How do we know there are pets in heaven? Because it wouldn't be heaven without them, or so it's said. That doesn't apply to space however. In that case they become an expensive luxury, one humans will not likely opt to afford any time soon. Why? Because pets (please think larger mammals for the moment) consume noticeable amounts of precious resources if not room, and return nothing. ("But they do give us something Mr. Spock, they give us love.") They produce waste that must be disposed satisfactorily. If scientists could only genetically engineer a creature that operates without food, air, or water, it would find a welcome home with any space pioneer. Presuming it doesn't shed or smell bad!

All organisms, flora and fauna, microbe and multi-cellular, that exist in an environment comprise its ecosystem. Some ecosystems, like that of Biosphere1 (also known as "Earth"), are said to be "closed" in that no material need be supplied to it or removed from it. All species inside a closed ecosystem can self-sustain given all other organisms. (The illogic of driving species into extinction is not at issue here.) A closed system can be difficult to establish, but once running will do so indefinitely.

In contrast, an "open" ecosystem must be externally supplied in order to function. ISS is an example of an open ecosystem, with food arriving regularly and waste being jettisoned or removed. The advantages of an open ecosystem are many: quicker to establish, more resilient, and a variety restricted only by supply. But that last bullet is also an open system's greatest weakness, in that disturbing the supply line can critically effect the ecosystem's performance (if not eliminate it altogether!).

Animals will make the trip inevitably, returning to orbit as not seen since the birth of the planet's space program, though they will serve primarily as a resource (an edible one, if necessary) and only secondarily as companionship. Porthos may travel with Archer in the open ecosystem of NX-01 but for a future involving closed systems I expect our faithful companions won't be joining us for quite some time. At least that is, until closed systems are mature and expansive enough to accommodate the resource loss without measurably disturbing the remaining system.

Alternately, space pioneers setting up house may compromise with extremely smaller pets, those that don't consume much over their lifetime and don't leave much behind for the system to reclaim. Like goldfish perhaps, for as Archie Bunker noted, "Long before you grow tired of them, they die."