b. We know little enough about how our planet formed, so how can we speculate about the formation of planets outside our solar system? It could be stars themselves with their own characteristics (including metallicity and size) or their natural histories dictate. We have no good model of what sorts of planets should form around a dwarf star of spectral categories F, G, K, or M.    

 c. One should reasonably assume that any star not likely to have gone into a destructive phase within the time in which the star's light reaches us. Excessive caution might force people to assume that a main-sequence star such as Sirius might have exploded in a supernova event (even though a star the size of Sirius does not go supernova) or met a destructive collision in the time between a few years ago and now. One might not be so sure with a larger star such as Betelgeuse or Deneb much farther away. Unless one has cause to believe that what appears true of a star now visible is no longer true, then one must take the approach that what one sees of a normal star a few hundred light-years away is still true.  

 d. Of course I would expect a planet with a mass decidedly larger than that of Earth to have different characteristics, including the sorts of gases that its atmosphere could hold. A super-Earth about as cool as the Earth might have a helium-rich atmosphere but little uncombined hydrogen. Rough atomic weights for some of the most common gases in the universe are hydrogen (2), helium (4), methane (16), ammonia (17), water vapor (18), neon (20), carbon monoxide (28), nitrogen (28), oxygen (32), argon (40), and carbon dioxide (44). 

 Venus and Mars, planets smaller than the Earth but with very different temperatures, have atmospheres rich in nitrogen and carbon dioxide  but practically no water vapor. Earth's atmosphere can hold methane and ammonia (although both are thermodynamically unstable in the presence of free oxygen) and of course free oxygen   but not helium or hydrogen. Could a planet have a stable atmosphere rich in helium but not hydrogen? Would its greater pressure itself create a temperature too high for complex life as known on Earth?