Ganymede: Facts About Jupiter's Largest Moon Ganymede: Facts About Jupiter's Largest Moon By Kim Zimmermann | June 15, 2016 10:53am ET MORE NASA's Voyager 2 spacecraft snapped this color image of Jupiter's moon Ganymede, the largest satellite in the solar system, on July 7, 1979 from a distance of 745,000 miles (1.2 million kilometers). Credit: NASA Jupiter's moon Ganymede is the largest satellite in the solar system. Larger than Mercury and Pluto, and only slightly smaller than Mars, it would easily be classified as a planet if were orbiting the sun rather than Jupiter. The moon likely has a salty ocean underneath its icy surface, making it a potential location for life. The European Space Agency plans a mission to Jupiter's icy moons that in 2030, is planned to arrive and put special emphasis on observing Ganymede. Facts about Ganymede Age: Ganymede is about 4.5 billion years old, about the same age as Jupiter .

Distance from Jupiter: Ganymede is the seventh moon and third Galilean satellite outward from Jupiter, orbiting at about 665,000 miles (1.070 million kilometers). It takes Ganymede about seven Earth-days to orbit Jupiter. [ Photos of Ganymede, Jupiter's Largest Moon ] Size: Ganymede's mean radius is 1,635 miles (2,631.2 km). Although Ganymede is larger than Mercury it only has half its mass, classifying it as low density. Temperature: Daytime temperatures on the surface average minus 171 degrees Fahrenheit to minus 297 F, and night temperatures drop to -193C. In 1996, astronomers using the Hubble Space Telescope found evidence of a thin oxygen atmosphere. However, it is too thin to support life as we know it; it is unlikely that any living organisms inhabit Ganymede. Magnetosphere: Ganymede is the only satellite in the solar system to have a magnetosphere. Typically found in planets, including Earth and Jupiter, a magnetosphere is a comet-shaped region in which charged particles are trapped or deflected.

Ganymede's magnetosphere is entirely embedded within the magnetosphere of Jupiter. This montage compares New Horizons' best views of Ganymede, Jupiter's largest moon, gathered with the spacecraft's Long Range Reconnaissance Imager (LORRI) and its infrared spectrometer, the Linear Etalon Imaging Spectral Array (LEISA). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute Discovery and exploration of Ganymede Ganymede was discovered by Galileo Galilei on Jan. 7, 1610. The discovery, along with three other Jovian moons , was the first time a moon was discovered orbiting a planet other than Earth. Galileo's discovery eventually led to the understanding that planets orbit the sun, instead of our solar system revolving around Earth. Galileo called this moon Jupiter III. When the numerical naming system was abandoned in the mid-1800s, the moon was named after Ganymede, a Trojan prince in Greek mythology. Zeus, a counterpart of Jupiter in Roman mythology, carried Ganymede, who had taken the form of an eagle, to Olympus, where he became a cupbearer to the Olympian gods and one of Zeus' lovers.

Several spacecraft have flown by Jupiter and its moons. Pioneer 10 arrived first, in 1973, followed by Pioneer 11 in 1974. Voyager 1 and Voyager 2 returned striking photos during their flybys. The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons and produced detailed images. The European Space Agency plans a mission called JUICE (JUpiter ICy moons Explorer) that would launch from Earth in 2022 for arrival at Jupiter in 2030. While the mission will look at three moons (Ganymede, Callisto and Europa), Ganymede will be the focus because it shows how icy worlds evolve and could be habitable in general, ESA said on its website. Scientists will try to figure out more about its ocean and icy crust, map its surface in detail, learn about the interior, probe the atmosphere and study the magnetic field.

Ganymede sound and signal illustration Characteristics of Ganymede Ganymede has a core of metallic iron, which is followed by a layer of rock that is topped off by a crust of mostly ice that is very thick. There are also a number of bumps on Ganymede's surface, which may be rock formations. In February 2014, NASA and the United States Geological Survey unveiled the first detailed map of Ganymede in images and a video animation created using observations from NASA's Voyager 1 and Voyager 2 spacecraft, as well as the dedicated Jupiter-orbiting Galileo spacecraft. Ganymede's surface is made up of primarily two types of terrain: about 40 percent is dark with numerous craters, and 60 percent is lighter in color with grooves that form intricate patterns to give the satellite its distinctive appearance. The grooves, which were likely formed as a result of tectonic activity or water being released from beneath the surface, are as high as 2,000 feet and stretch for thousands of miles. A global image mosaic of Jupiter's moon, Ganymede created with images from the Voyager and Galileo missions.

Credit: Wes Patterson It is believed that Ganymede has a saltwater ocean below its surface. In 2015, a study by the Hubble Space Telescope looked at Ganymede's auroras and how they change between Ganymede's and Jupiter's magnetic fields. The “rocking” seen by the auroras gives evidence that the probable ocean underneath is salty , more salty than oceans of Earth, scientists said at the time. Some scientists are skeptical that Ganymede could host life, however. Due to its internal structure, it is believed that the pressure at the base of the ocean is so high that any water down there would turn to ice . This would make it difficult for any hot-water vents to bring nutrients into the ocean, which is one scenario under which scientists believe extraterrestrial life would occur. Additional reporting by contributor Elizabeth Howell. Additional resource Ganymede Moon - Ganymede Moon For Kids Ganymede is one of the many satellites , or moons, that orbit round the great planet, Jupiter. None of these moons can be seen with the naked eye but the four largest ones, Io , Europa , Ganymede and Callisto , can be seen with a small telescope.

