitable zone around a very sun like star 127 light years away. [http://exoplanet.hanno-rein.de/system.php?id=HD+10180+g](http://exoplanet.hanno-rein.de/system.php?id=HD+10180+g) > **[Rich exoplanet system discovered](https://www.bbc.co.uk/news/science-environment-11070991)** > > Astronomers discover a planetary system containing at least five planets orbiting a star much like our Sun. As far as I know gas giants can exist at any distance from the star, by migrating from where they originally formed. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 17, 2012, 2:22am UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/5 "2012-11-17T02:22:43Z")
Mars’ scarcity of atmosphere is due more to its lack of magnetic field than to its mass. Earth and Mars both have atmospheres much thinner than what would be expected, though for different reasons. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [November 17, 2012, 2:50am UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/6 "2012-11-17T02:50:12Z")
thanks Chronos, any comments on the other questions? Wild speculations welcome. ---
**Author:** ![brujaja](https://avatars.discourse-cdn.com/v4/letter/b/4af34b/32.png) [@brujaja](https://boards.straightdope.com/u/brujaja)\ **Post date:** [November 17, 2012, 8:47am UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/7 "2012-11-17T08:47:08Z")
If the earth-like moon was tidally locked to the gas giant, then what happens in its oceans? It seems to me that orbiting without rotating would have the oceans acting completely differently than oceans do on Earth. Also, it would fundamentally change the nature of weather. Depending what extremes would result from these conditions, it would have to have a significant impact on culture. Also, having a great big planet all the time in the sky would be awesome. I’m just sayin’. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [November 17, 2012, 10:24am UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/8 "2012-11-17T10:24:50Z")
> [@brujaja](#): > > If the earth-like moon was tidally locked to the gas giant, then what happens in its oceans? Good question. Also, the day-night cycle is going to be long, any moon that was in too close orbiting fast would be deep in the radiation field of the planet. Could intelligent life evolve with a 30 day long day/night cycle? Maybe with some kind of hibernation mechanism. What about with a 7 day one? ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [November 17, 2012, 2:03pm UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/9 "2012-11-17T14:03:28Z")
> [@coremelt](#): > > Good question. Also, the day-night cycle is going to be long, any moon that was in too close orbiting fast would be deep in the radiation field of the planet. Could intelligent life evolve with a 30 day long day/night cycle? Maybe with some kind of hibernation mechanism. > > What about with a 7 day one? It sounds like a job for Poul Anderson. 🙂 ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [November 17, 2012, 2:20pm UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/10 "2012-11-17T14:20:29Z")
There would still be tides on a tidally-locked moon of a gas giant in the habitable zone, but they would be caused by the (local) sun, not by the planet. The length of day for such a moon would depend on how far it was from the planet, and on the mass of the planet itself. The greater the mass of the planet, the shorter the orbital period around it for any particular orbital radius. To get a reasonably short day length you need a massive planet, or a small orbital radius, or both. Another problem could be the magnetic field of the gas giant; if it is anything like the one around Jupiter, there would be a vast flux of charged particles trapped in the field, impinging on the planet’s outer atmosphere. Perhaps the moon could have a magnetic field of its own, which might make the surface (or part of the surface) more habitable. Tidal heating from interactions with other moons could be problematic, and might raise the temperature of a temperate moon too much (but this heating could possibly raise the temperature of a colder moon into habitability). Some calculations show that there is a limit to the mass of a moon around a gas giant, and that an Earth-sized moon would be unlikely; but it seems entirely possible to me that such moons will occur on occasion, although they might not be all that common. WIKIPEDIA article on the subject here; > **[Habitability of natural satellites](https://en.wikipedia.org/wiki/Natural_satellite_habitability)** > > The habitability of natural satellites describes the study of a moon's potential to provide habitats for life, though is not an indicator that it harbors it. Natural satellites are expected to outnumber planets by a large margin and the study is therefore important to astrobiology and the search for extraterrestrial life. There are, nevertheless, significant environmental variables specific to moons. > It is projected that parameters for surface habitats will be comparable to those of planets lik... ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [November 17, 2012, 6:42pm UTC](https://boards.straightdope.com/t/life-on-a-gas-giant-moon-in-the-habitable-zone/641206/11 "2012-11-17T18:42:42Z")
> [@Chronos](#): > > Mars’ scarcity of atmosphere is due more to its lack of magnetic field than to its mass. Earth and Mars both have atmospheres much thinner than what would be expected, though for different reasons. [Earth, Venus and Mars are all losing their atmospheres at similar rates](http://www.space.com/11187-earth-magnetic-field-solar-wind.html) (somewhat greater for Mars but mainly due to its size; Venus doesn’t have a magnetic field either); the magnetic field deflects the solar wind but doesn’t deflect it completely; rather, it is funneled into the polar regions: > [@](#): > > Essentially, the solar wind interacting with the Earth’s magnetic field transfers some of its energy into the upper atmosphere in the polar regions. The auroras that are visible at high latitudes are one manifestation of this transfer. But it also heats up atmospheric ions enough that they escape up out of the poles, forming Earth’s “polar ion outflows.” > > “The magnetic field is an obstacle to the solar wind, but it is also a funnel,” Strangeway says. The effect of the solar wind on Earth is less uniform than on Mars and Venus, but apparently the net loss rate is about the same. Also, the loss rate for Earth and Venus currently isn’t that high, equivalent to less than 4 inches of water (as oxygen ions, assuming twice as much hydrogen is lost) over 3.5 billion years; it was probably higher, possibly much higher, earlier, especially for Mars.