Key Facts & Summary
- Since it is the fourth brightest object in the sky, Jupiter was observed since ancient times and thus no one can be credited for its discovery. However, the first telescopic observations were conducted by Galileo Galilei in 1609 and in 1610 Galileo also discovered the major moons of Jupiter, but of course not the smaller ones.
- Since many cultures observed Jupiter, they all gave it different names but the Roman name remained used in the majority of cultures. Jupiter is named after the principal Roman god, the equivalent of the Greek god Zeus.
- Jupiter is one of the five visible planets (Mercury, Venus, Mars, Saturn), being the fifth most distant from the Sun at an average distance of 5.2 AU, its closest approach is at 4.9 AU and at its farthest 5.4 AU. Its exact position can be checked online since the planet is constantly tracked.
- It is the biggest planet of the Solar System, with a mean radius of 43.440 miles / 69.911 km, a diameter at the equator of about 88.846 mi / 142.984 km, and at the poles, the diameter is only 83.082 mi / 133.708 km.
- Jupiter is also twice as massive as all the other planets combined, having 318 times the mass of Earth.
- The gas giant has a gravity of 24.79 m/s², a little more than twice of Earth. Its powerful gravity has been used to hurl spacecraft into the farthest regions of the solar system.
- Jupiter rotates once every 10 hours – A Jovian day - thus it has the shortest day of all the planets in the solar system.
- A Jovian year is about 12 Earth years, quite long in comparison to its short days.
- Since Jupiter has a small axial tilt of only 3.13 degrees, it has little seasonal variations.
- Jupiter does not have a solid surface being comprised mostly out of swirling gases and liquids such as 90% hydrogen, 10% helium – very similar to the sun.
- A very small fraction of the atmosphere is made up of compounds such as ammonia, sulfur, methane, and water vapor. Jupiter’s atmosphere is the largest planetary atmosphere in the solar system. It makes up almost the entire planet.
- It holds a unique place in the history of space exploration since after it was observed through the telescope, some of its moons were also discovered and because of this, their movements were observed thus ending the belief that everything orbited the Earth.
- Though it remains the biggest planet, Jupiter has been dethroned as the moon king by Saturn, which now has 82 moons. Jupiter currently has only 79 known satellites.
- Among these satellites, four of them are quite famous: Io – for its volcanic activity, Ganymede – for its size, being the largest known moon of any planet, Europa – for hosting favorable conditions to find present-day environments suitable for some form of life beyond Earth, and Callisto – that may also host a subsurface ocean. They are known as the Galilean moons.
- Jupiter has 3 ring systems though they are fainter and smaller than Saturn’s. They are mostly made up of dust and small rocky pieces.
- It has a very strong magnetosphere, almost 20 times stronger than Earth’s magnetic field and 20.000 times larger.
- As a result, the aurora of Jupiter is stronger as well. It produces almost a million Megawatts – Earth’s aurora produces about 1.000 Megawatts.
- A distinct feature of Jupiter is its Great Red Spot – a persistent high-pressure region in the atmosphere that produces an anticyclonic storm, the largest in the solar system. It has been observed since 1830, and it is active for hundreds of years. It is also shrinking.
- Jupiter is surrounded by a plasma torus, produced by its strong magnetic field. It is a field of extremely charged particles making it difficult for a spacecraft to approach the planet, yet some zones are a bit safer. The charged particles also come from Io’s volcanic activity.
- The combination of the powerful magnetic field and the charged particles in the plasma torus creates the brightest auroras in the solar system. Sadly, they can only be seen through ultraviolet.
- It is now known if Jupiter has a core and recent analysis suggests that the atmosphere extends up to 3.000 km / 1.864 mi down, and beneath this is an ocean of metallic hydrogen going all the way down to the center. About 80-90% of its radius is now believed to be a liquid or technically, an electrically conducting plasma, maybe similar to liquid mercury.
Jupiter is the fourth brightest object in the sky, visible to the naked eye. It shines so brightly that even Venus dims in comparison. Because of this, it has been observed since ancient times by many different cultures. The discovery of Jupiter cannot be attributed to someone.