They were first seen and described by Galileo in 1610, and so they are known as the “Galilean moons” Figure 1. The Galilean moons of Jupiter seen through a small telescope. Ganymede is the moon third in distance from the planet They are sometimes also called the moons of the “Jovian System”. “Jovian” is the adjective from Jupiter, so Jovian System means the system of Jupiter . Astronomers refer to the “Jovian System” because Jupiter with its moons in orbit is very similar to the Solar System with the planets in orbit. Ganymede is the third moon from Jupiter . Ganymede is the largest moon in the entire Solar System. It is larger than the planet Mercury. Figure 2. Ganymede, the largest moon in the Solar system. An image from the NASA Galileo spacecraft In spite of its size Ganymede is called a moon and not a planet, because it orbits Jupiter and not the Sun. Scientists believe that the lighter area was formed on top of the darker, rougher crust. The surface of Ganymede shows millions of years of geological activity. Figure 3.

The surface of Ganymede, showing the deep grooves present in the lighter, and younger, areas. Ganymede has an atmosphere containing oxygen, but not enough to support any form of life. Ganymede gets his name, like the other moons, from characters in Greek mythology who were close to the Greek sky god, Zeus, known to the ancient Romans as Jupiter. Ganymede was a beautiful young boy whom Zeus (Jupiter) captured and carried to the top of Mount Olympus, where the Gods lived. Zeus captured Ganymede by turning himself into an eagle and swooping down on the boy as he played. He then grabbed him in his talons and flew off with him. Ganymede (Moon) Facts Ganymede Eris Ganymede Moon Facts Ganymede is Jupiter’s largest moon and also the largest moon in the solar system. Ganymede was discovered in 1610 by astronomer Galileo Galilei and is named for the mythical Greek son of a King who was carried to the sky by Zeus posing as an eagle.

Ganymede Moon Profile 1.48 x 10^23 kg (2.0 Moons) Orbits: Ganymede size compared to the Moon and Earth Jupiter’s Galilean moons size comparison (Io, Europa, Ganymede and Callisto) Facts about Ganymede Ganymede is the largest moon in the solar system, and is larger than the planet Mercury. If it were not orbiting as Jupiter’s second-largest moon, it could be considered a dwarf planet. Ganymede is the only moon in the solar system known to have a substantial magnetosphere. That implies there is something inside helping to generate a strong magnetic field. Like Europa, Ganymede is thought to have a subsurface ocean, overlying a liquid iron and nickel core. That core is what helps generate the magnetic field. The surface of Ganymede is icy and covered with two main types of landscape: young, lighter regions and darker, older and cratered terrain. The dark areas appear to contain clays and organic materials. Ganymede was likely formed in place around the infant Jupiter in the early solar system. Several smaller worlds likely accreted together to make this moon.

Ganymede has a thin atmosphere that appears to contain oxygen. This was confirmed by Hubble Space Telescope observations. The oxygen is likely freed as water ice on the surface is broken apart into hydrogen and oxygen by solar radiation. The first mission to explore Ganymede up close was Pioneer 10, followed by the Voyager missions, Galileo, and New Horizons. Several missions to explore Ganymede in more detail have been suggested, but most have been cancelled or are still on the drawing boards. Sources: Jupiter's Moon Ganymede - Universe Today Universe Today by Matt Williams In 1610, Galileo Galilei looked up at the night sky through a telescope of his own design . Spotting Jupiter, he noted the presence of several “luminous objects” surrounding it, which he initially took for stars. In time, he would notice that these “stars” were orbiting the planet, and realized that they were in fact Jupiter’s moons – which would come to be named Io , Europa , Ganymede and Callisto . Of these, Ganymede is the largest, and boasts many fascinating characteristics. In addition to being the largest moon in the Solar System, it is also larger than even the planet Mercury.

It is the only satellite in the Solar System known to possess a magnetosphere, has a thin oxygen atmosphere, and (much like its fellow-moons, Europa and Callisto) is believed to have an interior ocean. Discovery and Naming: Though Chinese astronomical records claim that astronomer Gan De may have spotted a moon of Jupiter (probably Ganymede) with the naked eye as early as 365 BCE, Galileo Galilei is credited with making the first recorded observation of Ganymede on January 7th, 1610 using his telescope. Together with Io, Europa and Callisto, he named them the “Medicean Stars” at the time – after his patron, the Grand Duke of Tuscany, Cosimo de’ Medici. Simon Marius, a German astronomer and contemporary of Galileo’s who claimed to have independently discovered Ganymede, suggested alternative names at the behest of Johannes Kepler. However, the names of Io, Europa, Ganymede and Callisto – which were all taken from classical mythology – would not come to formally be adopted until the 20th century. Illustration of Jupiter and the Galilean satellites.

