Solar System's Biggest Moon

Updated: Oct 19

Ganymede, Jupiter's moon, is proving to be a fascinating place. Aside from being the largest moon in our solar system, more significant than Mercury and Pluto combined, NASA's Hubble Space Telescope has found the best evidence that Ganymede has an underground saltwater ocean. The ocean contains more water than all the water on Earth's surface combined. The sea on Ganymede is estimated to be 60 miles (100 kilometers) thick - 10 times deeper than Earth's ocean - and is covered by a 95-mile (150-kilometer) thick ice crust. In the search for habitable worlds beyond Earth and for life as we know it, the identification of liquid water is crucial.


Image credit- https://earthsky.org

In 1996, NASA's Galileo spacecraft discovered that Ganymede had its own magnetic field. On the north and south poles of the moon, the magnetic field produces auroras, which are ribbons of glowing, hot, electrified gas. Ganymede's magnetic field is embedded in Jupiter's magnetic field because of its proximity.


Auroras on Ganymede also change when Jupiter's magnetic field changes, rocking back and forth. Scientists led by Joachim Saur of the University of Cologne in Germany came up with the idea of using the Hubble space telescope to study the inside of the moon by watching the rocking motion of the two auroras.


In Ganymede, there are two distinct types of terrain: large, bright regions with ridges and grooves that cut across older, darker regions. Scientists believe that Ganymede's crust has been under tension due to global tectonic processes. In June 2021, NASA's Juno spacecraft took the most recent images of Ganymede's surface.


Galileo Galilei discovered Ganymede on Jan. 7, 1610. It was the first time a moon orbiting a planet other than the Earth was discovered (along with three other large moons around Jupiter). The discovery eventually led to the realization that planets in our solar system orbit the Sun rather than our solar system rotating around us. (Jupiter now has 53 named moons and 26 provisional moons awaiting confirmation of discovery).


Image credit- https://solarsystem.nasa.gov


According to a 2014 computer model of Ganymede's interior, primitive life might have developed there. According to the model, salt water may be in contact with the icy moon's rocky sea bottom. In order for life to develop, water and rock must interact.


Our solar system's largest moon, Ganymede, has a radius of 1,635 miles (2,631 kilometers). It is bigger than Mercury and Pluto combined. Jupiter orbits about 484 million miles (778 million kilometers) from Ganymede, which is about 665,000 miles (1.07 million kilometers) away. The distance between Jupiter and the Sun is 5.2 astronomical units. Sun's light travels 43 minutes to the Jovian system from this distance.


In addition to orbiting Jupiter about every seven Earth days (7.155), Ganymede orbits the Sun every 12 Earth years with Jupiter and its other satellites.


There is a resonance between Ganymede, Io, and Europa - every time Ganymede orbits Jupiter once, Europa orbits twice, and Io orbits four times. Orbital resonance refers to this pattern in their orbits. The orbits of most large satellites or planets tend to become circular over time, but not for these three. As a result of their resonance, their orbits are slightly elliptical or eccentric. Satellites line up at the same points in their orbits over and over, giving each other a gravitational tug to keep their orbits from becoming circular.


Ganymede is tidally locked, meaning that like Earth’s Moon, the same side of Ganymede always faces Jupiter. The other three Galilean moons are also tidally locked.


As Jupiter condensed from the initial cloud of gas and dust surrounding the Sun, Ganymede and Jupiter's other large moons (Io, Europa, and Callisto) likely formed from leftover material. It is likely that Ganymede is about the same age as the rest of the solar system - about 4.5 billion years old.


In order to gain a better understanding of Jupiter and its satellites, NASA's Juno spacecraft is currently orbiting Jupiter. By understanding Jupiter, scientists hope to gain a better understanding of our solar system, as well as other planetary systems.


Image credit- https://www.missionjuno.swri.edu


A metallic iron core lies at its center, surrounded by a spherical shell of rock (mantle) and surrounded by a spherical shell of mostly ice. A billion-year-old rock formation may be hiding deep beneath Ganymede's icy surface. Scientists discovered the irregular lumps beneath Ganymede's ice shell.


Scientists first suspected Ganymede had an underground ocean in the 1970s when computer models showed it might have several layers of ice and oceans.

A thin oxygen atmosphere on Ganymede has been detected by NASA's Hubble Space Telescope, as well as evidence of an underground saltwater ocean.


According to spacecraft images, two types of terrain can be seen on Ganymede's surface. Thirty percent of Ganymede's surface has highly cratered dark regions, while sixty percent has light-grooved terrain, which creates intricate patterns on the moon. The grooves are as high as 2,000 feet (700 meters) and they extend thousands of miles across Ganymede's surface. Due to settling on the soft icy surface, Ganymede's large craters are mostly flat. Around Ganymede's craters, there are both bright and dark rays of ejecta.


In 2004, scientists discovered irregular lumps beneath the icy surface of Ganymede. The irregular masses may be rock formations, supported by Ganymede's icy shell for billions of years. This tells scientists that the ice is probably strong enough, at least near the surface, to support such rock masses from sinking to the bottom of the ice. However, this anomaly could also be caused by piles of rock at the bottom of the ice.

Image credit- https://www.nasa.gov


Hubble Space Telescope observations have revealed that Ganymede has a thin oxygen atmosphere. The researchers think the oxygen is coming from Ganymede’s icy surface. Ganymede is much colder than Earth, with daytime surface temperatures ranging from -297 to -171 degrees Fahrenheit (90 to 160 Kelvin). Jupiter and its moons receive less than 1/30th the amount of sunlight that the Earth does, and Ganymede doesn’t have a dense atmosphere to trap heat.


Ganymede's magnetosphere was discovered by Galileo, the first spacecraft to orbi