[DBrow]

A free-floating planet far from a star would have a temperature of 25K, if that. The blackbody temperature would be lower, I’m assuming some warmth from radioactive dacay, assuming the same amount of U and K as here.

I read a paper that discussed tracking long-period or one-time comets back to their origins, and they postulated the passage of a planetary mass that kicked their orbits inward.

[cripplecreek]

I know that astronomers have discovered some “clumping” in the Ort cloud that may be the result of something large stirring things up.

It 50 years old, I’m not too worried about it.

[Joe Brower]

That was my first impression -- any planet not in close proximity to a star is going to be far too cold for any chemical reactions to occur; certainly not the complex reactions that a "life bearing" world would require.