Credit: NASA Prior to this, the Galilean Moons were named Jupiter I through IV based on their proximity to the planet (with Ganymede designated as Jupiter III). Following the discovery of the moons of Saturn, a naming system based on that of Kepler and Marius was used for Jupiter’s moons. In Greek mythology, Ganymede was the son of King Tros (aka. Ilion), the namesake of the city of Troy (Ilium). Size, Mass and Orbit: With a mean radius of 2634.1 ± 0.3 kilometers (the equivalent of 0.413 Earths), Ganymede is the largest moon in the Solar System and is even larger than the planet Mercury. However, with a mass of 1.4819 x 10²³ kg (the equivalent of 0.025 Earths), it is only half as massive. This is due to Ganymede’s composition, which consists of water ice and silicate rock (see below).

Ganymede’s orbit has a minor eccentricity of 0.0013, with an average distance (semi-major axis) of 1,070,400 km – varying from 1,069,200 km at periapsis to at 1,071,600 km apoapsis. Ganymede takes seven days and three hours to completes a single revolution. Like most known moons, Ganymede is tidally locked, with one side always facing toward the planet. Its orbit is inclined to the Jovian equator, with the eccentricity and inclination changing quasi-periodically due to solar and planetary gravitational perturbations on a timescale of centuries. These orbital variations cause the axial tilt to vary between 0 and 0.33°. Ganymede has a 4:1 orbital resonance with Io and a 2:1 resonance with Europa. Ganymede is the largest satellite in our solar system, larger than Mercury and Pluto, and three-quarters the size of Mars. Credit: NASA/JPL Essentially, this means that Io orbits Jupiter four times (and Europa twice) for every orbit made by Ganymede.

The superior conjunction between Io and Europa occurs when Io is at periapsis and Europa is at apoapsis, and the superior conjunction between Europa and Ganymede occurs when Europa is at periapsis. Such a complicated resonance (a 4:2:1 resonance) is called the Laplace Resonance . Composition and Surface Features: With an average density of 1.936 g/cm3, Ganymede is most likely composed of equal parts rocky material and water ice. It is estimated that water ice constitutes 46–50% of the moon’s mass (slightly lower than that of Callisto) with the possibility of some additional volatile ices such as ammonia being present. Ganymede’s surface has an albedo of about 43%, which suggests that water ice makes up a mass fraction of 50-90% the surface. Near-infrared and ultra-violet surveys have also revealed the presence of carbon dioxide, sulfur dioxide, and possibly cyanogen, hydrogen sulfate and various organic compounds. More recent data has shown evidence of salts such as magnesium sulfate and possibly sodium sulfate, which may have originated from the subterranean ocean (see below).

Ganymede’s interior appears to be fully differentiated, consisting of a solid inner core made of iron, a liquid iron and iron-sulfide outer core, a silicate mantle, and a a spherical shell of mostly ice surrounding the rock shell and the core. The core is believed to measure 500 km in radius, and has a temperature of about 1500 – 1700 K and pressure of up to 10 GPa. Artist’s cut-away representation of the internal structure of Ganymede, with layers shown to scale. Credit: Wikipedia Commons/kelvinsong The most compelling evidence for the existence of a liquid, iron-nickel-rich core is Ganymede’s intrinsic magnetic field. The convection in the liquid iron, which has high electrical conductivity, is the most reasonable model of magnetic field generation.The density of the core is believed to be 5.5 – 6 g/cm³, while the silicate mantle has an estimated density of 3.4 – 3.6 g/cm³. This mantle is composed of silicate materials, most likely chondrites and iron.

The outer ice shell is the largest layer of all, measuring an estimated 800 km (497 miles) thick. The precise thicknesses of this and other layers in the interior of Ganymede depends on the assumed composition of silicates and amount of sulfur in the core. Scientists also believe that Ganymede has a thick ocean nestled between two layers of ice – a tetragonal layer between it and the core and a hexagonal layer above it. The presence of this ocean has been confirmed by readings taken by orbiters and through studies of how Ganymede’s aurora behaves. In short, the moon’s auroras are affected by Ganymede’s magnetic field, which in turn is affected by the presence of a large, subsurface salt-water ocean. Ganymede’s surface is a mix of two types of terrain. There’s the very old, highly cratered, and dark regions, and the somewhat younger, lighter regions marked with an extensive array of grooves and ridges. In a way that is similar to Europa, Ganymede’s surface is asymmetric, with the leading hemisphere being brighter than the trailing one.

The dark terrain, which comprises about one-third of the surface, is so-colored because the surface ice in these regions contains clays and organic materials. It has been theorized that these have been left behind by impactors, which accords with the fact that impact craters are far more extensive in the areas of dark terrain. Meanwhile, the grooved terrain is believed to be tectonic in nature; which could be due in part to cryovolcanism , but is thought to be mostly the result of tidal heating events. The tidal flexing could have heated the interior and strained the lithosphere, leading to the development of cracks, graben and faults that erased the old, dark terrain on 70% of the surface. Though craters are more common in the darker areas, they are seen all over the surface. Ganymede may have experienced a period of heavy cratering 3.5 to 4 billion years ago similar to that of the Moon. If true, the vast majority of impacts happened in that epoch, whereas the cratering rate has been much smaller since.