However, Galileo Galilei is the first astronomer to have observed Jupiter through his telescope. He began extensive observations of the planet in 1609. During this time and until 1610, Galileo discovered the four largest moons that orbit Jupiter: Io, Europa, Ganymede, and Callisto. They are called the Galilean moons in his honor.
He first thought of them as “fixed stars” but over time he witnessed that the objects changed positions, and he even almost correctly deduced their periods. This discovery was revolutionary since, at the time, most of Europe still endorsed the theory that all the planets orbited Earth.
Galileo’s discovery paved the way for the heliocentric model of the solar system, in which the planets orbit the Sun. Jupiter was known to the Babylonians as Marduk, the patron deity of the city of Babylon. The Romans called it “the star of Jupiter” - as they believed it to be sacred to the principal god of Roman mythology, whose name comes from the Proto-Indo-European vocative compound *Dyēu-pəter.
Jupiter is the counterpart to the mythical Greek king of the gods, Zeus, this name is retained even now in the modern Greek language. The ancient Greeks used to call Jupiter, Phaethon, which means “blazing star.” As supreme god of the Roman pantheon, Jupiter was the god of thunder, lightning, and storms, and appropriately called the god of light and sky.
Throughout the universe, there are many planetary systems similar to ours. Most of them contain terrestrial planets like our own and gas giants like Jupiter. However, they also contain super-Earths – planets that are several times more massive than Earth.
This indicates that our own Solar System should also have these types of planets and it is hypothesized that we did have them but they collided with Jupiter in the early formation of the Solar System. This resulted in Jupiter’s migration from the inner solar system to the outer solar system and thus allowed the inner solar planets to form. This theory is called the Grand Tack Hypothesis.
There are theories that hypothesize the fact that Jupiter may have formed before the Sun while others state that Jupiter formed after the sun about 4.5 billion years ago. Gravity pulled swirling gas and dust and resulted in the creation of Jupiter. Sometime around 4 billion years ago Jupiter settled in its current position in the outer solar system.
Distance, Size and Mass
It is the fifth most distant from the Sun with an average distance of about 5.2 AU. The closest approach is at 4.9 AU and at its farthest 5.4 AU. Its exact position can be checked online since the planet is constantly tracked.
It is the biggest planet of the Solar System, with a mean radius of 43.440 miles / 69.911 km. Almost 11 times bigger than Earth. Jupiter's radius is about 1/10 the radius of the Sun, and its mass is 0.001 times the mass of the Sun, so the densities of the two bodies are similar.
The diameter at the equator of about 88.846 mi / 142.984 km, and at the poles, the diameter is only 83.082 mi / 133.708 km. The average density of Jupiter is about 1.326 g/cm3, much smaller than all the terrestrial planets.
Jupiter is also 2.5 times more massive than all the other planets combined, having 318 times the mass of Earth. It has a volume of about 1,321 Earths.
Orbit and Rotation
Jupiter rotates once every 10 hours – A Jovian day - thus it has the shortest day of all the planets in the solar system. A Jovian year, on the other hand, is about 12 Earth years, quite long in comparison to its short days. The orbital period is about two-fifths that of Saturn. The orbit of Jupiter is elliptical, inclined about 1.31 degrees when compared to Earth.
The eccentricity of the orbit is about 0.048. This results in its distance from the Sun varying from its perihelion to aphelion by about 75 million km / 46 mi. Jupiter’s upper atmosphere undergoes differential rotation since it’s made out of gases.
Since Jupiter has a small axial tilt of only 3.13 degrees, it has little seasonal variations Because of this low tilt the poles constantly receive less solar radiation than at the planet’s equatorial region.
Jupiter does not have a solid surface being comprised mostly out of swirling gases and liquids such as 90% hydrogen, 10% helium – very similar to the sun.
