Jupiter King of Planets
Jupiter, named after the king of the Roman Gods, reigns supreme among the nine planets of our solar system, rivaling the Sun in its grandeur. Giant Jupiter contains two-thirds of the planetary mass of the solar system. In composition it resembles a small star. Its interior pressure may reach 100 million times the surface pressure on Earth. Jupiter's magnetic field is immense, even in proportion to the size of the planet, stretching millions of miles into the solar system. If the magnetic field were visible, it would rival the apparent size of our Moon. Electrical activity in Jupiter is so strong that it pours billions of watts into Earth's own magnetic field every day. No planet has greater influence on its neighbors.
Jupiter is the innermost of the 4 giant planets (the others are Saturn, Uranus, and Neptune), and clearly the most dynamic. Jupiter has its own 'mini solar system' of 60 moons. Scientists are most interested in the Galilean satellites - the four largest moons discovered by Galileo Galilei in 1610. Europa, may have an ocean under its frozen surface. Calisto's crater-pocked landscape may be the oldest in the solar system. Ganymede is the solar system's largest moon. It is bigger than Pluto and Mercury. And little Io has more volcanoes than anywhere else in the solar system.
Its atmosphere bristles with lightning and swirls with huge storm systems including the Great Red Spot, a storm that has persisted for at least 100---and perhaps as long as 300---years. With its dynamism, huge energy output, and entourage of satellites, Jupiter is in many ways like a small sun, and the Jovian system resembles a miniature solar system. Although Jupiter is a stellar composition----most of its mass is hydrogen and helium---it does not burn like the Sun. Models of star formation suggest that Jupiter's mass is only about one-eightieth of the mass needed for ignition, which occurs due to heating from internal gravitational collapse. Jupiter's smaller size leaves its center too cool to ignite, sustaining instead internal masses of liquefied gas.
Jupiter's intricate, swirling ring system is formed by dust kicked up as interplanetary meteoroids smash into the giant planet's four small inner moons, according to scientists studying data from NASA's Galileo spacecraft. Images sent by Galileo also reveal that the outermost ring is actually two rings, one embedded within the other.
Rings are important dynamical laboratories to look at the processes that probably went on billions of years ago when the Solar System was forming from a flattened disk of dust and gas. Furthermore, similar faint rings probably are associated with many small moons of the Solar System's other giant planets.
In the late 1970s, NASA's two Voyager spacecraft first revealed the structure of Jupiter's rings: a flattened main ring and an inner, cloud-like ring, called the halo, both composed of small, dark particles. One Voyager image seemed to indicate a third, faint outer ring.
New Galileo data reveal that this third ring, known as the gossamer ring because of its transparency, consists of two rings. One is embedded within the other, and both are composed of microscopic debris from two small moons, Amalthea and Thebe.
Scientists believe that dust is kicked off the small moons when they are struck by interplanetary meteoroids, or fragments of comets and asteroids, at speeds greatly magnified by Jupiter's huge gravitational field, like the cloud of chalk dust that rises when two erasers are banged together. The small moons are particularly vulnerable targets because of their relative closeness to the giant planet.
In these impacts, the meteoroid is going so fast it buries itself deep in the moon, then vaporizes and explodes, causing debris to be thrown off at such high velocity that it escapes the satellite's gravitational field. If the moon is too big, dust particles will not have enough velocity to escape the moon's gravitational field. With a diameter of just eight kilometers (five miles) and an orbit that lies just at the periphery of the main ring, tiny Adrastea is most perfectly suited for the job.
As dust particles are blasted off the moons, they enter orbits much like those of their source satellites, both in their distance and in their slight tilt relative to Jupiter's equatorial plane. A tilted orbit wobbles around a planet's equator, much like a hula hoop twirling around a person's waist. This close to Jupiter, orbits wobble back and forth in only a few months.
Jupiter's diameter is approximately 143,000 kilometers (86,000 miles). The ring system begins about 92,000 kilometers (55,000 miles) from Jupiter's center and extends to about 250,000 kilometers (150,000 miles) from the planet.
