What If Earth Had the Moons of Jupiter? | Unveiled

What if Earth Had the Moons of Jupiter?

For billions of years, Earth’s moon has loyally watched over us, becoming an integral part not only of human culture but the planet’s entire ecosystem. We depend on the moon for all kinds of things, and it’s hard – or even impossible – to imagine where we’d be without it. But what if instead of one moon, we had dozens?

This is Unveiled, and today we’re answering the extraordinary question; what if Earth had the moons of Jupiter?

When it comes to moons, every single planet is different. The planet in the solar system with the most moons is Saturn, with at least 82; and this is in addition to hundreds of moonlets. Jupiter comes in second, with 79 moons. These are just “known moons” – they probably both have more that we just haven’t detected yet.

Jupiter is the second-largest celestial body in the solar system after the sun and has an immense gravitational pull; since gas giants are generally large and gravitationally powerful, that’s why they have many more moons than small, terrestrial planets. In fact, while there are four inner planets, there are only three moons between them; Earth has one moon and Mars has two. Neither Mercury nor Venus has a moon at all.

And Jupiter’s moons aren’t anywhere near as barren as Earth’s – some of them are extremely interesting. The four largest moons are called the Galilean moons since they were first observed by Italian astronomer Galileo; they are Ganymede, Callisto, Io, and Europa. Ganymede is actually the largest moon in the solar system, and has its own magnetic field - potentially making it more like a liveable world than any other satellite. In fact, Ganymede is bigger than the planet Mercury. Io, while being pretty much inhospitable, is intriguing for other reasons, absolutely riddled with volcanoes and incredibly volcanically active. Sometimes nicknamed the Pizza Moon, it’s actually bright yellow because it’s covered with so much sulfur. Meanwhile, Europa boasts a vast subsurface ocean that’s long been theorized to host alien life.

Saturn also has its fair share of large and interesting moons - among them Enceladus and Titan. Like Europa, Enceladus is also believed to have a large internal ocean. Titan is the most Earth-like body in the solar system, with similar atmospheric pressure and gravity to Earth. It’s also the only celestial body other than our home planet with stable bodies of surface liquid, in the form of hydrocarbon lakes - which could feasibly also harbour life.

But having lots of moons or even no moons at all is far more common than the Earth-Moon system humanity exists within. As a general rule, the moon systems of a gas giant are about 10,000 times less massive in total than the planet itself; any more mass and the planet might not be able to sustain the system, and moons could fall out of orbit, tumbling into the planets themselves. But our moon is only 80 times less massive than Earth! For comparison, though Mars has two moons – Phobos and Deimos – they’re actually very small. Whereas our own moon’s diameter is roughly 2160 miles, the diameters of Phobos and Demios respectively are just 13.8 and 7.8 miles. These moons aren’t stable, either – Phobos has been nicknamed a “Doomed Moon” because its erratic orbit means it will one day crash into Mars or disintegrate.

The moon is weirder yet because we don’t actually know for sure how it formed. There are a lot of theories about this, and the one that’s probably correct – and is most widely accepted – is that the moon is the remnant of a collision between Earth and a protoplanet billions of years ago. It’s an enormous piece of planetary debris that was close enough to be pulled into a stable orbit, becoming a vital part of Earth’s ecology; where would we be without the moon to control the tides and keep our oceans moving? It’s downright bizarre that Earth has such a large, natural satellite in a stable orbit, especially when the moon is comparable in size to the largest moons of the largest planets. So, while we might think Jupiter and Saturn are strange, it’s actually Earth that’s the odd one out here.

But could Earth ever sustain a moon system like the Jovian one? Well, Earth does have a few natural satellites other than the moon. However, these are distant, smaller, quasi-satellites, and some are temporary. If we did have dozens of moons all of a similar size to Mercury or even Mars, things probably wouldn’t end well for mankind. Again, the moon was likely formed from a planetary collision over four billion years ago. Given Earth’s relatively low mass compared to the gas giants, we’d be constantly at risk of similarly massive collisions if we had numerous large moons. Our planet’s gravity just wouldn’t be enough to maintain stable orbits.

In roughly 30 to 50 million years, Phobos is going to be destroyed. It might be ripped apart into dust and debris, or it could crash down to the Martian surface – and hopefully, people won’t be living on Mars by the time this happens. An object with a diameter of 13.8 miles might seem small relative to the size of an entire planet, but this is already twice as large as the estimated size of the Chicxulub Impactor, the notorious asteroid that wiped out the dinosaurs 66 million years ago. What would happen if Earth had the four Galilean moons and their orbits all became unstable? Ganymede has a diameter of almost 3,300 miles, and Titan isn’t far behind – if just one of these moons crashed into Earth, the entire planet and moon would be destroyed. It’s been estimated that an asteroid just 60 miles in diameter would wipe out all life on our planet; Earth would be broken apart by a collision fifty times larger than this, completely obliterated.

And this is a far more likely outcome than Earth ever being able to sustain such a large moon system. Collisions like this have happened to the gas giants many times, which once had far more moons. Of course, nobody lives inside the atmospheres of gas giants for these collisions to affect them, but many moons have been lost over the years when they’ve been swallowed up by the gas giants they orbit. If Earth had a satellite system like Jupiter , the planet might not have survived long enough for life to develop at all; one collision billions of years ago could have shattered the planet, leaving small remnants that wouldn’t be able to generate a magnetosphere and atmosphere like Earth has today.

But let’s just suppose that there was a way for Earth to beat the odds, and have a vast moon system that wasn’t going to crash into us and kill us? After all, we’ve already got one weird moon, what’s a few more? There could be astonishing potential for life in such an arrangement. You’d have multiple, planet-sized worlds in the Sun’s habitable zone already close to amino acids and the elements necessary for life. We have all those things in abundance on Earth, and the same process that brought them to Earth or created them here could have happened on its large satellites, too. If we had moons the size of Ganymede and Titan, we would essentially have alien planets right on our doorstep. Life on these worlds would all be carbon-based, but there could be completely different sentient species than humans; what’s stopping a more temperate Europa from developing intelligent sea life in its deep oceans? Or a hotter moon than Earth supporting reptilian humanoids?

The best part is that since these moons would be so close, we’d never have to worry about the vast distances and communication delays that come with trying to contact potential aliens in different star systems. They’d be so near that we could have practically instant communication. Powerful enough telescopes would even be able to see what was happening out there. It would also make colonizing other worlds much simpler; rather than journeying all the way to Mars to set up shop, we could just branch out to our various moons.

On the other hand, multiple, habitable moons could make geopolitics even more complex than it already is. What would happen if we started going to war with the other moons? Would the consequences of these be as world-shattering as the collisions themselves?

Ultimately, the likeliest possibility is that an Earth with Jupiter’s moons wouldn’t be Earth for long, because just one collision with a small moon could eradicate us. One moon is plenty. And that’s what would happen if Earth had the moons of Jupiter.