The largest planet in this solar system is Jupiter. Till date, 79 satellites have been discovered of the planet. Today we will discuss about Europa, the most well-known and famous satellite of Jupiter.
As mentioned earlier, Europa is the satellite of largest planet in the solar system as well as the fourth largest satellite of the same which is located at the fifth distance from the Sun. In terms of overall size, this satellite is the sixth largest satellite after the moon of earth. The satellite was discovered on 8th January 1610 by Galileo Galilee, one of the greatest enlighten person of European Renaissance and one of the best astronomers of all around the world. On the same day, another satellite of Jupiter, Io was discovered by him. The four satellites of Jupiter, discovered by Galileo were called the Galilean Moon. Europa is the smallest of those.
According to Greek mythology, the satellite was named after Europa, the learned daughter of Agener, king of Tire, one of the wives of Zeus, and mother of Minos, king of Crete. Johannes Kepler, another German astronomer and mathematician of seventeenth-century, was the first to propose such a naming in Europa. Simon Marius, another German astronomer of seventeenth-century, later proposed the same thing. When Europa was first discovered, Europa was the second-distanced satellite from Jupiter. With the discovery of four more satellites between Europa and Jupiter, Europa now ranks sixth in terms of distance. Even so, according to the rules, introduced by Galileo, Europe is still called Jupiter-II.
With a diameter of 1,561 km, the satellite is orbiting Jupiter in an almost circular orbit at an average distance of 6,70,900 km from Jupiter. This satellite, like other Galilean moons, is bound to Jupiter in synchronous rotation. So in this case the diurnal motion of Europa is almost equal to its annual motion. One day in Europa is a little more than 3.55 days on Earth. At about the same time, Europa is orbiting Jupiter once. At present, however, after a more in-depth observation and study of Europa, there is a bit of doubt in the minds of scientists about its synchronous rotation. Europa's average orbital velocity is 13.74 km per second and its escape velocity (Escape Velocity: The minimum velocity that a moving body must have to escape from the gravitational field of a celestial body) is 2.025 kilometer per second or 7,290 kilometer per hour. The slight abnormality in the orbit of Europa is due to the attraction of other Galilean moons. For this reason, the heat inside Europa helps to keep the oceans of Europe in liquid form. While orbiting, when Europa comes closer to Jupiter, which means in the Perigee Position, the shape of Europa changes into elongation due to the intense gravitational force of Jupiter. Once again, at the farthest point from Jupiter, that means in the Europa's Apogee Position, when the effect of Jupiter's intense gravitational force diminishes, it regains its former spherical shape.
Europa is mainly composed of silicate rocks. Its crust and surface are made up of water-ice, and the core is probably made up of iron (Fe) and nickel (Ni). This satellite is one of the smoothest surfaces, located in this solar family. This kind of surface indicates that there may be a huge sea of water beneath the surface of Europa. It goes without saying that this satellite has almost no presence of high mountain ranges or giant craters. However, a small number of ditches have been found here. In the equatorial region of Europa, a maximum of 15 meter tall spike-like shape, made up of water-ice, has been observed. They are called Penitent. Plumes of water vapor have also been seen here by various spacecraft. It is speculated that this may have been caused by an eruption in the cryo-geyser. Scientists hope these plumes could be used to search for life in Europa.
Plumes reach an altitude of about 200 km and emit an average of 7,000 kilogram of water-vapour per second. However, these events are periodic and their existence is revealed only when Europa is present far away from Jupiter (Apogee position). The Galileo spacecraft and the Hubble Telescope have assisted in locating and explaining the events.
The surface water level in Europa is about 100 km deep with some of it being a thick layer of ice which is as hard as Granite because of the extremely low temperatures in Europa. The average temperature in the equatorial region is -163.1 degree Celsius and in the polar region -223.1 degree Celsius. The rest of the surface water may be in the form of salty seas beneath the thick layer of ice. The reason for the presence of a liquid sea beneath the surface of Europa is said to be that the heat energy, generated by the shape change of Europa due to the intense gravitational pull of Jupiter, helps to keep the surface sea water in a liquid state. Again, some scientists speculate that the decay of radioactive elements inside Europa may have produced that heat. However, the most interesting feature of Europa is the presence of some cracks and crisscross network of shallow lines on its surface. Usually the length of long lines can be up to 20 kilometer. These lines areas are quite dark. These lines are, thought to have formed from the eruption of the warm water-vapour, coming from the ocean just below the surface of Europa. On the surface of the Europa are small circular or elliptical shaped areas called Lenticulae. Their surface may be smooth or uneven. These lenticels can coexist individually or in jumble. Although some hypotheses have been heard about their formation but the mist about lenticulae has not yet been removed. So there is a need for more in-depth research on this topic in the future. The presence of reddish spots on the surface of Europa is also attributed to the presence of either water-soluble Magnesium Sulphate or Sulfuric Acid with impurities (mainly due to the presence of Sulfate compounds) or deposition of organic products Tholins.