Jupiter holds clues to many of the mysteries of the early solar system. About 4.5 billion years ago, when the solar system formed out of a swirling mass of gases and dust called the solar nebula, Jupiter's core probably began as a solid mass of ice and rock about 15 times the bulk of Earth. The ice content of Jupiter's mass was high because it formed in the colder outer region of the solar system, where the nebula contained a lot of ice particles, principally water and methane. Probably because icy masses can adhere and compress into a single large body faster than plain rock can, the outer planets formed their cores before the rocky inner planets did. The gravity of the large icy cores of Jupiter and Saturn attracted most of the light hydrogen and helium gas in the nebula, and it is these gasses that we find dominating their atmospheres today. Jupiter, the innermost of the icy giants, "grew" the largest atmosphere. In fact, the face of Jupiter that we see is really just the top of its atmosphere. What goes on inside is even more intriguing.
Jupiter's massive atmosphere creates tremendous pressures as you move closer to the center of the planet. The substances inside the atmosphere are subject to extreme conditions, leading to exotic chemistry. For example, scientists have reason to believe that the inner layers of hydrogen in Jupiter's atmosphere, under the pressure of the atmosphere above, may have formed into a planet-encircling layer of what is called liquid metallic hydrogen. Not exactly an ocean, not exactly atmosphere, this layer of hydrogen would have properties that stretch our understanding of chemistry. Instead of the simple, free-moving and loosely bonded behavior of gaseous hydrogen, liquid metallic hydrogen is a strange matrix capable of conducting huge electrical currents. The persistent radio noise and improbably strong magnetic field of Jupiter could both emanate from this layer of metallic liquid. Some scientists theorize that beneath this layer there is no solid mass at the center of Jupiter, but that the unique temperature and pressure conditions sustain a core whose density is more like liquid or slush.
Farther from the planet's core, in what we can more certainly call the atmosphere, we see gases behaving in a more familiar manner, moving in general planetary circulations driven primarily by the rotation of the planet. Jupiter is believed to have three cloud layers in its atmosphere. At the top are clouds of ammonia ice; beneath that ammonium-hydrogen sulfide crystals; and in the lowest layer, water ice and perhaps liquid water. Jupiter is noteworthy for its turbulent cloudtops, and its long-standing storm, the Great Red Spot. The origins of these colorful features are uncertain, but scientists believe that they are caused by plumes of warmer gases that rise up from deep in the planet's interior. The plumes' colors are probably caused by their chemical content. Although the amount of carbon, for example, in the Jovian atmosphere is very small, carbon readily combines with hydrogen and trace amounts of oxygen to form a variety of gases such as carbon monoxide, methane, and other organic compounds. The orange and brown colors in Jupiter's clouds may be attributable to the presence of organic compounds, or sulfur and phosphorus.
Missions of Discovery
Jupiter is one of the planets visible to the naked eye, and its path through the night sky has been traced for thousands of years. In 1610, the Italian astronomer Galileo Galilei discovered four large moons -- Io, Europa, Ganymede, and Callisto (known as the Galilean satellites) -- orbiting Jupiter. This was one of the earliest astronomical discoveries made with a telescope. It fueled the controversial argument of the time that the Sun and not the Earth was the center of the solar system. In the centuries since then, as telescopes improved, Jupiter because known primarily for its size and the Great Red Spot, which was imagined to be an island in a Jovian sea. As Earth-based astronomy continued to improve, we came to realize that the few fuzzy "surface" features we could see were constantly changing in position, size, and color, suggesting that they were atmospheric phenomena. With the advent of radio astronomy, we discovered that Jupiter is a source of strong radio-frequency noise, suggesting electrical activity. Out fascination with Jupiter increased.
