The series "Imaginary Earths" speculates what the world might be like if one key aspect of life was changed, be if the planet or with humanity itself. What might Earth be like if it had rings, or if everyone could photosynthesize like plants?
The rings of Saturn grant the planet a majesty befitting a world named after the king of the Titans. Made nearly completely of bits and chunks of ice and spanning thousands of miles wide, Saturn's rings have been its most spellbinding feature ever since Galileo discovered the first signs of them in 1610.
What might Earth be like crowned with rings? Space and science- fiction illustrator Ron Miller created extraordinary images of how the sky might look if Earth possessed rings of the same proportions to our planet that Saturn's are to it.
Since the most stable place for rings is around a planet's equator, the appearance of the rings would depend on the latitude you are located at on the world's surface. For instance, near the equator at Quito, Ecuador, you would see the rings from edge on, so they would look like a thin line rising straight up from the horizon.
In comparison, near the Arctic Circle, the rings might look like a hump on the horizon.
At more temperate latitudes, the rings would look like a giant arch, crossing from one end of the sky to the other.
These glittering rings would never rise or set, but would always appear in the exact same place in the sky. These cosmic landmarks would be visible both day and night.
Bright rock
If Earth did have rings, they would differ in one key way from Saturn's — ice. Earth lies much closer to the sun than Saturn, and sunlight would cause any ice in Earth's rings to sublime away.
Still, even if Earth's rings were made of rock, that might not mean they would look dark. Moon rock is largely grey, and the moon only reflects about 12% of the light falling onto it, but the full moon "looks really bright because there's a lot of light falling on it, and because it's so close to us," Scharf said.
How bright might Earth's rings get? "About 1,300 watts of sunlight per square meter hits the top of Earth's atmosphere," said Caleb Scharf, director of astrobiology at Columbia University in New York. "If rings reflected even 10% of that, we're talking about each square meter reflecting as much light as produced by a 130-watt light bulb.
Closer than the moon
Just how close might the rings get to Earth? The absolute closest they could get is somewhere above the atmospheric layer known as the thermosphere, which reaches up as high as 620 miles (1,000 km). Atmospheric drag would bring down any ring matter that descended that low.
Just how far might the rings extend from Earth? Any object orbiting within a certain distance of Earth, known as its Roche limit, will break apart to form a ring due to the force of Earth's gravity. Any object the size of Earth's moon that fell below about 7,365 miles (11,850 kilometers) from Earth's surface would disintegrate, forming a ring around the planet.
All in all, Earth's rings would likely orbit even closer to our planet than does Earth's moon.
Ring or rings? Moon or moons?
Whether or not Earth would possess one ring or many depends on whether or not Earth also possessed "shepherd moons," small moons that clear gaps between rings and help keep particles confined within a ring. Saturn's rings possess a number of shepherd moons, such as Prometheus. Shepherd moons in Earth's rings might resemble shining pearls circling around the edges of the rings.
It's unlikely Earth could have longstanding rings if it possessed as large a moon as it does, Scharf said. The same gravitational forces the moon exerts on Earth to cause tides might disrupt any rings, he explained.
Falling shadows
Depending on the time of day, the season of year, and the latitude one is located, Earth's shadow might fall on the rings. Earth's shadow would look oval-shaped on the rings, "and move as time goes by," Scharf said.
What the sky might look like if Earth had rings like Saturn, from the perspective of the Tropic of Cancer, with Earth's shadow falling on the rings. Credit: Ron Miller.
During the equinoxes, the sun will lie on the same plane as the rings. At these times, at Earth's middle latitudes, the planet's shadow will appear to stretch across the rings to its greatest extent, casting large portions of them into darkness. At the equator, the rings will appear to divide the sun, casting a dramatic shadow over half the world.
What the sky might look like if Earth had rings like Saturn, from the perspective of the equator during an equinox. Credit: Ron Miller.
The rings themselves would cast shadows on Earth. During the summer in the northern hemisphere and the winter in the southern hemisphere, the rings would cast their shadows on the southern hemisphere, and vice versa. This could mean that winters in both hemispheres might be colder and more severe than they are on our Earth. However, at the same time, "ringshine" might increase the total light Earth receives, "so the climate effects are tricky to pinpoint," Scharf said.
The mythologies surrounding the rings
As celestial landmarks that never change their position in the sky, the rings would almost certainly play a key role in mythologies. At temperate latitudes, one might imagine that the rings' appearance as an arch might symbolize a bridge between heaven and Earth.
Since the rings' appearance changes with latitude, so too what they mean to people might change. Given how wars on Earth have stemmed from opposing views of religious doctrine, one might wonder what might happen as people start roaming the planet and seeing the rings change in appearance.
And the ring might very well entice people to wander the world. Given how the rings can resemble giant arches, explorers might want to see where the arches touch down, much like a person might want to see what's at the ends of a rainbow.
In addition, Scharf noted that around the edges of Earth's shadow on the rings, one would see light that was filtered through Earth's atmosphere. "You might get some funky colors at the shadow's edges, maybe a blood-red rim," he said. "I could imagine all sorts of mythologies built around that."
Moreover, depending on the latitude and the season, the path of the sun may cross behind the rings. The particles making up the rings would likely scatter the sun's light, making it appear hazy or veiled. "It's interesting to think what spiritual significance a civilization might ascribe to the sun going behind the rings," Scharf said.
A guide for navigators
The rings might potentially serve as extraordinary navigational aids. One might wonder how they might support travel, exploration, trade, migration and invasion.
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