NeoScience Daily · SUN 25 OCT 2026 · Issue 05

Jupiter spins like crazy and has never done a thing for you

It turns more than twice as fast as Earth, which is a lot for something you can't even stand on, and down under the water clouds its belts and zones turn into something else, not that you'd ever get to see it.

Why care about the biggest planet?

Jupiter is the biggest planet we've got, sure, but you can't land on it, you can't breathe on it, you can't even stand on it, because there's nothing to stand on. It's a giant ball of gas about 483 million miles from the Sun with a big red storm on it that you saw in a school textbook once, and it's never done a single thing for you personally. So why should you and I give a damn?

Well, because it's basically the landlord. Jupiter is more than twice as massive as every other planet in the solar system put together, and when something's that big, everyone else lives on its terms. It shaped where the planets ended up. It throws comets around like a bored kid with a bag of rocks. And it's got a collection of moons that are more interesting than most planets, including one that probably has more liquid water than Earth, sealed under ice, and might be the best place to find life anywhere within reach.

Jupiter doesn't know any of that, of course, and it doesn't care. It's got about 318 Earths' worth of mass and four and a half billion years of seniority, and you're a tenant who's never once seen the lease.

So that's what this issue is about: why on earth you and I should care about the solar system's enormous landlord, and why we maybe shouldn't. Along the way we'll get into why you'd never hit the ground if you fell in, how its moons got Galileo in trouble and handed us the speed of light, the radiation that'll fry a person in days, the robots we sent wearing armor, the ocean moon that could change everything, and whether Jupiter is really our protector, or just an extremely large neighbor who occasionally throws things.

But first you need a sense of how big this thing is, because the textbook picture doesn't prepare you.

Juno and the winds of Jupiter

A LONG WAY OUT Five years after leaving Earth to make a 1.7 billion-mile journey (1.7 billion miles), the Juno spacecraft entered orbit around Jupiter on July 4, 2016.

SIZE AND WINDS With a radius of 43,440.7 miles, Jupiter is 11 times wider than Earth. Stormy Jupiter is swept by over a dozen prevailing winds, some reaching up to 335 miles per hour at the equator.

The landlord

Jupiter is fifth in line from the Sun, about 483 million miles out, roughly five times as far as we are, and the first thing you need to get straight is the size. It's about 87,000 miles wide, around 11 times the width of Earth, and you could fit about 1,300 Earths inside it. Add up every other planet in the solar system and you still don't get half of its mass. So when people talk about the solar system, what they really mean is the Sun, Jupiter and some rounding errors, and you and I live on one of the rounding errors.

It's made mostly of hydrogen and helium, the same stuff as the Sun, which is why people like to call it a failed star, and that's a bit generous. To start the kind of fusion that makes a star shine, it would need to be about 80 times more massive than it is, so calling Jupiter a failed star is like calling me a failed NBA player because I've touched a basketball.

There's also no surface. What you see in the pictures is the tops of clouds, and if you kept going down, the gas just keeps getting thicker and hotter until at some point it's more like a hot liquid, with no line where one ends and the other begins. Somewhere between a tenth and a fifth of the way down, the pressure gets so high that hydrogen starts behaving like a metal, a liquid that carries electricity, which is something we can barely make for an instant in a lab on Earth. That spinning metallic ocean is what drives Jupiter's magnetic field, the strongest of any planet, around 20,000 times Earth's by some measures. If you could see that field in the night sky, it would look bigger than the full Moon, even though Jupiter's about 2,000 times farther away.

And it moves fast, for something so large. A day on Jupiter lasts just under 10 hours, the shortest of any planet, so the equator's whipping around at about 28,000 miles per hour, and the whole planet bulges out in the middle from the spin, like all of us eventually. A year takes about 12 of ours, so you'd only ever have about seven birthdays there, which sounds nice until you remember the rest of this section.

All that spin pulls the clouds into the stripes you've seen, with winds running in bands at hundreds of miles per hour, and then there's the Great Red Spot, a storm that's been going for well over a century and possibly a lot longer. It's a hurricane wider than Earth, or at least it is for now, since it's been shrinking for decades, from about 25,000 miles wide in the 1800s to around 9,900 miles today. Nobody's fully sure why it's that color or how it's kept going this long. So the biggest storm in the solar system has been raging since before your great-great-grandparents met, and it may finally be running out of steam, which is more than you can say for your uncle.