It is now known if Jupiter has a core and recent analysis suggests that the atmosphere extends up to 3.000 km / 1.864 mi down, and beneath this is an ocean of metallic hydrogen going all the way down to the center. About 80-90% of its radius is now believed to be liquid or technically - electrically conducting plasma – it may be similar to liquid mercury. The Juno mission will reveal more about Jupiter’s inner structure and if indeed it has a core.
The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System, spanning over 5.000 km / 3.000 mi in altitude. It is perpetually covered with clouds composed of ammonia crystals and possibly ammonium hydrosulfide.
The clouds are located in the tropopause and are arranged into bands of different latitudes, known as tropical regions sub-divided into lighter-hued zones and darker belts. Because of their interactions, having conflicting circulation patterns, storms and turbulences are created.
Wind speeds of 100 m/s – 360 km/h are common in the zonal jets. The cloud layer is only about 50 km / 31 mi deep, consisting of at least 2 decks of clouds – a thin clearer region and a lower thick one.
The upper atmosphere is calculated to be comprised of about 88-92% hydrogen and 8-12% helium. Since helium atoms have more mass than hydrogen atoms, the composition changes. The atmosphere is thus estimated to be approximately 75% hydrogen and 24% helium with the remaining 1% of the mass consisting of other elements such as methane, water vapor, ammonia, silicon-based compounds, carbon, ethane, oxygen and more.
The outermost layer of the atmosphere contains crystals of frozen ammonia. The interior denser materials by mass are roughly 71% hydrogen, 24% helium and 5% other elements. These atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial solar nebula.
The magnetic field of Jupiter is fourteen times stronger than that of Earth. It ranges from 4.2 gauss / 0.42 mT at the equator to 10-14 gauss / 1.0 – 1.4 mT at the poles.
This makes Jupiter’s magnetic field the strongest in the Solar System, with the exception of some phenomenon named “sunspots”, that occur on the Sun that are even stronger.
It is believed that the liquid metallic hydrogen present in Jupiter is responsible for this along with the volcanic activity present on Jupiter’s moon Io that emits large amounts of sulfur dioxide forming a gas torus along the moon’s orbit. This gas is ionized in the magnetosphere and through different influences creates a plasma sheet in Jupiter’s equatorial plane. This causes the deformation of the dipole magnetic field into that of a magnetodisk.
As a result, the aurora of Jupiter is stronger as well. It produces almost a million Megawatts – Earth’s aurora, in comparison, produces about 1.000 Megawatts. The combination of the powerful magnetic field and the charged particles from Io in the plasma torus creates the brightest auroras in the solar system. Sadly, most of them can only be seen through ultraviolet.
Because Jupiter is surrounded by this plasma torus, produced by its strong magnetic field, it makes it very difficult for a spacecraft to approach the planet, yet some zones are not so dangerous but the radiation is still present.
Data suggests that the temperature on Jupiter varies from -145 degrees Celsius / -234 degrees Fahrenheit in the clouds too much higher temperatures near the planet’s center. Some estimates concluded that it would get even hotter than the surface of the Sun.
One of the key features of Jupiter is its Great Red Spot. A storm that’s existed since 1831, and possibly since 1665. This oval-shaped object is greater in size than Earth and rotates counterclockwise within a period of six days. Its maximum altitude is about 8 km / 5 mi above the surrounding cloud tops. Since its discovery, it has decreased in size and recent observations state that it decreases in length by about 930 km / 580 mi per year. Storms are common on Jupiter, some are small and last hours while others are huge and last for centuries. Wind speeds of 100 m/s – 360 km/h are common on certain parts of the planet.
Jupiter was the king of the moons since recently, having a total of 79 known satellites. Recently, Saturn dethroned Jupiter having a total of 82 known satellites. These rankings can change as observations continue.
Out of the 79 satellites, 63 are less than 10 km / 6.2 mi in diameter, and have only been observed since 1975. The Galilean moons, Io, Europa, Ganymede, and Callisto are large enough to be seen from Earth with binoculars. They are among the largest satellites discovered in the Solar System with Ganymede being the largest out of all the satellites in our solar system.
