Jupiter’s moon Ganymede is the largest and most massive of the Solar System’s moons. It has a mean radius of 2,634.1±0.3 km (about 1,636 miles, or 0.413 Earths). For comparison, our Moon‘s radius is 1,737.1 km (1,079 miles). Have you ever wondered what it would be like if Ganymede were the Earth’s second moon? How would it look in the sky if it were at the same distance as the Moon?
If Ganymede were the Earth’s second moon, it would, of course, cause much higher tidal forces than the Moon. What’s more, Ganymede’s crust is very rich in water ice. If it were orbiting Earth, that ice would quickly melt, turning it into an ocean moon. It would also rapidly develop an atmosphere, likely composed mostly of water vapor but also containing various other volatiles trapped in the ice. Therefore, it wouldn’t look like the photo for long; it would quickly transform into a blue-and-white swirly ball.
There is some speculation that Ganymede’s existing internal ocean, which may contain more water than all of Earth’s oceans combined, could be hospitable for life. This means there might already be native Ganymedan life, probably just microorganisms. If human civilization survives the tidal effects of such a change, Ganymede could become a scientific gem.
Additionally, the increased tidal forces from Ganymede could have significant impacts on Earth’s geological activity. The stronger tides could lead to more frequent and intense volcanic activity and earthquakes, especially in coastal regions. This could alter Earth’s landscape and potentially affect climate patterns due to increased volcanic aerosols in the atmosphere.
Ganymede
With a mean radius of 2,634.1±0.3 km (about 1,636 miles), Ganymede is even 8% larger than the planet Mercury (2,439.7 km), though it is only 45% as massive. It holds the title of the largest and most massive of the Solar System’s moons.
Ganymede’s mass is 10% greater than Titan’s (Saturn), 38% greater than Callisto’s (Jupiter), 66% greater than Io’s (Jupiter), and 2.02 times that of Earth’s Moon.
As the ninth-largest object in the Solar System and the largest without a substantial atmosphere, Ganymede presents unique characteristics. In 1996, astronomers using the Hubble Space Telescope discovered a thin oxygen atmosphere on Ganymede, although it is far too thin to support life as we know it.
Remarkably, Ganymede is the only moon known to have its own magnetic field, which creates auroras. There is also strong evidence of an underground ocean beneath its icy surface.
Ganymede orbits Jupiter at a distance of 1,070,400 kilometers (665,116 miles). It was discovered by Galileo Galilei on January 7, 1610, along with three other Jovian moons. This discovery marked the first observation of moons orbiting a planet other than Earth and eventually led to the understanding that planets in our solar system orbit the Sun, rather than the entire system revolving around Earth.
Ganymede is named after a Trojan prince who was made cupbearer to the ancient Greek gods by Zeus (known as Jupiter to the Romans).
The Galilean moons, consisting of Io, Europa, Ganymede, and Callisto, are the four largest moons of Jupiter. They were first observed by Galileo Galilei in January 1610 and identified as satellites of Jupiter by March 1610.
German astronomer Simon Marius (1573-1625) likely made an independent discovery of these moons around the same time as Galileo, and he may have sighted them up to a month earlier. However, Galileo is credited with the discovery because he published his findings first.
Completed missions to Ganymede
Several space probes have explored Ganymede more closely, including flybys in the 1970s and multiple passes in the 1990s and 2000s.
Pioneer 10 approached Ganymede in 1973, followed by Pioneer 11 in 1974. These missions returned valuable information about the moon, including more precise determinations of its physical characteristics and surface features, resolving details down to 400 km (250 miles). Pioneer 10’s closest approach was 446,250 km.
Next, Voyager 1 and Voyager 2 passed by Ganymede in 1979. These missions refined our understanding of its size, revealing that Ganymede was larger than Saturn’s moon Titan, which was previously thought to be bigger. They also provided detailed images of the grooved terrain.
In 1995, the Galileo spacecraft entered orbit around Jupiter and conducted six close flybys of Ganymede between 1996 and 2000. These flybys, designated G1, G2, G7, G8, G28, and G29, provided extensive data. During the closest flyby (G2), Galileo passed just 264 km (164 miles) from Ganymede’s surface. The G1 flyby in 1996 led to the discovery of Ganymede’s magnetic field, and in 2001, the presence of an underground ocean was confirmed.
Galileo transmitted a large number of spectral images and discovered several non-ice compounds on Ganymede’s surface.
The most recent close observations were made by the New Horizons spacecraft, which recorded topographic and compositional mapping data of Europa and Ganymede during its flyby of Jupiter in 2007, en route to Pluto for its historic mission.
Sources
- Ganymede on Wikipedia
- “Ganymede: Facts” on the NASA Solar System website
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