Io is the innermost Galilean moon. It is the 4th largest moon in the solar system. It was referred as the first satellite of Jupiter.

Europa is the second moon of the four. It is the second closest satellite to orbit Jupiter and the smallest. It is reported to be slightly smaller than the Earth's Moon.

Ganymede is the third satellite to orbit Jupiter. This Galilean moon is named after a cupbearer of the Greek gods. It is the largest satellite in the Solar System, and it is actually larger than planet Mercury.

Callisto is last Galilean moon/satellite. This fourth moon is the second largest among the four, and it in the solar system, it is the 3rd largest. Callisto consists of roughly equal amounts of ice and rock. These components make it the least impenetrable of the Galilean moons/satellites. It has a basin, called Valhalla, as one of its major features with a width of 3000 km.

Galilean Moons of Jupiter

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Solar System's outer planets Jupiter, Saturn, Uranus and Neptune are all gas giants. Jupiter and Saturn are composed mainly of molecular hydrogen, metallic hydrogen and helium. While Uranus and Neptune, the ice giants, are made up of water, ammonia and methane ices on their mantle, and hydrogen, helium and methane gases on the surface. Hence, their beautiful baby blue and ultramarine colors.

The sad apart about these gas giants is that landing with a spaceship on them isn't possible because they don't have any surface. And as one goes closer to their cores gaseous atmospheres become thicker and denser. The difference between a rocky planet and a gas giant is that unlike the former, the latter's atmosphere is also indistinguishable with its mantle. So extraterrestrial creatures from Jupiter, Saturn, Uranus, Neptune and other gas giants in the Universe are quite unthinkable.

Gas Giants

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Jupiter

Next to planet Venus and the moon, Jupiter is also defined as the brightest object present in the sky. However, there are still occasions when Mars is able to exceed this brightness. Planet Jupiter has a notable feature called the Great Red Spot. This feature is defined as a giant storm in which existence gained popularity ever since the 17th century. Unlike the planet Saturn that can be identified easily through its rings, a lot of people may not be aware that Jupiter has within its planet a planetary ring system that is faint. The system is just a few thousand kilometers away from its inner fuzzy edge, starting from the outer edge, which can continue up to the atmosphere of the planet. It owns 63 moons at the least and one of these moons is actually larger than Mercury.

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Jupiter

This prominence makes Jupiter one of the first planets to be discovered by humans. But if you are asked when the planet was actually discovered, the inquiry is futile. Jupiter has been known to exist since the pre-historic times. Therefore, no records of when the actual discovery was made to exist. The case is the same for the first five planets from the sun in the solar system. Because they were easily visible without the use of a telescope, the pre-historic people knew their existence.

What the pre-historic people didn’t know was that Jupiter is actually a planet just like Earth. Remember that before Galileo Galilee, people believed Earth was the core or the center of the solar system. It was Nicolas Copernicus who corrected this notion, claiming that Jupiter, Earth, and all the other planets actually rotate around the sun, which is the solar system’s center. The father of modern science and scientific inquiry, Galileo Galilee, further improved the people’s knowledge of Jupiter thanks to his telescope. One of the very first discoveries regarding the solar system’s largest planet: the Galilean moons, the first four out of the more than 60 moons of Jupiter to be discovered.

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Because Jupiter is considered a gas planet, its atmosphere is then considered its surface. Jupiter does have a surface but it is not solid and there is still not a term scientists have assigned to it. Unlike other gas planets, Jupiter is colossal with very low density. Jupiter can have as much as four more times its mass but would still remain the same size because the density will rise. Jupiter size or mass is 318 times more than the Earth’s. Another characteristic Jupiter and the Earth share is their shape which is an oblate spheroid or poles that are a bit flattened and has a bulge in its equatorial region.

Aside from being massive and gaseous, Jupiter is also known for its rings and the Great red spot. Jupiter has an orbiting planetary ring which contains gases, space debris and others. Jupiter is also known to have the most number of moons. There are at least 63 known moons. The majority of Jupiter’s atmosphere is made up of hydrogen and a little percentage of helium.

NASA Explores Jupiter

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Galilean Moons – are the four moons of Jupiter discovered by Galileo Galilee in 1610.

Io – With a diameter of 3,642 km it is the 4th largest natural satellite in the solar system. It was named after a priestess who became one of Zeus’ human lovers. It has over 400 volcanoes and is the most geologically active celestial body in the solar system.

Europa – Is only marginally smaller than Earth’s moon having a 3121.6 km diameter. Its atmosphere is composed mainly of oxygen. Its surface is mostly made of ice and it has the smoothest surface in the solar system.

Ganymede – It is the largest moon in the solar system with a 5262.4 km diameter. Though it is larger than Mercury, Ganymede only has half the planet’s mass.

Callisto – It is the third largest moon in the solar system with a 4820.9 km diameter. It is the least dense Galilean moons being composed mainly of rock and ice.

Amalthea Group

Metis – The moon closest to Jupiter and due to tidal acceleration it will crash on Jupiter’s surface eventually.

Adrastea – It is the first moon to be discovered with the use of a spacecraft instead of a telescope. Very little is known about this moon aside from the fact that it is tidally locked to the planet.

Amalthea – It was discovered in 1892 by Edward Bernard and was the last moon discovered through visual observation.

Thebe – Like the rest of the Amalthea group, rotates in synchronicity with its orbit, which means it always faces on side away from the planet.

Himalia group
Leda – 10 km mean radius.
Himalia – 85 km mean radius.
Lystheria – 18 km mean radius.
Elara – 43 km mean radius.

