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
Moons of Jupiter As of 2021, Jupiter has nearly 80 confirmed moons orbiting the planet. These moons are separated into three groups: Inner moons. These orbit the closest to Jupiter and are sometimes called the Amalthea group. The inner moons are Metis, Adrastea, Amalthea, and Thebe. Galilean moons. These are largest of Jupiter’s moons and were discovered by Galileo Galilei in 1610 – Ganymede, Callisto, Europa, Io. Outer moons. These moons are much smaller and further away from Jupiter. They also have irregular, elliptical orbit paths and many are captured asteroids. More information and facts about Jupiter What is even more provocative is the theory that Jupiter is a failed star. Current scientific knowledge suggests that if Jupiter had, in fact, been roughly 80 times more massive, nuclear fusion would have taken place in its core; thus, Jupiter would have become a star, not a planet. Regardless, it is still tempting to look at the number of satellites orbiting Jupiter and consider it and its moons as, in many ways, a mini solar system. Although our scientific knowledge of Jupiter has been greatly expanded as a result of the numerous planetary missions beginning in the 1970s, these missions are unnecessary for viewing the planet’s surface features. Instead, most of these features can be observed using Earth-based telescopes. For example, as recently as 1994, the Hubble Space Telescope provided stunning images of the impact of the Shoemaker-Levy 9 comet into Jupiter.
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

Metis: Discovered by Stephen Synnott through images taken by the Voyager 1 in 1979, Metis is the closest moon to Jupiter. It has a diameter of 40 km (25 miles) and orbits Jupiter in 0.294780 Earth days, which is faster than Jupiter rotates on its axis. It is named after the Greek Titaness Metis, who was the first wife of the god of the skies, Zeus. It is thought that Metis is an asteroid that was captured by Jupiter’s gravity. The moon orbits at 128,000 km (79,500 miles) from Jupiter and has a mass of 9 x 1016kg. Adrastea: The second closest moon to Jupiter is Adrastea which has a diameter of 20 km (12 miles)12 miles (20 km) and orbits 129,000 km (80,000 miles) from Jupiter. It was discovered in 1979 by David Jewitt using the Voyager 2 and is named for the Greek goddess Adrasteia, who passed out rewards and punishments. Adrastea has a mass of 1.91 x 1016kg and like Metis it orbits Jupiter faster than it takes for Jupiter to rotate on its axis – in 0.29826 Earth days. Amalthea: Amalthea is the third moon from Jupiter and is the reddest object in the solar system. It was discovered by Edward Emerson Barnard in 1892. Amalthea is not a spherical moon with a diameter of 232 x 146 x 134 km (145 x 91 x 83 miles). It orbits 181,300 km (112,700 miles) from Jupiter, located in the faint Gossamer ring. The moon is named for Amalthea in Greek mythology, who was the foster-mother of Zeus and nursed the god of the skies when he was a baby with goat’s milk. It is the largest of the inner moons of Jupiter and is most likely an asteroid captured by Jupiter. It takes Amalthea 0.49817905 Earth days to orbit Jupiter and like all the inner moons, it is tidally locked to the planet – the same side of the moon always faces Jupiter. Amalthea also gives off more heat than it receives from the Sun. Thebe: The fourth moon from Jupiter is Thebe. It has a diameter of 110 x 90 km (68 x 56 miles) and orbits 222,000 km (138,000 miles) from Jupiter. Thebe was discovered by Stephen P. Synnott in 1979 and officially named in 1983. In Greek mythology, Thebe was a nymph and the daughter of the river god Asopus. It is likely that Thebe, along with Amalthea, provide the dust for the Gossamer ring where they are located. Thebe has a mass of 8 x 1017kg and it takes the moon 0.6745-day Earth days to orbit Jupiter. (c) The Planets.org

