As Galileo noted, much to his detriment, it all revolves around the sun.

I’ve mentioned how much I love Yuval Harari’s new book, Sapiens, and I recall something he wrote about our dear star: Every 90 minutes enough energy is delivered to Earth to power the planet for a year. We won’t really be doomed in the immediate future by energy scarcity but perhaps by want of ideas in harnessing it. 

But if the sun dies eventually, could we live on another planet, a star-less rogue one, and survive, even thrive in the gloom and on the margins? Perhaps, but it won’t be easy, as Sean Raymond writes in “Life in the Dark,” the latest great Aeon essay. The opening:

I’s 10,000 years in the future. You are a space explorer, preparing to land on the surface of a newly discovered world that might support life. This planet is dark, so dark that you can’t identify any of its surface features. All you can see is an ominous black circle blocking the stars. You enter its atmosphere and descend through a thick layer of clouds detectable only by the spaceship’s sensors. There is no light outside your ship. No sunlight. No stars. You turn to your commander, perplexed, and shout: ‘Wait a minute! This planet has no Sun! What the hell are we doing here?’

The Sun gets a lot of good press. Nearly everyone likes sunny days and rainbows. Solar panels are virtuous. Sunlight drives photosynthesis, which produces the oxygen we breathe. Our bodies make such mood-improving substances as vitamin D from sun exposure. Sun worship and solar deities appear throughout recorded history. We love our Sun.

But, does the Sun live up to the hype? Do we really need it? Yes, we do. If the Sun were to suddenly turn off, Earth would freeze over into an ice ball. Our planet’s geological thermostat – the carbonate-silicate cycle – is useless without the Sun. Lakes, rivers and ponds would freeze first. It would take decades but the ocean would eventually freeze solid. Some heat would continue to leak out of Earth’s interior at volcanoes and mid-ocean ridges. Eventually, Earth would look like Hoth, the ice-covered planet from the film The Empire Strikes Back. Most of Earth’s life would vanish.

Earth was born and grew up with the Sun. It’s not playing fair to just make the Sun disappear. Let’s consider a different type of planet, an Earth that never had a Sun, a ‘rogue’ or ‘free-floating’ planet. These planets don’t orbit stars. They wander the stars. They are free citizens of the galaxy. It might seem like the stuff of science fiction but several free-floating gas giants have been found in recent years.

Our own gas giants, Jupiter and Saturn, are leashed to the Sun on well-behaved orbits, but this might not be the norm in our galaxy. One study, published in Nature in 2011, suggests that the Milky Way contains two rogue gas giants for every star. That particular study remains controversial, but most astronomers agree that rogue planets are common in our galactic neighbourhood. And for every rogue gas giant there are likely to be several rogue Earth-sized rocky worlds. There are likely tens to hundreds of billions of these planets in our galaxy.

A free-floating Earth would miss out on many of the things we enjoy on our actual Earth. There would be no seasons or sunsets. And with no Sun to revolve around, no birthdays. But could a rogue planet support life, let alone a vibrant biosphere like Earth’s?•