Carme group
Carme – 23 km mean radius
Taygete – 5 km diameter
Eukelade – 4 km diameter
S/2003 J 5 – 4 km diameter
Chaldene – 3.8 km diameter
Isonoe – 3.8 km diameter
Kalyke – 5.2 km diameter
Erinome – 3.2 km diameter
Aitne – 3 km diameter
Kale – 2 km diameter
Pasithee – 2 km diameter
S/2003 J 9 – 1 km diameter
S/2003 J 10 – 2 km diameter

Ananke group
Ananke
Praxidike
Iocaste
Harpalyke
Thyone
Euanthe
Euporie

Pasiphae Group
Pasiphae
Sinope
Callirrhoe
Megaclite
Autonoe
Eurydome
Sponde

Moons of Jupiter

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Jupiter’s atmosphere

There are four main divisions of the atmosphere: the troposphere, stratosphere, thermosphere and exosphere. The troposphere is the lowest level of the atmosphere. Its clouds are composed of ammonium hydrosulfide, ammonia and water. The ammonia clouds on the upper part of the atmosphere are visible in Jupiter’s surface. They are organized in such a way that they are parallel to the equator. They are kept that way by jets (winds) known as the zonal atmospheric flows. Belts are the dark bands while zones are the light ones.

Zones are cooler than belts. They are upwellings. Belts on the other hand are descending air. The zones' are lighter because of ammonia ice. It is uncertain what gives belts its darker color. It is unknown where this kind of banded structure originated from but hypothesis have been formed such as the “shallow model,” and the “deep model,” to try to explain the phenomenon. These belts and zones along with the white and red spots that fill up the atmosphere, give Jupiter the “marbled” look it is so well known for.

Jupiter’s atmosphere is very dynamic. Lots of phenomena occur such as cyclones and anticyclones (vortices), band instabilities, storms and lightning. Storms are seen from the earth as large red, white or brown ovals. The Great Red Spot and the Oval BA are two of the largest red spots on Jupiter. These are anticyclones. White spots are smaller anticyclones.

Triple Eclipse Near Jupiter

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There are four different components that comprise Jupiter rings: the Halo ring, the Main ring, the Amalthea gossamer ring, and the Thebe gossamer ring. The halo ring is composed of thick particles, the main ring is the brightest but thin and the two gossamer rings are wide and thick but faint. The gossamer rings were named after Jupiter’s moons Amalthea and Thebe, where the materials came from.

The main ring is more than 122,000 km radius, 6500 km wide and is 30 – 300 km thick. Adrastea, Jupiter’s smallest moon, orbits in the same place as the main ring. The main ring is noted for its brightness but it depends on where it is viewed. The brightness of the main ring decreases as it moves closer to Adrastea’s orbit and is most bright near the center.

The halo ring is the thickest, vertically, out of the four rings. It has a radius of 92,000 km to 122,500 km, a width of 30,500 and a thickness of 12,500 km. It becomes thicker the closer it is to Jupiter. Astronomers believe that the halo ring is composed of tiny dust particles. This is used to explain the color and composition of the halo.

The Amalthea gossamer ring has a radius of around 129,000 to more than 180,000 km, a width of 53,000 km and a thickness of 2,000 km. Due to the brightness of the main ring, the inner boundaries of the Amalteha gossamer ring is hard to determine. The Thebe gossamer ring has a radius of about 129,000 km to 226,000 km; it is 97,000 km wide and 8,400 km thick. It is the faintest among Jupiter’s rings. The dust particles that comprises the gossamer rings come from the satellites from which it is named.

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Still, the knowledge of its existence before recorded history makes it impossible to know who specifically discovered Jupiter. The credit is given not to the person who discovered its true nature, but to the person who discovered it exists (for instance, the discoverer of Uranus presented it as a comet, not a planet). Therefore, no one gets the credit for Jupiter’s discovery.

Of course, as with the other classical planets, there were astronomers who observed the movement and status of the planet. For instance, Babylonian astronomers observed the planet back in the second millennium—centuries before Galileo Galilee and Nicolas Copernicus discovered the true nature of the planet. The Indian astronomers also observed the planet and wrote the observations in their Surya Siddhanta, credited to astronomer Brahmarishi Mayan. Eastern astronomers also observed the planet and estimated its distance from Earth.

However, it is perhaps Galileo who made the first ground-based research on the planet, thanks to his telescope. Because of this, he was the first to discover the moons of Jupiter. Callisto, Europa, Io, and Ganymede, the Jupiter’s four largest moons, were also called the Galilean moons. All in all, Jupiter has 60 moons and irregular satellites.

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Jupiter

Needless to say, for it to be considered a star, the planet would have to be 60 times larger than its actual size in order for it to generate enough gravitation force to initiate nuclear fusion. The heat and light that the planet generates comes from the heat that it has generated and compressed over time.

As for the planet’s composition, besides the aforementioned gases, one would also be able to find ammonia, water and methane mixed in. Underneath this layer of gases would be a layer of liquid nitrogen and right below that would be a mixture of both liquid and metallic hydrogen. This liquid nitrogen was produced by the staggering pressure generated by Jupiter itself. The planet’s inner core is comprised of iron and rock.

Jupiter is one of the four gas giants in our Solar System. They are referred to as such because of the fact that they are not primarily composed of solid materials. These gas giants are also often referred to as the Jovian Planets. They differ from other Terrestrial planets because they do not have a definite surface but instead have layer upon layer of materials that become progressively denser as your go further down.

Jupiter – The Largest Planet in our Solar System

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