Io

Io is a large, rocky and volcanically active moon which is very vivid with bright colors due to the molten sulfur that they volcanoes spit out. These violent conditions mean that it is not the kind of world which would be able to sustain human life. In fact, Io lies in the doughnut-shaped plasma cloud around Jupiter, known as the “Io plasma torus” which is the result of Jupiter’s very strong magnetic field. As Io rotates, this torus strips ions from Io as it rotates, effectively making it an electrical reactor. The result is a level of radiation on Io that is 1000x stronger than the level needed to kill a human being. With a diameter of 3,636 km (1,942 miles), Io is very close in size to Earth's Moon and it is around 422,000 km (220,000 miles) from Jupiter. Io has a mass of 8.93×1022 kg and takes 1.77 Earth days to orbit Jupiter. Io was the first discovered moon after Earth’s moon. Galileo Galilei discovered Io on January 8th, 1610 and the discovery, along with the three other Jovian moons Europa, Ganymede and Callisto, were the first moons discovered that were orbiting a planet other than Earth. Technically, Galileo discovered Io the night before, but he wasn’t able to distinguish between Io and Europa until the following night. The discovery of Io and the Galilean moons led to the understanding that planets orbit around the Sun – and that Earth was not the center of our solar system. The moon is named after a nymph seduced by Zeus in Greek mythology. Io was a nymph loved by the Greek god of the skies, Zeus, and the planet which was formerly known as Jupiter I was named for this nymph in the mid-1800s. In the mythological story, Zeus turned Io into a heifer (a cow) to hide his infidelity from his wife Hera. Everything we know about Io comes from the Voyager and Galileo spacecraft missions. A number of spacecraft have flown past the planet Jupiter and its moons – sending back images and a lot of information about the Jovian worlds. Pioneer 10 was the first spacecraft to visit in 1973, and was followed shortly after by Pioneer 11 in 1974. The Voyager 1 and Voyager 2 missions were the first to return photos of Io and the Jovian worlds during their flybys. The Galileo spaceprobe arrived at Jupiter in 1995 after a six-year flight and passed as low as 162 miles (261 km) over the surfaces of the Galilean moons, producing the detailed images of the objects we have today. NASA describes Io as “a giant pizza covered with melted cheese and splotches of tomato and ripe olives”. The interior of Io is made of an iron or iron sulfide core but its brown silicate outer layer which gives the planet its distinctive splotchy orange, yellow, red, black and white appear is the most interesting and noticeable. The colorful appearance is down to the silicates (such as orthopyroxene), sulfur, and sulfur dioxide which frosts the surface and forms the yellow to yellow-green regions. Radiation on Io is 1000x stronger than is needed to kill a human being. Io lies in the doughnut-shaped plasma cloud around Jupiter, known as the “Io plasma torus” which is the result of Jupiter’s very strong magnetic field. As Io rotates, this torus strips ions from Io as it rotates, effectively making it an electrical reactor which produces radiation levels so strong that a human being could not survive. Io receives about 3,600 REM (36 Sv) of radiation per day. Doses greater than 100 rem received over a short time period would result in death in just a few weeks. Io has over 400 active volcanoes. Io is the only world other than Earth that is observed to have active volcanoes and is the most geologically and volcanically active object in the solar system. Volcanic plumes can rise 300 km (190 miles) above the surface. This was originally discovered by NASA’s Voyager 1 mission in 1979. The reason for this volcanic activity is the tidal heating which happens as Io is stretched and squeezed while it orbits Jupiter. This tidal bulge also shifts Io’s surface up by as much as 100 m throughout its orbit. The irregular orbit of the moon around Jupiter increases the tidal activity which is what makes the moon so volcanic. Io has mountains larger than Mount Everest. The surface of Io is dotted with more than 100 mountains – a result of the compression at the base of its crust that uplifted the surface. Some of these peaks are taller than Mount Everest. These mountains have an average height of 6 km (4 miles) and a large average length of 157 km (98 miles) long. Io is composed of silicate rock surrounding a molten iron or iron sulfide core. While most moons in the outer solar system, like Callisto, for example, are made up of mostly water ice and rock, Io is composed of silicate rock which surrounds either a molten iron or iron sulfide core. This makes Io closer to the terrestrial planets in bulk composition than the satellites of the outer solar system. Io has a density of 3.5275 g/cm3, which is higher than any moon in the solar system and significantly higher than the other Galilean moons of Jupiter. It is denser than Earth’s Moon as well. Io played a large role in the development of astronomy. In the 17th and 18th centuries, the discovery of Io furthered to adoption of the Copernican model of the solar system – a Sun-centric system in which planets revolve around a relatively stationary Sun at the center. It also furthered the development of Kepler’s law of motion – three scientific laws describing the motion of planets around the Sun – and the first measurement of the speed of light. (c) The Planets.org
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Europa

