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Among the planets in our solar system, Jupiter is the eldest and largest, and it often appears as the second brightest in the night sky after Venus. Scientists have long tracked this streaked gas giant ever since they started constructing simple telescopes. In 1610, Galileo Galilei observed Jupiter through his telescope and discovered four large moons. The finding prompted him to suggest the then-heretical notion that Earth, like these four Galilean satellites, may be encircling some larger astronomical body instead of being surrounded by minions at the center of the universe.
Jupiter’s extreme heft is its most characteristic feature. Owing to its gravitational prowess, Jupiter plays a “big brother” role in the solar system—it has had a hand in many historical events. Four billion years ago, the behemoth conspired with Saturn to combine their gravitational might to hurl comets and asteroids across the solar system. Such an event may have even brought about a cataclysmic period known as the Late Heavy Bombardment—when planetesimals peppered the inner solar system and potentially forged many of the craters that pockmark the surface of the moon today.
In the last 50 years, spacefaring missions and the development of more powerful telescopes have allowed scientists to peer past Jupiter’s clouds and dissect the planet with unprecedented clarity. Scientists have found that Jupiter’s environment is extremely hostile. Long-lasting storms jet around the planet and paint the surface in multicolor bands. Lethal levels of radiation threaten to fry any interloper. Like their mother planet, the Galilean moons are also far from being placid worlds.
With its gorgeous swirling overcoat and nature of extremes, Jupiter has long captured the public imagination and continues to inspire scientific study. Recent discoveries have only heightened Jupiter’s mystique, enticing researchers to probe this far-flung realm. Here are some of the most enthralling findings scientists have made about Jupiter and its moons in the last five decades.
Jupiter has a strange core
As a gas giant, Jupiter isn’t terra firma—all the way down to its fuzzy core. At its center is a diluted mixture of heavy-element solids and gases squeezed beyond recognition by gravity. Imagine biting into day-old boba that’s still soft on the outside but has hardened somewhat in the middle—Jupiter has a similar consistency, one of a fluffy outer layer that transitions into a dense core in one continuum.
Jupiter’s strange interior was discovered by the Juno mission in 2017 through gravity field measurements, a technique that maps the subtle variations in the gravitational tug on a spacecraft as it skims all across the planet. The gravity data looked nothing like that for planets with a sharp solid-fluid boundary, prompting scientists to propose that Jupiter has a fuzzy core. “We still don't fully understand exactly what is going on,” says Heidi Becker, a NASA planetary scientist and one of Juno’s co-investigative leads.
Understanding the core provides clues into Jupiter’s formation. Most proto-planets start accreting solids first until they become massive enough to switch to recruiting gases. To explain the Jupiter data, scientists theorize that perhaps Jupiter never stopped accreting solids as it grew. As a result, the planet may be an uneven mixture of solids and gases from center to surface. Another speculation is that a giant impactor, one that formidably matched Jupiter in size and heft, fell into Jupiter and stirred up the planet’s insides, blurring out the core-mantle boundary.
A powerful magnetosphere creates energetic streams
Earth’s magnetic field arises from swirling molten iron in its core that generates a dynamo. On Jupiter, a curious form of matter known as metallic hydrogen powers the magnetic field instead.
Jupiter’s heft translates to immense pressures deep inside its heart, which fashions exotic matter found nowhere else in the solar system. Hydrogen, the lightest element on the periodic table and typically a gas, is pinched inside the planet until its electrons detach from the atoms and swarm freely. This sea of mobile electrons creates the dynamo that gives Jupiter its powerful magnetic field. Jupiter’s sphere of magnetic influence is the largest object in the solar system, several times wider than the sun. This magnetosphere is mammoth enough to protect the planet from solar winds, sweeping the sun-flung particles as far as Saturn’s orbit.
Jupiter may be untouchable by solar winds, but the Jovian system—Jupiter and its moons— generates its own energetic particles. They are trapped and accelerated by the very magnetic field that protects the planet from external ionic bombardment.
“The presence of the magnetic field has pros and cons,” says Cheng Li, a planetary scientist at the University of Michigan and a Juno co-investigator.
The charged particles come from Jupiter’s most volatile moon, Io, whose volcanic spew becomes electrified as the magnetic field rips electrons from its molecules. The stray electrons zip around Jupiter near the speed of light and release radio waves. These radio emissions are a nuisance from a scientific perspective, because they drown out radar signals from scientists aiming to probe the planet’s interior from Earth. The electron shield also creates a radiation belt that pummels visiting spacecrafts. With this hazard in mind, scientists built Juno “like an armored tank,” Becker says—all its sensitive electronics sit inside an electron-shielding titanium vault that weighs almost 400 pounds.
Nevertheless, Jupiter’s strong-arm magnetosphere creates spectacular auroras when the electrons it directs invariably smash into other atoms in the atmosphere to release bursts of light. Given that the magnetic field is large enough to envelop the moons, it also ferries ejecta from Io elsewhere. Scientists have detected contaminants all the way on Europa, another Jovian moon that’s hundreds of thousands of miles from Io.
Jupiter runs hot
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Jupiter isn’t done cooling off from its primordial days. Heat still emanates from the planet billions of years after it formed. Scientists think that this heat helps drive the intense storms that hog Jupiter’s atmosphere.
