Re: An Earth-size planet is careening untethered through the galaxy,

[email protected] says...
> Do they ever explain how advanced forms of life developed
> on a planet without warmth from sun/star light?

This passage is the most detail given.  From Chapter Nine of 
_Peggy Sue_ by Doug L Hoffman:


In the interstellar void between Beta Comae and a red dwarf known to 
humans as Ross 1015, a dark world five times a massive as Jupiter 
followed its own lonely path around the Galaxy. A dark imitation of a 
stellar system, the rogue planet possessed its own swarm of orbiting 
satellites. Half a dozen of those sizable moons were inhabited by 
creatures as intelligent as humans, perhaps more so.

These creatures reveled in the darkness, on worlds barely lit by faint 
star light. Possessing no eyes, they found their way using sound, 
vibrations through the ground beneath their jumble of short straw-like 
legs and the thick atmosphere around them. They never saw the carbon 
dioxide icebergs floating on seas of liquid nitrogen, or the occasional, 
spectacular cryovolcanic eruptions that sent plumes of methane, ammonia 
and other gases into surrounding space, renewing the moons? atmospheres.

Warmed tepidly by tidal stress and radioactive decay deep within their 
worlds, the creatures could only live at temperatures that would freeze 
Earth life solid. The low temperatures also slowed the rate of chemical 
reactions, making the pace of life on these dark worlds sluggish and 
deliberate. But that was fine with the creatures, their lives were long 
and contemplative ? perhaps that was why they hated warm life, with its 
ephemeral lifespans and frenetic existence.

Ranging in height from one to two meters, their bodies were disc shaped 
hollow sacks, normally indented on either side. At the front of the sack 
was a vertical opening, fringed with long hair-like tentacles, a visage 
that could only in charity be called a face. The closest parallel among 
Earthly life was the trap sack of certain microscopic carnivorous plants 
commonly known as bladderwarts. Only these ?plants? could move slowly 
about on the short legs that sprouted from their bases like bristles 
from a brush. Communication was accomplished using small vibrating 
membranes on either side of the mouth opening, conversation that would 
sound like random buzzing and humming to human ears.