Iapetus is the third-largest moon of Saturn and the 17th largest natural satellite in the Solar System. Iapetus was discovered in 1671 by the Italian astronomer Giovanni Domenico Cassini.
There are eight planets in the Solar System, arranged in order of decreasing distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. When arranged by size, Saturn ranks second, only after Jupiter.
The planets in the Solar System.
How did Saturn get its name? It is said that ancient observers noted the planet’s earthy yellow color with the naked eye, and in line with the Yin-Yang and Five Elements theory, they named it “Saturn.”
As a gas giant much larger than Earth, Saturn is primarily composed of hydrogen, helium, and other elements. Its core consists of rock and ice, surrounded by layers of hydrogen and metallic gas.
Over 400 years ago, the Italian astronomer Galileo Galilei invented the astronomical telescope and turned it toward the stars, opening a new era of observation and exploration of the universe for humanity.
Italian astronomer Galileo Galilei
When Galileo pointed his telescope at Saturn, he discovered something that resembled a human ear on both sides of the planet, which piqued his curiosity. Many decades later, Dutch astronomer Christiaan Huygens, after extensive observation, determined that what appeared to be human ears was actually a flat ring (ring system) around Saturn. This ring system is Saturn’s famous planetary rings, mainly composed of ice, rock, and dust.
Among the eight planets in the Solar System, Mercury and Venus have no moons and are very small; Earth has one moon, the Moon; Mars has two moons; Neptune has 14 confirmed moons; Uranus has 29 confirmed moons; Jupiter has 79 confirmed moons; while Saturn has 82 confirmed moons, making it the planet with the most moons in the Solar System.
Additionally, there are dozens to hundreds of small moons with diameters ranging from 40 to 500 meters within Saturn’s rings, but these small moons are not considered true moons.
Despite the advanced science and technology of today, we have yet to uncover all the secrets of Saturn’s moons, such as Titan.
Titan is Saturn’s largest moon and the second-largest moon in the Solar System (after Ganymede). Moreover, Titan is the only moon in the Solar System with a significant atmosphere.
Titan is the only moon in the Solar System with a significant atmosphere.
Even more astonishing, many scientists suspect that Titan may harbor life, and they have long speculated that the methane in its atmosphere could be a basis for the existence of life.
However, the most mysterious moon of Saturn is Iapetus. It is the third-largest moon of Saturn and the largest non-hydrostatic object in the Solar System.
In 1671, French astronomer Cassini first observed Iapetus and noted that whenever this moon moved eastward of Saturn, it would suddenly disappear.
More than 30 years later, Cassini used a more advanced telescope and observed that whenever Iapetus moved to a specific area, its brightness would significantly decrease. From this, Cassini hypothesized that Iapetus must be divided into two bright and dark sides. As a result, many astronomers also refer to it by another name: “the Yin-Yang face” due to the stark color difference between its two hemispheres.
Whenever Iapetus moved to a specific area, its brightness would significantly decrease.
In 1997, NASA launched a planetary probe called the Cassini-Huygens spacecraft. The Cassini-Huygens spacecraft is the largest and most complex planetary probe ever launched by humanity; it truly consists of two smaller probes, one being Cassini, tasked with exploring Saturn, and the other being Huygens, tasked with conducting lander missions to Titan.
Cassini-Huygens spacecraft.
In 2004, the Cassini probe approached Saturn and successfully flew by Iapetus, capturing clear images of the moon. After the images were sent back to Earth, all staff members were shocked!
In the equatorial region of Iapetus, there is indeed a “ridge” stretching up to 1,300 km. This ridge is clearly higher than the surrounding area, with an elevation of up to 13 km. Based on the geological conditions near this ridge, astronomers believe it has existed for a long time.
In the equatorial region of Iapetus, there is indeed a “ridge” stretching up to 1,300 km.
The discovery of the ridge has sparked lively discussions in the astronomical community, and astronomers from many countries have put forth their predictions. Some astronomers believe that Iapetus might be an abandoned spacecraft. Before human civilization appeared, extraterrestrials visited the Solar System and left after carefully examining it. Somehow, they left a spacecraft in orbit around Saturn. Since then, the spacecraft has orbited Saturn as one of its moons.
Some astronomers believe that Iapetus might be an abandoned spacecraft.
However, this conjecture has not been widely accepted in the academic community, as to date, we have not been able to confirm its true structure based solely on a “ridge” with a similar appearance.
There is also a viewpoint suggesting that this is actually a natural bulge caused by centrifugal forces during Saturn’s rotation. When Iapetus began to form, it was in a molten state, close to a solid-liquid state, and the centrifugal forces generated by its rotation would cause its equatorial region to bulge. Later, as Iapetus gradually cooled, this bulge solidified and has remained to this day.