In March 1972, NASA launched the Pioneer 10 spacecraft to observe the asteroid belt and Jupiter. Arriving at Jupiter in December 1973, Pioneer 10 revealed Jupiter's intense radiation output, its tremendous magnetic field, and the probability of a liquid interior. One year later, Pioneer 10's sister spacecraft, Pioneer 11, flew by Jupiter on its way to Saturn, and provided even more detailed imagery and measurements, including our first close-up look at the giant planet's polar regions. Then, in August and September 1977, NASA launched the two Voyager spacecraft to the outer solar system. The Voyagers' 1979 encounters with Jupiter provided us with startling, beautiful imagery of the king of the planets, revealing thousands of features never before seen. Swirling multicolored turbulence surrounded the Great Red Spot. Rising plumes and spinning eddies formed and dissipated, suggesting a strong source of heat bubbling up from within the planet.
The Voyager imagery, with its exposure of so many small details, told us that Jovian dynamics were much more complex than previously imagined. Yet many of the features resemble effects we know of in out own and other planetary atmospheres, magnified by the enormity and extremity of the Jovian environment. In studying Jupiter we can learn more about atmospheric effects and interactions that are subtle on Earth, such as magnetosphere-atmosphere interactions.
Subsequent missions to the giant planet will help us improve models of atmospheric dynamics, and will help us understand the chemistry and behavior of Earth's own relatively thin, but very precious, atmosphere.
Voyagers 1 and 2
still operational after more than 15 years in space and are traveling out of the Solar System. The two Voyagers are expected to last until at least the year 2015 when their radioisotope thermoelectric generators (RTG) power supplies are expected for fail. Their trajectories give negative evidence about possible planets beyond Pluto. Their next major scientific discovery should be the location of the heliopause. Low-frequency radio emissions believed to originate at the heliopause have been detected by both Voyagers.
Both Voyagers are using their ultraviolet spectrometers to map the heliosphere and study the incoming interstellar wind. The cosmic ray detectors are seeing the energy spectra of interstellar cosmic rays in the outer heliosphere
Voyager 1 has passed the Pioneer 10 spacecraft and is now the most distant human-made object in space.
Jupiter orbiter and atmosphere probe, now in Jupiter orbit. It will make extensive surveys of the Jovian moons and the probe has descended into Jupiter's atmosphere to provide our first direct evidence of the interior of a gas giant.
Galileo has already returned the first resolved images of two asteroids, 951 Gaspra and 243 Ida, while in transit to Jupiter. It has also returned pictures of the impact of Comet SL9 onto Jupiter from its unique vantage point.
Efforts to unfurl the stuck High Gain Antenna (HGA) have essentially been abandoned. With its Low Gain Antenna Galileo transmits data at about 10 bits per second. JPL has developed a backup plan using enhancements of the receiving antennas in the Deep Space Network and data compression (JPEG-like for images, lossless compression for data from the other instruments) on the spacecraft. This should allow Galileo to achieve approximately 70% of its original science objectives with the much lower speed Low Gain Antenna. Long term Jovian weather monitoring, which is imagery intensive, will suffer the most.
Distance from Sun
778.3 Million Kilometers
Period of Revolution
11.86 Earth Years (1 Jovian Year)
Hydrogen and Helium (Main Components)
In Ascending Distance from Planet:
Inclination of Orbit
1.3 degrees to Ecliptic
Eccentricity of Orbit
9 Hours 55 Minutes (1 Jovian Day)
Inclination of Axis
The exciting list of discoveries started even before Galileo was able to get a close glimpse of Jupiter. As it crossed the asteroid belt in October 1991, Galileo snapped images of Gaspra, returning the first ever close-up image of an asteroid. Less then a year later, the spacecraft got up close and personal with yet another asteroid, Ida. Images from Ida revealed the asteroid has its own little "moon," Dactyl, the first known moon of an asteroid.
In 1994 the spacecraft was in the right place at the right time and made the only direct observation of a comet impacting a planet. It took images of fragments of comet Shoemaker-Levy 9 crashing into Jupiter. Images of the impact, which was not visible from Earth, helped scientists better understand this type of event.
