[X] My Assistant

[Toymaker]

http://www.nature.com/nature/journal/v441/...ature04828.html
Over the past two years, the search for low-mass extrasolar planets has led to the detection of seven so-called 'hot Neptunes' or 'super-Earths' around Sun-like stars. These planets have masses 5–20 times larger than the Earth and are mainly found on close-in orbits with periods of 2–15 days. Here we report a system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days, orbiting the nearby star HD 69830. This star was already known to show an infrared excess possibly caused by an asteroid belt within 1 au (the Sun–Earth distance). Simulations show that the system is in a dynamically stable configuration. Theoretical calculations favour a mainly rocky composition for both inner planets, while the outer planet probably has a significant gaseous envelope surrounding its rocky/icy core; the outer planet orbits within the habitable zone of this star.

[Guest_Myran_*]

Toymaker wrote:
Magnetic field IIRC could strip the atmosphere.
Also IIRC they could be locked in one position with night/day permenent spheres.

I reply to the latter one here:
Yes its most likely that any moon will have bound rotation and so have the same hemisphere facing the planet all the time.
But that doesnt cause one hemisphere to be cast in permanent darkness as it appear that to me that your writing.
The duration of daylight on such a moon would be about half of each orbit. Yes about, eclipses by the main planet can make it a bit shorter on the planet facing hemisphere, on most of the out-facing hemisphere of that moon world the eclipse would happen in the night and would not be seen.
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As for finding such moons with a Terrestrial planet finder type of instrument would be hard. First we would have to remove the stellar light, but then the Neptune mass (and perhaps sized) planet would be much brigher than any moon in orbit. The large planet might perhaps not be a complete showstopper, but I do think it adds a major complication for such a search.