1. What Are Jupiter's Stripes Made Of?
The pale stripes are called zones and the darker orange-brown ones are called belts. NASA describes the bands as flowing east and west in opposite directions, with white and reddish cloud bands wrapping around the planet [1]. So the stripes are not only a pattern of paint-like color. They line up with moving air.
Researchers who study Jupiter's winds call these streams jets. A zone or a belt usually sits beside each jet: for an eastward jet, a zone is typically found to its south and a belt to its north, and for a westward jet the order flips [2]. That rule is typical rather than universal, so some jets do not follow it.
Jupiter has a wide eastward jet around the equator and several more jets in each hemisphere; the exact number depends on how they are counted [2]. The strongest one blows at roughly 140 m/s near 23° north, measured by tracking clouds [2]. That is about 500 km/h (about 310 mph). The number refers to how fast clouds are carried along, which is how these winds are measured.
2. How Does Jupiter's Fast Spin Shape Its Winds?
Jupiter is about 11 times wider than Earth, yet it turns once in about 9.9 hours, the shortest day of any planet [1]. Earth takes about 24 hours. In one Earth day, Jupiter turns a little more than twice.
Why does that matter for stripes? On a quickly spinning planet, a moving mass of air is pushed sideways by the rotation (the same effect that bends hurricanes on Earth). In a big, fast-spinning atmosphere this keeps air flowing along lines of latitude much more easily than across them. Think of a river held between two banks: the water can run along the banks, but not through them. A simple way to picture it is that fast rotation builds invisible "banks" at certain latitudes. This is an analogy, not a statement from the sources.
That is why the stripes are sideways. An east-west stripe is an east-west jet with clouds of different color on each side. Why north-south stripes do not form is not something this jet picture alone can settle.
3. Why Does Jupiter Have Several Separate Jets and Not Just One?
A review of Jupiter's and Saturn's deep winds states that a theory of "geostrophic turbulence" explains the width of the jets and their overall number, and that the observed numbers on both planets match what the theory predicts [2]. In plain words: when a fast-spinning atmosphere is stirred up by small, messy swirls, the energy does not stay in the swirls. It gathers into a small number of long, wide east-west streams.
Tracking cloud motions backs this up. A research group in Oxford found that energy is fed into Jupiter's weather layer at fairly small scales, and then flows both to larger scales, mostly into the jets away from the equator, and to smaller scales [3]. The weather layer is the thin top region of the atmosphere that sunlight and rising heat from inside affect most.
Sources do not claim the whole puzzle is solved. Some features, such as the Great Red Spot and other compact ovals, are not yet produced by computer models on their own [3]. What controls the jets, a thin weather layer or deeper movements, was also a long-running question, and it leads straight to the next one.
4. How Far Down Do Jupiter's Jets Reach?
For a long time, scientists could argue about two pictures. In the "shallow" picture, the jets live only in a thin weather layer near the cloud tops. In the "deep" picture, the stripes at the top are linked to columns of moving gas that go far inside the planet [2]. Nobody could look beneath the clouds to find out.
The NASA spacecraft Juno found a way. It measured Jupiter's gravity as it flew close by. The gravity field turned out to be slightly uneven between north and south, in the same pattern as the visible zones and belts. Deeper jets carry more mass, so the size of that unevenness shows how deep the jets go. NASA and the Nature papers from March 2018 concluded that the east-west jets reach about 3,000 km (about 1,900 miles) down [4]. The layer above that depth holds about one percent of Jupiter's mass, which is around three Earth masses [4].
To get a feel for the size: 3,000 km is only about 1/23 of the way to the center of a planet whose radius is about 70,000 km [1]. Even so, the part of Jupiter that the jets stir is enormous compared with a thin weather layer.
The review that combined Juno and Cassini gravity data also found a similar depth, about 9,000 km, for Saturn, and suggested that deeper down the gas becomes electrically conductive enough for the planet's magnetic field to hold the winds back [2]. That is a proposed explanation, not a settled fact.
5. Do the Winds Go Straight Down, or Along Cylinders?
A study published in Nature Astronomy in October 2023 used Juno's gravity data again and reported that Jupiter's winds penetrate the planet in a cylinder shape, parallel to the spin axis [5]. In NASA's illustration, the strongest jet sits near 21° north at cloud level, but the same jet is near 13° north at 3,000 km depth. A dashed line that follows the jet's peak at each depth makes a tilted, cylinder-like shape [5].
This comes from fitting models to gravity data, so nobody has seen the cylinders directly. Treat it as an estimate from a model, not a photograph.
6. Why Do Bright Zones and Dark Belts Look Different?
A common textbook picture says the bright zones are rich in ammonia and the dark belts have less. Juno's microwave radiometer, which can sense the gas below the visible clouds, gave a messier answer. In the first flyby results, ammonia was found to be depleted nearly everywhere down to a pressure of 50 to 60 times Earth's air pressure at sea level, except within a few degrees of the equator, and the North Equatorial Belt was especially low [6]. So the simple picture of "ammonia-rich zones and ammonia-poor belts" does not describe what Juno measured at those depths. The paper calls its analysis preliminary and based on the first flyby.
The overall story still holds: the stripes are tied to winds, and winds are tied to how a fast-spinning planet moves its air. What makes a stripe bright or dark is still under study.
7. How Can You Check the Stripes Yourself?
Find two or three photos of Jupiter taken at different times, in a library book, on a museum website, or from a NASA image gallery. Trace the stripes with a finger and see whether they stay sideways in every photo. Then count how many dark belts you can see in the northern half and in the southern half. Your counts may differ from your friends'. Image processing, camera filters, and the date of the photo all change what you see, so two sources can honestly give two numbers.
If you want more, ask a science teacher, planetarium, or astronomy club: "What decides how deep a planet's winds go?" Scientists are still working on that, and the primary sources listed below are written for people who want to follow the real papers.