The solar system consists of an average star called the Sun and nine planets namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto(Pelt 203). There are also comets, moons, asteroids, meteoroids and the interplanetary medium surrounding each planet. This system is bound gravitationally. This means that the planets are held by the gravitational force of the sun and the comets, moons and asteroids are held by the gravitational forces of the planets to which they revolve.Jupiter is the largest of these planets. It has a total of 67 known moons which is the largest number of moons that any planet in the solar systempossesses (Pelt 203).Out of these 67 moons of Jupiter there are four of them which are considered the largest.They were discovered by Galileo Galilei in the year 1610, and are therefore referred to as the Galilean moons. They are four in number and they include Callisto, Io, Europa and Ganymede. Europa is the smallest of the four but the sixth largest moon in the solar system while Ganymede is the largest of the four but the largest moon in the solar system(Pelt 203). Being Galilean satellites, Europa and Ganymede are nearly spherical in shape due to having planetary mass. Due to this property they would have qualified as planets if they were in direct orbit with the sun.
Europa is 3100 kilometers in diameter and has a mass of kilograms, making it 0.245times the size of planet Earth(Pelt 204). It is slightly smaller than the Earth’s moon and lies at an average distance of 670900 kilometers from Jupiter. However, its orbit is eccentric and therefore its distance from planet Jupiter varies. It is 664862 kilometers during periapsis which is the period when it is closest to Jupiter and 676938 kilometers during apoapsis which is the period when it is furthest from Jupiter (Pelt 204).Europa takes about 3.55 Earth days to revolve around Jupiter. On the other hand, Ganymede is 5262.4 kilometers in diameter, but has a low density meaning that its mass is also low(Pelt 204). Although it is larger than planet Mercury, it has half its mass. Ganymede orbits at about 1.070 million kilometers and it takes it about 7 Earth days to complete a single orbit around Jupiter.
A prominent feature of Europa is its light reflectivity caused by its icy crust(Bagenal, Dowling and McKinnon 441). It has a rocky interior above which is a layer of water ice that is estimated to be about 100 kilometers thick. It is believed that there is a water ocean between the rocky interior and the frozen upper surface crust. If present, this ocean is likely to be oxygenated, salty and warm-water heated by Europa’s geologically-active core. It can therefore accommodate life. Its surface has few large-scale features such as mountains and craters due to the push and pull forces on the surface ice caused by the water beneathand is considered to be one of the smoothest objects in the Solar system. Ganymede has a layer of rock in between a metallic iron core and a thick ice crust on the surface. There are also rock formations as evidenced by the bumpy nature of its surface. About 40% of this surface is dark while 60% is lighter in color and therefore reflective. Ganymede is also believed to have a salty ocean underneath its icy surface(Bagenal, Dowling and McKinnon 441). However, due to its internal structure, the pressure at the base of the ocean is so high that any water down there would turn to ice. It therefore cannot support life.
Ganymede is the only satellite in the solar system that possesses a magnetosphere(Lisle 136). This is mostly found in planets including Earth and Jupiter. A magnetosphere is a region in which charged particles are trapped or reflected. Ganymede’s magnetosphere is completely embedded within Jupiter’s magnetosphere.Ganymede’s daytime temperature averages -112oC to -182oC, while night temperatures drop to -193oC (Lisle 136). Its atmosphere has a very thin layer of oxygen which can hardly support life. Unlike Ganymede, Europa’s atmosphere is composed of a relatively thick layer of oxygen which is not of biological origin(Lisle 137). Instead, it is formed by radiolysis whereby ultraviolet radiation from the Jovian magnetosphere collides with the icy surface thereby splitting water into oxygen and hydrogen. Some of the molecular oxygen formed is not released to the atmosphere due to its mass and Europa’s gravity, and therefore this oxygen may make its way to the ocean beneath, aiding in biological processes. Meanwhile, the hydrogen is lost to space because it lacks the mass needed for it to be retained as part of the atmosphere.Ganymede’s temperature at its equator is about -160oC while at the poles, it is -220oC (Lisle 137).
The possibility of human colonizing extra-terrestrial bodies especiallyEuropa and Ganymede has been explored at length considering the advantages that it has over other extra-terrestrial bodies in the solar system(Lisle 138).Key among these is the availability of water which would be a boon for colonists, although it would be difficult to access since it requires drilling to great depths. Apart from providing drinking water, this interior ocean could be used to manufacture breathable air for use.However, colonizing and terra-forming or landscaping Europa and Ganymede also present several problems. One is the high amount of radiation coming from Jupiter which is enough to kill a human being with a single ray (Lisle 138). This therefore would require that the colonists be shielded appropriately. Also, the low gravity of these bodies would pose challenges for human settlement and make navigation impossible.There are speculations of alien organisms existing in some of these bodies. This would therefore cause conflicts between the aliens and the human colonists.With appropriate research and studies, other planets and extra-terrestrial bodies could be made habitable to human beings. Therefore the population of planet Earth could be reduced by settling people there.
Bagenal, F., Dowling, T. and McKinnon, W.Jupiter: the planet, satellites and magnetosphere. Cambridge: Cambridge University, 2006, Print.
Lisle, J. The stargazer’s guide to the night sky. Green Forest, Ark.: Master Books, 2012, Print.
Pelt, M. Space invaders: how robotic spacecraft explore the solar system. New York: Springer, 2007, Print.