igh axial inclination, the ice cap may completely disappear during that hemisphere’s summer. The activity of the biotic community on alien worlds will be similar to that on Earth as each season is experienced. The hemisphere entering Spring, a time of increases sunlight and warmth, will come out of winter dormancy and experience growth.
In the hemisphere entering Fall, the biotic community will be gearing down for the approaching Winter. The plants will winterizes, the animals will migrate, build up energy reserves, prepare for hibernation and/or utilize other adaptive mechanisms.
On planets with approximately a 30ºC APST, we may find the absence of true ice caps. In their place may exist the relatively more temperate permafrost fields with perennially frozen ground or nearly permanent frost.
Frost caps require an annual temperature of about -3ºC (26ºF) or less in order to exist; however, the temperature range over the entire area may run from -36ºC to 4ºC (-32ºF to 39ºF). Precipitation in these regions is under 15 inches per year. Climatic conditions in the permafrost zone is are cold and dry, with long winters and cool summers.
[Illustration at right: Ice Cap & Snow Field expansion on a cool planet with varying degrees of axial inclination.]
On any world with a permafrost region either covering the poles or circumventing the icecap, an explorer would find large expanses of flat land and rounded hilly terrain, where the effects of freezing and thawing would have reduced rocks to small particles. The soils of these regions would be poorly drained and poorly aerated on planets with low axial inclination and just the opposite planets with high axial inclination.
Remember, if the planet were orbiting a relatively cool G9 or K0 spectral class star, it’s orbit would be near the star, providing a short year. If the planet orbited a much hotter, F24 or F4 star, its orbit would fall further from the star giving it a year perhaps twice as long as our own, hence a ‘quarter year’ of about 6 months- plenty of time for small plants to go through their life cycle, or even a couple of generations.
Permafrost environments are typically a low energy areas offering little year around food to the larger animals. Most of the animal life consists of small burrowing types with insulated feet and various seasonal visitors. I suspect that small animals would inhabit permafrost regions on planets orbiting cool stars. Larger migrating species would be more important on planets orbiting hotter stars, where the growing season is longer, where a larger deposit of biomass has accumulated and where the season length would allow the larger species to migrate.
Small (short height) plant life would only have a few months, depending on the planets sidereal period (length of year) to carry out their life cycle before
reduced temperatures would bring about dormancy.
Planetary Bio-Zones, Plant Growth & Limiting Factors
On all of our model worlds, we could expect to encounter a mix of the following environments: cold, warm or hot arid deserts, rivers, marsh land, fresh water lakes, bays, hills, meadows and plains. We would expect to find a vast assortment of analogous physical surface structures, i.e., rock, sand, gravel, humus with partially decayed organic material, cliffs, etc. We would see common atmospheric phenomena, the parent sun in the sky, stars visible at night, fog, rain, snow, wind, clouds, storms-all with great variation in quantity, frequency and intensity as the stellar and planetary parameters were varied.
The biological community whose evolutionary histories track back through a particular environment, will display adoptions peculiar to that environment. It’s also reasonable to believe that similar environments on different alien worlds will tend to carry life forms who share somewhat similar morphological and very general behavioral patterns.
Atmospheric Circulation & Biotic Zone Diagram
The following Illustration: Atmospheric Circulation and Biotic Zones provides a general view of the effects of precipitation and atmospheric circulation.
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