Tidal heating

An astrobiologist at UW-Seattle claims that the "habitable zone" (where water can be liquid) around red dwarfs isn't quite as large as you'd guess from naive luminosity estimates, because the planets have to orbit so close to the cool star that tidal forces will heat the planet's core. As the planet rotates different parts get squeezed (the popular article fails to mention that, btw), and friction heats the rock; at least until the planet's rotation decreases to the point where it keeps one face at the star all the time (tidal locking). Then the only squeezing comes from the different forces at different times in a non-elliptical orbit (which the article does describe).

It seems plausible. But the devil is in the details. Some back-of-the-envelope with how long tidal locking would take with an earth-sized planet at half Mercury's orbit and a star 1/10 the Sun's mass gives about 6E10 years. If that's the timescale for heating I don't think the temperature would rise much. But I may be leaving something out, and there's a fair bit of tweaking room. For example, at 1/10 of Mercury's orbit, the time scale is only 4 million years. And my model of an iron planet isn't very realistic (I only get 100 degrees C rise). It would take a few days work to research a decent model, and it is getting late at night...