[ETL]

The search for habitable alien planets will be harder because tidal forces could remove water from planets to leave them dry worlds.

I would think this is the case only because the primary way of detecting exoplanets at this time is via the gravitational effect they have on the star they're orbiting. They 'tug' on it causing a 'wobble' in the light signal from the star (back and forth redshift-blueshift). Planets with a significant gravitational effect on their star usually get very close to it at some point and/or are very massive. Planets and Moons only experience tidal heating when they are sufficiently close to a star or planet(in the case of moons). Tidal heating is a gravitational effect. In other words, Earth is obviously a habitable planet, yet it isn't massive enough (or close enough to the Sun) to cause much of a wobble of the Sun. Therefore, we can't easily detect Earth-size planets at the Earth-Sun distance or greater using the current techniques, and so many such planets are 'invisible' to us at the moment.

[cripplecreek]

I would think this is the case only because the primary way of detecting exoplanets at this time is via the gravitational effect they have on the star they're orbiting.

Agreed. We haven't even come close to beginning to scratch the surface and there are hundreds of billions of stars in our own galaxy. Also there's the fact that we aren't really even looking for moons which probably number many thousands around the exoplanets we know about. After all, there are more than 200 moons in our own solar system.

[Erasmus]

There’s also the photometric measurements of the periodic occultations, and they’re hoping to get some direct imaging with the latest earth-based or orbital telescopes.

If they do get imaging of some exoplanets, they can tell more about their composition; however, the sample size is likely to be small.

[SunkenCiv]

Well said!