Follow this link to skip to the main content

International Edition Winners 2010: Romania, Target 1 -- Grade 10-12

International Edition Winners 2010: Romania, Target 1 -- Grade 10-12

Radu Iordache, Catalin Munteanu-Ene, Cosmin Ion
Radu Iordache
Catalin Munteanu-Ene
Cosmin Ion

Teacher Advisor: Ioana Stoica
Tudor Vianu National High School of Computer Science


"Rhea is the second largest of Saturn's approximately 200 satellites and the largest one without an atmosphere. It was discovered in 1672 by the Italian astronomer Giovanni Domenico Cassini. It has a mean radius of 764 km (roughly a tenth of the Earth's radius) and an orbit lying at 527000 km from Saturn. Rhea is particularly interesting to study, because of its unique characteristics: unusual lightness for its size, big differences between the two hemispheres and traces of a ring system.

One interesting observation regarding Rhea is that the mass obtained through calculations is much lower than the one estimated using on the moon's volume. This indicates a particularly low density, possibly due to the presence of a high content of water ice in its core, beneath the rocky surface. In fact, its mean density of 1.233 g/cm3 suggests that it's made of only 25 percent rock, the rest being ice. Although the composition is not yet certain, if Rhea does contain frozen water, it could prove a valuable water source in the future, so further study of its composition would be highly useful.

Another exciting fact about Rhea is the difference between the two hemispheres. Rhea has a synchronous rotation period, thus a viewer from Saturn could only observe one of its sides. The leading hemisphere (the one facing Saturn) is heavily cratered and much brighter than the trailing one. This is quite unusual, because it is expected that the trailing hemisphere is more prone to be hit. The difference in brightness between the two sides is also intriguing. The dark hemisphere features some bright lines that might be fractures caused by tectonic plates or frozen water resulted from the ice volcanoes in a time when Rhea's core was perhaps made up of liquid water.

The third intriguing characteristic of Rhea is the possibility of it having a ring system. This discovery would make Rhea the first moon to develop a dust ring, located above its equator. This theory is supported by the finding of small ultraviolet bright spots along the moon's equator, which could be impact points of deorbiting ring material. Although the Cassini camera couldn't image any such ring so far, we believe that a closer look on the leading side might show shadows of potential debris spinning around Rhea, provided that the debris is large enough. Thus, a further study of Rhea's surface would be highly useful because it would elucidate the existence of a ring, and clarify the source of the ultraviolet spots.

Albert Einstein once said, "There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle." We believe that Rhea, with its various unique and intriguing characteristics, can be considered a miracle and should be studied accordingly. In the Greek mythology, Rhea was the mother of the Olympians. In the same way, we hope that Rhea, the moon, will become a baseline for our knowledge of the universe."