Galileo began its tour of the jovian system in December 1995. Carefully designed orbits allowed the spacecraft to observe Jupiter's atmosphere, revealing numerous large thunderstorms many times larger than those on Earth, with lightning strikes up to 1,000 times more powerful than terrestrial lightning. Data collected by the descent probe made the first in-place studies of the planet's clouds and winds, and it furthered scientists' understanding of how Jupiter evolved. The probe also made measurements designed to assess the degree of evolution of Jupiter compared to the Sun.
As the first spacecraft in long-term residence in jovian orbit, Galileo also successfully studied the global structure and dynamics of Jupiter's magnetic field. Galileo also determined that Jupiter's ring system is formed by dust kicked up as interplanetary meteoroids smash into the planet's four small inner moons. Data also showed that Jupiter's outermost ring is actually made up of two rings, one embedded within another.
Galileo extensively investigated the geologic diversity of Jupiter's four largest moons: Ganymede, Callisto, Io and Europa. Stunning images revealed the contrasting and changing surfaces of these moons.
Io has extensive volcanic activity, which is continually modifying the surface. The heat and the frequency of eruption can be 100 times more than that of Earth, something reminiscent of Earth's early days. The similarities make Io an ideal laboratory for the study of what Earth was like more than 3 billion years ago.
The moon Europa, Galileo unveiled, could be hiding a salty ocean up to 100 kilometers (62 miles) deep underneath its frozen surface. Images also reveal ice "rafts" the size of cities that have broken and drifted apart to create a scalloped and broken surface. There are also indications of volcanic ice flows, with liquid water flowing across the surface. These discoveries are particularly intriguing since liquid water is a key ingredient in the process that may lead to the formation of life.
The biggest discovery surrounding Ganymede was the presence of a magnetic field, the first moon of any planet known to have one. Images of this moon featured a faulted and fractured surface that demonstrated high tectonic activity. Like Europa and Io, Ganymede has a metallic core. Galileo magnetic data also provided evidence that Ganymede might have a liquid-saltwater layer as well.
Galileo determined that, while Callisto doesn't have a metallic core, its surface shows evidence of extensive erosion. Data collected raise the question of whether Callisto's surface may also hide an ocean.
Galileo's own discovery of a likely ocean hidden under Europa's surface raises the possibility of life there and concern about protecting it. For that reason, in its final victory lap the Galileo spacecraft will dive into the atmosphere of the gaseous planet and disintegrate. Predictably, some of the spacecraft findings raised intriguing questions that will have to be answered by future mission. But Galileo Galilei, the first modern astronomer, would be immensely proud of the discoveries made by the spacecraft that carries his name.
Busy Galileo spacecraft showed jovian system is full of surprises
September 17, 2003
After orbiting Jupiter 34 times and surviving four times the amount of radiation it was design to withstand, the resilient Galileo spacecraft is finally at the very end of its 14-year mission. To avoid even the most remote possibility of colliding with a pristine moon in the jovian system, the out-of-fuel spacecraft will dive into Jupiter on Sunday, Sept. 21, 2003.
Since its launch in 1989, the sturdy spacecraft traveled more than 4.6 billion kilometers (almost 2.8 billion miles), about the equivalent of seven times the distance between Earth and Jupiter. Despite communication problems and a temperamental tape recorder, Galileo returned 30 gigabytes of data, including 14,000 pictures.
This wealth of information drastically expanded our understanding of the solar system's biggest planet and its moons. The mission was possible because it drew its power from two long-lasting radioisotope thermoelectric generators provided by the Department of Energy.
NASA's Juno Peers Inside a Giant
June 29, 2016
NASA's Juno spacecraft will make its long anticipated arrival at Jupiter on July 4. Coming face-to-face with the gas giant, Juno will begin to unravel some of the greatest mysteries surrounding our solar system's largest planet, including the origin of its massive magnetosphere.
