This article was originally published on conversation. This publication is a feature of Space.com Expert Voices: Commentary and Insights.
Maureen Cohen He is a Postdoctoral Research Fellow in Venus Global Climate Modelling at the Open University.
Do aliens sleep? We might take sleep for granted, but research suggests that many planets on which life could potentially evolve don’t have a day-night cycle. While this is hard to imagine, there are organisms that live in light-free habitats on Earth, deep underground, or at the bottom of the ocean, which gives us an idea of what alien life without circadian rhythms might be like.
Our galaxy has billions of habitable planets. How did we get this number? The Milky Way has 100 billion and 400 billion Star.
Seventy percent of these are small, cool red dwarfs, also known as M dwarfs. A detailed exoplanet survey published in 2013 found that: 41% of M dwarfs The planet orbits within the “Goldilocks” zone, a distance where the temperature is just right to support liquid water.
These planets are Host Liquid WaterHowever, we still don’t know if these planets actually have water, let alone life. Still, there are 28.7 billion planets in the Goldilocks zone of M dwarfs alone — and that’s without even taking into account other types of stars like our Sun.
Rocky planets orbiting in the habitable zone of an M dwarf star are called M-Earths. M-Earths are fundamentally different from Earth. First, M dwarf stars are much cooler than the Sun, and therefore lie closer to it, making the star’s gravity on the planet much stronger.
The star’s gravity pulls harder on the planet’s near side than on its far side, creating friction that resists the planet’s rotation and slows it down for hundreds of millions of years until it can get in sync with its orbit. This means that most M-shaped Earths are thought to be tidally locked, with one hemisphere always facing the Sun and the other always pointing away from it.
A year on a tidally locked planet is the same length as a day on that planet. Because the Moon is tidally locked to Earth, we can only see one side of the Moon at any one time, never the other side.
Tidally locked planets may seem unusual, but most habitable planets are probably Like thisThe closest planet to Earth, Proxima Centauri b (located 4 light years away in the Alpha Centauri system), is probably a tidally locked M-type terrestrial planet.
Unlike our Earth, M-Earth has no days, nights or seasons. However, life on Earth is From bacteria Humans have a circadian rhythm that is tied to the day-night cycle.
Sleep is just the most obvious example of this. Influence of circadian cycle Biochemistry, body temperature, cell reproduction, behavior, etc. For example, people who get vaccinated in the morning Develop more antibodies Because the immune system’s response changes throughout the day, someone who receives the vaccine in the afternoon will have a stronger immune response than someone who receives the vaccine in the afternoon.
It’s unclear how important periods of inactivity and regeneration are to life: organisms that evolved without cyclical time may be able to keep moving without rest.
To support our speculations, we can look to organisms on Earth that thrive far from sunlight, such as cave-dwelling organisms, deep-sea creatures, and microbes that live in dark environments like the Earth’s crust or the human body.
Many of these organisms have biorhythms synchronized with stimuli other than light. Naked mole rats spend their entire lives underground and never see the sun, but They have an internal clock According to daily events and seasons Temperature and precipitation cyclesDeep sea mussels and Hot Bent Shrimp Synchronized with ocean tides.
Bacteria that live in the human intestine Synchronize with melatonin fluctuations Melatonin is a hormone your body produces in response to darkness.
Temperature changes due to thermal vents, fluctuations in humidity, and changes in environmental chemistry and ocean currents can all trigger bio-oscillations in living organisms, suggesting that biorhythms may have intrinsic benefits.
Recent studies suggest that M-Earth may have an alternative cycle of days and seasons. To study these questions, scientists have refined climate models to simulate what the environment on M-Earth, including our neighboring planet Proxima Centauri b, might be like.
In these simulations, the contrast between the dayside and nightside of the Earth Jet stream If the planet has water, the dayside is probably Forms thick clouds filled with lightning.
The interaction of winds, atmospheric waves, and clouds can cause the weather to vary between different states. Causes regular cycles The length of the cycles of temperature, humidity, rainfall, etc. varies from planet to planet, ranging from tens to hundreds of days on Earth, but has no relation to the rotational period of the planet. In the skies of these planets, the environment changes even while the stars are fixed.
Perhaps life on M-Earth will evolve biorhythms synchronized with these cycles, as it may have to do if biological clocks organize the biochemical oscillations within the body.
Or maybe evolution will find an even stranger solution: We could imagine a species living on the day side of the planet and migrating to the night side to rest and regenerate — a circadian clock in space rather than time.
This idea should remind us that if life exists in the universe, it would challenge all our assumptions. The only thing we can be sure of is that it will surprise us.
