Could life be formed without a fluid medium
About stars: extraterrestrial life in space
Life has to be made of something. There is matter and energy in our universe. Energy cannot form life because it cannot unite into such complex forms. So only matter remains. How dark matter is able to interact with one another is unknown, we know almost nothing about it, it is only communicated to us through its gravitation. So it is ruled out for life, at least for what we can also discover. The atoms we are familiar with remain, which are found everywhere in the universe in stars and clouds.
Atoms alone are not enough, they have to combine with each other - to form molecules. First to simple, then to more and more complex, because this is a prerequisite for something that can be called life. Simple molecules such as water (H.2O) there is a lack of skills such as reproducing and storing sufficient data.
A large part of the matter accessible to us is in stars. However, these have temperatures of 2500 degrees upwards. This is fatal for most molecules, they break down into their atoms. A few particularly stable ones such as titanium dioxide (TiO2) can withstand temperatures of several thousand degrees, but not much life can be made with titanium dioxide alone. So stars are ruled out.
It looks different with the numerous clouds of matter. Here you usually find much lower temperatures and organic molecules such as formic acid (HCOOH) were actually discovered in such clouds, albeit without the associated ants. But these clouds have another problem: they are extremely large, many light years, and very thin. They consist almost entirely of hydrogen and helium, other elements are rare. So life there would be very lonely. And they are usually very cold (dark clouds like the coal sack fog), which makes the chemistry there extremely slow. Luminous clouds like the Orion Nebula, on the other hand, are too hot. Clouds of matter are therefore not seriously considered suitable for life.
The environment of stars - planets remains. The number of stars with planets is between one and 20 percent, so there are enough of them. Depending on the type of star, planet and their distance, there are numerous possible combinations in which many could meet the conditions for life. These conditions are: pleasant temperatures (in which range is very uncertain, let's say a generous 100 - 500 Kelvin, maybe only 250 - 350, depending on whether e.g. liquid water is an indispensable requirement or not), a suitable star (main sequence star red to white) and a rocky planet or moon with atmosphere.
The temperature depends on the temperature on the star and the distance from the planet. However, hot blue stars emit very unhealthy radiation, UV radiation that tends to break up complex molecules. In addition, these stars are short-lived. So they drop out. With the little red dwarfs, a planet is only in the life zone when it is very close. But then its rotation is synchronized, i.e. it always stretches the same side towards its star. What this leads to is not entirely certain. In any case, the front is very hot and the back is very cool and there are strong winds. They may be able to distribute the temperatures fairly evenly over the planet. Then life would be possible, albeit differently than we know it from Earth, because photosynthesis is much more difficult in red light. Or perhaps the nearby star will quickly blow away the atmosphere on its side, leaving behind a half-glowing and half-frozen lump of rock (like Mercury).
We know from our sun that yellow stars make life possible. Orange and white stars should also be suitable.
The planet must also meet some conditions: gas planets are likely to be unsuitable. In the vast atmosphere, conditions are too destructive from pressure, storms and electrical discharges. And it doesn't look any better on the rocky core, the pressure here can be many millions of atmospheres. In addition, the atmosphere consists almost entirely of hydrogen and helium.
So rock planets and moons remain. These have lost most of the light elements hydrogen and helium and if they are not older than 8-10 billion years there should be enough heavy elements. Moons, like Titan, are quite capable of maintaining an atmosphere worth mentioning. And giant planets like Ypsilon Andromedae d could well have Earth-sized moons. With these bodies there is a wide range which would be suitable for the development of life. But not all make it. We know that from our solar system.
So what is the condition for evolution to begin? That is the big unknown factor. You need at least an atmosphere and a liquid medium like water, but methane could also be suitable. In addition, a pressure that is not too extreme and pleasant temperatures. Then a chemical evolution can produce e.g. amino acids and proteins from which the first living things can develop after a long time.
Our earth is 4.6 billion years old. There have been primitive unicellular organisms there for 3.5 billion years, multicellular cells for 1 billion years, vertebrates for 530 million years, humans for about 5 million years, and we have called ourselves intelligent for a few thousand years. Whether this speed of development is representative of other forms of life can be assumed, because complex things take longer and longer.
The universe contains around 100 billion galaxies, each with around 100 billion stars. So enough space. The question of extraterrestrial life can only be answered in probabilities at the moment. These would be:
Life in space: very, very likely.
Intelligent life in space: very likely.
Life near us (~ 100 light years): probably.
Intelligent life near us (~ 100 light years): very very unlikely.
How can we discover foreign life if it does not communicate with us, i.e. if neither radio signals nor UFOs reach us? One possibility would be the detection of ozone on foreign planets, since ozone apparently can only arise through metabolic processes in living beings. A corresponding project for the detection of ozone is being planned.
Back: About stars
N 63 in the Large Magellanic Cloud.
Photo: S. Points, C. Smith, R. Leiton, and C. Aguilera / NOAO / AURA / NSF and Z. Levay (STScI)
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