Craters on Ganymede are also flatter than those on the Moon and Mercury, which is probably due to the relatively weak nature of Ganymede’s icy crust. Ganymede also has polar caps, likely composed of water frost, which were first seen by the Voyager spacecraft. Since the discovery, several theories have been proposed for their formation, ranging from the thermal migration of water vapor to higher latitudes to plasma bombardment turning the ice brighter. Data obtained by the Galileo spacecraft – which noted a very close correspondence between the polar cap boundary and the boundaries of the moon’s magnetic field – suggests that the latter theory is correct. Atmosphere: Similar to Europa, Ganymede has a tenuous oxygen atmosphere. Also similar to Europa is how the atmosphere formed, which involves water ice on the surface being split into hydrogen and oxygen through interaction with UV radiation, the hydrogen being lost to space and the oxygen being retained. The surface pressure of this atmosphere is thought to lie within the range of 0.2–1.2 micro Pascals. Montage showing New Horizons’ views of Ganymede taken by it’s infrared spectrometer and LORRI and LEISA instruments.

Credit: NASA/Johns Hopkins University APL/SwRI The presence of this atmosphere also causes an airglow effect, a faint emission of light caused by the interaction of atomic oxygen and energetic particles. This effect is not uniformly distributed (as with Europa), but instead causes bright spots to appear above the polar regions – which could be “polar auroras” – due to the planet’s magnetic field. Additional evidence of the oxygen atmosphere comes from the detection of various gases trapped in the ice on Ganymede. This evidence consisted of the spectroscopic detection of ozone (O³), as well as absorption features that indicated the presence of oxygen gas (O²). Another constituent of the atmosphere is hydrogen, which (despite most being lost to space) still exists at a surface in very minor concentrations. The existence of this neutral atmosphere implies that an ionosphere should exist since oxygen molecules are ionized by the impacts of the energetic electrons coming from the magnetosphere and by solar electromagnetic UV radiation. However, the existence of an ionosphere remains controversial, due to conflicting data gathered by different missions. Magnetosphere: Ganymede is unique among moons in the Solar Systems in that it alone has a magnetosphere.

The value of the moon’s permanent magnetic moment is estimated to be 1.3 x 10¹³ T·m³, which is three times larger than the magnetic moment of Mercury. The magnetic dipole is tilted with respect to the rotational axis of Ganymede by 176°, which means that it is directed against the Jovian magnetic moment. The magnetic field of Jupiter and co-rotation enforcing currents. Credit: Wikipedia Commons/Ruslik0 The dipole magnetic field created by this permanent moment has a strength of 719 ± 2 Teslas (nT) at Ganymede’s equator, and roughly twice that at the poles (1440 nT). This magnetic moment also carves a part of space around Ganymede, creating a tiny magnetosphere embedded inside that of Jupiter with a diameter of about 10,525 – 13,156 km. The Ganymedian magnetosphere has a region of closed field lines located below 30° latitude, where charged particles (electrons and ions) are trapped, creating a kind of radiation belt.

The main ion species in the magnetosphere is single ionized oxygen, which fits well with Ganymede’s tenuous oxygen atmosphere. The interaction between the Ganymedian magnetosphere and Jovian plasma is in many respects similar to that of the solar wind and Earth’s magnetosphere. The plasma co-rotating with Jupiter impinges on the trailing side of the Ganymedian magnetosphere much like the solar wind impinges on the Earth’s magnetosphere. In addition to the intrinsic magnetic moment, Ganymede has an induced dipole magnetic field who’s existence is connected with the variation of the Jovian magnetic field near Ganymede. The induced magnetic field of Ganymede is similar to those of Callisto and Europa, indicating that this moon also has a subsurface water ocean with a high electrical conductivity. Artist’s concept of aurorae on Ganymede. Credit: NASA/ESA However, the existence of Ganymede’s magnetosphere remains a bit of a mystery. On the one hand, its existence is believed to be the result of Ganymede’s a dynamo effect caused by conducting material moving in the core, similar to Earth.

However, other bodies that have differentiated metallic cores don’t have magnetospheres, and the relatively small size of Ganymede’s core suggests that it should have cooled sufficiently that fluid motions are no longer possible. One explanation for this incongruity is that the same orbital resonances that may have disrupted the surface also allow the magnetic field to persist. With tidal heating increasing during such resonances, the mantle may have insulated the core, preventing it from cooling. Another explanation is a remnant magnetization of silicate rocks in the mantle, which is possible if the satellite had a more significant dynamo-generated field in the past. Habitability: There is some speculation on the potential habitability of Ganymede’s ocean. An analysis published in 2014 , taking into account the realistic thermodynamics for water and effects of salt, suggests that Ganymede might have a stack of several ocean layers separated by different phases of ice, with the lowest liquid layer adjacent to the rocky mantle below. This is important, since the layer closest to the rocky interior would be subject to heating due to tidal flexing in the mantle. This heat could be transferred into the water via hydrothermal vents , which could provide the necessary heat and energy to sustain life.

Combined with oxygenated water, life forms could exist at the core-mantle boundary in the form of extremophiles, in a way that is similar to what is found in Earth’s oceans (and presumed to exist in Europa’s interior ocean). Exploration: Several probes flying by or orbiting Jupiter have explored Ganymede more closely, including four flybys in the 1970s, and multiple passes in the 1990s to 2000s. The first approaches were conducted by the Pioneer 10 and 11 probes, which approached the moon in 1973 and 1974, respectively. These missions returned more specific information on its physical characteristics and resolved features to 400 km (250 mi) on its surface. The next missions came in 1979, when the Voyager 1 and 2 probes passed the moon, refining estimates of its size and revealing its grooved terrain for the first time. In 1995, the Galileo spacecraft orbited Jupiter and went on to make six close flybys between 1996 and 2000.