So how did we find out about any of this? We started by looking at the things around it, and that turned out to be a problem for some very powerful people.

How a planet's spin is read

Jupiter's spin rate is known, and that fast spin sorts its clouds into dark belts and bright zones.

Time the spin Jupiter rotates once in about 10 hours, more than twice as fast as Earth.

Mark Io's place The Io phase is 0 degrees when Io is directly behind Jupiter as seen from Earth.

Spin sorts the clouds Jupiter's fast rotation creates strong jet streams. They separate its clouds into dark belts and bright zones across long stretches.

Four dots that got a man arrested

Nobody discovered Jupiter, since it's one of the brightest things in the sky and people have been tracking it for thousands of years. The Babylonians followed it so closely that they worked out its motion with what looks a lot like early calculus, about 1,400 years before Europeans came up with something similar, and we only found that out in 2016, when someone finally translated the right clay tablet. The Romans named it after the king of their gods, which is one of the few things the ancient world got completely right about the planets.

The moment it changed everything came in January 1610. Galileo pointed his homemade telescope at Jupiter and saw three small dots lined up next to it, then a fourth, and over the next few nights he watched them shift position, back and forth. He worked out what they were: moons, going around Jupiter. At the time the official view was that everything in the universe goes around the Earth, and here were four things that very clearly didn't. Those four dots, Io, Europa, Ganymede and Callisto, blew a hole in a model of the universe more than a thousand years old, and they helped land Galileo in front of the Roman Inquisition, where he got house arrest for the rest of his life for saying what anyone could see with a tube and two lenses.

Those same moons then handed us something nobody was even looking for. In 1676 a Danish astronomer named Ole Rømer was timing when Io disappeared behind Jupiter, and he noticed the timing kept drifting: Io ran late when Earth was far from Jupiter and early when we were close. The delay, he worked out, was the extra time light was taking to cross the distance, and until then a lot of people assumed light was instant. So the first real evidence that light has a speed at all came from watching a moon of Jupiter duck behind it, and the rough number that came out of it, about 137,000 miles per second, wasn't bad for a guy with a clock in 1676.

Then in July 1994, Jupiter gave everyone a demonstration of what it can do. A comet called Shoemaker-Levy 9 had wandered too close and been torn apart by Jupiter's gravity into a string of more than 20 pieces, and over about six days those pieces slammed into the planet one after another. Humans had never watched two bodies in the solar system collide before, and every telescope on Earth was pointed at it. The biggest impact left a dark scar about as wide as Earth, and it was only one of many. If any one of those pieces had hit us instead, the 1990s would be remembered for something other than bad jeans.

So Jupiter's the planet that took down our idea of the universe and gave us the speed of light, and it eats comets. You'd think we'd want to go there and see it up close. Well, about that.

Galileo and the moons

Galileo Galilei (1564 to 1642). Galileo Galilei first observed Jupiter's four largest moons, Io, Europa, Ganymede, and Callisto, in 1610. He used an early version of the telescope.

How Jupiter kills you

So let's say you're out there, you've got a very good ship, and you're thinking of having a look. Long before Jupiter lets you near its clouds, it's already started killing you, because that huge magnetic field traps charged particles and whips them up to enormous speeds, creating radiation belts that make Earth's look like a warm bath. Hang around near Europa and, by one widely repeated estimate, you'd take about 5 sieverts of radiation a day, which on its own is enough to kill most people within a few weeks. Move in close to Io, and by one rough estimate it's more like 36 sieverts a day, so you've got an unpleasant few days, tops. For comparison, the natural background on Earth is about 2.4 millisieverts a year, so one day near Io gets you about 15,000 years' worth, and I'm going to go ahead and say that voids the warranty.

Say you've got that handled and you decide to go in. You'd hit the top of the clouds at about 31 to 37 miles per second, because Jupiter's gravity is about 2.5 times what you're used to, and it's been pulling you in the whole way. That's over 105,000 miles per hour, or about 50 times the speed of a rifle bullet, and that's before you've even met the weather.

If you survived that, you'd fall through ammonia clouds at about -180 °F, the air so cold it'd freeze you, while winds shove you sideways at up to about 370 miles per hour. Keep falling, and it starts to warm up. There's a layer of ammonium hydrosulfide clouds, which smell like rotten eggs and cat pee, and then water clouds further down that might be something close to room temperature, for a moment, the last comfortable place you'll ever be. You can't stop there, however, since there's nothing to land on, and there's no bottom.

