Over the course of my life, I’ve read a lot of science fiction books. Along the way, I’ve been introduced to different concepts of alien life, such as the Masters in the Tripods trilogy (now a quartet) by John Christopher. Later, I met the Moties in The Mote in God’s Eye and the Fithp in Footfall, both by Larry Niven and Jerry Pournelle.

In many ways, Isaac Asimov outdid himself in The Gods Themselves with the Hard Ones and the Soft Ones, the latter of which consist of triads, each comprising three sexes: Rationals (or “lefts”), which are the logical and scientific sex; Emotionals (or “mids”), which are the intuitive sex; and Parentals (or “rights”), who bear and raise any offspring.

Then there were the Spiders in A Deepness in the Sky (the prequel to A Fire Upon the Deep) by Vernor Vinge. Of course, there were the mechanoid civilizations in Great Sky River by Gregory Benford, but I think we should focus on biological entities here (yes, I know all about They’re Made Out of Meat by Terry Bisson).

When I was a young whippersnapper, I vaguely thought that alien life would be somewhat similar to our own, at least insofar as breathing oxygen and living on the surface of a planet. In Asimov’s Nightfall novelette, for example, the aliens in question live on the planet Lagash (“Kalgash” in the later full-length novel), which is constantly illuminated by at least one of the six suns of its multiple star system.

Nightfall is an absolute classic, but we don’t have time to go into it here. Suffice it to say that we are never told what the aliens look like, we know them only by their professions of journalist, scientist, etc. As a result, we start to think of them as being and acting like humans, until… but no, you can’t trick me into telling you anything more.

One of the things I used to contemplate as a youngster was what would happen if our Sun were to suddenly disappear. I knew it took light about 8 minutes to travel from the Sun to the Earth, so if the Sun were to vanish, it would take 8 minutes before “the lights went out.” Presumably, the Earth would continue to orbit our now non-existent star for the same amount of time before gravity (or the local curving of the spacetime continuum) ceased, at which point we would head off into interstellar space.

I wondered how long it would take for everything to cool down to the point where we all froze to death. (I actually had a happy, trauma-free childhood — honest!)

Another thing I believed when I was younger was that our scientists knew what they were talking about and that our solar system had formed out of dust with the Sun in the middle and rings of surrounding material that eventually coalesced into the planets we know and love so well in the positions they currently occupy. It was much later, circa 2005, that scientists discovered that the system probably formed with many more planets than there are now, and that — in the words of the authors — “…the beginning was more like a gigantic game of cosmic billiards…” At some stage, Jupiter and Saturn drifted closer to the Sun — herding smaller planets into the Sun or ejecting them from the solar system completely — before meandering their way back out to their current orbits.

I also used to think that rogue planets (a.k.a. nomad planets, unbound planets, orphan planets, etc.) were few and far between, but current theories hold that there may be many more rogue planets than there are planets orbiting suns. Furthermore, I used to think that there was little chance of life surviving on a planet that went rogue, and no chance whatsoever of life starting and evolving on such a planet. All of which goes to show how little I know.

The reason I’m waffling on here is that I recently read Imagined Life by James Trefil and Michael Summers. After refreshing our minds as to what we know and don’t know about life, the authors introduce us to various scenarios by which life could evolve on ice worlds, ocean worlds with no dry land, worlds where the oceans are surrounded by shells of ice, halo worlds that are tidally locked with their sun, super massive planets, and — yes — rogue worlds.

In each case, the authors consider the effects of the environment and the problems life would have to overcome (they also close each chapter with a conversation between two aliens called Mike and Jim, who explain why theirs is the only sort of planet upon which life could develop, and why life couldn’t get a start on a planet like Earth).

Consider the life surrounding the thermal vents on the Earth’s ocean floors, for example. In the case of a large rogue world, sufficient heat may be generated by its core to support such life even in the absence of a sun. Or take a halo world, where fierce winds would blow from the desert side facing the sun to the frozen side facing outer space. At the transition band, known as the terminator, between the two, you might find mile-high glaziers on the cold side with lakes or even a narrow sea ringing the planet between the desert on one side and the ice wall on the other.

I tell you; my head is now buzzing with possibilities. What say you? What do you think about all of this?