The probe’s findings included the discovery of Ganymede’s magnetic field, the moon’s interior ocean, and a large number of spectral images that showed non-ice compounds on the surface. Artist impression of New Horizons conducting its flyby of Jupiter. Image credit: NASA/JPL/JHUAPL The most recent mission to Ganymede was made by the New Horizons probe in 2007. While en route to Pluto, the probe obtained topographic and composition mapping data of Europa and Ganymede during its flyby of Jupiter. Their are no missions to Ganymede currently in operation, but several missions have been proposed for the coming decades. One such proposal is the joint NASA/ESA Europa Jupiter System Mission (EJSM), which would explore Jupiter’s moons (including Ganymede) and has a proposed launch date of 2020. The mission would consist of NASA’s Jupiter Europa Orbiter, the ESA’s Jupiter Ganymede Orbiter, and possibly a JAXA Jupiter Magnetospheric Orbiter.

The ESA’s contribution was renamed the Jupiter Icy Moon Explorer (JUICE) in 2012, and obtained a launch slot aboard the ESA’s Cosmic Vision science program (scheduled for launch in 2022 or 2024). This may include a partner mission from the Russian Space Research Institute – known as the Ganymede Lander (GL) – and would involve JUICE examining Ganymede from orbit and conducting multiple flybys or Europa and Callisto. A Ganymede orbiter based on the Juno probe was also proposed in 2010 for the Planetary Science Decadal Survey. As part of the committee report presented at the Survey – titled “ Vision and Voyagers for Planetary Science in the Decade 2013-2022 ” – a concept study for a possible Ganymede Orbiter was proposed, which included recommendations on instrumentation. Artist’s concept of the Jupiter Icy Moons Orbiter (JIMO), a cancelled program that envisioned sending a spacecraft to inspect Callisto, Ganymede and Europa.

Credit: NASA/JPL A canceled proposal for a Ganymede orbiter was the Jupiter Icy Moons Orbiter (JIMO), which would have performed a flyby of Europa, Ganymede and Callisto. Designed to use nuclear fission for power and an ion engine for propulsion, JIMO would have studied Ganymede in greater detail than an previous orbiter. However, the mission was canceled in 2005 because of budget cuts. Colonization: Ganymede is considered a possible candidate for human settlement – and even terraforming – due to the many advantages it presents. For one, as Jupiter’s largest moon, Ganymede has a gravitational force of 1.428 m/s2 (the equivalent of 0.146 g) which is comparable to Earth’s Moon. Sufficient enough to limit the effects of muscle and bone degeneration, this lower gravity also means that the moon has a lower escape velocity – which means it would take considerably less fuel for rockets to take off from the surface. What’s more, the presence of a magnetosphere means that colonists would be better shielded from cosmic radiation than on other bodies.

The prevalence of water ice means that colonists could also produce breathable oxygen, their own drinking water, and would be able to synthesize rocket fuel. Unfortunately, beyond this, Ganymede presents numerous challenges for colonization. For starters, the presence of a magnetosphere does not shield Ganymede from enough cosmic radiation to ensure human safety, due to the fact that it is overshadowed by Jupiter’s powerful magnetic field. This results in the surface receiving some 8 rem of radiation per day – which is 333 times the average of what Earth-bound organisms experience in a year. Artist’s concept for a future settlement on Ganymede. Credit: futuretimeline.net The dominance of Jupiter’s magnetic field also means that Ganymede’s magnetosphere is not strong enough to retain an atmosphere of sufficient density to sustain human beings. It would also be insufficient to retain much heat. Hence, settlements on the surface would need to be heavily insulated, shielded from radiation, and contain a breathable atmosphere. A possible solution to this, similar to what has been proposed for Europa, would be for colonists to build settlements within the icy mantle, or possibly under the surface of the ice entirely.

These embedded (or aquatic habitats) would be shielded from harmful cosmic radiation by the icy mantle. They could also function as conduits between the ocean and the surface, piping water in and processing it into fuel for export. However, such possibilities are still far from realization and in the meantime, exploring Ganymede and deciphering its deeper mysteries remains the priority. And of these, Ganymede has several! Much like the other Galilean moons, Ganymede possesses a wealth of unique and mysterious attributes, many of which still defy comprehension. In addition to being the largest moon in the Solar System, it is the only moon other than Earth (and the gas giants) to have a magnetic field. And of course, there’s the possibility that life could exist beneath its icy crust, possibly in microbial or extreme form. All of these make Ganymede an intriguing prospect for future exploration. We have many interesting articles on Ganymede and Jupiter’s Moons here at Universe Today. Here is a list of the Galilean Moons , as well as Jupiter’s entire system of moons . Here is one about Ganymede’s interior ocean , and how an amateur astronomer made a detailed map of Ganymede .

