Jupiter has been a topic of curiosity for astrophysicists for a long time. Jupiter is not just a big ball of gases floating in the Milky Way but also the planet with the strongest gravitational pull. Because of Jupiter, Earth is protected from the asteroid belt between Mars and Jupiter. The strong gravitational pull of Jupiter is the reason why it has one of the largest numbers of natural satellites revolving around it. These moons of Jupiter are not just known because of their numbers but because of different characteristics that have been discovered lately. The last time humans were interested in the moons of Jupiter and not just the planet was back in the 1990s, and that was solely based on the most active volcano on ‘Lo’, one of the most substantial moons of Jupiter.
Recently, the European Space Agency (ESA) launched a mission called the ‘Jupiter Icy Moons Explorer’ (JUICE), which is solely based on unravelling the mysteries that lie underneath the surface of icy cold oceans of the ‘Galilean Moons‘. As of the current explorations with different scientists, agencies worldwide have counted 79 moons that revolve around the giant planet. Most of these moons are not as significant because of their small size and asteroid-like nature. Scientists are more interested in the Galilean Moons: Europa, Lo, Callisto and Ganymede.
Source: Reddit / Galilean Moons of Jupiter
In the year 1610, Galileo Galilei was the one who discovered four of the largest moons of Jupiter in the night sky. Being the inventor of the telescope was another crown jewel in his career as a space explorer. Lo, Callisto, Ganymede and Europa have recently become the main topic of interest for scientists because of the different characteristics of these natural satellites. Out of respect for the discoverer, these moons have been called the Galilean Moons by space agencies worldwide. The biggest reason agencies like NASA and ESA are so interested in these moons is because of what mysteries lie beneath their surfaces. The surface of Europa has an icy ocean that still contains water molecules even though it lies outside the habitable zone of the Milky Way. On Earth, water is the core that supports all of life. From the biggest species like the Dinosaurs to the microbial organisms, life on Earth started from water. This is why scientists are so eager to explore the waters of Europa and even Callisto, as it too shows signs of having subsurface oceans.
As mentioned earlier, Jupiter is known to have 79 moons in total that revolve around this giant planet because of the strong gravitational pull that it has. The force of gravity that it exhibits is largely because of its large size and the extreme heat at its core due to the collection of various gases under pressure. Out of all these moons, more than 60 moons are said to have asteroid-like properties since they have a diameter of fewer than 6.2 miles. Thus, scientists are not much interested in all the moons of the planet, but the larger ones have surely caught their attention.
These moons revolve around Jupiter and have different durations to complete their revolutions. Some of the moons that lie in the inner orbit of Jupiter complete one revolution in seven hours, while the ones that lie in the outer orbit take as much as three Earth years to complete the revolution. The strong gravitational pull of Jupiter creates irregular orbits around the planet, which is the reason behind the difference in the duration of the revolution. One of the most interesting moons of Jupiter, apart from Galilean Moons, is ‘Mneme’. Mneme belongs to the Ananke group of natural satellites.
According to the history of the moons of Jupiter, Ananke was a big asteroid that revolved around Jupiter and collided with other asteroids to break into 15 moons. The gravity of this giant planet captured these, and since then, Mneme and its 14 other siblings have revolved around Jupiter. These moons revolve in a direction which is opposite to the direction of rotation of the planet.
Mneme had been named after one of the daughters of Zeus. Mneme is the moon of Jupiter named after a muse, which is a pretty interesting fact. The name itself means memory, and scientists have chosen the name ending with ‘e’ because of the international policy for outer designation moons that had retrograde orbits. Retrograde orbit means the orbit in which a satellite revolves in the direction opposite to the one exhibited by its planet’s rotation. This moon of Jupiter, named after a muse, along with its siblings, actually has an eccentric orbit.
The facts that this family of Ananke satellites has eccentric orbits that revolve opposite to the direction of Jupiter’s rotation and are not being inclined by the equatorial plane of the planet support the claim that all of these 15 moons originally were asteroids near Jupiter that were pulled by the planet in its captivity.
The mysteries of Jupiter’s moons have always fascinated astrophysicists around the world. The discovery of subsurface oceans on the moons, Europa, Ganymede and Callisto, has also intrigued astrobiologists’ interests. They are interested in knowing the existence of water on their surface even though these natural satellites are outside the habitable zone of our Sun.
According to Dr Mark Fox-Powell, “At least five objects in the outer solar system have sub-surface oceans”. He is an astrobiologist at Open University and suggests that scientists are interested in finding the reason behind water’s existence on these surfaces. The traditional habitable zone of the Sun is the region where its heat is neither too much nor too little. It allows water to exist in either form and our solar system; the habitable zone lies from Earth to somewhere near Mars.
