Jupiter & Moons
- Equatorial Diameter: 142,984 km
- Polar Diameter: 133,709 km
- Mass: 1.90 × 10^27 kg (318 Earths)
- Moons: 79 + (Io, Europa, Ganymede, & Callisto)
- Rings: 4
- Orbit Distance: 778,340,821 km (5.20 AU)
- Orbit Period: 4,333 days (11.9 years)
- Effective Temperature: -148 °C
- First Record: 7th or 8th century BC; Babylonian astronomers
Jupiter is the fourth brightest object in the solar system.Only the Sun, Moon and Venus are brighter. It is one of five planets visible to the naked eye from Earth.The ancient Babylonians were the first to record their sightings of Jupiter.This was around the 7th or 8th century BC. Jupiter is named after the king of the Roman gods. To the Greeks, it represented Zeus, the god of thunder. The Mesopotamians saw Jupiter as the god Marduk and patron of the city of Babylon. Germanic tribes saw this planet as Donar, or Thor.Jupiter has the shortest day of all the planets.It turns on its axis once every 9 hours and 55 minutes. The rapid rotation flattens the planet slightly, giving it an oblate shape.Jupiter orbits the Sun once every 11.8 Earth years.From our point of view on Earth, it appears to move slowly in the sky, taking months to move from one constellation to another.Jupiter has unique cloud features.The upper atmosphere of Jupiter is divided into cloud belts and zones. They are made primarily of ammonia crystals, sulfur, and mixtures of the two compounds.The Great Red Spot is a huge storm on Jupiter.It has raged for at least 350 years. It is so large that three Earths could fit inside it.Jupiter’s interior is made of rock, metal, and hydrogen compounds.Below Jupiter’s massive atmosphere (which is made primarily of hydrogen), there are layers of compressed hydrogen gas, liquid metallic hydrogen, and a core of ice, rock, and metals.Jupiter’s moon Ganymede is the largest moon in the solar system.Jupiter’s moons are sometimes called the Jovian satellites, the largest of these are Ganymede, Callisto Io and Europa. Ganymede measures 5,268 km across, making it larger than the planet Mercury.Jupiter has a thin ring system.Its rings are composed mainly of dust particles ejected from some of Jupiter’s smaller worlds during impacts from incoming comets and asteroids. The ring system begins some 92,000 kilometers above Jupiter’s cloud tops and stretches out to more than 225,000 km from the planet. They are between 2,000 to 12,500 kilometers thick.As of 2021, eight spacecraft have visited Jupiter.Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini, Ulysses, and New Horizons missions. The Juno mission arrived in July 2016. Other future missions may focus on the Jovian moons Europa, Ganymede, and Callisto, and their subsurface oceans. Jupiter’s Great Red Spot Situated 22° south of Jupiter’s equator, the Great Red Spot is a storm that has been raging for at least 186 years. In fact, upper estimates suggest that this red and turbulent storm could have been in existence for over three and a half centuries. A giant red spot was seen on Jupiter in the seventeenth century, when telescopes first started to be used. However, it is unknown whether this is the same red spot that we see today, or whether Jupiter has had many such storms that have come and gone as the centuries pass. The red spot circulates anticlockwise and takes six (earth) days to rotate completely. Another mystery surrounding the red spot is what makes it red: scientists have come up with several theories (for instance, the presence of red organic compounds) but as yet nobody knows for certain. That will be a question for future astronomy!Jupiter’s Atmosphere Jupiter’s atmosphere is special because it is the solar system’s largest planetary atmosphere. It is made up of hydrogen and helium, in roughly the same proportions as are found in the sun. However, it also contains much smaller amounts of other space gases, such as ammonia, methane and water. 90% of the atmosphere of Jupiter – a huge proportion – is made of hydrogen. It would be impossible for humans to breathe in this atmosphere. So, if you are thinking of travelling to space to do some hands on astronomy research, you would have to wear a breathing suit when visiting this planet. © Space Facts.com
Atmosphere The vertical dimension (i.e., thickness) of Jupiter’s atmosphere is more difficult to define than those of the terrestrial planets. For example, whereas the lower boundary for the atmosphere on Earth is its solid planetary surface, there is no such equivalent on Jupiter. Essentially, Jupiter’s atmosphere transitions from a gaseous outer zone into the planet’s liquid layer. However, for practical purposes scientists have designated the depth at which the atmospheric pressure equals ten times the pressure at sea level on Earth as Jupiter’s “surface”. Those layers of the atmosphere visible to Earth-based telescopes are divided into lighter and darker horizontal bands. Scientists believe these bands to be layers of high and low pressure. As a result, storms often develop on the boundaries between two adjacent bands. The Great Red Spot, visible in Jupiter’s southern hemisphere, is one such storm. Amazingly, this storm has raged for centuries and is 25,000 km across— is big enough to hold two Earths! The composition of Jupiter’s atmosphere is very interesting. At roughly 90% hydrogen and 10% helium, Jupiter’s composition is nearly the same as the Sun’s. The only difference between the two is that the Sun is much more massive than Jupiter. This composition supports the theory that Jupiter could have been a star.
