What is the fate of the Earth? | The basics of astronomy

Artist’s concept of a red giant star burning a planet orbiting around it. Image via ESO / L. Calçada.

The Earth exists because of our sun, formed in orbit around it from a huge cloud of gas and dust in space, 4.5 billion years ago. Likewise, the sun will ruin the Earth for living things in about 5 billion years. As the sun evolves, it will expand to become a giant red star and fry our planet to ashes. Additionally, Earth’s death will occur against a backdrop of galactic-scale change. Our Milky Way galaxy and the Andromeda galaxy will be in the midst of a colossal collision that will forever alter our galactic home in space.

Our sun is a type G star currently at about half of its life cycle. This type of star is very stable for most of its life, quietly fusing hydrogen into helium within its interior for billions of years. One day, the hydrogen inside the sun will be depleted. At this point, the inward gravity pressure will outweigh the outward pressure of the sun’s internal fusion, until the sun warms enough to start fusing helium. At this point, the sun will balloon outward to become a red giant star.

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As the sun warms up and expands, its outer layers will envelop the innermost planets, Mercury and Venus. The outer edge of the sun will grow larger to roughly orbit Earth. The water and atmosphere of our planet will boil, leaving nothing but charred, lifeless rock. Mars will take some time to warm up, but eventually Mars will also be outside the habitable zone for humans. At this point, the moons of the outer planets – like Jupiter and Saturn – will be the only places left in our solar system for human colonies.

But these locations will also only be temporary fixes in the search for a new home.

As our sun expands into the red giant phase, the habitable area around it will be pushed out into the solar system. Image via NASA / Wendy Kenigsburg.

The red giant phase of the sun could continue for about a billion years, but the helium will eventually run out as well. Then the sun will blow out an envelope of gas. Astronomers looking through telescopes in other star systems will see our sun as what we call a planetary nebula, a large shell of gas surrounding a dying star. Ultimately, this shell will dissipate into space and what remains of our sun will become a white dwarf star.

Earth astronomers can look out into space to see the future of Earth. For example, 400 light years away, a star known to astronomers as SDSS J1228 + 1040 is a white dwarf with its burial shroud of a gas nebula, and within it astronomers have found the signature of a planetesimal still orbiting its native sun long after its calamitous. dead.

And what about the Milky Way galaxy itself, the great island of stars containing our Earth and our sun? By the time our sun balloons into the red giant phase – long before it settles down as a white dwarf – the Milky Way itself will undergo an inevitable long process of collision with the neighboring giant spiral galaxy, the galaxy. from Andromeda. The last humans on Earth – if there are any remaining in a few billion years – will see the Andromeda Galaxy grow larger and brighter in the night sky. It is currently barely visible to the naked eye from a dark sky site. But, in a few billion years, the Andromeda galaxy will be a breathtaking and incomparable whirlwind of stars, easily visible in the night sky to everyone on Earth.

As Andromeda and the Milky Way come closer, the great mass of the Andromeda galaxy will begin to affect the stars of our Milky Way. Our galaxy is wide and flat, like a pancake. We on Earth currently see its stars on a dark August evening as a large misty strip across the sky. But as Andromeda’s gravity warps their paths, the stars of the Milky Way will be scattered across our skies.

It may sound incredible, but the stars in galaxies are so far apart that even when the two giant spirals collide, there will be little fireworks from collisions between stars. However, the gas clouds in the two galaxies are likely to collide, forming vast conglomerates of new stars.

This series of illustrations shows the planned merger between our Milky Way galaxy and the neighboring Andromeda galaxy. Image via NASA.

Ultimately, the Milky Way and Andromeda galaxies will settle down to form a massive new drop-shaped galaxy. At this point, the Earth, our sun, and the rest of our solar system could be in an entirely new location relative to the galactic center. Currently, Earth is approximately 25,000 light years from the center of the Milky Way. After the merger of Andromeda and the Milky Way, astronomers believe that our home in space will have been torn off into a new galactic orbit some 100,000 light years from the center of the new and large combined Andromeda-Milky Way galaxy. . As theorist TJ Cox of the Harvard-Smithsonian Center for Astrophysics put it:

You could say that we are being sent to a retirement home in the country.

And what will be the fate of humanity? It’s impossible to say. If he survives, humanity’s future will depend on our ability to move away from our dying sun and set up camp elsewhere.

Fortunately, we have a few billion years to figure out how to accomplish this monumental task.

Conclusion: what will be the fate of the Earth? The Earth is called to become a dry, scorched rock, because our sun becomes a red giant star. Additionally, as the Milky Way and Andromeda galaxies collide, our Sun and Earth (and the rest of our Solar System) should be projected outward, away from the galactic center, to the outskirts of a new large galaxy created during the collision. .