Jupiter has both regular moons and irregular moons with further sub-divisions.
The regular moons of Jupiter consists of the Galilean moons and an inner group of 4 small moons with diameters less than 200 km / 124 mi, and orbits with radii less than 200.000 km / 124.274 mi. They all have orbital inclinations of less than half a degree. The Galilean moons orbit between 400.000 and 2.000.000 km – 248.548 mi and 1.242.742 mi. These moons are believed to have been formed together with Jupiter since they have nearly circular orbits near the plane of Jupiter’s equator.
Despite being the largest known satellite in the solar system, it lacks a substantial atmosphere. It is the 9th largest object in the solar system with a diameter of 5.268 km / 3.273 mi and is 8% larger than the planet Mercury, although only 45% as massive.
It was named after the mythological cupbearer of the Greek gods, who was kidnapped by Zeus for this purpose. It is the only moon known to have a magnetic field and though it posseses a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System.
Outward from Jupiter, it is the seventh satellite completing an orbit around Jupiter in about 7 Earth days. It is in a 1:2:4 orbital resonance with the moons Europa and Io. It is comprised mostly of equal amounts of silicate rock and water ice, having an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth’s oceans combined.
A third of its surface is covered by dark regions covered in impact craters and a light region, crosscut by extensive grooves and ridges possibly due to tectonic activity due to tidal heating. It has a thin atmosphere comprised of oxygen, ozone and other elements. There is some speculation on the potential habitability of Ganymede's ocean.
The innermost and third-largest of the four Galilean moons of Jupiter, Io is the fourth-largest moon the solar system with the highest density and the least amount of water molecules of any known astronomical object in the Solar System.
Named after the mythological character Io, a priestess of Hera who became one of Zeus’ lovers, Io is the most geological active object in the Solar system having over 400 active volcanoes.
This extreme geological activity is due to tidal heating caused from friction generated within Io’s interior as it is pulled between Jupiter and the other Galilean moons.
It takes Io 1.77 Earth-days to orbit Jupiter. It is tidally locked to Jupiter, showing only one side to its parent planet, and has a mean radius of 1.131 miles / 1.821 km, slightly larger than Earth’s moon.
Many of Io’s volcanoes produce plumes of 500 km / 300 mi above the surface. More than 100 mountains are uplifted by extensive compression at the base of Io’s silicate crust. Some of these peaks are taller than Mount Everest, the highest point on Earth’s surface.
Io is composed primarily of silicate rock that surrounds a molten iron core. The plains of Io are coated with sulfur and sulfur-dioxide frost. The materials produced by Io’s volcanism make up its thin atmosphere, and result in the large plasma torus around Jupiter.
Europa is the smallest of the four Galilean moons and the sixth largest of all the moons in the Solar System. It was named after the Phoenician mother of King Minos of Crete and lover of Zeus.
It is slightly smaller than Earth’s moon having a diameter of 3.100 km / 1.900 mi. It is primarily made of silicate rock and has a water-ice crust, and a probably iron-nickel core.
Its atmosphere is thin, composed primarily of oxygen. The surface is very smooth. In fact it is the smoothest of any known solid object in the Solar System. The apparent youth of the smoothness of the surface led to the hypothesis that a water ocean exists beneath it, which could conceivably harbor extraterrestrial life.
Currently, Europa probably has the highest of either having or developing life, and thus it is one of the most closely studied objects in the solar system.
Callisto is the second-largest moon of Jupiter and the third-largest moon in the Solar System after Ganymede and Saturn’s moon Titan. It has a diameter of about 4.821 km / 2.995 mi, having about 99% the diameter of the planet Mercury but only a third of its mass.
Named after a nymph of Greek mythology, also another one of Zeus’s lovers, Callisto is the farthest Galilean moon orbiting Saturn at a distance of 1.8 million km. It is not in a orbital resonance like the other three Galilean moons and thus it is not appreciably tidally heated like the others. It is tidally locked with Jupiter and it is less affected by Jupiter’s magnetosphere than the other inner satellites because of its remote orbit.
