From time to time members of some millenarian sect knock on the door of our house, frightening us with the imminent arrival of the end of the world. They always inform us that only the just and the good will be saved and, curiously, the only good men are, in all fairness, them.
We can sleep peacefully. There is no reason to assume that these terrible cosmic cataclysms with which they intend to scare us will happen in the near future. However, it is true that the end of the world will come upon us. Of course, it is not something imminent, but a catastrophe that will take place in 7,000 million years , day up, day down. The culprit of everything will be, ironies of life, who today gives us life.
The fate of the Sun is known quite accurately. Just as cars run out of fuel, the day will come when the hydrogen in its center, the fusion reactor zone, will run out. What will happen next? The core will contract and the shell will slowly expand. And it will slowly engulf and vanish Mercury, and it will engulf and vanish Venus . The heat released will completely change the appearance of the solar system. Not only will it vaporize the inner planets, but it will bring spring to the Kuiper belt, a repository of comets, asteroids and planetoids in the orbit of Neptune and to which Pluto belongs. During the expansion, the solar surface will become increasingly cold and will acquire a reddish hue. What is not known is whether it will reach Earth’s orbit before stopping its expansion. For any extraterrestrial astronomer, in 7,000 million years the Sun will not be a small yellow star but a red giant , a star that will have entered the last million years of its life: our Sun will be an old man.
If Earth survives the expansion we will find ourselves in a lifeless hell, glowing a pale red. An Earth that will always show one of its faces to the Sun due to a peculiar long-term gravitational effect called tidal coupling, in ways that synchronize the rotation period with the translation period. In the part of the world illuminated by a Sun that covers the sky threateningly, for it will be 250 times larger than it is today, the surface will be at more than 2000º C: an ocean of magma and vaporized rocks in an air inflamed by heat . In the other half of eternal midnight, temperatures are more difficult to predict: it all depends on whether the planet has a perceptible atmosphere. In that case, weak winds would carry heat from the daytime hemisphere turning the dark side into something akin to a toaster . But if for some reason there wasn’t a shred of air left, the cold would be icy. The most similar place is Mercury, where with a weak atmosphere temperatures at midday reach 350º C -lead melts- and at night they plummet to -170º C. Predictions for Earth determine that the dark zone will be even darker. cold, around -240º C.
In such a fantastic environment, exotic climatic behaviors appear. On the warm side, metals such as silicon, magnesium, and iron, along with their corresponding oxides, will evaporate from the magma ocean and enter the atmosphere .
In the unusual twilight zone, or terminator, that separates perpetual day from night, these vapors will condense: it will rain iron and perhaps snow silicon monoxide. Already on the dark side the snow will be potassium and sodium. The cold there will be enough to freeze the carbon dioxide, sulfur dioxide and argon forming an immense layer under which pure ice can be found, if all the water on the planet has not already been lost. With luck, some liquid water can also be found in the twilight zone, a sad memory of what was once known as the blue planet.
Looking at the sky from the oceans of magma, an extraordinary process will be observed: the outermost layers of the star will slowly be lost in space in a process that will last several million years to end up forming a planetary nebula. The glowing gases will pass through our planet in an incredible spectacle that will last millions of years creating an envelope around the Solar System that will eventually dissipate like a smoke ring. Meanwhile, the Sun’s core will shrink to a white dwarf , where matter is so compressed that a single teaspoon of white dwarf weighs more than a ton.
Unfortunately, it is quite possible that our planet will not be able to attend such a spectacle. According to the calculations of the astronomers Klaus-Peter Schröder and Robert Connon Smith, the Sun will lose a third of its mass in its evolution to a red giant. In short, when the Sun reaches the red giant stage it will be 256 times larger and 2,730 times more luminous than today.
The burned Earth, practically immersed in the solar chromosphere, will produce in it something similar to a lump of gas that will follow our planet in its orbit. The resulting friction will slow it down and it will eventually fall towards the star. The end of the trip. Meanwhile, the immutable Sun will continue on its way to its death as a black dwarf .