Europa is a large, dense and icy moon of Jupiter with a very smooth surface – it is the smoothest object in our solar system. The surface of Europa is covered with long, crisscrossing trackway but it has few craters. Around 3.8 to 4.1 billion years ago, many objects in the solar system were bombarded with asteroids and comets – a period known as the Late Heavy Bombardment Period. Since Europa is so smooth, it is believed that the moon, like Earth, has been able to recover its surface. One scientific theory is that Europa contains a large liquid water ocean heated by its core beneath the frozen icy shell – making it a world that may be able to sustain human life. Europa has a diameter less than 3,138 km (2,000 miles) making it smaller than the Earth’s moon. Europa orbits Jupiter in 3.55 days, sits at a mean distance of 670,900 km (420,000 miles) from Jupiter and has a mass of 4.80×1022 kg. The discovery of Europa and the other Galilean moons lead to the discovery of a Sun-centered solar system. The discovery of these moons of Jupiter by Galileo is what eventually lead scientists to the understanding that the Sun was the center of our solar system, with the planets orbiting around the almost stationary star. Before this, it was believed that the Earth was the center of the solar system and the planets orbited around Earth. The moon is named after a Phoenician noblewoman who became queen of Crete in Greek mythology. Europa was a noblewoman which the continent of Europe was named after. Europa was abducted by Zeus – the Greek counterpart for the Roman Jupiter – after the god of the skies transformed into a bull. He took her to the island of Crete to be his lover. She became the queen of Crete and had a number of children with Zeus. Europa is the smoothest object in the solar system. The surface of Europa is made of frozen water and has the smoothest surface of any other objects in the solar system – i.e. it lacks large features such as mountains or craters. There are very few craters on the surface of the moon because it is tectonically active and relatively young. Europa is about 4.5 billion years old but its surface is only 20 to 180 million years old. The moon is one of the brightest objects in the solar system with an albedo (light reflectivity) of 0.64, one of the highest of all moons. This reflectivity suggests a young and active surface to Europa of somewhere between 20 and 180 million years – much less than the moon itself with is around the same age as Jupiter, 4.5 billion years. Radiation on Europa is high enough to kill a human being in one day. Radiation levels on the surface of Europa are around 5400 Sv (540 REM) per day, a dose which would cause severe illness and death in a human being exposed for just one day. Like Io, this radiation is the result of solar radiation and energetic particles produced by Jupiter’s very strong magnetic field. Europa has a liquid ocean of saltwater beneath its surface. Scientists believe that there is a liquid ocean somewhere around 100 km (60 miles) beneath the thick, icy crust of Europa. It is thought that the tidal affects between Europa and Jupiter are what heat and keep the water in a liquid form. If it is proven that this ocean exists, Europa may be one of the most promising places in our solar system, beyond Earth, to search for life. Europa may have twice as much water on it as Earth. If the scientists’ theories prove to be correct, the estimated volume of water on Europa is approximately 3 × 1018 m3. This is slightly more than double the volume of water in the oceans on Earth. NASA’s Galileo mission is responsible for most of what we know about Europa. Launched in 1989, the Galileo mission took 6 years to reach Jupiter and it remained in orbit from December 8, 1995 until September 21, 2003. It provided the most detailed examination of the Galilean moons to date with numerous close flybys of Europa. Europa and the moons of Jupiter have also been visited by a number of other spacecraft – including Pioneer 10 and 11 in 1973 and 1974, Voyager 1 and 2 in 1979, and the New Horizons mission as it flew through the Jovian system on its way to Pluto and beyond. One day on Europa lasts as long as one year – 3.5 Earth days. One day on Europa – the time it takes for the moon to rotate on its axis – is 3.551 Earth days. It also takes Europa 3.551181041 Earth days to orbit Jupiter. This means that a day on Europa takes the same length of time as one year on Europa. Europa is tidally locked to Jupiter. Like almost all moons in the solar system, Europa is tidally locked – locked by gravity – to Jupiter and the same side of the moon always faces the planet.Europa has a very weak atmosphere. Europa has a weak oxygen atmosphere which is most likely because of charged particles from the Sun hitting water molecules on its surface. This breaks those molecules into oxygen and hydrogen atoms. The hydrogen escapes the surface of Europa but the oxygen is left being – leaving a tenuous oxygen based atmosphere. (c) The Planets