It is composed primarily out of equal amounts of rock and ices, with a density of about 1.83 g/cm3, the lowest of Jupiter’s satellites. Investigations by the Galileo spacecraft suggest that Callisto has a silicate core and possibly a subsurface ocean of liquid water at depths of 100 km.
Interestingly, the surface of Callisto is the oldest and most heavily cratered in the Solar System. It has an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen.
The presence of an ocean within Callisto opens the possibility that it could harbor life but conditions are thought to be less favorable than on Europa. Regardless, it is considered the most suitable planet for a human base for future exploration of the Jovian system due to low radiation levels.
The irregular moons are small and have elliptical and inclined orbits. They are thought to be captured asteroids or fragments of captured asteroids. Their exact number is unknown but they are further divided into sub-divisions – groups, in which they share similar orbital elements and thus may have a common origin.
There are 4 groups:
- The Himalia group – a clustered group of moons with orbits around 11 million to 12 million km / 6 to 7 million mi from Jupiter.
- The Ananke group – a group with a retrograde orbit with rather indistinct borders, averaging from 21 million km / 13 million mi from Jupiter with an average inclination of 149 degrees.
- The Carme group – they are a group with a fairly distinct retrograde orbit that averages from 23 million km / 14 million mi from Jupiter with an average inclination of 165 degrees.
- The Pasiphae group – a very dispersed and only vaguely distinct retrograde group that covers all the outermost moons.
- There are three irregular moons that stand out from these groups:
- Themisto – it orbits halfway between the Galilean moons and the Himalia group.
- Carpo – it is at the inner edge of the Ananke group and orbits Jupiter in prograde direction.
- Valetudo – this moon has a prograde orbit but overlaps the retrograde groups and may result in future collisions with those groups.
Jupiter has a faint planetary ring system composed of three main segments: an inner torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring.
They appear to be made out of dust rather than ice as with Saturn’s rings. It is believed that the main ring is made of material ejected from the satellites Adrastea and Metis.
In a similar manor, the moons Thebe and Amalthea probably produce the two distinct components of the dusty gossamer ring.
Since it doesn’t have a true surface but rather swirling fluids it is not conducive to life as we know it. Ganymede, Callisto, and Europa on the other hand, have higher chances of sustaining life.
Future plans for Jupiter
Juno is a spacecraft that was launched in 2011 and even now it is still analyzing Jupiter and sending data. Future missions are already set in motion for Ganymede, Europa, Callisto and Io. They are set to be launched on 2020 and 2026. The high probability of life, the powerful volcanic activity and the overall missing details of Jupiter are strong factors in driving these missions.
Did you know?
- When Jupiter was formed it had twice its current diameter.
- Jupiter shrinks 2 cm every year because it radiates too much heath.
- Jupiter is so massive that its barycenter with the Sun lies above the Sun's surface at 1.068 solar radii from the Sun's center. It is the only planet whose barycenter with the Sun lies outside the volume of the Sun.
- If Jupiter would be 75 times more massive, it would probably become a star.
- If a person who weighs 100 pounds on Earth would somehow stand on the surface of Jupiter, that person would weigh about 240 pounds due to Jupiter’s gravitational force.
- Although Simon Marius, a German astronomer, is not credited with the sole discovery of the Galilean satellites, his names for the moons were adopted.
- Jupiter experiences almost 200 times more asteroid and comet impacts than Earth
- Jupiter has been called the Solar System's vacuum cleaner, because of its immense gravity well. It receives the most frequent comet impacts of the Solar System's planets.
- It was thought that the planet served to partially shield the inner system from cometary bombardment. However, recent computer simulations suggest that Jupiter does not cause a net decrease in the number of comets that pass through the inner Solar System, as its gravity perturbs their orbits inward roughly as often as it accretes or ejects them. This topic remains controversial.
- Jupiter may have been responsible for the Late Heavy Bombardment of the inner Solar System's history.