Magnetospheres are the result of a collision between a planet's intrinsic magnetic field and the supersonic solar wind. Jupiter's magnetosphere – the volume carved out in the solar wind where the planet’s magnetic field dominates –extends up to nearly 2 million miles (3 million kilometers). If it were visible in the night sky, Jupiter's magnetosphere would appear to be about the same size as Earth’s full moon. By studying Jupiter's magnetosphere, scientists will gain a better understanding about how Jupiter's magnetic field is generated. They also hope to determine whether the planet has a solid core, which will tell us how Jupiter formed during the earliest days of our solar system.
In order to look inside the planet, the science team equipped Juno with a pair of magnetometers. The magnetometers, which were designed and built by an in-house team of scientists and engineers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, will allow scientists to map Jupiter's magnetic field with high accuracy and observe variations in the field over time.
"The best way to think of a magnetometer is like a compass," said Jack Connerney, deputy principal investigator and head of the magnetometer team at Goddard. "Compasses record the direction of a magnetic field. But magnetometers expand on that capability and record both the direction and magnitude of the magnetic field."
The magnetometer sensors rest on a boom attached to one of the solar arrays, placing them about 40 feet (12 meters) from the body of the spacecraft. This helps ensure that the rest of the spacecraft does not interfere with the magnetometer.
However, the sensor orientation changes in time with the mechanical distortion of the solar array and boom resulting from the extremely cold temperatures of deep space. This distortion would limit the accuracy of the magnetometer measurements if not measured.
To ensure that the magnetometers retain their high accuracy, the team paired the instruments with a set of four cameras. These cameras measure the distortion of the magnetometer sensors in reference to the stars to determine their orientation.
"This is our first opportunity to do very precise, high-accuracy mapping of the magnetic field of another planet," Connerney said. "We are going to be able to explore the entire three-dimensional space around Jupiter, wrapping Jupiter in a dense net of magnetic field observations completely covering the sphere."
One of the mysteries the team hopes to answer is how Jupiter's magnetic field is generated. Scientists expect to find similarities between Jupiter's magnetic field and that of Earth.
Magnetic fields are produced by what are known as dynamos — convective motion of electrically conducting fluid inside planets. As a planet rotates, the electrically susceptible liquid swirls around and drives electric currents, inducing a magnetic field. Earth's magnetic field is generated by liquid iron in the planet's core.
"But with Jupiter, we don't know what material is producing the planet's magnetic field,” said Jared Espley, Juno program scientist for NASA Headquarters, Washington. “What material is present and how deep down it lies is one of the questions Juno is designed to answer."
The observations made by Juno's magnetometers will also add to our understanding of Earth's dynamo, the source of our planet’s magnetic field, which lies deep beneath a magnetized layer of rocks and iron.
Imagine Earth's crust strewn with refrigerator magnets as you try to peer beneath the surface to observe the dynamo. The magnetization of Earth's crust will skew your measurements of the magnetic field.
"One of the reasons that the Juno mission is so exciting is because we can map Jupiter’s magnetic field without having to look through the crustal magnetic fields, which behave like a jumble of refrigerator magnets," Connerney said. "Jupiter has a gaseous envelope about it made of hydrogen and helium that gives us a clear and unobstructed view of the dynamo."
These observations will also add to the general understanding of how dynamos generate magnetic fields, including here on Earth.
Editor: Karl Hille
Hubble Captures Vivid Auroras in Jupiter’s Atmosphere
June 30, 2016
Astronomers are using the NASA/ESA Hubble Space Telescope to study auroras — stunning light shows in a planet’s atmosphere — on the poles of the largest planet in the solar system, Jupiter. This observation program is supported by measurements made by NASA’s Juno spacecraft, currently on its way to Jupiter.
Jupiter, the largest planet in the solar system, is best known for its colorful storms, the most famous being the Great Red Spot. Now astronomers have focused on another beautiful feature of the planet, using Hubble's ultraviolet capabilities.
