Jupiter, Europa, Io, Callisto, and Ganymede

Jupiter is the fifth planet from the Sun and is the largest in size and mass. Jupiter was named after the Roman god of the same name who was the equivalent of the Greeks' Zeus. Jupiter has 62 known satellites, the four biggest (Europa, Io, Callisto and Ganymede) are known as the Galilean Moons, because they were discovered by Galileo in 1610. Jupiter has a ring system but it is not visible from Earth. Jupiter is famous for it's Great Red Spot, a large storm system which rotates counter-clockwise. Jupiter is mainly comprised of hydrogen and helium, and because of the great pressure the hydrogen is a metallic liquid.
Jupiter and its moons have helped us in many scientific studies. For example, Ole Romer, a Danish astronomer used observations the eclipses of Io to demonstrate the speed of light. He saw that the the orbit differed by about 20 minutes depending on how far away Jupiter was. He calculate the speed of light as being 225,000 km/sec. in 1676 (it is actually 299,792 km/sec).

The Formation
Jupiter’s Formation
Jupiter began with the build up of icy dust in the outside of the solar nebula. As the particles came together they formed a larger objects, when young planet had gathered enough mass the gravity began to gather helium and hydrogen and more dust. The heavier elements sunk towards the core of early Jupiter while the light hydrogen and helium were in its atmosphere.
Jupiter was much hotter when it first formed; the heat expanded it to twice its current size. As Jupiter cooled down, it began to shrink, and it still is shrinking at about 2 centimeters each year.
In Jupiter's formation, many scientists believe, it stopped the formation of other planets and might have helped the formation of life on earth. In the earlier Solar system, because Jupiter was so big, it possibly threw off the orbit of some newer planets and cleared many asteroids (which is how many scientists think that it helped life on Earth). Jupiter's formation it may have eaten most of its potential moons as many gas giants do.
The Galilean Moons' Formation
One theory towards the formation of Jupiter’s moons states that moons closer to Jupiter would be denser than those farther out. This is based on the idea that young Jupiter would have emitted heat, which would have prevented the lower density material from forming. The Galilean moons fit this idea with Io, being the closest and densest as it is made mainly of iron and rock.

Physical Characteristics
Jupiter's Characteristics
Jupiter is a giant ball of gas and liquid with little, if any, solid surface. Instead, the planet's surface is composed of dense red, brown, yellow, and white clouds. The clouds are arranged in light-colored areas called zones and darker regions called belts that circle the planet parallel to the equator.
Jupiter is also the largest planet in the solar system. Its diameter is nearly 90,000 miles, which is more than 11 times that of Earth, and about 1/10 that of the sun. It would also take more than 1,000 Earths to fill up Jupiter from the inside. Basically, Jupiter is a monster. The distance between Jupiter and the Sun is 483,780,000 miles, more than 5 times the distance between the Sun and our own planet. Even with this massive distance, Jupiter is still commonly the second brightest planet in the sky.
Jupiter's Great Red Spot

The Galilean Moons' Characteristics

Io is a large, rocky, volcanically active moon of Jupiter. Its volcanoes erupt molten sulfur, making Io have a yellowish color. It is Jupiter’s closest moon out of the four large moons (it’s average distance from Jupiter is 220,000 miles), and is the third largest. It has a diameter of almost 2,000 miles, which is very close in size to our moon. There is a doughnut-shaped plasma cloud around Jupiter near Io’s orbit known as the “Io plasma torus”. This torus is caused by Jupiter’s strong magnetic field, which strips ions from Io as it rotates.
Europa is a large, dense, icy moon of Jupiter. Europa happens to be the smoothest object in our solar system. Its surface is covered with long, crisscrossing trackways on water ice (see possibility of life).
Also, frozen sulfuric acid has been found on its surface. Europa is the smallest of the four large moons, and is the secondclosest (average distance 420,000 miles). Europa’s diameter is less than 2,000 miles, making it smaller than our own moon.Ganymede is the largest moon of Jupiter, and is also the largest moon in our solar system. In fact, it is larger than both Mercury and the former planet Pluto. Its diameter is 3,400 miles and it orbits Jupiter with an averagedistance of 664,000 miles.
Ganymede is riddled with impact craters and manyparallel faults, and is so large that it has its own magnetic field and probably has a magnetic core.
Callisto, the furthest of all of Jupiter’s major moons (average distance 1,170,000 miles), is a large, icy, dark-colored, low-density moon that is scarred with impact craters and ejecta. It is the second largest of Jupiter’s moons, with a diameter of roughly 3,000 miles. That is approximately the size of Mercury. Callisto has the largest-known impact crater in the Solar System, Valhalla, which has a bright patch 600 km across and rings that go out to almost 3000 km.

