Rocky planets in the habitable belt of an M dwarf are called M Earths. M-Earths are fundamentally different from our Earth. One difference is that M dwarf stars are much cooler than our Sun. Also, M Earths are located at a close distance from their star, and for this reason, the gravitational influence of the star on them is strong.
The star’s gravity exerts a stronger force on the near side of the planet than on the far side. By creating friction, the planet’s rotation slows down until its orbital and translational rotations become synchronized over millions of years. Thus, M fields are likely to be deadlocked; So that one hemisphere of them is always facing the star and the other hemisphere is always behind it.
The year of a mortally locked planet is as long as its day. Earth’s moon also has a deadly lock on us. For this reason, we always see one side of it and cannot observe its hidden side.
A planet in mortal lock looks strange; But most possible habitable planets are of this type. Our nearest planetary neighbor, Proxima Centauri b, located in the Alpha Centauri system four light-years from Earth, is likely a fatally locked M-Earth.
As a result, unlike our Earth, M Earths have no day or night and even seasons; But terrestrial life, from bacteria to humans, have circadian rhythms corresponding to the day and night cycle. Sleep is one of the most obvious consequences of circadian rhythm.
On earth, some creatures live in absolute darkness
The circadian cycle affects biochemistry, body temperature, cell regeneration, behavior and much more. For example, people who are vaccinated in the morning produce more antibodies than people who are vaccinated in the afternoon; Because the response of the immune system is different during the day.
We cannot yet say with certainty how much periods of inactivity and regeneration affect life. Perhaps organisms that evolved without cyclical time never needed to rest.
If you doubt it, you can look at terrestrial organisms such as cave dwellers, deep sea life, and microscopic organisms in dark environments such as the earth’s crust and the human body that thrive in space away from daylight.
Many life forms have biological rhythms that are synchronized to stimuli other than light. Naked burrowing mice spend their entire lives underground and never see the sun; But their day and night hours are proportional to the daily and seasonal cycles of temperature and rainfall. Also, deep-sea bivalves and thermal well shrimps coordinate with ocean tides.
Bacteria that live in the human gut synchronize with melatonin fluctuations in the host’s body. Melatonin is a hormone in the body that is produced in response to darkness. Temperature changes that occur in thermal wells, humidity fluctuations and chemical changes and environmental currents can all cause biological fluctuations in the body of living organisms.
According to new research, M-Earths can have alternate cycles for days and seasons. To evaluate days and seasons on exoplanets, scientists have adapted climate models to simulate the environment of M-Earths and planets such as Proxima Centauri b.
According to the simulations, the contrast between the night and day sides of the planets produces gusts and atmospheric currents similar to Earth’s gust currents. If a planet has water, its dayside is likely to have thick thunderclouds.
The interaction between winds, atmospheric waves and clouds can change the climate and produce regular cycles of temperature, humidity and rainfall. The length of these cycles varies from hundreds to thousands of Earth days depending on the state of the planet; But it has nothing to do with the rotation period of the planet. Although the stars in the sky of these planets remain constant, the environment changes.
Perhaps life on M-Earths evolved to match biological rhythms and climatic cycles, or perhaps evolution arrived at a more exotic solution. One can imagine species that live on the day side of the planet going to the night side to rest and regenerate themselves.
These descriptions remind us that if life is out there, it can challenge assumptions we are unaware of. The only certainty is that it will surprise us.
