Some of you will be aware of a science fiction game that is quite popular in these parts. It is called Warhammer 40,000 (or 40K for short) and amongst its eight-foot-tall, eugenically modified, xenophobic protectors of Mankind (Space Marines, for those who know, not Imperial Guardsman) there are a myriad of other intriguing biophysics problems (even Space Marines provide some interesting discussion points, like the fact that they can absorb someone's memories from eating a part of them—I can't remember which part, though).
The foremost of these is the Tyranids. Tyranids are a (fictitious, fortunately) race of space-faring organisms that operate under a 'hive mind'. Besides the spacefaring organisms, there are also all manner of scouting, eating, digesting and fighting organisms, each with its own degree of indpendence from the overarching hive mind. While there are plenty of things to discuss, the first I was thinking of is the fact that they are space faring.
Is a space-borne organism feasible? What would it require, regardless of any hive-mind activity. Of course, such an organism must be able to travel vast distances in space if it is to move between planets, let alone galaxies! (In the story, Tyranids invaded our galaxy from another). What kind of thermodynamic constraints are there to keep it alive? Speed, of course, is no problem in space until you have to slow down but what amount of energy is consumed when lifting off from a planet?
Eagerly awaiting your (gribbly) replies. I will think of more ideas after some brain recovery.
As a Hive Tyrant of the Hive Fleet Leviathan I too shall have to ponder spaceborne organisms...
ReplyDeleteMy initial thoughts are that it would be relatively simple for a large organism to survive in space, provided that it had a sufficient onboard supply of appropriate nutrients, gases, etc.
As a first estimate, picture a large sphere. This shape is no problem in vacuum, and for a large enough creature a spherical body is probably desirable merely to decrease the amount of structural support required. A large sphere has a huge volume to surface area ratio, so the amount of flesh actually close to vacuum is quite small. This could then be insulated by all manner of methods. Much like earthbound animals, it might be possible to include insulating layers of blubber, perhaps surrounded by some sacrificial epidermal layer which bears the brunt of solar winds and radiation.
Such a creature could even lower its metabolic rate by employing many sub-circulatory systems rather than one single large one (remember the allometric laws derived last year), allowing it to maintain a reasonable body heat whilst not metabolising too rapidly.
That is all well and good, but the organism must also be able to sense objects (in the sense of being nearby in interplanetary terms). The electromagnetism sensitivity of such a creature would presumably be governed by the prevalent conditions of its region of space rather than the spectral output of a particular star, so it would be reasonable to imagine a creature that sees in radio. This would require only simple antenna-like structures which could be fairly resistant to vacuum, rather than the more complex and fragile human eye. Human nerves acts like radio antennas, so we could simply imagine a large set of nerve lines which act as photoreceptors embedded in the skin.
The main problems are run into when we consider how such an organism would feed and deal with high temperatures. `Feeding' should also be synonymous with breathing for such a large creature, since it is unlikely that it would be able to carry enough photosynthetic symbionts (and expose them to enough light) to regenerate its own internal atmosphere (assuming it has one... a large creature like this could even incorporate transport processes like convection into its physiology). The problem is that feeding requires food, which presumably requires a gravity well, as you mentioned.
A true Tyrandid-style feeding tower is not feasible unless it is divided into segments of a few metres each, and fluid is transferred between each segment before being pumped upwards. This process is slow but allows the creature to remain in orbit and use the pressure of the atmosphere below to drive a significant porion of the foodstuff upwards. Once sufficiently high peristaltic actions could take over without having to be at ridiculously high operating pressures.
I have overlooked another major facet of extraterrestrial life: a spaceborne organism requires ejection mass. Without this it has no method of propelling itself through the aether! After feeding one could imagine such a creature grappling nearby debris to increase its velocity (presumably it has some manner of outsized cilia-like appendages), whereas at the other end of its journey it could use solid wastes as ejection mass.
These are just preliminary ramblings, but I thought the question was interesting.
James
PS: I would be especially interested to hear your thoughts on a subdivided circulatory system and the possible incorporation of convection into it/them.