Interior The interior of Jupiter is believed to consist of three regions. The first is a rocky core composed of various elements with a mass between 12 and 45 times that of the entire Earth. The core is surrounded by the second region, a layer of electrically conductive liquid hydrogen. It is due to this layer, which comprises most of the planet’s mass, that Jupiter has such a strong magnetic field. The third region consists of ordinary hydrogen with traces of helium, which transitions into the planet’s atmosphere. A fascinating property of Jupiter is that it emits more energy than it receives from the Sun. This is due to the planet being so massive. As a result of such a large mass, Jupiter exerts a strong gravitational force on itself, thus resulting in the compression of the planet as a whole. The cumulative effect of all this inward force is the production of a large amount of heat, which is then radiated into space.
Orbit & Rotation With a mean orbital distance of 7.78 x 108 km, Jupiter is, on average, a little more than five times the distance from the Earth to the Sun. This means that it takes about 43 minutes for sunlight to reach Jupiter. Also, Jupiter’s orbital eccentricity of .04838 is fourth largest among the planets, giving it a perihelion of 7.41 x 108 km and an aphelion of 8.16 x 108 km. Jupiter’s year is about 4,333 Earth days in length— that’s about 12 times the length of one Earth year! Jupiter’s axial tilt of 3.17° is extremely small, second lowest in the Solar System behind Mercury. What this means is Jupiter doesn’t experience seasons at all. Two things stand out about Jupiter’s rotation. The first is its speed. At just under 10 hours, Jupiter has the shortest rotational period in the Solar System. (Saturn is a close second at 10.7 hours.) This quick rotational speed causes the planet to bulge near its equator, making it less spherical than most of the other planets. The second stand-out characteristic of Jupiter’s rotation is that different parts rotate at different speeds. This is due to Jupiter’s not being a solid body. For example, the polar atmosphere rotates about 5 minutes more slowly than that found at the equator.
Rings Although the rings of Saturn are well-known, it is uncommon to hear anything about Jupiter’s rings. Nevertheless, Jupiter does have a ring system. Jupiter’s rings are lesser known than Saturn’s (or even Uranus') because they are primarily composed of dust, which makes them very difficult to see. The formation of these rings is believed to have come about through Jupiter’s gravity having captured material ejected from its moons.
Aurora Recently the Hubble Space Telescope captured an amazing event on the North Pole of Jupiter. As you can see from the image below, Jupiter, like Earth, has an Aurora (Northern Lights) which instead of a mystical green like on Earth, appears to be an electric blue color. © The Planets.org
The Moons of Jupiter
- Jupiter has four large moons which were discovered by Galileo in 1610 using a 20-power telescope. These moons are known as the Galilean moons and they are called Io, Europa, Ganymede, and Callisto. Jupiter also has dozens of other smaller moons that are thought to have originated from passing asteroids. So how many moons does Jupiter have? At the current count there are nearly 80 confirmed moons of Jupiter.
- Jupiter’s moons are often split into three specific groups:
- Inner moons
- These are the moons which orbit closest to Jupiter and they are sometimes known as the Amalthea group. The names of the inner moons of Jupiter are Metis, Adrastea, Amalthea, and Thebe.
