Starship Asterisk*

Now a team of scientists have looked at how these worlds form and suggest that many of them may be a lot less clement than was though. They find that planets that form from less massive cores can become benign habitats for life, whereas the larger objects instead end up as 'mini-Neptunes' with thick atmospheres and probably stay sterile.

http://www.sciencedaily.com/releases/20 ... 074925.htm