Some Facts About Ganymede; A Moon of Jupiter

Jupiter‚Äôs moon Ganymede is the largest moon in our solar system, bigger than the planet Mercury and dwarf planet Pluto. NASA‚Äôs Hubble Space Telescope has found the best evidence yet for an¬†underground saltwater ocean on Ganymede. The ocean is thought to have more water than all the water on Earth’s surface. Ganymede‚Äôs ocean is estimated to be 60 miles (100 kilometers) thick ‚Äď 10 times deeper than Earth’s ocean ‚Äď and is thought to be buried under a 95-mile- (150-kilometer-) thick crust of mostly ice. Identifying liquid water is crucial in the search for habitable worlds beyond Earth, and in the search for life as we know it.

Ganymede is the only moon known to have its¬†own magnetic field¬†‚Äď a discovery made by NASA‚Äôs Galileo spacecraft in 1996. The magnetic field causes auroras, which are ribbons of glowing, hot, electrified gas, in regions circling the north and south poles of the moon. Because Ganymede is close to Jupiter, its magnetic field is embedded in, or lies within, Jupiter‚Äôs magnetic field.

When Jupiter‚Äôs magnetic field changes, the auroras on Ganymede also change,¬†‚Äúrocking‚ÄĚ back and forth. It was by watching the rocking motion of the two auroras, that a team of scientists led by Joachim Saur of the University of Cologne in Germany came up with the idea of using the Hubble space telescope to learn more about the inside of the moon.

Discovery and Name

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

In mythology, Ganymede (“GAN uh meed”) was a beautiful young boy who was carried to Olympus by Zeus (the Greek equivalent of the Roman god Jupiter) disguised as an eagle. Ganymede became the cupbearer of the Olympian gods.

Potential for Life

A computer model of Ganymede’s interior created in 2014 supported the idea that the development of primitive life might be possible there. The model indicated the icy moon’s rocky sea bottom might be in contact with salt water. Scientists think water and rock interacting are key for the development of life.

Size and Distance

Ganymede has a radius of 1,635 miles (2,631 kilometers) and is the largest moon in our solar system. It’s bigger than Mercury and Pluto. Ganymede is about 665,000 miles (1.07 million kilometers) from Jupiter, which orbits about 484 million miles (778 million kilometers) from the Sun. Jupiter is 5.2 astronomical units away from the Sun. One astronomical unit (abbreviated as AU) is the distance from the Sun to Earth. From this distance, it takes sunlight 43 minutes to travel from the Sun to the Jovian system.

Orbit and Rotation

Ganymede orbits Jupiter at a distance of 665,000 miles (1,070,000 kilometers), making it third in distance from Jupiter among the Galilean satellites. Ganymede completes an orbit around Jupiter about every seven Earth days (7.155). Ganymede orbits the Sun along with Jupiter and its other satellites every 12 Earth years.


Ganymede and Jupiter‚Äôs other large moons (Io, Europa, and Callisto) likely¬†formed from leftover material¬†after Jupiter condensed out of the initial cloud of gas and dust surrounding the Sun, early in the history of our solar system. Ganymede is likely about the same age as the rest of the solar system ‚Äď about 4.5 billion years old.


Astronomers using the Hubble Space Telescope have found evidence of a thin oxygen atmosphere on Ganymede. 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.

Burnley 0 Arsenal 5

Kai Havertz said Arsenal are “all in this together” after the Gunners continued their blistering goalscoring form to thrash Burnley and close the gap at the top of the Premier League to two points. Following their 6-0 win at West Ham last week Arsenal were soon among the goals again, captain Martin Odegaard opening the scoring on four minutes with a crisp strike into the bottom corner after Gabriel Martinelli’s pass. Bukayo Saka converted from the spot to double the lead after Lorenz Assignon fouled Leandro Trossard in the box. England forward Saka got his second just after the restart as Arsenal kept up the pace, latching on to a clever Odegaard pass then cutting inside and rifling a shot into the roof of the net.

Havertz’s scuffed effort was blocked in the box but Trossard was alert to curl in for his third goal in as many league games. Jakub Kiwior’s long throw down the line then found an unmarked Havertz, who ghosted in behind the defence and drilled past home goalkeeper James Trafford to complete a comprehensive win for the Gunners. Arsenal, who have 21 goals in five straight wins, move two points behind leaders Liverpool, while Burnley remain in the relegation zone. The Gunners, following up last week’s comprehensive win at London Stadium, have started a calendar year with five consecutive league wins for the first time in their history, and blew Burnley away with their slick football.

And the in-form Gunners may even have scored more at Turf Moor, with Trossard going close on two occasions before he eventually found the net. Havertz continually caused problems by picking up pockets of space with his movement off the ball while Saka, Trossard and Martinelli interchanged in the box to regularly threaten. Odegaard led by example, scoring his first goal since December 2 and providing the assist for Saka’s second strike. Saka has scored in four consecutive league appearances for the first time in his career, netting six across those four games, more than in his previous 19 league games. When Mikel Arteta’s side are on song, they are hard to stop. Goalkeeper David Raya didn’t have a save to make as Arsenal kept consecutive top-flight clean sheets for just the second time this season.