Is IO tidally locked with Jupiter?

Answer 1

Yes. But it is still experiencing strong tidal forces due to the eccentricity of the orbit around Jupiter (the orbit is very elliptic because of orbital resonance Io has with Ganymede and Europa (the other two satellites are closest to Io regular and periodic, so even they exert a small pull on Io, the influence over time is large )). Simply put, in one orbit, Io is twice close to and twice significantly further from Jupiter. That puts Io in different gravitational potential gradient (how the gravitational pull changes over distance ). When it is close to Jupiter the gravitational pull difference between the side facing Jupiter and the opposite side elongates Io toward Jupiter. When furthest away that gravitational pull difference is smaller, so the deformation is much smaller. That continuous squeezing (like a balloon) is the tide Io is experiencing and that's what generates heat and makes it so volcanic.

Hope it helps.

Answer 2

Yes, Io is tidally locked with Jupiter, meaning that Io's rotation period is synchronous with its orbital period around Jupiter. This causes the same side of Io to always face Jupiter. The intense gravitational forces from Jupiter and its other moons create tidal heating on Io, leading to volcanic activity and a geologically active surface.