Here’s a list of all the largest moons in the Solar System, and a listing of the largest moons and smallest planets at Solar Views. Universe Today has whole series of podcasts about the Solar System at Astronomy Cast . Share this: Ganymede, Solar System's Largest Moon, Gets 'On The Map' - Seeker Feb 12, 2014 04:13 PM ET Ganymede, Solar System's Largest Moon, Gets 'On The Map' The first geologic map of Jupiter's moon Ganymede has been created, revealing its varied and complex terrain. Continue reading → Credits: NASA/Science Channel On August 4, the much-anticipated "Wonders of the Solar System" documentary will premier on the Science Channel. Presenter and physicist Prof. Brian Cox will show you the hidden mysteries of our interplanetary neighborhood, as well as breathtaking sights of the planets, moons and the sun. Cox will also examine some of Earth's extreme environments to see how life has adapted, perhaps helping us understand whether life can exist elsewhere in our solar system.

To provide a taster of what you can expect from "Wonders," Discovery News has gathered some facts, figures and the best images of our solar system to assemble a special Wide Angle supporting this groundbreaking documentary. Let's begin, in the orbit of the solar system's biggest planet, Jupiter... Credit: NASA/JPL-Caltech/Galileo Moons of Jupiter: Io Welcome to Jupiter, the solar system's biggest planet and host to more than 63 peculiar moons -- a steady contender for moons compared to satellite-strewn Saturn. From sulfur-spewing furnaces to ice-encrusted oceans, these Jovian satellites are anything but normal! Browse through 10 of our favorites here. If you're looking for a fiery, volcanic spectacle, head to Io, the innermost of Jupiter's "big four" moons. Jupiter's gravity pulls at Io so strongly that the land has tides of up to 300 feet (100 meters). This gravitational tug-of-war produces scorching heat and raises more volcanic activity here than anywhere else in the solar system. Io has a sulfurous surface, and its volcanoes spew silicate magma, causing the hellish moon's surface look like a pizza.

Credit: NASA/JPL-Caltech/Galileo Moons of Jupiter: Metis While it doesn't look like much in this image (the highest-resolution available!), Metis is Jupiter's closest companion -- for now. It's orbiting the gas giant at a distance of just 75,500 miles (128,000 kilometers) and moving faster than Jupiter spins. Metis is so close to Jupiter's surface, in fact, that it will gradually succumb to the planet's gravity and plunge into its churning clouds. This same principle applies to man-made satellites orbiting the Earth; if their orbit is too low, they'll eventually fall. Credit: NASA/JPL-Caltech/Galileo Moons of Jupiter: Adrastea Like Metis, Adrastea is on its way down, eventually: Its orbit is just 1,000 kilometers (621 miles) outside of its fellow doomed moon. The two bodies probably provide lots of the material making up Jupiter's main ring, shown in this Galileo spacecraft image. Adrastea is also tiny at a wee 12 miles (20 kilometers) in diameter.

Credit: NASA/JPL-Caltech/Galileo Moons of Jupiter: Ganymede If Ganymede orbited the sun instead of Jupiter, it would be a planet of its own -- it's even bigger than Mercury. Its interior is made from layers surrounding a rocky core, and its surface is covered in water ice. Although Ganymede doesn't have much of an atmosphere, it does have some ozone gas near its surface. This gas comes from charged particles in Jupiter's magnetic field smacking into the moon's icy crust. Credit: Courtesy of Damien Perrotin Moons of Jupiter: Themisto We're not entirely sure what Themisto looks like, but scientists know it one odd little satellite. Unlike most other moons, Themisto is oblong and doesn't fit into the traditional groups of Jovian moons. Because this body is so small -- just 5 miles (8 kilometers) in diameter -- astronomers in 2000 confused it for a new object when it was originally found in 1975. Shown here is a speculative illustration of how the irregular moon might be shaped.

Credit: NASA/Voyager Moons of Jupiter: Callisto Along with Io, Ganymede, and Europa (which is yet to come in this slide show), Callisto is one of the four Galilean satellites. These are the moons of Jupiter that Galileo discovered while looking through a telescope in 1610. Callisto is about the same size as Mercury, and it's a heavily cratered moon that has almost no geological activity. Callisto's surface may also be one of the oldest landscapes in the solar system, including Earth's moon -- about 4 billion years old. Credit: NASA/JPL-Caltech/Galileo Moons of Jupiter: Thebe Along with Metis and Adrastea, Thebe was discovered by scientists studying images from the Voyager spacecraft in 1979 and 1980. It's closer to Jupiter than Io is, but it's not so close that it's in danger of losing its altitude. The material in Jupiter's Gossamer ring probably comes from Thebe and another moon, Amalthea.

Credit: NASA/Michael Carroll Moons of Jupiter: Amalthea Speaking of Amalthea, shown here is an artist's rendition of the mysterious moon (inset: our best real view so far). Astronomers don't know much about it, but they do know it's the reddest body in the solar system. Unlike the other three moons that lie within Io's orbit -- Thebe, Metis and Adrastea -- Amalthea wasn't discovered by the Voyager science team. Edward Emerson Barnard discovered Amalthea it in 1892, and it had been almost 300 years since anyone had discovered a new moon orbiting Jupiter. Before that, the last person to discover a Jovian moon was Galileo. Credit: University of Hawaii/Scott Sheppard/D Moons of Jupiter: S/2000 J11 This not-to-be-named moon marks an interesting dividing line in the wealth of satellites orbiting Jupiter. S/2000 J11, named after it was found in 2000, moves in the same direction that Jupiter spins -- as do all the moons that are closer to the planet.