Ganymede

The largest moon of Jupiter is Ganymede – a large, icy moon with a diameter of around 5,268 km (3,400 miles) that is scarred with craters. It is larger in diameter than the planet Mercury and the dwarf planet Pluto. In fact, Ganymede is the largest moon in the solar system. Named for the handsome Trojan boy that Zeus took away to be the cup bearer for the gods, Ganymede has a magnetic field and is believed to have a molten iron core. It takes the moon 7.15 earth days to orbit Jupiter. Ganymede’s mass is 1.48×1023 kg and it orbits Jupiter at a distance of around 1,070,000 km (664,000 miles). If Ganymede were orbiting the Sun it would be a planet. Ganymede is larger than both Mercury and Pluto, and is 2/3 the size of Mars with a diameter of 5,268 km (3,273 miles) – 8% larger than Mercury. It has the highest mass of all planetary satellites and has more than twice the mass of the Earth’s Moon. The moon is named after a Trojan prince in Greek mythology. Originally called Jupiter III by Galileo, Ganymede was named after a suggestion from German mathematician and astronomer Johannes Kepler. In the Greek story Zeus, a counterpart of Jupiter in Roman mythology, carried the prince Ganymede to Olympus, where he became a cupbearer for the Olympian gods. It takes Ganymede 7.1 Earth days to orbit Jupiter at a speed of 39,165 km/h. The moon orbits at 39,165 km (24,321 miles) an hour and takes 7.15455296 Earth days to complete its orbit around Jupiter. Like most moons in the solar system, Ganymede is tidally locked to Jupiter and one side is always facing the planet. Interestingly, for every orbit of Ganymede, Europa orbits Jupiter twice and Io orbits four times. Ganymede is the only moon in the solar system known to have its own magnetic field. It is believed that the magnetosphere of Ganymede is likely to have been created through convection within the liquid iron core of the moon. The field is very small though and is barely noticeable because it is buried within Jupiter’s much larger magnetic field. The moon is composed of equal amounts silicate rock and water ice and has several layers. Ganymede is made of rocky material and water ice. It has a metallic iron and iron sulfide core which is surrounded by a rocky mantle and a very thick icy crust. There may be an ocean layer of liquid water beneath the surface of Ganymede. A study published in 2014 suggests that there might be a stack of several saltwater ocean layers separated by different phases of ice as far as 124 miles below the surface of Ganymede. The lowest liquid layer may be right next to the rocky mantle below and could be sign for sustainable life on Ganymede. 40% of Ganymede’s surface is covered with highly cratered dark regions. These dark regions are believed to be from heavy impact by asteroids and comets and date back to around 4 billion years ago. The lighter regions of the moon’s surface are not quite so old and cover the rest of Ganymede. The cause of the light terrain’s disrupted geology is thought to be the result of tectonic activity caused by tidal heating – a buildup of friction, orbital and rotational energy that are dissipated as heat in the crust of the moons and planets involved. Ganymede has a very thin atmosphere and it does contain small amounts of oxygen but there is not enough to support any form of life. Six spacecraft have visited Ganymede since 1973. Pioneer 10 and 11 were launched in March 1972 and April 1973 respectively and made successful flybys of Ganymede in December 1973 and December 1974. They sent back limited data with blurry images of the moon. Voyager 1 and 2 returned much more high quality and detailed images in 1979 which showed the grooved terrain and also discovered that Ganymede was larger than first thought – replacing Saturn’s moon Titan as the largest satellite in the solar system. The Galileo spacecraft in 1995 passed as low as 162 miles (261 km) over the surfaces of the Galilean moons, sending back a lot of new data such as the discovery of the magnetic field, the ocean beneath Ganymede’s surface, and the highest resolution close up images of the moon. Finally, New Horizons in 2007 sent back images and made topography and composition maps of Ganymede before continuing on towards Pluto and the Kuiper Belt. (c) The Planets.org