The Voyager mission measured how much warmth Jupiter was giving off when it skimmed past the gas giant in 1979. Scientists realized then that Jupiter was shedding more heat than models had predicted: Some parts of the planet were burning at nearly 800 degrees Fahrenheit above what researchers had expected.
The mystery of the clandestine heat was resolved four decades later when scientists at the Keck Observatory mapped Jupiter’s temperatures. The planet ran coldest near the equator and hottest near the magnetic poles, where the auroras flared most intensely. This demonstrated that the auroras present an additional heat source. Plasma from Io collides with Jupiter’s atmosphere to create spectacular auroras, and it rubs against Jupiter’s fast-moving winds to generate enough friction that it raises temperatures globally.
Jupiter boasts eclectic moons
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Jupiter does more than help shuffle chemicals between its moons. The planet can also heat its moons from a distance through its gravitational field.
This long-range heating is apparent among its four Galilean moons. Jupiter’s gravitational influence has remade these moons into the tantalizing worlds they are today. “They’re not just these static rocks that are sitting around in space gradually getting bombarded,” says Michael H. Wong, a planetary scientist at the University of California, Berkeley, who’s also involved in the Juno mission.
The Galilean moons stay geologically active through a mechanism known as tidal heating. As the moons dance near and away from Jupiter along their elliptical orbits, a gravitational tug-of-war between the moons and Jupiter generates levels of friction large enough to cook the satellites. “It’s almost like they’re being drawn and quartered,” Becker says.
As a result, the Galilean moons look nothing like dead worlds such as Earth’s own moon. Of the quartet, Io is the closest, so it experiences the full wrath of Jupiter’s gravity. A speck compared to its mother planet, Io is the most volcanically active locale in all of the solar system. Its icy sibling, Europa, may look nothing like Io, but it hides a vast ocean of liquid water under a frozen shell. Europa is a prime target for exploring planetary habitability, thanks to Jupiter’s tidal heating processes that keep Europa balmy enough to potentially harbor life.
Jupiter’s clouds and atmosphere are nothing like Earth’s
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Although Jupiter’s atmosphere is 90 percent hydrogen, the air is rich with other compounds that give the planet its iconic hues of white and orange. At the surface, acetylene, hydrogen sulfides and phosphine molecules brush the planet into varied swirls that ring the planet.
In 1995, the Galileo Probe descended into Jupiter’s gaseous body and took a whiff. It found that Jupiter had three kinds of clouds: those made up of ammonia, ammonium hydrosulfide and water ice. As such, different kinds of rain fall through Jupiter’s skies, depending on the altitude.
The probe also detected enriched levels of heavy gases—more than scientists had initially thought Jupiter should harbor, given its present size and position. This chemical clue points at a peripatetic past: Jupiter may have formed farther away from the sun, where it was cold enough to attract ice and frozen gases. Then, scientists theorize, it gradually drifted closer to the sun until it was held back by Saturn’s gravity. “Saturn helped Jupiter move outward,” Li says, “otherwise Jupiter probably would have been engulfed by the sun.”
Exotic weather patterns abound
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Jupiter brews up some impressive storms. One of the most recognizable features is the Great Red Storm, a vortex clocking 400 miles per hour and extending as deep as 300 miles. Although the Great Red Storm has persisted for over two centuries, it is shrinking—the eye of the storm used to be as large as three Earths linked together; now, its width can barely fit one, though this size still makes it the largest living tempest in the solar system.
Jupiter’s upper atmosphere also hosts shallow bursts of lightning. That discovery came in 2020 when Juno pointed its camera at the dark side of the planet and caught weak flashes of light. On Earth, lightning occurs when colliding ice particles and water droplets inside clouds build up a separation of positive and negative charges. Scientists initially thought such lightning on Jupiter was impossible, as they suspected that the temperatures at these heights were too frigid to host liquid water. But Jupiter has managed to whip up liquid water high up in its atmosphere, thanks to the presence of ammonia gas that acts as an antifreeze.
Storms also hurl ice particles up from the deep, and the ice encounters ammonia and forms what scientists think are ammonia-water “mushballs,” a kind of hailstone containing both solid ice and liquid water. Though scientists haven’t directly observed these mushballs, they can speculate—“in my imagination, it would be like if you got a Slurpee and formed it into a ball,” Wong says. When the clouds rain out, the mushballs capture other ammonia gases on the way down, which explains the pockets of missing ammonia throughout the atmosphere that Juno has also observed.
Yes, Jupiter has a ring
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“A lot of people don’t even realize it has one,” Becker says. Too puny to be observed with a backyard telescope, Jupiter’s dusty wreath remained undetected for a long time. Discovered only in 1979 during the Voyager 1 flyby, the ring has since been viewed with more powerful ground telescopes and other visiting spacecraft.
Like any ring encircling other planets in the solar system, Jupiter’s is a glorified debris field. Detritus from crash-landed meteorites congregate around Jupiter. This loose mélange of ice, dust and rock spans 32,000 to 130,000 miles in width from the planetary surface.
When other celestial objects pass through the ring, they can leave behind tracks in the dust stream. One of the most famous of wakes came from the Comet Shoemaker-Levy 9 crashing into Jupiter in 1994. Years later, the Galileo and New Horizons spacecraft found ripples in Jupiter’s ring that were kicked up by shards from the comet, the celestial equivalent of footsteps in freshly fallen snow.
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