Living with a star is both a blessing and a curse. On the one hand, our Sun provides us with light, warmth, and the energy that allows plants to grow, fuelling our entire ecosystem. On the other hand, it will eventually destroy our planet, and with it whatever life has the bad fortune to remain.
A recent study using data from the Kepler Space Telescope made headlines by pointing out that, contrary to conventional wisdom, our planet might be at risk from solar “superflares” – giant bursts of high-energy particles and radiation from the Sun.
Our previous understanding was that producing such extreme events was a habit a star would grow out of in its later years. However, the new data suggest that while these outbursts become rarer, they don’t go away entirely. We might still be at risk – albeit perhaps only once every few thousand years.
And while these superflares should get less powerful with time, they could still cause major disruptions to satellites, power systems, and communication systems, and possibly even damage the protective outer layers of our atmosphere.
Even relatively mild solar outbursts can wreak havoc. One such historical event, with about 1% the power expected for a superflare, brought the global telegraph network to its knees in 1859, before the era of satellites and ubiquitous electronics.
Given that it’s only a matter of time before we experience something similar (or worse), we would be wise to invest now in hardening our power grid and making sure we have contingency plans if all our electronics get knocked out at once.
Superflares, while potentially troublesome, will not be a real threat to life on Earth, especially if we are aware of the issue and take some basic precautions. On billion-year timescales, though, we (or whoever occupies this planet when humanity has evolved or died out or moved on) will reach a point at which no amount of technological preparation will save us.
Our Sun (for which the official astronomer-approved name is “the Sun”) is a G-type star, of middling mass, about five billion years into its adult life. Since it first ignited, it’s been steadily converting hydrogen into helium in its core and producing light as a by-product.
This process can’t last forever, however. The Sun will eventually exhaust its core’s hydrogen, making further fusion impossible. And long before the hydrogen is fully spent, the Sun will go through a series of life changes, drastically altering our cosmic habitat.
Right now, Earth is just the right distance from the Sun to be comfortable. We are close enough for the Sun’s radiation to keep our surface water from freezing, but not so close as to boil it all away. This careful balance between the Sun’s energy output and our distance places us in the “habitable zone,” where liquid surface water is possible.
Over the next few billion years, our distance from the Sun will not change, but its brightness will. As the Sun works its way through its hydrogen supply, its core will start to burn hotter and faster, slowly expanding its outer layers in the process. The amount of radiation we receive will start to climb. Within a billion years, or maybe two, that radiation will be enough to boil off all the oceans of the Earth. Even microbes will struggle to survive on such an arid rock.
What happens to this charred remnant of Earth after that is still a matter of some debate. As the Sun expands, it will engulf the orbit of Mercury, and perhaps Venus, consuming those planets in its fiery outer layers. It will eventually blow off its tenuous atmosphere, creating what will likely be a beautiful planetary nebula, if viewed from a safe vantage point.
This might disturb our orbit, sending us plunging into the hot but tiny stellar core, which will at that point be classified as a white dwarf star. Or we might continue to orbit within the nebula indefinitely, far enough now from the tiny star to be ice cold.
Perhaps we should not be too hopeful. Astronomers who study white dwarfs frequently find disturbing features in the spectra of their light: hints of heavy elements that could come only from the debris of recently consumed planetary material. If we someday meet this fate ourselves, we, too, might be detected by other curious civilisations as merely a bit of “contamination” in the otherwise pure elemental spectrum of a bright distant point of light.
Still, a billion years is a long time. It’s possible we will find ways to adapt to our changing stellar neighbourhood, or to leave it entirely. Meanwhile, let’s spare a thought for those unfortunate worlds that, once born from stardust, to stardust have returned.
Katie Mack is an astrophysicist at North Carolina State University.
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