Jupiter's rotation is the fastest of any planet in our solar system, it takes only 9 hours and 56 minutes to spin all the way around. Because scientists cannot calculate this directly they have used two different methods: 1. averaging the speeds of the visible clouds and, 2. measuring the radio waves sent out by Jupiter which has a pattern that repeats every 9 hours and 56 minutes. Jupiter's axis only has a tilt of 3 degrees and therefore does not have seasons.
Despite this rapid rotation, Jupiter's orbit around the sun takes 4,333 Earth days, or about 12 Earth years, to complete. Jupiter's orbit is elliptical, and on average is 778,330,000 km away from the Sun. At it's aphelion (the point it is farthest away) it is 815,700,000 km away and at it's perihelion (closest point to sun) it is 749,900,000 km away.

Comet Impact on Jupiter
The maroon blotches are the marks left by Comet Shoemaker Levy 9

In March of 1993, 3 scientists (Eugene Shoemaker, Carolyn Shoemaker, and David H. Levy) discovered a comet (later named Comet Shoemaker Levy 9) close to Jupiter, which had been pulled out of its orbit by Jupiter’s gravity. When it was discovered it was in broken into 21 pieces. They calculated that it would crash into Jupiter’s atmosphere in July of 1994. Astronomers all over the world observed the collision through major telescopes and with the Hubble Space Telescope and the space probe Galileo. The fragments fell on the backside of Jupiter (as viewed from Earth and Hubble), but because of the rotation of Jupiter they were able to see the impacts sites in less than half an hour. Scientists estimate that the largest fragments were around 2.5 in diameter. The impacts would have been directly observable from Galileo, it was within around 150 million miles of Jupiter, however, this was limited because of damage to some of the probe’s instruments. These impacts caused large explosions, most likely due to the compression, heating and rapid expansion of the atmospheric gases. The explosions scattered comet debris over large areas some with diameters larger than Earth’s. These debris eventually spread a dark haze of fine materials, which stayed there for several months in the upper atmosphere. This shows that if a comet collided with Earth, it might produce a haze, which would cool the atmosphere and darken the planet because it would absorb sunlight.jupiter_legacy-hi.jpg


There have been 6 explorations to Jupiter: (1) Pioneer 10, (2) Pioneer-Saturn, (3) Voyager 1, (4) Voyager 2, (5) Ulysses, and (6) Galileo, all in a span of 30 years (1973-2003). These explorations have uncovered many secrets of Jupiter, including the severe effects of Jupiter's radiation belt on spacecraft and Jupiter’s enormous magnetosphere. There are currently no plans to send another probe to Jupiter in the near future, but there is a new proposal to visit Ganymede and Europa to try and solve the mystery of the possibility of life on Europa. Many of these explorations succeeded in their goals to unearth the mysteries of Jupiter.
Possibility of Life
While it is obvious that life would be impossible to sustain on the planet itself, many scientists have debated the possibility of life on Europa, one of Jupiter’s moons. We have discovered a possible giant subterranean ocean on Europa’s surface, perhaps hinting at the possibility of life. Even though Ganymede has a similar frozen water layer, it is much too cold and rigid to support life.
Jupiter is the biggest planet in our solar system. It has many moons, and each have unique characteristics. They have help scientists discover more about our universe, whether the first estimate of the speed of light, or just what happens when a comet collides into a planet. Jupiter has also helped the formation of life on our planet, as it is hypothesized that it swallowed many asteroids, which could have bombarded our planet. No doubt, this gigantic planet is a unique and important one.

Picture Sources


"Featherweight Jovian moon is likely a jumble of pieces"
Origin of Europa and the Galilean Satelites
Galileo Project: The Moons and Rings of Jupiter

Universe Today
Nine Planets
Solar Views
Enchanted Learning
Explorations to Jupiter