Almost every distant moon, however, orbits in the opposite (retrograde) direction, as this diagram shows. The only known exception is Carpo, sometimes known as Karpo, which was discovered in 2003. Ganymede, The Largest Moon In Our Solar System | Outer Space Universe Ganymede, The Largest Moon In Our Solar System November 3rd, 2010 | Author: Greg - Staff Writer Ganymede - The Largest Moon in the Solar System Did you know that the largest moon in our Solar System orbits the largest planet in our Solar System? Ganymede, a moon orbiting Jupiter wins the prize as the largest moon in our Solar System. Ganymede holds the position as the seventh moon outward from the surface of Jupiter. It has a diameter of 3,270 miles. For comparison, Earth’s moon is 2,159 miles in diameter. If you want to compare Ganymede to a planet, it is 8% bigger than the planet Mercury! The next biggest moon in the Solar System happens to orbit the planet Saturn. It is called Titan. You would think the biggest moon would be called Titan – not Ganymede – wouldn’t you?

The Four Galilean Satellites The four biggest moons orbiting Jupiter – Ganymede, Callisto, Io, and Europa – are called Galilean Satellites. They are named after Galileo Galilei who discovered them in 1610 through a homemade telescope. Ganymede is made of equal amounts of silicate rock and water ice. It is thought to have a liquid core with a saltwater ocean laying nearly 200 km below it’s icy surface. It’s surface is quite unusual, having dark regions loaded with impact craters and wide expanses of light regions that have pronounced groves and ridges. It is generally thought that these areas have been created by tidal heating of ice below the surface. Another unique thing about Ganymede is that it is the only moon in the Solar System known to have a magnetosphere, which is probably being generated by it’s liquid iron core. It also has a thin oxygen atmosphere. The first man-made spacecraft to visit Ganymede was Pioneer 10. It flew by the giant moon on December 3, 1973.

Related articles: One Response to “Ganymede, The Largest Moon In Our Solar System” johannes Huijgen Photos of Ganymede, Jupiter's Largest Moon Photos of Ganymede, Jupiter's Largest Moon By Space.com Staff | February 13, 2014 11:03am ET MORE Ganymede Global Geologic Map and Global Image Mosaic Credit: USGS Astrogeology Science Center/Wheaton/NASA/JPL-Caltech Jupiter's moon Ganymede is the largest satellite in the solar system. Larger than Mercury and Pluto, and only slightly smaller than Mars, it would easily be classified as a planet if were orbiting the sun rather than Jupiter. IN THIS IMAGE: To present the best information in a single view of Jupiter's moon Ganymede, a global image mosaic was assembled, incorporating the best available imagery from NASA's Voyager 1 and 2 spacecraft and NASA's Galileo spacecraft. This image shows Ganymede centered at 200 west longitude. This mosaic (right) served as the base map for the geologic map of Ganymede (left).

[ Read the Full Story and video of the Ganymede map ] Global Map of Ganymede, Jupiter's Largest Moon Credit: USGS Astrogeology Science Center/Wheaton/ASU/NASA/JPL-Caltech A geologic map of Jupiter's largest moon Ganymede is superimposed over a global color mosaic of the Galilean moon made of images from NASA's Voyager 1, 2 and Galileo spacecraft. [ Read the Full Story and video of the Ganymede map ] Jupiter's Moon Ganymede Credit: NASA NASA's Galileo spacecraft obtained this image of Ganymede, one of Jupiter's moons and the largest moon in our solar system. Image undated. Ganymede Interior Cross-Section Credit: NASA, ESA, and A. Feild (STScI) Ganymede's interior, seen here, is composed of an iron core, rocky mantle, icy mantle, 100 kilometer deep liquid ocean and icy crust. Image released March 12, 2015. Magnetosphere of Ganymede Credit: NASA, ESA, and A.

Feild (STScI) This sketch shows the magnetic field lines around Ganymede, which originate in the moon's iron core. Image released March 12, 2015. Ganymede's Auroral Belts Credit: NASA/ESA Ganymede's auroras helped scientists see that the moon is likely harboring a vast, deep and salty liquid ocean below its surface. Image released March 12, 2015. Ganymede's Magnetic Fields Illustration Credit: NASA/ESA This artist’s conceptual illustration shows the moon Ganymede orbiting giant planet Jupiter. Jupiter's magnetosphere appears as yellow field lines. Image released March 12, 2015. Artist's Conception of Ganymede with Auroras Credit: NASA/ESA Ganymede might have a vast liquid ocean under its crusty outer shell, new data from the Hubble Space Telescope has shown. Image released March 12, 2015. Ganymede Magnetic Field Rocking Credit: NASA, ESA, and A.

Feild (STScI) This diagram examines the excursion of a pair of auroral belts on Jupiter's moon Ganymede, providing insight into the moon's interior. The rocking motion of the two aurorae indicates that that a large amount of saltwater exists beneath Ganymede's crust. Image released March 12, 2015. Jovian Moon Plays Peekaboo Credit: NASA, ESA, and E. Karkoschka (University of Arizona). This photo, snapped by Hubble on April 9, 2007, shows Jupiter's moon Ganymede just before it ducks behind its giant host. Voyager View of Jupiter Moon Ganymede Credit: NASA NASA's Voyager 2 spacecraft snapped this color image of Jupiter's moon Ganymede, the largest satellite in the solar system, on July 7, 1979 from a distance of 745,000 miles (1.2 million kilometers). Jupiter's Family Portrait Credit: NASA This "family portrait," a composite of the Jovian system, includes the edge of Jupiter with its Great Red Spot, and Jupiter's four largest moons, known as the Galilean satellites.