The pressure keeps building as you sink, and we know because NASA actually tried this in 1995, when the Galileo mission dropped a probe into Jupiter's atmosphere. It was built like a tank, it survived the entry, and it parachuted for about 58 minutes, getting about 93 miles below the cloud tops before the pressure, around 23 times Earth's, and the heat finished it off. That's a tiny fraction of the way in. What was left of it almost certainly melted and then vaporized, so it's now just part of Jupiter, and you'd go the same way, only sooner, without touching anything solid at any point. So you wouldn't die from the landing, because there is no landing. You'd just keep falling until the planet digested you, and it wouldn't notice that either.

So Jupiter will irradiate you, freeze you, crush you and cook you, in that order, and you'll never hit the ground. Naturally, we built robots in armor and sent them anyway.

Craft that went to Jupiter

NASA spacecraft crossed the gulf to the giant planet and went into orbit around it, and what the verified record says they did.

Galileo, eight years at Jupiter NASA's Galileo spacecraft orbited Jupiter for almost eight years. Its primary mission included a 23-month, 11-orbit tour of the Jovian system, including 10 close encounters of Jupiter's major moons. The mission ended when the spacecraft deliberately impacted Jupiter on Sept. 21, 2003.

Juno arrives at Jupiter in 2016 The Juno spacecraft entered orbit around Jupiter on July 4, 2016, five years after leaving Earth. With their gravity data, the Juno team was able to constrain the extent of the Great Red Spot to a depth of about 300 miles below the cloud tops.

That is the length of the journey the Juno spacecraft made to reach Jupiter.

Robots in armor

The first machines to go past Jupiter were NASA's Pioneer 10 and 11 in 1973 and 1974, mostly to find out whether you could survive the trip at all, and the radiation nearly killed them. Then the two Voyager spacecraft flew past in 1979, and that's when Jupiter got weird. They found out it has thin rings, and then a navigation engineer named Linda Morabito, looking at a Voyager 1 image, noticed a strange plume on the edge of Io, which turned out to be a volcano erupting into space. It was the first active volcano ever found anywhere other than Earth, on a moon most people had assumed was dead.

In December 1995 NASA's Galileo spacecraft became the first to go into orbit around Jupiter, and it stayed for nearly eight years, though its main antenna had failed to open properly on the way out, so the whole mission ran through a much smaller one, like running a business off a fax machine. It still found evidence of a salty ocean under Europa's ice, and that discovery ended up deciding its fate, because once it was low on fuel, NASA deliberately flew Galileo into Jupiter in 2003 so it could never crash on Europa and contaminate the place with germs from Earth. So we killed a working robot so it wouldn't accidentally sneeze on a moon, which should tell you how seriously they take that ocean.

Today the one on the job is Juno, which has been orbiting since 2016 with its brains locked in a titanium vault weighing about 440 pounds, the kind of thing you'd build for a bank, except this bank is being shot at by the planet. It runs on sunlight, even though the Sun's about 25 times dimmer out there, which is why it needs three solar panels each about 30 feet long, and its orbit swings in low over the poles to dodge the worst of the radiation, like someone sprinting through a bad neighborhood. What Juno found is that the planet's insides are messier than anyone thought. Its core appears to be fuzzy and partly dissolved, its winds reach down about 1,900 miles, and its poles are covered in clusters of cyclones arranged in neat geometric patterns, each one roughly the size of a continent, and scientists are still working out why they stay in formation like that.

The most exciting thing those robots found isn't on the planet at all, however. It's going around it.

Pictures from Juno and Galileo

UNDER THE CLOUD TOPS The hero picture shows the Great Red Spot. Juno's data shows that the belts and zones undergo a transition around 40 miles beneath Jupiter's water clouds. With gravity data, the Juno team constrained the extent of the Great Red Spot to a depth of about 300 miles below the cloud tops.

A FIELD TO MATCH Jupiter's enormous magnetic field is 16 to 54 times as powerful as that of the Earth.

ALMOST EIGHT YEARS The first small picture is an artist's rendering of NASA's Galileo spacecraft, which orbited Jupiter for almost eight years. Its primary mission included a 23-month, 11-orbit tour of the Jovian system, with 10 close encounters of Jupiter's major moons. Over the whole mission it had 35 such encounters.

