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What If Earth Had 2 Suns?

VO: Ashley Bowman WRITTEN BY: Owen Maxwell
We often take that big, bright ball of light in our sky for granted. But we all know how vital the sun is for life on Earth. So, what would happen if we had two of them? Would doubling up on suns be a good thing, or bad? Our hypothetical lives in a new-look solar system would definitely be VERY different...

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What If The Earth Had Two Suns?

With all the constant change the world faces on a day-to-day basis, few things in life are as certain as the rise and fall of the sun. By its mere existence, the Sun heats our planet and supplies the energy most plants and animals need to survive. It sets our weather and atmospheric conditions in motion, and generally controls more aspects of our daily lives than we even notice. Needless to say, that orange-red ball of light is the single most important celestial body to Earth.
And after over four billion years, it’s still going strong, staging hydrogen/helium reactions to create heat of between 10,000 degrees Fahrenheit on the surface, and around 27 million degrees at the core. But while we’re still discovering new effects of one sun on our planet, what if there were two of them?
Though something like Tatooine in “Star Wars”is what probably first comes to mind, in reality it’d all depend on the sizes of the double suns and their distance from Earth. Looking at existing planets in solar systems which orbit around two stars, better known as binary systems, scientists have actually already found several planets in potentially habitable zones – though clearly no confirmation of life, just yet. The larger their suns are and the closer to them they move, the hotter these planets obviously get. So, if Earth was to inherit a second sun, we’d need to stay within the so-called Goldilocks Zone, or else we’d all fry, freeze or find ourselves unavoidably annihilated in some other way.
However, say our two suns are smaller, but just as far from us as our current solar centrepiece? Going by observations of existing binary system planets like Kepler 16b, Earth would likely be seriously cold. Though Kepler 16b is even closer to its two suns than we are to our one, it registers temperatures of around minus-100 degrees Fahrenheit. So, if we kept our same distance despite doubling up on smaller suns, Earth would be a bleak and icy place – and the chances of life would be extremely low.
But, what about if the climate remained the same – as unlikely as that is. Unfortunately, the orbital upheaval brings its own dangers. With two nearby suns acting upon the Earth, scientists suggest our planet could wobble between their two pulls. Most orbits in binary systems are unstable, and fall out of their normal paths quite easily. And so, the unusual force exerted by the existence of two suns could cause planets to crash into each other. To ensure long-term survival, Earth would either have to achieve a precise balance between both bodies, or have the pull of one sun completely overpower the other.
However, some systems have also shown that if their planets are an adequate distance from two suns, then they could orbit a combined center of mass between the two stars – instead of their individual masses. This outcome requires some exceptionally lucky circumstances – based on some incredibly intricate mathematics – but it would result in largely stable, collision-free orbits for all.
So, assuming we land in a stable orbit within a habitable zone not unlike our own… What then? Life on Earth would still be vastly different to what it is today. Multiple suns and their varying paths would change our climates, weather, and daily patterns.
Our standard solitary sun provides us with a fairly consistent day and night cycle. But, throw a second sun into the mix you push even these basic concepts into flux. Even if Earth managed to maintain its 24-hour rotation, scientists believe that daylight hours would become incredibly unpredictable, with days routinely (though unreliably) stretching beyond our usual 12 hours. Others even suggest that darkness and night could completely disappear for weeks, months or years – or could in fact become intensified, should we switch to a cycle of two suns overhead, then zero, and so on.
Two suns would also mean that the solar energy which controls our seasons would fluctuate dramatically, and much more often. Large fluctuations would cause seasons to change more rapidly, and at unexpected times. Planets orbiting binary suns can experience sudden shifts within days, so there’d be no telling what the seasons would even look like – meaning we’d probably stop relying on them altogether. And that’s before we’ve tackled the almost definite change to Earth’s axis tilt, which could redefine the planet’s regions, and completely transform it over time.
But assuming these kinds of changes are still fairly liveable, the weather and sky patterns could be quite exciting. Multicoloured, ever-changing sunsets could become the norm, as could a horizon on which one sun rises as the other sets. While any kind of eclipse is a rarity in our current solar system, two suns could turn them into an almost weekly occurrence. Plus, we'd see solar-solar eclipses for the first time, where one sun passes over another. Perhaps surprisingly, these eclipses would actually reduce the amount of heat and light reaching Earth.
Studies also suggest that the new sky would be even more observable, thanks to clearer conditions. Increased water vapor in the atmosphere, but limited cloud coverage, could increase humidity and cause temperatures to stay relatively constant – meaning the only significant shifts would come from the eclipses, or the rare moments when neither sun is beaming on your particular side of the planet.
Finally, the gravity of two suns would likely affect our lives in subtler ways, that we might not even notice at first. In a habitable system with safe orbits and a similar luminosity, the combined mass of both stars could be about 1.7 times that of our current sun. Here, the increase in gravitational pull would speed up our orbit and reduce our year length to about 280 days. Likewise in systems with multiple but much smaller suns, the reduced mass would trigger years much longer than our current 52 weeks.
No matter what size the suns are however, the difference in gravity we experience on Earth would be minimal. Given our distance from the sun, its current pull is less than one percent of the Earth's own gravity. Though additional or reduced mass would trigger some change, it's unlikely to be perceivable to us.
Clearly a binary system could become an incredibly dangerous place. But, if all the conditions are met, a two-sun set-up could actually cause an increase in liveable celestial bodies – particularly if the stars are low mass and closely bound. Even previously uninhabitable planets could become more hospitable – after a few million years or so. Which means, if Earth's new and unavoidably messed up cycles did become overwhelming, we’d have more viable options to migrate our species to. The likelihood of that reality isn’t all that high, however. So, for now let’s just be grateful for the sun we have, and hope it doesn’t disappear anytime soon.

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