From top to bottom, the moons shown are Io, Europa, Ganymede and Callisto. Smacks in the Face Explain Unique Looks of Two Moons Credit: SwRI Jupiter (right) and the Galilean satellites (right to left) Io, Europa, Ganymede, and Callisto. Cutaways show the interior states of Ganymede and Callisto after many impacts by icy planetesimals during the late heavy bombardment. Skywatcher's Brightness Map of Jupiter Moon Ganymede Credit: Manos Kardasis The original observations (top) and interpretations (bottom) of the first ever amateur albedo map of Ganymede. Amateur Astronomer Photographs Jupiter and Ganymede Credit: Manos Kardasis Amateur photographs of Jupiter and Ganymede, accompanied with a professionally obtained labeled map (bottom right). New Map Reveals Geology of Jupiter's Moon Ganymede Credit: Wes Patterson A global image mosaic of Jupiter's moon, Ganymede created with images from the Voyager and Galileo missions.

Jupiter's Moons in 1979: Ganymede by Voyager 2 Credit: UCL Faculty of Mathematical and Physical Sciences This image shows Jupiter moon Ganymede taken by Voyager 2 in 1979. Voyager probes 1 and 2 visited the Jovian system in 1979, before taking different paths through the outer reaches of the Solar System, studying the giant planet as well as making numerous images of its moons. The relatively narrow field of view, combined with the Voyager probes' close flybys meant that the photos had to be stitched together, which in the days before powerful computer graphics software meant printing them out and sticking them together by hand, like a giant jigsaw puzzle, interspersed with hand-written notes and computer printouts of technical information relating to the photographs. Amateur Map of Ganymede and Known Surface Features Credit: Manos Kardasis Albedo maps of Ganymede (left) and how they relate to known surface features (right).

SP_120928_ganymedeYourUniverse.jpg News | Largest Solar System Moon Detailed in Geologic Map News | February 12, 2014 Largest Solar System Moon Detailed in Geologic Map More than 400 years after its discovery by astronomer Galileo Galilei, the largest moon in the solar system - Jupiter's moon Ganymede - has finally claimed a spot on the map. A group of scientists led by Geoffrey Collins of Wheaton College has produced the first global geologic map of Ganymede, Jupiter's seventh moon. The map combines the best images obtained during flybys conducted by NASA's Voyager 1 and 2 spacecraft (1979) and Galileo orbiter (1995 to 2003) and is now published by the U. S. Geological Survey as a global map. It technically illustrates the varied geologic character of Ganymede's surface and is the first global, geologic map of this icy, outer-planet moon. The geologic map of Ganymede is available for download at: ).

"This map illustrates the incredible variety of geological features on Ganymede and helps to make order from the apparent chaos of its complex surface," said Robert Pappalardo of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This map is helping planetary scientists to decipher the evolution of this icy world and will aid in upcoming spacecraft observations." The European Space Agency's Jupiter Icy Moons Explorer mission is slated to be orbiting Ganymede around 2032. NASA is contributing a U.S.-led instrument and hardware for two European-led instruments for the mission. Since its discovery in January 1610, Ganymede has been the focus of repeated observation, first by Earth-based telescopes, and later by the flyby missions and spacecraft orbiting Jupiter. These studies depict a complex, icy world whose surface is characterized by the striking contrast between its two major terrain types: the dark, very old, highly cratered regions, and the lighter, somewhat younger (but still very old) regions marked with an extensive array of grooves and ridges.

According to the scientists who have constructed this map, three major geologic periods have been identified for Ganymede that involve the dominance of impact cratering, then tectonic upheaval, followed by a decline in geologic activity. The map, which illustrates surface features, such as furrows, grooves and impact craters, allows scientists to decipher distinct geologic time periods for an object in the outer solar system for the first time. "The highly detailed, colorful map confirmed a number of outstanding scientific hypotheses regarding Ganymede's geologic history, and also disproved others," said Baerbel Lucchitta, scientist emeritus at the U.S. Geological Survey in Flagstaff, Ariz., who has been involved with geologic mapping of Ganymede since 1980. "For example, the more detailed Galileo images showed that cryovolcanism, or the creation of volcanoes that erupt water and ice, is very rare on Ganymede." The Ganymede global geologic map will enable researchers to compare the geologic characters of other icy satellite moons, because almost any type of feature that is found on other icy satellites has a similar feature somewhere on Ganymede.

"The surface of Ganymede is more than half as large as all the land area on Earth, so there is a wide diversity of locations to choose from," Collins said. "Ganymede also shows features that are ancient alongside much more recently formed features, adding historical diversity in addition to geographic diversity." Amateur astronomers can observe Ganymede (with binoculars) in the evening sky this month, as Jupiter is in opposition and easily visible. The project was funded by NASA through its Outer Planets Research and Planetary Geology and Geophysics Programs. NASA's Jet Propulsion Laboratory is managed by the California Institute of Technology, Pasadena. News Media Contact

Question: Gannymede is the largest moon, orbiting which of the planets?
Answer: JUPITER