Moons of Jupiter

The moon is friend for the lonesome to talk to.- carl sandburg

Astronomy always fascinates us.
People always admire dark nights with glimmering stars in reign of darkness. But do you know that modern astronomy is said to be begun with Copernicus’s heliocentric discovery in 1543. But in 1609, Galileo’s groundbreaking discovery of moons of Jupiter called jovian moons sparked new lights in field of astronomy. With the help of his telescope, he saw unknown world that were never be seen by anyone before him. When he pointed his telescope towards Jupiter, he saw ‘stars’ like structure around planet but soon he figured out that they are actually moons. This important observation was very influential in the debate over the heliocentric vs. geocentric models of the Solar System. Ancient astronomers used to believe that Earth is centre of universe and and all other heavenly bodies revolve around Earth. This important discovery turned down many false beliefs of astronomers in understanding of universe

Jupiter has been referred to as a mini solar system because of thousands of small bodies are orbiting to it which are influenced by its strong gravitational pull. There are 79 moons which are also orbiting to it and that makes it highest number of moons orbiting a planet in solar system. First four moons out of 79 are called Galilean moons because they were discovered by Galileo. The Galilean moons are Ganymede, Callisto, Io and Europa. Galilean moons are bigger in size and heavier in mass. They are biggest moon in our solar system. All are differ in their property

Io :-

Io is innermost moon of Jupiter and fourth largest moon in our solar system with radius of 1821 km. It was first discovered in 1610 by Galileo along with other Galilean moon. Io played significant role in development of astronomy in 17th and 18th century. It helped astronomers to compute speed of light and Kepler’s law of planetary motion. Two voyager probes send by NASA confirmed that there are large number of volcanoes and mountains on Io’s surface. It is estimated that there are about 400 active volcanoes on its surface that makes it most geologically active moon in our solar system. This is because of heating of Io’s interior by continuous deformation caused by Jupiter and other moons.

Io’s surface is yellowish because of continuous volcanic eruption of sulfur and sulfur compounds. Some volcanoes erupt huge amount of sulfur fumes which go as high as 300 miles above the surface of Io.


Europa .This image was taken by NASA’s Galileo spacecraft in the late 1990s. The Europa’s surface is smooth , frozen and covered with icy layers.

Europa is smallest of the four Galilean satellites and second innermost moon of Jupiter which orbits the Jupiter in just three and half days. Europa is tidally locked just like Earth’s moon , that means its one hemisphere always face to Jupiter. The Europa’s surface is smooth, frozen and covered with thick layers which sits on surface of ocean which lies beneath it. This is because of tidal force of Jupiter which deforms its shape continuously which causes friction in its interior and hence produce a heat which is enough to keep the water in liquid form. This hypothesis suggests that Europa could be habitable and and harbour Extraterrestrial life.

In may 2018, astronomers confirmed the evidence of water vapour plumes on surface of Europa based on data collected by Galileo space probewhich orbited Jupiter between 1995 to 2003. Such water vapor plumes give a big hope in search of life on Europa. European space agency has set mission to sent a probe called Jupiter Icy Moon Explorer( JUICE) in 2022 which will search ET on its surface.


Ganymede is largest and most massive moon in our solar system. It is larger than planet Mercury and third innermost moon of planet Jupiter. It was discovered by Galileo Galilei on 7th January 1610. Jupiter is made up of equal composition of silicate Rocks and water. It is hypothesised that its core contain more iron rich liquid water than water on earth element has thin atmosphere which contain O2 and O3 and O.


Callisto – outermost Galilean moon looks similar to Earth’s moon with craters on its surface. It was individually named by the German astronomer Simon Marius with other Galilean moons , who discovered them the same year as Galileo. It is second largest Galilean moon and third largest in our solar system after Ganymede and Titan (a Saturn’s moon). Callisto is tidally locked with Jupiter similar to Earth’s moon . Callisto is surrounded by thin atmosphere , contains large fraction of carbon dioxide.

Other moons of Jupiter

These moons are called irregular satellites because they are irregular in shape , small and far from Jupiter . They have high inclinations and eccentricities. Many of these moons are captured asteroids pulled in by the gravitational forces of Jupiter. Some of theme do retrograde motion.

Why does Jupiter have so many moons ?

This is general question arise in our mind. Well , short answer is because of its gravitational pull.

Unlike terrestrial planets, Jovian planets are very large and massive. They have more gravitational influence than terrestrial planets. Since Jupiter is largest among other jovian planets, it attracts other masses more strongly. Therefore it holds more masses around it.

According to a hypothesis , Jupiter thoughts to originate very far from sun. and then migrate inwards. Along the way, their moons get caught in a game of celestial tug of war. If this hypothesis is true , then Jupiter had more moons than now. Since sun has more gravitational pull than Jupiter, sun will steal moons of Jupiter in course of this inward migration.

Read more in details

I am science enthusiast and I love to write blogs for students and youths who love science. I have deep interest in astronomy and cosmology. I believe that science is most effective tool to serve humankind. .