FIRST, AND LAST On October 29, 1991, Galileo became the first spacecraft ever to encounter an asteroid, Gaspra. The mission ended when the spacecraft deliberately impacted Jupiter on Sept. 21, 2003.

FIRE ON IO The second small picture is a near true-colour mosaic of Io. Io is about one-quarter the diameter of Earth itself, yet it is the most volcanically active world in the solar system. It has hundreds of volcanoes, some erupting lava fountains dozens of miles high. Io even has lakes of molten silicate lava on its surface.

The moons that do the real work

Jupiter has more than 110 known moons, most of them small captured rocks, however the four that Galileo found are worlds of their own, and they get stranger the closer you get to Jupiter.

Start with Io, the closest of the four, about the size of our Moon and the most volcanically active place in the solar system, with hundreds of volcanoes. What powers them is Jupiter itself, since its gravity and the tug of the other moons keep stretching and squeezing Io as it goes around, raising the solid ground by up to about 330 feet, and all that squeezing turns into heat, the same way a paperclip gets hot if you keep bending it. So the surface keeps getting repaved by lava, and there's nothing that looks like a crater left on it. It's the universe's most aggressive skincare routine.

Further out you get Ganymede, the largest moon in the solar system, bigger than the planet Mercury and the only moon we know of with its own magnetic field. Past that is Callisto, nearly Mercury's size, old and heavily cratered, and far enough from Jupiter that the radiation drops low enough for you to maybe survive it. NASA even sketched a human base there in a 2003 study, though nobody's funding anything like that today.

And then there's Europa, and this is why anyone's paying attention. It's a bit smaller than our Moon, covered in a shell of ice, and underneath that shell is very likely a global ocean, kept liquid by the same squeezing that cooks Io. That ocean could be dozens of miles deep, and it might hold about twice as much water as all of Earth's oceans combined, on a moon about a quarter the width of Earth. We know it's there from the way Europa's magnetic signature behaves and from the look of its cracked, shifting surface, and possibly from plumes of water vapor shooting out of the ice, though that one's still argued about. And it might have what life needs, which is water, heat from below and maybe a chemical energy supply from the rock at the bottom. On Earth, whole ecosystems live around vents on the deep seafloor, in total darkness, and they've never seen the Sun.

So there might be something alive in the dark under that ice right now, and we've never looked, and we're finally going. NASA's Europa Clipper launched in October 2024, the biggest spacecraft NASA has ever built for a planetary mission, and it's due to arrive in 2030 to do about 49 close flybys of the moon. Europe's JUICE launched in 2023 and arrives in 2031, heading mainly for Ganymede. Neither will drill through the ice. They're going to find out whether it's worth coming back to do it. So we're a few years from even knowing if it's worth the trouble, and if you were hoping for a quicker answer, you've picked the wrong planet.

Io, the volcano moon of Jupiter

A MOON THAT PUZZLED EVERYONE This Planetary Radio compilation looks at volcanic activity across the solar system, and its stop at Jupiter is the moon Io. A volcanologist from the Jet Propulsion Laboratory recalls how the first spacecraft images of Io left the imaging team baffled, because the little moon looked unlike anything they had met before, with strange oranges, yellows and blacks.

THE PLUME ON THE EDGE The discovery of active volcanoes came from a navigation image. A member of the spacecraft navigation team spotted an odd plume on the edge of Io, and an infrared instrument then found heat matching it. Io became the first place beyond Earth where scientists had watched volcanoes erupting, which explained why the moon showed no impact scars.

A TUG OF WAR The guest explains why Io stays so active. It sits between giant Jupiter and the other large moons discovered by Galileo Galilei, so it is pulled in different directions all the time. That pull flexes its crust like a tide, the flexing makes friction and heat, and the heat keeps the interior molten. Without it, Io would have cooled long ago, like our own Moon.

WHAT JUNO FOUND The episode closes with recent results from the Juno spacecraft, whose close passes by Io mapped its lava lakes in infrared light. The scientists describe the lakes as enormous, and note that their edges run hotter than their middles, which seem to have crusted over, a detail that earlier missions could not show.

Is Jupiter really protecting us?

You've probably heard this one: Jupiter's our big brother. Its gravity catches the comets and asteroids that would otherwise hit Earth, and without it we wouldn't be here. It's a lovely thought, and Shoemaker-Levy 9 seemed to prove it.