In 1995, the Hubble Telescope reported the existence of a thin atmosphere in Europa consisting mainly of molecular oxygen and water vapour. Later, in 1997, the Galileo spacecraft discovered the existence of the ionosphere in the atmosphere of Europa. Oxygen in Europa's atmosphere is produced by radiolysis of water (Radiolysis: the process of separation of substances that make up matter by radiation of ionized particles). In this process, hydrogen is produced, along with oxygen, and travels into space overcoming the influence of the gravitational force of Europa, and combines with the oxygen particles to form a torus or ring near the orbit of Europa. Both Cassini and Galileo spacecrafts have discovered the existence of this torus.
So far, a total of six space missions have been carried out in Europa. Pioneer-10 achieved the glory of flying the first man-made spacecraft over Europa on December 3, 1973. At that time, the distance from Pioneer-10 to Europa was 3,21,000 km. Exactly one year after this incident, on December 3, 1974, Pioneer-11 made its flyby 5,86,700 km from Europa. (Flyby: According to the space-science, the shortest distance at the time of observation, between observation-spacecraft and planet or satellite.) The third expedition to Europa took place on March 5, 1979, when Voyager-I made its flyby 7,33,760 km from Europa. Only six months later, the Voyager-II spacecraft appeared in the sky of Europa. On July 9, 1979, the spacecraft made its flyby at a distance of 2,05,720 km from Europa. More than ten years later, the Galileo Spacecraft was launched on 18th October, 1989 to gather information about Jupiter and its satellites. Between 19th December 1996 and 3rd January 2000, the Galileo spacecraft made its flyby to Europa a total of 12 times. On 16th December, 1997, the spacecraft came closest to Europa. At that time, the distance between them was only 196 km and on 26th September 1998, the Galileo spacecraft flew the satellite the farthest. The distance between them was 3,562 km. Till now, this Galileo expedition has provided most of the information about Europa. The last space mission in Europa so far took place on 27th February, 2007. The ‘New Horizons’ Spacecraft, which set out for the dwarf planet Pluto on that day, flew 31 lakh km away from Europa, sending important information to earth and then to its own destination.
So far no trace of life has been found in Europa. However, among the various planets and satellites in the solar system, there is a strong possibility that life may exist in Europa. The interior of Europa's surface, in particular, may be like a lake or ocean beneath the thick ice sheets as that of our Earth's polar regions. Europa's lakes are completely covered by ice and separated from the ocean. Then it is very much possible that there may be life here too. Hydrogen peroxide (H2O2), available abundantly throughout Europa, produces large amounts of water and oxygen and this phenomenon can further accelerate the development of life. An inorganic substance with an organic substance called Phyllosiliate, also present in the earth, has also been found in Europa which indicates many possibilities.
Human space missions in Europa are set to increase in the future, depending on the existence of extraterrestrial life. The main purpose of these expeditions is to further analyze the composition of the topography of Europa and to find out the existence of life in the oceans and lakes that have been estimated deep in its surface.
To this end, the European Space Agency adopted the 'Jupiter Icy Moon Explorer' or 'JUICE' project in 2012. According to them, the 4,800 kilogram spacecraft will be launched in June 2022. In addition to Europa, the spacecraft will also observe other Jovian satellites such as Ganymede and Callisto. As such, the spacecraft will make its first flyby to Europa in October 2030.
In July 2013, NASA announced that in 2024 they would launch a spacecraft called the 'Europa Clipper', weighing 6,000 kilogram, which would reach Europa in 2031 and complete 44 flybys.
The last space mission announced for Europa so far was announced by NASA in 2017. This will be the first time a man-made spacecraft will land in Europa. The name of this space mission is 'Europa Lander'. The spacecraft will be launched in 2025 and will land in Europa after 2030. It will send the collected information directly to Earth or via another spacecraft, the Europa Clipper.
Seeing the effectiveness of these scientists, it is very clear that we are very interested in Jupiter's moon Europa and are observing and judging it very seriously. Who is to say that in the future, seemingly small satellites like Europa or Saturn's moon Rhea will not play a vital role in the survival of the creatures of the earth ? For now, we are waiting for the answer to that million dollar question.
Flyby on Europa
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