https://phys.org/news/2021-07-goldilocks-planets-tilt-complex-life.amp This article says (rather poorly) that only a relatively small axial tilt of a planet like with the Earth could be beneficial to life. But other sources seem to suggest an extreme axial tilt would be beneficial in that all the areas of the planet would evenly receive light. Could someone explain which is right or at least what this article might be saying better?
Exoplanets are now said to reside in a goldilock zone, when water will remain liquid on most of the planet, comparable to Earth. SF writers and popular science assume, that such a planet would be colonizable, because the average surface temperature would resemble Earth's. But it does not take temperature changes into account. Goldilock does not prove the planet will be habitable, partly for that reason. The rotation axis angle has everything to do with that.
A large tilt angle would be bad,
Despite residing in the goldilock zone, fluid water could become rare
Normally, planets are not in tidal lock. As a result of the axial tilt, seasons will occur and day lengths will vary. When water would freeze or evaporate completely, depending on the season, the criterium for goldilock (fluid water) would only be met during spring and autumn and never during summer and winter. A larger tilt angle would shorten these fluid water seasons even more, above a certain latitude winter season would be eternal darkness and summer season eternal light. Depending on the angle getting larger, only some small region below and above the equator would remain habitable. On the rest of the planet, difference between summer and winter becomes extreme.
1. Polar winter extends to much lower latitudes
With a small rotation axis tilt angle, like Earth has, the really cold parts of the planet (the poles) will see eternal light during summer and eternal darkness during winter. This does not affect temperature much, because the angle of sunlight reaching Earth in these regions remains very small. As a result, the polar summer is not really hot and the polar winter remains very cold. This polar winter region would extend to much lower latitudes, when the rotation axis angle is larger. This could render a goldilocks planet uninhabitable, despite a perfect distance to the sun. Water will freeze permanently, during winter. In spring and summer time, the ice will melt and evaporate.
2. Summer season would become very hot, also much hotter in polar regions
The polar summer would have a larger sunlight angle, and become much hotter.. and even on lower latitudes, the summer would have eternal light and warm up considerably compared to Earth, because the angle of sunlight is large already. It's like having eternal light, but unlike the eternal evening that occurs on Earth, the sun would climb to a much higher inclination each day, warming up the region. Water would evaporate all summer, resulting in desert. In autumn and winter time, this water would condensate as ice (snowfall)
The planet surface would matter. Suppose you'd have a lot of water, like Earth has, more heat would be transported and weather would become wild in the "moderate zone" above and below the Equator. Convection currents, extreme jet streams, prolongued rain season. When sunlight can reflect easily (e.g. silicon, lots of white sand) or the clouds become very thick, the temperature effect of eternal light would be moderated and ice formed during winter could survive the heat above a certain latitude. You'd get enormous polar regions. With little reflection, there would be no permanent ice anywhere. Any ice formed in the winter melts during summer.