Then scientists actually ran the numbers, and it turns out Jupiter does both. It does fling some comets out of the solar system entirely, and it does eat a few. It also knocks plenty of asteroids and comets out of their stable orbits and sends them toward the inner planets, including us. In one set of computer models from 2008, a Jupiter-sized planet actually gave Earth a slightly higher rate of asteroid impacts than having almost no giant planet, and one about a quarter of its mass was far worse. So the best way of describing Jupiter isn't "protector." It's a large man throwing things around a small room, where some of the things go out the window and some of them hit you.

It also might have had a much bigger hand in Earth's story than that. In a popular idea called the Grand Tack, young Jupiter drifted inward toward the Sun, maybe nearly as close as Mars is today, before Saturn's gravity helped pull it back out. If that's what happened, it would've scattered the early solar system's material on the way through, and it might be why Mars is so small and why the inner planets look the way they do. Nobody's proven it, but it shows how much of your address may have been decided by the landlord. Then there's the water you drink: the outer solar system's icy bodies, flung inward by giant planets, may have helped deliver water to young Earth. So there's a fair chance Jupiter both tried to kill us and delivered the drinks.

Three small facts about Jupiter.

What Jupiter actually offers you and me

So strip off all that mythology, and here's what Jupiter actually has to offer.

The big one is the chance to answer the biggest question we've got. If Europa's ocean has something living in it, even just microbes, then life started twice, independently, in one solar system, and it did it in a place with no sunlight, no air and no surface, and that would mean life could be almost anywhere, and I can't think of a mineral worth more than that.

It's also the best free ride in the solar system, and you've already used it. When a spacecraft swings close behind Jupiter it can steal a tiny bit of Jupiter's orbital speed, getting flung outward much faster, and it costs almost nothing. Voyager, Cassini, New Horizons and others have all done it. New Horizons got about an 8,700-mile-per-hour boost and cut about three years off its trip to Pluto. Jupiter didn't even notice, so a lot of our exploration of the outer solar system has been paid for out of the landlord's pocket, and he's never sent us a bill.

Further out in the future, those moons hold enormous amounts of water ice, and Callisto's low radiation makes it one of the few places out there a person might survive for a while, with Jupiter hanging huge in the sky. Jupiter also works as a sample, because planets its size are some of the easiest to find around other stars, and it's the closest one we've got, so what we learn here applies to thousands of others.

Now the honest limits. It's far. Even with a good boost it takes about five years or more to get there, and a radio signal takes between about 33 and 54 minutes each way. The radiation near the good moons will kill you, the planet itself has nothing to land on, and the only thing it's got that you could mine is hydrogen and helium, with no ground to stand on while you do it and gravity 2.5 times Earth's trying to keep it. There's also no plan to send anybody. So nobody's going to live at Jupiter in the lifetime of anyone reading this, and no billionaire is about to put a dome on Callisto.

No Jupiter print yet.

NeoPrint makes custom 3D printed objects. This is what the store lists today.

NeoPrint has no Jupiter print or kit yet. Its store today lists 7 objects in the Moon Collection, shown as concepts, plus the Fossil Collection and a Make Your Own page. None of them is a Jupiter product, so there is nothing to buy for this issue.

Visit the NeoPrint store

So, should you and I care about Jupiter?

Jupiter doesn't care about us. It's been the biggest thing in the neighborhood for four and a half billion years, and if we vanished tomorrow, it wouldn't even change the locks.

It's a world where you'd never touch the ground, that would kill you with radiation long before you got near it, and that's as likely to throw a comet at you as catch it. That being said, it also took down our idea of the universe with four dots, gave us the speed of light, and might have an ocean around it with something alive in the dark.

So yeah, give a damn, because the next big answer about whether we're alone in the universe may well be in orbit around this thing, and we've finally got a robot on the way. It'd be a shame if the biggest discovery in human history happened while you were still thinking of Jupiter as a storm on a classroom poster.

Next time, the daily updates take one piece of this and go all the way in. We'll fall through the clouds with the Galileo probe, stand on Io while it erupts, and drill down through the ice on Europa to see what's waiting in the dark.

What stuck?

  1. How does Jupiter's mass compare with the rest of the planets?
  2. If you fell into Jupiter, why would you never hit the ground?
  3. Ole Rømer noticed Io's disappearances drifting early and late. What did that show?
  4. Why is Io covered in volcanoes?
  5. Why did NASA deliberately fly the Galileo spacecraft into Jupiter in 2003?
  6. Is Jupiter really Earth's protector from comets and asteroids?

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