Originally Posted by Ilya

Sorry, but this is so far off, it is "not even wrong". Gliese 876 is 30 times the mass of Jupiter, and Gliese 876 d orbits at 3 million km from the star's center -- 7 times farther than Io. So tidal force at Gliese 876 d's distance is 30/7³ -- about 1/10 that on Io!

Now, tidal heating depends not only on tidal force, but also on the body's orbital eccentricity. With eccentricity zero, a tidally-locked planet (which Gliese 876 d almost certainly is) experiences no tidal heating at all. Io's eccentricity is 0.0041, so its 5 km tidal buldge flexes up and down about 100 meters on every revolution, which is where heat comes from. Gliese 876 d's eccentricity is unknown, but could be as high as 0.22. If that's the case, the planet's tidal buldge cold vary by about 300 meters, thus producing 9-10 times the energy per kg as on Io. NOT 10000-100000 times! (Much greater total mass of the tidal buldge is balanced out by proportionally greater mass of the planet to absorb the heat.) But that's with 0.22 ecc. If Gliese 876 d's ecc. is significantly smaller, than its tidal heating will be much less than on Io.