Well, so far we've done pretty well on Earth. Since our Sun formed 4.5 billion years ago, our proto-Earth formed in the inner solar system behind it, and the combination of initial conditions and a late heavy bombardment spawned our first oceans and atmosphere, we feel quite good here. For more than four billion years, the Sun has been constantly shining and life has flourished. But it won't last forever. One day the Sun will run out of its fuel, which will lead to our death.
An interesting question arises …
Is the sun's nuclear energy declining or remains stable? How long can we survive on Earth if the Sun's "nuclear potential" is slowly burning out?
Assuming that no catastrophes caused by the Earth itself (for example, a supervolcano that will cover the entire planet or destroy the biosphere) or the Universe (a sterilizing gamma-ray burst or a nearby supernova explosion) will occur, the Sun will one day destroy all life on Earth.
You see, stars like our sun live by nuclear fusion: by fusing the lightest and most abundant element in the universe (hydrogen) into the second lightest and most abundant element (helium) in a chain reaction. The chain reactions by which the sun receives most of its energy include:
- the fusion of two protons together with the formation of deuterium, a positron (which annihilates with an electron and produces high-energy photons), neutrinos and free energy;
- then the fusion of deuterium with a proton with the formation of helium-3, a high-energy photon and free energy;
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- and then the fusion of two helium-3 nuclei together with the formation of helium-4, two free protons and even more free energy.
It is the most common source of energy from the Sun, where a total of 0.7% of the original mass of four protons is converted to energy during this reaction using Einstein's formula E = mc2. Every second, 4 x 1038 protons synthesize helium-4, releasing about 4 x 1026 watts of energy on a constant basis.
The sun is huge and massive and consists of about 1057 particles. But no matter how huge that number is, the total amount of solar fuel is limited, and give it time - it will run out. An even more pressing problem is that hydrogen only fuses in the core of the Sun, where the temperature is highest. The very first protons are not synthesized until you travel more than halfway to the center of the Sun and detect a temperature of 4 million degrees Celsius. And only in the deepest part of the Sun, where the temperature reaches 10 million (or even 15 million) degrees, 99% of the Sun's energy is produced.
This means that over time, in the deepest depths of the sun, the fuel will run out faster, because it is there that hydrogen burns to form helium. You might think that over time the Sun will become dim as the fuel for its heat will burn out. But in the absence of such reactions taking place inside the nucleus, it will begin to contract, and the gravitational compression will release even more energy, which will lead to an increase in the internal temperature. The synthesis will begin to flow faster and wider. It turns out that over time, the output energy of the Sun will increase. In fact, this has been happening for over four billion years.
When our Sun was a young star, it burned at 75-80% of its current brightness. Thanks to the presence of flora, fauna, ocean and atmosphere on our planet, we have been able to adapt to this steady rise in temperature. But everyone has a limit: at some point, the luminosity of the Sun will increase so much that the Earth, at its current distance from the Sun, will become hot enough that the oceans will boil. When this happens, our planet will suffer the fate of Venus - a thick layer of clouds will envelop it - and life will cease to exist.
It is possible that some life forms will learn to survive in the upper layers of the clouds. It is also quite possible that humanity will be able to figure out how to survive in such conditions. But that will happen long before the sun's core runs out of hydrogen fuel. For 5-7 billion years, our Sun will pass through the following stages:
- hydrogen will run out in the core;
- the sun will expand to a very bright subgiant star while hydrogen burns in a shell around the core;
- when the temperature reaches a critical limit, helium will be synthesized in the core;
- the sun will expand to a real red giant;
- and will die, blowing out its outer layers into a planetary nebula - and the core will shrink to the state of a white dwarf.
But after one to two billion years (according to most estimates), the Sun will be hot enough to vaporize the oceans. By then we will have to find ourselves a new home. Ultimately, only this global warming will make sense.
ILYA KHEL