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 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, biggest moon in the solar system, has a saltwater ocean - CNET CNET Ganymede, biggest moon in the solar system, has a saltwater ocean Ganymede, biggest moon in the solar system, has a saltwater ocean NASA says new observations from the Hubble Space Telescope confirm the presence of a subsurface ocean on Jupiter's largest moon. Up Next Obama retaliates against Russia over election hacking This artist's concept shows Ganymede in the shadow of Jupiter, with its aurorae glowing.Photo by NASA/ESA NASA says new observations from the Hubble Space Telescope confirm the existence of a salty subsurface ocean on Ganymede , the largest moon in the solar system, which orbits our largest neighbor planet, Jupiter.

The ocean is estimated to be about 60 miles thick -- 10 times deeper than the Mariana Trench, the deepest part of the Pacific -- but is buried under a layer of mostly icy crust 95 miles thick. Ganymede joins other neighborhood moons like Europa, the asteroid belt dwarf planet Ceres , and Saturn's Enceladus and Titan that host strange icy or liquid layers, making them prime targets in the search for life beyond Earth. Scientists have hypothesized for decades that Ganymede might harbor an icy or even liquid ocean beneath its frigid surface. The key to confirming the presence of a saltwater ocean came from observing Ganymede's aurorae, which would look bright red to a human able to stand on the surface of the moon and gaze up through its thin oxygen atmosphere. But don't get too excited, it's much too thin to support life as we know it. 7 Jupiter's Ganymede moon hides a big ocean (pictures) Auroral phenomena -- think the bright northern lights of the aurora borealis or the aurora australis down south -- are not fully understood, but are linked to magnetic fields interacting with the solar wind.

Ganymede is the only moon in the solar system that generates its own magnetic field thanks to its liquid iron core, but it also lies within the magnetic field of massive Jupiter. As Jupiter's magnetic field changes, it affects the aurorae on Ganymede, causing them to "rock back and forth" according to Joachim Saur, a professor for geophysics at the University of Cologne, who presented the news on a NASA teleconference Thursday. Related stories See the submarine NASA wants to send to Saturn's moon Titan Saur explained that the rocking effect seemed to be dampened by something else. Rather than altering the aurorae six degrees, as models suggested that they should given the electromagnetic fields involved, they only changed by two degrees, leading scientists to conclude that the rocking is inhibited by a salty subsurface ocean. "This confirms the existence of an ocean and simultaneously rules out the absence of an ocean," he told reporters. 9 more habitable planets found A NASA discovery means there are a lot more planets that may be able to support life. Also, Amazon takes on YouTube. Get all caught up in tech right here.

by Iyaz Akhtar Close Drag The news comes on the heels of the finding earlier this week that Saturn's moon Enceladus may contain enough warm water to support life. Ganymede will also now be more competitive when it comes to garnering attention among the Jovian moons -- its sibling Europa and its presumed subsurface ocean has long excited space geeks, even working its way into the priority list for future NASA missions. Looks like NASA may now need to add another moon to its itinerary for that deep-space journey. Ganymede | The Solar System Wiki | Fandom powered by Wikia THE SOLAR SYSTEM WIKI Share Ad blocker interference detected! Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers Wikia is not accessible if you’ve made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected. Ganymede Alternate Name(s) Jupiter III Ganymede, also called Jupiter III, is the largest moon in the Solar System, the largest of the Galilean moons, and the largest of Jupiter's moons. This moon belongs to the planet Jupiter , which is ironically the largest planet in the Solar System.

