Discussion in 'science, nature and environment' started by Santino, Nov 6, 2018 at 11:27 AM.
Or are all gas giant moons tidally locked?
even a tidally locked moon could potentially have a band of habitable area alike a girdle around its fat waist. Presumably the moons of Jupiter are out because of the hard radiation pouring off the big red yin
Ok, I'll rephrase - could a gas giant moon be an Earth-like planet, with a day and night approximately like our own? Assuming that the parent planet was in the habitable zone of the star system.
It's possible if the moon was massive enough and/or far enough orbit from the gas giant. Depending also on the age of the moon.
Day night cycles would be irregular unless the moons orbit was off the solar plane. Planet-rise would be awesome.
Tidal locking happens to every orbiting body eventually; it's just a matter of time. The larger the moon the quicker it happens, so even with a distant orbit, an Earth-sized moon would probably lock well before intelligent life could evolve.
If the orbit is eccentric, you can have an integer ratio of day:year like Mercury's 3:2, which could help shorten your day, but you're still talking about days lasting hundreds of hours at best. And if your gas giant has many moons, they'll tend to regularise each other's' orbits to being very circular.
The orbit round the gas giant would give it a day night. Its entirely plausible for a super jupiter "cold gas giant" to be in orbit near where the Earth and to have an Earth sized moon or perhaps captured planet. There would be a possible issue with the Roche Limit that would take some number crunching. The one downside is it would be a "bullet magnet" for bolides unless something bigger further out was doing the Jupiter job of sweeping everything up. Magnetic fields and charged particles could be an issue. Tidal forces would give it some interesting weather, but they would also ensure it was very seismically active.
Mercury's day/night cycle is a massive headfuck. Although it rotates on it's own axis three times for every two trips round the sun, if you were standing on Mercury you'd only observe one 'day' every two years.
This is all very disappointing.
Dunno about that, I'm genuinely impressed with the sheer knowledge here. Over the moon, even.
Why do you need day and night to support human-like life? If anything the fact that we evolved so that our brain has to shut down, reconfigure and reboot for at least a quarter of each day strikes me as weird. It wouldn't be surprising if we discovered something with a brain (or similar) that could actually function constantly would it?
I just want a planet that is like Earth, but orbits around a gas giant, with relatively normal days and nights.
Yeah, not like you're asking for the moon.
Oh come on. Brexit won't be that bad.
Thanks to tidal flexing and friction, if you are lucky:
If we terraformed a planetoid of Earth size, and set it spinning to give it c. 24 hour days around a gas giant in the right region of a star system, how long before it became tidally locked?
Given a particular set of circumstances, it's possible for a gas giant moon to be reasonably hospitable to life-as-we-know it. Some observations:
1) This moon would need to orbit a "hot Jupiter", that is a gas giant nearer to its star than Jupiter is to our Sun, so that the moon can receive enough solar radiation to render it temperate. Interesting effect: "midnight-at-noon" cooling effect on the planet-facing side of the moon when it is eclipsed by the gas giant for an hour or two during the moon's midday, orbital geometry permitting.
2) Tidal locking is virtually assured. But there is still a "day" - that is a sunrise/sunset cycle - its duration is determined by the orbital period of the moon about the giant. For instance, Mimas, a moon of Saturn, circles Saturn once every 23 hours. Standing anywhere on Mimas, you would see the sun rise and set during a 23 period. On the face of a moon facing "outwards", you would never see the gas giant, and experience a reasonably normal diurnal cycle.
But the planet-facing side would be spectacular.
Standing in the middle of the planet-facing side: the gas giant would be permanently directly overhead, half its disk illuminated at local sunrise, fading away to unilluminated during the noon eclipse, and then growing to half-a-disk at sunset. Then the lightshow starts: by midnight the full disk of the gas giant is shining overhead, thousands of times brighter than our full moon. This planet-facing side would never know true darkness - the gas giant would always be there, at a fixed point in the sky, cycling through its phases.
3) The moon would need to be near enough to Earth-sized - which is not impossible: Ganymede and Titan, the biggest moons of Jupiter and Saturn respectively, each possesses a radius a respectable 40% of the Earth's.
Fields and particles
4) For the required benign radiation environment: either the gas giant does not possess formidable Jupiter-type radiation belts, or the moon lies outside such belts, or the moon itself has a sufficiently powerful magnetic field to protect its surface from the Primary's radiation belts.
5) A much more complicated, and eventful environment than Earth's. Here, >99.9% of heat input comes from the Sun (the rest is geothermal seepage). On a hypothetical exomoon, the daily eclipse blocks some solar energy, while the huge night-time disc of the gas giant contributes reflected solar heat as well as light. And then there is tidal flexing - a big feature of Jovian moons, making for a hot subsurface and lots of seismic activity.
Also tidal friction and radiogenic heating and maybe a small input from primordial heat to consider too.
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