Discovered by Cassini, Rhea is the second-largest moon of Saturn. It has a silverish-grey color with a catered surface.
Interesting Rhea Facts
- Rhea was discovered by Giovanni Cassini in 1672.
- It was named in the honour of King Louis XIV, along with 3 other moons.
- The name Rhea comes from Greek mythology. It was the name of a Titan and the mother of gods.
- Rhea has a diameter of 1530 km.
- It is the second largest moon of Saturn.
- It is the ninth largest moons in the solar system.
- Rhea is 527,000 km away from Saturn.
- It takes 4 days and 12 hours to rotate about its own axis and complete one revolution of Saturn.
- It is tidally locked to Saturn.
- It is the second smallest body with known measurements to be in hydrostatic equilibrium.
- Rhea has a silver-grey appearance.
- It has a heavily cratered surface.
- It is mostly composed of ice and water.
- It does not have a magnetic field of its own.
- It has been explored by space crafts such as Voyager 1 and 2 and Cassini.
The moon Rhea was discovered by the Italian astronomer, Giovanni Domenico Cassini in 1672. It was the third moon of Saturn to ever be discovered and the 2nd discovered by Cassini.
A total of 4 moons of Saturn were discovered by Cassini. They are Tethys, Dione, Rhea, and Iapetus. They were named Sidera Lodoicea which means “Stars of Louis”. It was done so to honor King Louis XIV.
The name Rhea comes from Greek mythology. Rhea was the name of a Titan and the mother of gods. Though the planet was discovered in 1672, it was given its name in 1847 at the suggestion of John Herschel, William Herschel’s son.
Rhea has a mean diameter of about 1530 km. It is the second-largest moon of Saturn. It is also the ninth-largest moon in the solar system. It is the second smallest body with well-defined know measurements to be in the state of hydrostatic equilibrium that is the state at which the flow velocity of the fluids is constant.
Saturn’s moon Rhea has a mass of 2.31 ×1021 kg (0.1199 Earths or 0.44 Moons).
Rhea has a silverish grey appearance. Its cratered surface is also clearly visible in its image. It is said to resemble a dirty snowball due to its appearance. It also has high reflectivity.
Surface and Composition
Rhea has a heavily cratered surface, much like most moons of Saturn. It can be divided into a leading and trailing hemisphere. The trailing hemisphere is the side of the Moon which is in the direction opposite of its orbit’s motion.
It is mostly the leading hemisphere that is heavily created. In fact, the difference between the heavily cratered regions and the less cratered regions suggests that the was an event that took place in the history of Rhea which resulted in the resurfacing of the moon, though a long time ago.
Major surface features include plains, craters, basins, and canyons all over.
As mentioned before Rhea has the appearance of a dirty snowball. It is mostly composed of Ice and has a low density. About 25% of it is made up of rock and 75% consists of water or ice.
Recent studies of the Moon indicate that Rhea has a homogeneous interior surface i.e. there is a presence of some compressed ice at its center. This fact is contradictory to the earlier exemption of Rhea having a rocky core.
Rhea has a lesser internal warmth as compared to other moons such as Dione and Tethys. The reason for this is the fact that Rhea does not have ample tidal variation from Saturn. Thus, there is nothing to cause internal heating.
This is the reason why Rhea is more heavily cratered than other moons as the absence of internal heating results in a smaller number of plains where liquids could have flattened surfaces on freezing, hence erasing craters or other surface features.
It is unlikely that Rhea has a magnetic field of its own. However, it is known that it comes under the influence of the magnetic field of Saturn. Magnetic field particles from the planet are known to pepper the icy surface of Rhea.
Orbit and Rotation
Rhea is 327,500 miles or 527,000 kilometers away from Saturn. It is one of the farthest significant moons of the planet. It has an orbital period of approximately 4 days and 12 hours on Earth.
A lot of information that we have about the atmosphere of Rhea is thanks to NASA’s spacecraft Cassini.
Rhea is known to have a very thin atmosphere or an exosphere. This exhaust air is mainly composed of Oxygen and Carbon dioxide in the ratio of 5 is to 2.
Most of the oxygen is believed to come from the radiolysis of water ice on the surface. This process is triggered by the science that is supplied by the magnetosphere of Rhea’s parent planet, Saturn.
When the magnetic field of Saturn rotates over the moon the particles trapped in it influence the moon’s surface. This results in chemical reactions which decompose the surface, releasing oxygen.
The main source of carbon dioxide is not known for sure. One of the theories says that it may be related to oxidation. Of all the organic material present on the surface.
The first images of Rhea ever to be obtained by human-made spacecraft were provided by NASA’s Voyager 1 and 2 in the years 1980 and 1981. Before this, Rhea had only been observed through telescopes.
The Cassini orbiter flew by the moon from close 5 times between 2005 to 2013. The closest of these flybys was conducted on 26 November 2005 when Cassini was as close as 500 km from the surface of the moon.
No spacecraft has ever been able to land on the surface of the moon as yet. It has obviously also never been visited by human beings due to obvious reasons of extreme temperature and pressure conditions.
However, scientists are making continuous efforts to explore the moons of different planets in more detail.
Potential for Life
No evidence of life has ever been found on Rhea. This is due to the extreme temperature and pressure conditions. If any life does exist on the moon, it would be very different from that on the Earth. The possibility of finding life forms elsewhere in the universe can never be ruled out.
People continue to be fascinated by the planets in the solar system as well as their moons. Rhea has been mentioned in several elements of pop culture such as films, television shows, books, video games, etc, either individually, or collectively as a part of the Saturnian moon system.
- 1672: Rhea is discovered by Cassini
- 1847: Rhea is given its name by John Herschel
- 1980-1981: Voyager 1 and 2 explore the Saturnian moon system and provide first images of Rhea
- 2005-2013: Cassini flies by Rhea five times