Callisto

Callisto is the eighth moon of Jupiter and is a large, dark but low-density moon which is covered with impact craters. It is home to the Valhalla crater, which is nearly 4,000 km in diameter and the largest crater in the solar system. It is the outermost of the Galilean moons, orbiting 1,883,000 km (1,170,000 miles) from Jupiter. It takes Callisto 16.7 days to complete its orbit around Jupiter and during that time it will have travelled more than seven million miles. Callisto has about 99% the diameter of the planet Mercury, but has only 1/3 the mass at 1.08×1023 kg. The name of the moon comes from Greek mythology. Callisto was a nymph who had an affair with the king of the gods, Zeus. His wife Hera then changed her into a bear before Zeus transformed her into a star and placed her in the sky as the constellation Ursa Major. This constellation is also known as the Great Bear, or the Plough. There is also a Little Bear constellation which was the son of Zeus and Callisto. All of the moons of Jupiter are named for Greek mythological figures seduced by Zeus. Callisto is 99% the diameter of Mercury but only 1/3 the mass. At a diameter of 4,820.60 km, Callisto is only 58.40 km less than the planet Mercury, but the mass of the moon is only around a third of Mercury’s mass – 107,593,737,963,819 billion kg compared to 330,104,000,000,000 billion kg for Mercury.There are more craters on Callisto than any other object in the solar system. The surface of Callisto is the most heavily cratered and also one of the oldest landscapes in our solar system. Scientists believe it is a dead world with no signs of geologic activity like plate tectonics or volcanism on its surface. The moon is made of around 60% rock/iron and 40% ice and may contain liquid water. Callisto is composed of both rock and ice, in approximately equal measures, and there are also traces of water ice, carbon dioxide, silicates, and organic compounds on the surface. The Galileo spacecraft also revealed that the moon may have subsurface ocean of liquid water 100 km or more below the surface. Through a telescope, Callisto is brighter than our Moon. Despite being 628,300,000 km from Earth, Callisto appears much brighter in the sky than our Moon when viewed through a telescope – despite our Moon being only 384,400 km. This is because the surface of Callisto is made up of a very thick layer of ice which reflects the Sun much more than the surface of our Moon. Callisto is not affected by the gravity of other moons of Jupiter. Unlike Io, Europa and Ganymede, Callisto doesn’t suffer from an orbital gravitational pull. This means there is less of a tidal heating – a buildup of friction, orbital and rotational energy that are dissipated as heat in the crust of the moons and planets involved – which have caused the melting of surface ice from the rocky mantle of the Europa moon, for example. The reason it is less affected by Jupiter’s magnetosphere is that it orbits further away from the planet. Callisto is over a million miles from Jupiter. Earth’s Moon orbits around 238,855 miles from us, however Callisto orbits Jupiter at an average distance of 1,169,856 miles (1,882,700 kilometers).One orbit of Jupiter takes Callisto 16.7 days. It takes Callisto 16.7 earth days to orbit Jupiter and during that time it will have travelled more than seven million miles – 7,345,927 miles (11,829,191 kilometers) to be exact. Callisto has an orbital speed of around 18,400 miles per hour (29,530 kilometers per hour). Callisto is tidally locked to Jupiter. Similar to Earth and its Moon, Callisto is tidally locked to Jupiter. This means that the same face of Callisto is always pointing toward Jupiter, and Jupiter would appear to be still when viewed in Callisto’s sky. The largest crater on Callisto is nearly 4,000 km across. The largest impact craters on Callisto are huge multi-ring basins which are surrounded by concentric rings that appear to be cracks that have been smoothed out by the slow movement of the ice over a long period of time. Valhalla is the largest of these impact craters and stretches to around 3,800 km in diameter from the outer trough zone. It is named for Valhalla, the Norse God Odin’s hall where warriors are taken after death. Callisto has a very thin atmosphere. The atmosphere of Callisto is very tenuous and is composed mostly of carbon dioxide and probably molecular oxygen as well. Callisto may have formed from the gas and dust that surrounds Jupiter. Unlike Earth’s Moon which may have been a piece of Earth that broke away after an impact billions of years ago, Callisto is thought to have formed by slow accretion from the disk of the gas and dust that surrounded Jupiter after the planet was formed 4.5 billion years ago. Callisto may be able to harbor life. Although it is not considered to be geologically active, the likely presence of an ocean beneath the surface of Callisto leaves open the possibility that it could harbor life. Also, it has low levels of radiation and has long been considered the most suitable place for a human base for future exploration of the Jovian system. However, it is though that the conditions may be more favorable on the nearby satellite, Europa. (c) The Planets.org

The Outer Moons of Jupiter

LedaLeda is the ninth moon from Jupiter and is also the smallest moon with a mean diameter of 16 km (9.9 miles). Charles Kowal discovered Leda in 1974. It is named for the queen of Sparta and the mother of Pollux and Helen of Troy – the father was Zeus. The moon has a mass of 5.68 x 1015kg. It takes 238.72 Earth days for Leda to orbit Jupiter and it orbits at a distance of 11,094,000 km (6,900,000 miles) from the planet.
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