Could a moon of similar size to the Earth orbiting a gas giant be tidally locked compared to its host planet? What effect would that have on the moon, especially the biosphere?

  • 2
    $\begingroup$ Tidal locking of a moon still results in a day/night cycle on the moon. Your main problem will be having a quick enough orbital period without being inside the Roche limit. But, Io for instance has a sidereal 'day' length of 1.7 Earth days while still being tidally locked. $\endgroup$
    – Samuel
    Commented Mar 7, 2018 at 0:04
  • $\begingroup$ "Could a moon of similar size to the Earth orbiting a gas giant be tidally locked" Sure, at the right distance. "What effect would that have on the planet?" Since the Moon is so tiny compared to gas giants... not much. $\endgroup$
    – RonJohn
    Commented Mar 7, 2018 at 0:04
  • $\begingroup$ I meant the moon, typo. $\endgroup$ Commented Mar 7, 2018 at 0:12
  • 1
    $\begingroup$ There are a large number of questions about tidally locked moons. I'm sure there's more than one that this question is effectively a duplicate of. $\endgroup$
    – sphennings
    Commented Mar 7, 2018 at 2:22

1 Answer 1


First Question:Yes, as Samuel and RonJon points out, Io is a moon orbiting a gas giant that is tidally locked to a gas giant Jupiter.

Second Question: As for the effects to the moon that is tidally locked (like Io is to Jupiter). As far as I can tell, heat! Neil Degrasse Tyson wrote a piece about Tidal Forces which are responsible for Tidal Locking and should shed some light on what we can expect as side effects.

When the Moon flexes Earth's oceans, they simply slosh back and forth. But when a Jupiter-sized tidal force acts upon a nearby solid body, then the internal stress can become a prodigious source of heat. In one of the more timely and impressive predictions in the history of space probes, Stanton Peale of the University of California and collaborators published a paper in 1979 titled, Melting of Io by Tidal Dissipation. Later that year, images sent by the Voyager 1 space craft revealed extraordinary volcanic activity, complete with mountain calderas and plumes.

The two quick and dirty rules for figuring out how much heat your moon will receive are:

  1. Closer the moon is to the planet -> MORE HEAT
  2. Smaller the moon, the more the gas giant will affect the moon via gravity -> MORE HEAT

(As you can see by comparison, a moon the size of earth would be quite large) is a]


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