Jupiter has the strongest gravity and extreme pressure and temperature on the surface. These are the reasons why scientists believe that Jupiter has developed a ‘habitable zone’ around itself. The reason to support this theory is that the strong gravitational force from Jupiter makes the moons expand and contract like a squash. The energy generated by such activity thus keeps the surfaces of these moons warm enough to support sub-surface oceans.
Source: Universe Today / European Space Agency’s JUICE mission
JUICE aims to discover the possibilities of microbial existence underneath the surface of these moons. ‘Europa acts like the poster child for Galilean Moons’, which is said so because the JUICE mission is highly intrigued to explore the oceans beneath its icy surface. One of the major problems that the spacecraft for this mission will face is accessing the oceans through the thick icy surface.
The spacecraft will not be able to land at the surface of the moon, which is why the Particle Environment Package will collect the ocean particles that rise above the surface. Scientists believe that the ocean beneath the thick icy surface of Europa interacts like the molten lava beneath Earth’s surface. Ocean particles tend to ooze out due to motion and pressure, and these are the ones that are to be collected and studied by scientists. Scientists are eager to understand the ecosystem that might have been created in the cold environment if life exists under the surface of Europa. The exchange of energy and survival of organisms are theoretical fantasies for scientists, but the spacecraft for the JUICE mission will provide enough material to study these fantasies.
Source: NASA / Callisto, the oldest moon of Jupiter
The spacecraft from the European Space Agency JUICE mission will pass by Europa twice to collect the ocean material, but the moon that will get much more attention is ‘Callisto’. Callisto has one of the oldest surfaces in the whole solar system and is unaffected by the radiation from Jupiter. It is the outermost moon of the famous quad and is said to have a 200-km deep ocean beneath the surface. The exploration spacecraft will pass by the moon 12 times and use special technology to unravel the mysteries underneath this moon’s surface.
The Radar for Icy Moons Exploration will send radio waves to the surface that will travel nine kilometres deep and will likely bounce back and be received by the spacecraft. The internal structure of Callisto’s surface will thus be revealed using this technology. To understand more about how water has been stacked under the surface, a 3GM instrument will be used to study the gravitational fields of Callisto. The oldest moon of Jupiter has many mysteries in its deep oceans and will be unravelled by the explorations.
Source: earth.com / Ganymede of the famous quad
Scientists have been particularly interested in Ganymede because of its large size and strong magnetic fields. “Ganymede is the most exciting body in the Solar System,” says Prof Michelle Dougherty. He is a professor at the Imperial College, London and says that the reason why this moon is so interesting is that it is even larger than the dwarf planet Pluto, larger still as compared even to Mercury. Ganymede also has an ocean underneath its surface, but scientists are thrilled because of its strong magnetism. There have been auroral lights at the poles of Ganymede, much like the ones on Earth. The magnetic fields of this moon interact with that of Jupiter.
Read more: Volcanoes in Space: Exploring Extraterrestrial Eruptions on Other Planets
The Hubble telescope and J-MAG instrument from the JUICE mission will help scientists understand exactly how the salty ocean on Ganymede results in such strong magnetic fields. Understanding the might of Ganymede’s magnetic field against Jupiter’s will also help understand whether or not life can exist in its oceans.
Source: Phys.org / Other important moons of Jupiter
Even after going through so many interesting facts like ‘what are the largest moons of Jupiter’ to ‘the moon of Jupiter named after a muse’, there still are so many mysteries yet to be unravelled about these mighty moons of Jupiter. Some of the less known facts about these moons can be studied here as well:
· Amalthea is another of the major moons of Jupiter after the famous quad. It is the fifth largest overall and was discovered in 1892. It is an irregularly shaped satellite with a surface full of craters, hills and valleys. It resides in the inner orbit of the planet and takes only 11 hours and 54 minutes to complete one revolution around the giant planet.
· Metis is the moon in the closest proximity to Jupiter. It has a radius of around 40 km and takes less than 0.294 Earth days to orbit the planet. It is named after one of the wives of Zeus.
· Lo has the highest volcanic activity in all of the solar system. As a result of the strong magnetic fields, the moon has been shaped in the form of a doughnut. The radiation on this moon is a thousand times harsher than the level needed to kill a human being.
So, these are some of the most important facts about various moons of the giant planet. There are many more mysteries that are yet to be discovered about the moons of Jupiter. Various space agencies are heading expeditions for these moons because of the probability of life under their surfaces and bizarre magnetic and electric interactions.