The Sun's Demise: What It Means for Life on Earth
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The Fate of Our Star
The Sun's eventual demise will unfold gradually. It will evolve into a red giant, potentially engulfing the Earth in the process. If we manage to survive that phase, the intense solar winds could still pose a threat. Ultimately, the Sun will transform into a white dwarf, a type of star around which life cannot exist. This suggests that humanity has approximately 5 to 7 billion years to develop interstellar travel technology if we hope to continue our existence.
NASA Goddard Space Flight Center, CC BY 2.0, via Wikimedia Commons
Discovering life on planets that orbit a white dwarf would be monumental for humanity. It would not only confirm that we are not alone in the universe but also demonstrate that life can persist even during the later stages of a star’s life cycle—or perhaps not.
Researchers at the University of Warwick have examined the potential fate of life on planets circling Sun-like stars as they reach the end of their life cycle. Their simulations suggest that humanity will cease to exist alongside the Sun unless we invent a means for interstellar travel by that time. Why is this perspective so grim?
Life Cycle of Stars
Stars with a mass similar to the Sun, or slightly larger (up to about 8 solar masses), do not explode as supernovae at the end of their life. Instead, when the hydrogen fuel in the core runs out, the core contracts, causing the temperature to rise and leading the outer layers to expand. This transition marks the beginning of the red giant phase.
In approximately five billion years, as the Sun swells to about 300 million kilometers in diameter, it will likely consume Mercury, Venus, and possibly Earth. During this phase, it will unleash powerful solar winds that will strike all the planets in the solar system.
[Photo: NASA/SDO (AIA), Public domain, via Wikimedia Commons]
As the Sun loses mass, the gravitational pull on the surrounding planets will diminish, causing them to drift into wider orbits.
The Role of Solar Winds
The solar winds will primarily drive the end of life on Earth. Currently, our planet is shielded from these winds by its magnetosphere, which is maintained by the liquid iron core beneath the surface. In contrast, Mars, with its partially solid core, has lost its magnetic field, leading to atmospheric erosion due to solar winds over billions of years. Earth’s robust magnetic field protects us, but it can falter during intense geomagnetic storms, resulting in temporary disruptions to power grids.
However, during the red giant phase, simulations suggest that Earth's magnetosphere will be compromised by the solar winds. Research indicates that to maintain an effective magnetosphere at this crucial evolutionary stage, our magnetic field would need to be at least a hundred times stronger than Jupiter's current magnetic field, which is fourteen times stronger than Earth's.
Temperature Changes and the Ecosphere
As the Sun expands, it will push the ecosphere—the region where liquid water can exist—farther from the Sun. Currently, this area stretches from Venus's orbit to nearly Mars's orbit, with Earth ideally positioned within it. However, as the Sun swells into a red giant, the ecosphere will retreat to about 6 billion kilometers from the Sun, well beyond Neptune's orbit.
At the end of the red giant phase, the Sun will shed its outer layers, leaving behind a hot core—a white dwarf roughly half the mass of the Sun and the size of Earth. This white dwarf will cool over hundreds of billions of years, but it will no longer emit solar winds. Unfortunately, by that time, life in the Solar System may no longer exist.
White dwarf — [Photo: NOIRLab/NSF/AURA/J. da Silva Image processing: M. Zamani and M. Kosari (NSF’s NOIRLab), CC BY 4.0, via Wikimedia Commons]
Nonetheless, it's conceivable that life could emerge anew on surviving planets over the next billion years, given ample time.
Searching for Life Around White Dwarfs
Should we seek out life on planets orbiting white dwarfs? It's possible, but keep in mind that any life found would have to develop after the star had already transitioned into a white dwarf.
To conclude on a hopeful note, we still have 5 to 7 billion years to figure out how to achieve interstellar travel. If we succeed, we could escape our solar system and explore younger stars. While such advancements may seem far-fetched, considering our rapid technological evolution over the past hundreds of thousands of years, perhaps in a billion or two, we will have the means to flee our Solar System. I sincerely hope for this future for both myself and future generations.
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