The day and night cycles experienced by organisms on Earth are essential for the normal functioning of life. This is not the case in many extraterrestrial worlds. Should life forms develop in such worlds, they would live through experiences different from what life on Earth is. Considering an alternate biological perspective of life without circadian cycles raises exciting questions about evolution in highly different environments.
Life Without Alternate Periods of Sleeping and AwakenessÂ
In humans, sleeping according to one’s internal biological clock affects every functional aspect, from brain activity to physical conditions such as inflammation and immune response. Still, some studies indicate that many exoplanets – planets outside our solar system – do not have a day-night cycle. Some organisms, such as those found in the deep sea trenches or cave systems on the Earth, must give, e ideas of how life would exist on planets with only light or dark.
The pervasiveness of Overseas Planets that Can Support Life
In our galaxy, the Milky Way, the total number of stars is between 100 and 400 billion star systems. The most significant fraction of those, about 70%, are red dwarfs, M-dwarfs, much smaller and cooler than our Sun. A survey of exoplSunts in 2013 estimated that M-dwarf stars exist, with 41% hosting planets within their Goldilocks zone.
That equals approximately 28.7 billion planets with suitable living conditions, just like M-dwarfs, without mentioning planets around solar-type stars. However, whether there is water or life on the planets is still a question to be answered.
M-Earths: The New Form of a Planet
Planets similar in composition to the Earth, which orbit around M dwarf stars in the potential habitable zone, are called M-Earths. The reason is that these worlds are unlike Earth in several aspects. Since M-dwarfs are more relaxed than the sun, their habitable zSun, as explained later, is narrower and closer to the star. The gravitational pull from the star creates a constraining mean tidal effect that reduces during the planet’s rotation over a long duration.
A planet synchronized with its star revolves around its axis over the same period it revolves around the tattoo. It is the same case with the moon, which is why it’s always the same side of the moon that we get to see as it always looks at the Earth.
Living without Body Clocks
Day and night, seasonal changes are dominant on Earth, but this is not the fate of the M-Earths. Day-night rhythm and the seasons are embedded in the way of life on Earth: sleep-wake, body temperature and metabolism, and even the activity of defence against pathogens. That is, the operating immune system goes in cycles.
As a result, life on such a planet may resemble the extremophiles found on Earth—specialized organisms that thrive in harsh conditions. This would give us insight into how evolution would take place in the diverse, alien worlds.