- Galilean moons
- The largest four moons of Jupiter – Io, Ganymede, Europa, and Callisto – were discovered by Galileo in 1610 and are known as the Galilean moons. They each have a radii larger than any of the dwarf planets and they are some of the largest objects in the solar system outside of the eight planets by mass. Ganymede is actually larger than Mercury in diameter.
- Outer moons
- The other moons are known as irregular satellites because of their eccentric and distant orbit paths. They are the furthest from Jupiter and are substantially smaller objects. Many of these moons are captured asteroids pulled in by the gravitational forces of Jupiter.
The Inner Moons of Jupiter
The Outer Moons of Jupiter
HimaliaJupiter’s tenth moon is Himalia, discovered by Charles Perrine in 1904. Himalia is 170 km (110 miles) in diameter and orbits 11,480,000 km (7,000,000 miles) from Jupiter. The moon is named after a nymph who produced three sons with Zeus (Jupiter). It has a mass of 9.5 x 1018kg and takes 250.5662 days to orbit Jupiter.
LysitheaThe eleventh moon from Jupiter’s surface is Lysithea, a world which is 24 km (15 miles) in diameter and orbits at around 11,720,000 km (7,200,000 miles) from Jupiter. It has a mass of 8 x 1016kg and takes 259.22 Earth days to orbit Jupiter. Lysithea is named after the daughter of Oceanus in Greek mythology. Lysithea was discovered in 1938 by Seth Nicholson.
ElaraElara was discovered in 1905 by Charles Perinne and is Jupiter’s twelfth moon. It has a diameter of 80 km (50 miles) and orbits Jupiter at a distance of 11,737,000 km (7,250,000 miles. Elara has a mass of 8 x 1017kg and takes 259.6528 Earth days to orbit Jupiter. It is named after Elara from Greek mythology, the mother of the giant Tityus, fathered by Zeus.
AnankeAnanke, Jupiter’s thirteenth moon, was discovered in 1951 by Seth Nicholson. Ananke has a diameter of 20 km (12.5 miles) and orbits 21,200,000 km (13,100,000 miles) from Jupiter. The moon has a mass of 4 x 1016kg and it take Ananke 631 Earth days to orbit Jupiter. The moon is also in a retrograde orbit – which means it orbits in the opposite direction of Jupiter. It is named after Ananke, the mother of Adrastea by Zeus, in Greek mythology.
CarmeDiscovered in 1938 by Charles Nicholson, Carme is the fourteenth moon of Jupiter. It has a diameter of 30 km (18.5 miles) and orbits at a distance of 22,600,000 km (13,800,000 miles) from Jupiter. Carme has a mass of 9 x 1016kg and orbits Jupiter in 692 Earth days. It is in a retrograde orbit which moves in the opposite direction of Jupiter. In Greek mythology Carme was the mother of Britomartis, a Cretan goddess, fathered by Zeus.
PasiphaePasiphae is the fifteenth moon of Jupiter and was discovered by P. Melotte in 1908. It orbits Jupiter at a distance of 23,500,000 km (14,600,000 miles) and has a diameter of 36 km (22 miles). Its mass is 2 x 1023kg and it takes Pasiphae 735 Earth days to orbit Jupiter in a retrograde orbit path. In Greek mythology, Pasiphae was the wife of Minos and mother of the Minotaur.
SinopeJupiter’s sixteenth moon is Sinope, discovered in 1914 by Seth Nicholson. Sinope has a diameter of 28 km (17.5 miles) and it orbits Jupiter at a distance of 23,700,000 km (14,700,000 miles). It has a mass of 8 x 1016kg and it orbits Jupiter in a retrograde orbit that takes 758 Earth days. In Greek mythology, Sinope was a woman who was courted unsuccessfully by Zeus, and she remained a virgin for her entire life.
CallirrhoeJupiter’s seventeenth confirmed moon was Callirrhoe, also known as S/1999 J 1, and was discovered by Tim Spahr on July 18, 2000. It has a diameter of 8.6 km (5.3 miles) and orbits Jupiter at a distance of 24,100,000 km (14,975,000 miles). Callirrhoe has a mass of 9 × 1014kg and orbits Jupiter in a retrograde orbit that takes 758.77 Earth days to complete. In Greek mythology, Callirrhoe was the daughter of the river god Achelous, one of Zeus’ (Jupiter’s) many conquests. © The Planets.org