The largest planet in the solar system and second most massive object after the sun, is Jupiter. It boasts at least seventy–nine moons… and the four largest of these, the Galilean moons, would all class as small planets themselves if they were orbiting the sun instead. So, does that mean that something like our own planet could ever become a Jovian moon, too?
Jupiter’s moons are large, none are larger than Earth. The largest, Ganymede (which is also the largest moon in the solar system full stop), is, though, bigger than the innermost planet, Mercury– so we already know that Jupiter can play host to planet–sized objects in general. In the layout of our particular star system, much depends on the distance an object is from all other objects that could exert a gravitational influence over it and balancing that with how far out that object is from the sun. So, size is important, but it isn’t make-or-breakin terms of what can orbit what. We see across the universe that objects of essentially any size can safely orbit each other… whether it’s the dwarf planet Pluto which has at least five, tiny moons, or the two massive central expanses in a binary black hole system. Physically speaking, Earth could, at the right distance, under the right conditions, orbit Jupiter… but it would mean major upheaval in the solar system. But
what about orbiting Jupiter and retaining life?
It’s nowhere near as simple. Despite its impressive size, Ganymede is still very unlike Earth, and one reason why is that it has such an incredibly weak atmosphere. A handful of Jovian moons at present do boastan atmosphere of some sort, but most don’t. And of those that do, none are even closeto Earth’s. We see in other planets like Venus, whichis clogged with CO2, just how important atmospheric conditions are… And we know that life can only exist on Earth because its own atmosphere is just right. So, were Earth to orbit Jupiter and still host life, it would have to somehow keep hold of its life–enabling atmosphere, too.
The nearest match in terms of “Jovian moons with the potential for life” is thought to be Europa — but even it has a very thin atmosphere. Europa, though, is still often touted as mankind’sbest bet for a second home anywhere in the solar system, or even as a potential source of alien life… with various claims that extraterrestrial somethings could be thriving in its subsurface oceans. It’s the predicted presence of liquid water that’s key, here, suggesting that parts of Europa must be reasonably temperate; not too
But, if there are subsurface oceans on Europa, then there’s something else at play, another means to retain warmth, with most explanations leaning toward tidal flexing. Presumed to be what’s happening on some icy moons like Europa (as well as on Saturn’s Titan), tidal flexing is when a big enough planet’s strong enough gravity creates the motion of the tides on its moon. That motion then creates heat through friction which, in the case of Europa, ensures that subsurface oceans stay liquid. Jupiter does also emit a certain amount of heat of its own, but nothing even closely comparable to the sun.
So, tidal flexing could be key to how Europa works, and if Earth were to wind up in a similar position… it would be crucial for its survival, too. With or without tidal flexing, though, the change in distance from the sun would certainly cause turmoil in how our planet fundamentally works. Rather than trying to curb global warming, for example, orbiting Jupiter would mean we’d be desperately trying to increase it — totop up on heat by any means necessary. Not that humans aren’t capable of living in freezing environments. One of the coldest continually inhabited placeson Earth is the village of Oymyakon in rural Russia, where winter temperatures have been known to plummet to minus–ninety degrees Fahrenheit. By contrast, Europa’s oceans are warmer, or else they wouldn’t exist. Io, another of Jupiter’s moons, a volcanic one, is also known to be hotter… although the trade–off is that Io is also noted for producing high volumes of deadly sulfur. Were Earth to suddenly orbit Jupiter, then, we’d have to find a way of making heat without risking the air we breathe; a difficult, potentially impossible task. All while finding a way of maintaining an atmosphere thick enough to protect against radiation, including increased radiation from Jupiter, too. And there aren’t many solar system objectsat all with an atmosphere thick enough for that. And so, we’re back to the problem of “atmosphere”. Because, even were the sun and planets torealign so that it was physically possible for Earth to orbit Jupiter, would it still resemble Earth if it did so? More than likely not, but that doesn’t meanthat there aren’t some moons “out there” which could still be Earth–like. For most astrophysicists, because moons areso common in our own star system, the existence of exomoons (moons around exoplanets in otherstar systems) is generally a given… even if it is debatable whether we’ve actually observed one yet. The problem in studying them is that exomoonsare generally too small, or too far away, or too complex for us to identify with confidence…but it is at least plausible that somewhere out there in the universe there’s a gas giant (like Jupiter) with a rocky moon (like Earth would be), at just the right distance from its star, holding alien life. Much as life on Earth relies on the current balance of this solar system, it would all depend on that exomoon existing in life-enablingequilibrium with everything else around it. For the same thing to happen to a hypotheticalEarth around Jupiter, well, the chances aren’t great at all. Yes, it’s physically possible that an object the size of Earth could orbit around an object the size of Jupiter… but the fundamental makeup of a Jupiter–orbiting Earth would almost certainly be totally different. And the question of how Earth would get toits new location (what would send it on its way? And could it ever hope to survive such a journey?)is one for another video. Perhaps in a far–off future, we’d even have tech advanced enough to purposefully move planets into whatever position suits us best…to the point where, in some kind of Kaddishes
Type Five society, the question wouldn’tbe “Could Earth orbit Jupiter?”
, but “Remember when it did?”. For now, the prospect of something the size of Earth around Jupiter is something which could happen. The likelihood of it happening and Earth still retaining life, though, is incredibly small. Between here and there, this world would simply have to go through too many changes. So, we should thank our lucky stars that we’renot Jupiter bound, just yet.