Titan and Rhea are referred to as the two largest moons of Saturn. They are far away from the Earth and it requires much time and considerable efforts to get to these moons. The diameter of Rhea counts 949 miles, while Titan's diameter is 3200 miles. The latter moon is twice wider compared to the Earth's Moon. In spite of the fact that Titan and Rhea are not similar in terms of their size, structure, and surface, they are the natural satellites of one planet and, thus; possess a set of common features. Therefore, the paper will deal with the investigation of the most important characteristic features of Titan and Rhea.
The Discovery of the Moons
Titan was discovered 17 years earlier than Rhea. The first astronomer who discovered Titan was Christian Huygens. This Dutch scientist managed to do this in 1655. In late 1672 the Italian-French astronomer Giovanni Cassini succeeded to discover Rhea. The name of the Saturn's moon is derived from the name of the Greek goddess Rhea. This goddess was also famous for giving birth to the Greek gods.
Thus, Rhea was the mother of Zeus and some other gods of Mount Olympus. The scientists named Rhea as Saturn V. In such a way the astronomers denoted the fifth moon in distance from the planet. Moreover, Cassini called Rhea one of the four Stars of Louis (after King Louis XIV).
General Facts about Titan and Rhea
Titan is referred to as the largest moon of multiple Saturn's natural satellites. Only Ganymede, the Jupiter's moon, extends Titan. Rhea is regarded as the ancient second largest moon of Saturn. The most significant feature of this moon is the fact that Rhea is largely cratered. It has a wide range of pocks and scars on its surface that are the results of various meteor activities taking place in the past. Thus, the pitted surface of Rhea differs considerably from the smooth surface of Titan. Although the moons are distinct in appearance, they bear a significant resemblance in composition. For instance, these two moons consist of a mixture of rock and water ice.
The atmosphere of Rhea is very thin atmosphere composed mostly of carbon dioxide and oxygen. At the same time, Titan's thick and smooth atmosphere gives the moon an unusual orange hue. The density of Titan is several times larger than the Earth's density. The scholars also point out that Saturn's moon is characterized by a hydrocarbon-based weather system.
As a result, methane rains frequently fall from the sky. Furthermore, Titan has several lakes that mostly consist of into methane liquid. Therefore, many astronomers assume that it is possible to find life on Titan. They assert that this moon is one of the most convenient places for life in the whole solar system.
Although Titan mainly consists of nitrogen and methane, it is characterized by relatively powerful gravity. Finally, Titan is much cooler compared to the other moons. The scientists assert that Rhea is composed of 75 percent of ice and 25 percent of the rock. Nevertheless, taking into account the observations made by Cassini, one may argue that Rhea is not characterized by a distinct rocky core. The moon consists of the mixture of rock and ice that makes it look like an immense dirty snowball.
The Atmospheres of the Moons
In 2010 the Cassini space probe managed to discover that Rhea was characterized by a very thin atmosphere consisting of carbon dioxide and oxygen. Catling and Hibbitt conclude that "these two elements were present in the proportion of 2 to 5" (p. 347). One should conclude that that was the first time when a spacecraft succeeded to find the proper atmosphere containing oxygen that existed on the other planet than the Earth.
Titan is considered as the only body in the entire Solar System, which has the atmosphere (except the planet Earth). The moon is regarded as having thick atmosphere rich in nitrogen. The atmosphere of Titan is composed of hydrogen, methane, ethane, and other hydrocarbons but it does not include oxygen. The molecules of the mentioned elements react with sunlight and thus, form thick layered smog. The astronomers assert that one of the smog layers creates an apparent hazy band of blue. Titan is encircled by this band.
The Unusual Characteristics of Titan and Rhea
At the end of the twentieth century, the Voyager images observed enigmatic straight lines that cut the surface of the Rhea moon. Those lines stretch for the lengths of tens to hundreds of miles over the whole surface. In 2006, the photos of Cassini spacecraft revealed that those mysterious lines might have been fracture cliffs creating canyons. The canyons have relatively bright walls since their darker parts tend to fall off them all the time and expose freshwater ice. This finding may prove that Rhea was tectonically active in the past.
The scientists claim that Titan is famous for having two crescent-shaped hoods located over its Polar Regions. Titan's polar hoods include swirling surface of dense gas located on high altitude. They tend to enlarge and dissipate when the seasons change. The seasons on Saturn and its moons continue for about seven Earth years.
At the time when Cassini reached the system of Saturn in 2004, there was already a thick hood above the Titan's the North Pole. It was considered as winter. As a result of the equinox in Saturn system that took place in 2009, Titan's northern hemisphere started moving into spring. The southern latitudes of the moon, on the contrary, began to head into autumn. This caused a polar vortex above Titan's south pole since it requires only nine hours to perform a full rotation.
The Rings of Rhea
Furthermore, one of the mysterious facts about Rhea is considered the theory of possible rings. In 2008 NASA introduced the initial suggestions concerning the presence of rings around the surface of the moon. The scientists Catling and Hibbitt argued that "the rings existed on Rhea because the altered patterns of the electrons' flow were observed" (p.186). The scholars believed that dust and debris were characterized by larger density near the moon. As a result, the dust created three rings of high density. Nevertheless, the observations carried out by the Cassini in 2010 did not find any evidence that could prove the theory of rings. Thus, the Cassini space probe only meant that some other corroborative evidence had to be found to prove the existence of rings.
The Flight to the Moons
The scientists have to take into consideration a few important factors in the process of the preparation for the mission. The first factor is whether the spacecraft will be launched toward Titan and Rhea, the second one is concerned about the type of engine the spacecraft is going to have. Finally, the third one is connected with the fact that it requires much time for the spacecraft to slow down. Thus, if the spacecraft is going to orbit on the moons, the flight to Titan and Rhea will last longer.
In the contemporary world, the most effective way to get to Saturn and its natural satellites is to apply the Cassini spacecraft. It has the mass and size of an ordinary bus and carries a set of scientific instruments and necessary communication equipment. In order to fly into space the spacecraft should overcome the earth gravity pull. It must have the speed of 11 km/sec.
According to the plan of the scientists, the spacecraft obtains limited kinetic energy from the launch rocket. As a result, Cassini is going to be restricted to our Solar system. Furthermore, the scientists assert that it is possible to get to and examine all the planets applying the principle of "gravity assist".
The possible investigation of Titan and Rhea is going to foster the future development of the astronomy. Mainly, in the course of the research, some useful data and significant evidence may be obtained. However, one should take into account the peculiar features of Titan and Rhea while preparing for the flight. Both of the moons are relatively ancient since they were discovered in the 17th century.
Titan is considered as the only moon in our solar system that has a proper atmosphere. Although Titan's atmosphere is thick and rich in nitrogen, it lacks oxygen largely. However, this moon is one of the most convenient places for life beyond the Earth in the whole solar system. Furthermore, Titan is characterized by relatively powerful gravity. The atmosphere of Rhea differs largely from the thick atmosphere of Titan. It is thin, much wispier and consists mostly of two elements: oxygen and carbon dioxide.
Furthermore, the pitted surface of Rhea differs considerably from the smooth surface of Titan. Rhea is famous for its mysterious lines stretching for hundreds of miles over its surface. They may serve as convincing proves of Rhea's past tectonic activity. Some astronomers argue that this moon has rings, though the theory has not yet been supported by corroborative evidence. To conclude, Titan and Rhea are characterized by similar and distinctive features but this cannot be considered as an impediment to the future investigation of the two Saturn's largest moons.