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A series of articles describing possible life-suitable planets
and the possible inhabitants of alternative “earths” is already quite extensive.
However, a common snippet in almost all cases is the conclusion that conditions
different from those on Earth may nevertheless be suitable for some unassuming
microorganisms. Of course, it’s not about the life “based on other principles”,
that can thrive in liquid gases or feed on liquid stone, because the reasoning
on this topic makes sense only if the ideas about the aforementioned “other
principles” are clear and detailed. And the appearance of such ones, as a rule,
means a sudden realization that these “other principles” do not work.
That is, the conditions for life worse than on the Earth in one way or another are relatively easy to imagine. So, what about the better ones? How will the planet look, which is more habitable compared to our one?
...It’s probably worth starting from the star. The mass of the Sun corresponds to the upper limit of the masses of the luminaries which habitable planets can revolve around. So, let’s take something hefty, but more modest — 0.8-0.9 solar mass. It will provide a higher level of stability of the conditions. In 4 billion years, the luminosity of the star will increase not by 40, but by 25-30 per cent. The latter means that the planet can be brought closer to the light source.
At the time of the formation of the Solar System, the Earth was at the outer boundary of the habitable zone. And already in the Archean it began to suffer from the cold, even freezing completely at least once. Curiously, the hot climate of the Paleozoic and Mesozoic was a consequence of these difficulties. Due to the relatively small area of tropical shallow waters where synthesis took place in earlier epochs, the problem of carbon dioxide mineralization was solved very late. By the time the Sun had already flared up properly, the atmosphere still created a strong greenhouse effect.
On an “ideal planet” with an initially high but stable illumination level, life will arise somewhat later, since initially, until the heat remaining from the formation stage dissipates, water can exist only in the form of steam. But this lag will be quickly made up due to more favorable conditions for synthesis and the absence of glaciation.
The positive effects of stability can be further enhanced by some increase in the mass of the planet itself. As a result, we’ll get a world, where the ozone layer and an oxidizing atmosphere are formed early, and the land is covered to the poles with dark-leaved vegetation even during the period corresponding to the Cambrian of the Earth. It takes place because the spectrum of the star, compared with the solar one, is shifted to the red zone, and the modification of chlorophyll corresponding to long waves is red.
In a certain sense, a planet which orbit is close to circular, and the axis of rotation is strictly vertical, can be considered as an ideal one. In such a world, there will be no change of seasons. But whether it turns out to be an advantage or a disadvantage depends on the average temperature. If the climate on the planet in general is hot, as on Earth in the Cretaceous period, or at least very warm, as in the Paleogene, the effects of the absence of seasons will not be too bright and, rather, positive. In temperate latitudes, the climate, already warm, will become mild “oceanic” without heat and cold. Then, closer to the equator, the change of seasons in any case is felt on the scale of natural disasters. The amount of disasters will be fewer, but the rest will remain the same.
On a planet with an initially temperate climate, like the Earth’s modern one, the consequences of the lack of seasonality will be favorable in the tropics and partly in the subtropics, where the temperature will become more comfortable and rather unpleasant in temperate latitudes. For example, in the Moscow region, the average annual air temperature will be only four degrees Celsius. So, it will turn out to be an eternal spring, but spring will be too early. The pointer of the thermometer will start to beat up and down randomly between +20 and -10 degrees, depending on whether the wind blows from the north or from the south. Night frosts will become the rule. Several times in an astronomical year, snow will fall (and melt in a few days). For plants, this mode is extremely inconvenient. It will be especially difficult for flowering plants. Mixed forests will be replaced by taiga with dark needles. Of course, beasts and birds will manage to adapt to frosts – but not to the foodless. Amphibians, reptiles and insects (except for “warm-blooded” bumblebees) will hardly be able to tolerate the conditions of the off-season, in which it is impossible to prepare for frosts in advance.
Farther north the things will get really bad. The Arctic Ocean, Siberia to the Amur river and most of Canada will disappear under the glacier. Wherever the average temperature is below zero, the ice will not have time to melt during the snowbreaks. Only mosses and lichens rooted on the rocks protruding from the snow will survive here.
The tilt of the rotation axis of the planet not only diversifies the life of its inhabitants with spring blooms and autumn colors, but also expands the habitable area. Even in the Arctic, in the territories “unfreezing” for only for three or four months a year, during the short summer, animals gain fat, and plants create biomass that can be extracted from under the snow at the polar night.
Translated by Pavel Volkov, 2021
The original Russian article is here