The extraordinary vivid glows shown in the new observations are known as auroras. They are created when high-energy particles enter a planet’s atmosphere near its magnetic poles and collide with atoms of gas. As well as producing beautiful images, this program aims to determine how various components of Jupiter’s auroras respond to different conditions in the solar wind, a stream of charged particles ejected from the sun.
This observation program is perfectly timed as NASA’s Juno spacecraft is currently in the solar wind near Jupiter and will enter the orbit of the planet in early July 2016. While Hubble is observing and measuring the auroras on Jupiter, Juno is measuring the properties of the solar wind itself; a perfect collaboration between a telescope and a space probe.
“These auroras are very dramatic and among the most active I have ever seen”, said Jonathan Nichols from the University of Leicester, U.K., and principal investigator of the study. “It almost seems as if Jupiter is throwing a firework party for the imminent arrival of Juno.”
To highlight changes in the auroras Hubble is observing Jupiter almost daily for several months. Using this series of far-ultraviolet images from Hubble's Space Telescope Imaging Spectrograph, it is possible for scientists to create videos that demonstrate the movement of the vivid auroras, which cover areas bigger than Earth.
Not only are the auroras huge in size, they are also hundreds of times more energetic than auroras on Earth. And, unlike those on Earth, they never cease. While on Earth the most intense auroras are caused by solar storms — when charged particles rain down on the upper atmosphere, excite gases and cause them to glow red, green and purple — Jupiter has an additional source for its auroras.
The strong magnetic field of the gas giant grabs charged particles from its surroundings. This includes not only the charged particles within the solar wind but also the particles thrown into space by its orbiting moon Io, known for its numerous and large volcanoes.
The new observations and measurements made with Hubble and Juno will help to better understand how the sun and other sources influence auroras.
Editor: Ashley Morrow
NASA's Juno Navigators Enable Jupiter Cyclone Discovery
Dec. 12, 2019
Jupiter's south pole has a new cyclone. The discovery of the massive Jovian tempest occurred on Nov. 3, 2019, during the most recent data-gathering flyby of Jupiter by NASA's Juno spacecraft. It was the 22nd flyby during which the solar-powered spacecraft collected science data on the gas giant, soaring only 2,175 miles (3,500 kilometers) above its cloud tops. The flyby also marked a victory for the mission team, whose innovative measures kept the solar-powered spacecraft clear of what could have been a mission-ending eclipse.
“The combination of creativity and analytical thinking has once again paid off big time for NASA,“ said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. “We realized that the orbit was going to carry Juno into Jupiter's shadow, which could have grave consequences because we're solar powered. No sunlight means no power, so there was real risk we might freeze to death. While the team was trying to figure out how to conserve energy and keep our core heated, the engineers came up with a completely new way out of the problem: Jump Jupiter's shadow. It was nothing less than a navigation stroke of genius. Lo and behold, first thing out of the gate on the other side, we make another fundamental discovery.“
When Juno first arrived at Jupiter in July 2016, its infrared and visible-light cameras discovered giant cyclones encircling the planet's poles — nine in the north and six in the south. Were they, like their Earthly siblings, a transient phenomenon, taking only weeks to develop and then ebb? Or could these cyclones, each nearly as wide as the continental U.S., be more permanent fixtures?
With each flyby, the data reinforced the idea that five windstorms were swirling in a pentagonal pattern around a central storm at the south pole and that the system seemed stable. None of the six storms showed signs of yielding to allow other cyclones to join in.
NASA's Juno Spacecraft Has a Close Encounter with Jupiter
Jan. 14, 2020
A multitude of swirling clouds in Jupiter's dynamic North North Temperate Belt is captured in this image from NASA's Juno spacecraft. Appearing in the scene are several bright-white ’pop-up’ clouds as well as an anticyclonic storm, known as a white oval.
Image Credit: Enhanced image by Gerald Eichstädt and Sean Doran (CC BY-NC-SA) based on images provided courtesy of NASA/JPL-Caltech/SwRI/MSSS