New Scientist ran an article a few years back on orphan worlds. One idea was that the lower size limit for lone bodies could be quite low and that perhaps...

interesting there have been times I thought that as well, but the science minded of the group always scoffed ________________________________ From: Carl Brown...

... Well, if the conditions really are as you describe, with an atmosphere that's not frozen, and trapped heat keeping the planet from cooling too far even...

depending on how the planet originally formed and from what,could radioactives within the planet contribute to maintaining heat ...

... I think any sufficiently large terrestrial (rocky) planet will have radioactives helping keep it warm. Mars isn't large enough, it's cooled off too much....