A recent University of Washington study discusses how exoplanets that once resembled the gas giant Neptune could have their oceans blown away by local stars. Additionally, the study shows how these gas planets are capable of leaving behind a potentially habitable core of a planet. The Milky Way galaxy is predominately comprised of class M dwarf stars that are typically smaller and cooler than the sun.
According to the Search for Extraterrestrial Intelligence (SETI), alien life is likely to form on planets orbiting at distances from their stars where liquid water could form on their surfaces. This habitable distance is also known as the “Goldilocks” zone. These transformed gas planets could form with thick atmospheres initially forming freezing cold, inhospitable worlds. Other forces can influence the planets’ orbital path to one that is closer to the sun–making these planets more hospitable to life. Other conditions such as tidal forces and the greenhouse effect could further transform planets into a possible home for alien life.
You can see the full study here – University of Washington Study as well as The Journal of Astrobiology.