Ganymede is one of the Gallilean moons, which were discovered by Galileo Galilei . Ganymede was discovered on January 7, 1610. It is a member of the Galilean moons, meaning it maintains hydrostatic equilibrium, meaning it can maintain a nearly round shape, showing it has a sufficient amount of mass. Contents A saltwater ocean is believed to exist or have existed beneath Ganymede's surface, but about 200 km deep. The ocean is believed to be sandwiched between different silicate rock and water ice layers. Surface Ganymede's surface is mostly covered with rocky caverns and craters from asteroid impacts. The rest of Ganymede is made up of light regions with crosscuts similar to the Earth's moon. Like Father, Like Son Edit Jupiter is the largest planet in the Solar System. Ganymede is one of Jupiter's satellites, or moons, and is the largest moon in the Solar System. In fact, it more than twice the size of the Earth's moon. Ganymede is even larger than the planet of Mercury and is one-tenth more massive than Mercury itself.

Relationship with the Galilean Moons Edit The Galilean moons are the most massive and the largest moons in the Solar System, making Ganymede, the largest moon in the Solar System, fit in perfectly. Ganymede, however, contains craters and mountainous areas, differing from the other Galilean moons. Callisto contains larger craters that appear to have crosscuts inside of them. Europa just has plain crosscuts on the surface, and last but not least, Io, has volcanic activity, differing from any moon belonging to Jupiter. Jupiter’s moon Ganymede, the largest moon in the Solar System | Anne’s Astronomy News Jupiter’s moon Ganymede, the largest moon in the Solar System Jupiter’s moon Ganymede is, with a diameter of 5,268 km the largest moon in the Solar System, even larger than the planet Mercury. It also has the highest mass of all moons, with 2.025 times the mass of the Earth’s Moon.

It is the seventh moon outward from Jupiter and one of the four so called Galilean moons (the other three are: Io, Europa and Callisto – all discovered by Galileo Galilei in the year 1610.) Ganymede orbits Jupiter at a distance of 1,070,400 km and completes a revolution every seven days and three hours. Like most known moons, Ganymede is tidally locked, with one side of the moon always facing toward the planet. Ganymede participates in orbital resonances with Europa and Io: for every orbit of Ganymede, Europa orbits twice and Io orbits four times. Its surface is composed of two main types of terrain. Dark regions, saturated with impact craters and dated to four billion years ago, cover about a third of the satellite. Lighter regions, crosscut by extensive grooves and ridges and only slightly less ancient, cover the remainder. The cause of the light terrain’s disrupted geology was likely the result of tectonic activity brought about by tidal heating. Ganymede is composed of approximately equal amounts of silicate rock and water ice, with additional volatile ices such as ammonia. Water ice seems to be ubiquitous on the surface.

The brighter, grooved regions have a more icy composition than the dark regions. Besides water, analysis has revealed several other materials on Ganymede’s surface, like carbon- and sulfur dioxide and various organic compounds. Especially the dark regions contain clays with organic materials. The large craters on Ganymede have almost no vertical relief and are quite flat. They lack central depressions common to craters. This is probably due to slow and gradual adjustment to the soft icy surface. These large phantom craters range from 50 to 400 km in diameter. Both bright and dark rays of ejecta exist around Ganymede’s craters — rays tend to be bright from craters in the light, grooved terrain and dark from the dark cratered. A saltwater ocean, which could potentially also host life, is believed to exist nearly 200 km below Ganymede’s surface, sandwiched between layers of ice. The magnesium- and sodium sulfates that were also found, likely originate from this subsurface ocean. Just how deep this ocean is, and whether it exists in pockets or as a continuous band around the moon, are questions the JUICE- team hopes to answer.

(JUICE is the next planned mission to the Jovian moons.) Ganymede appears to be fully differentiated, consisting of an iron-rich, liquid core, silicate mantle and an outer, very thick (maybe 800 km thick) ice mantle which might contain some rock mixed in. The existence of the iron-rich core provides a natural explanation for the intrinsic magnetic field of Ganymede. The convection in the liquid iron, which has high electrical conductivity, is the most reasonable model of magnetic field generation. Ganymede is the only moon in the Solar System known to possess a magnetosphere, although the meager magnetosphere is buried within Jupiter’s much larger magnetic field. But, this field is powerful enough to generate an aurora, like Earth’s. Ganymede also has polar caps which extend to 40° latitude, likely composed of water frost. The caps’ formation is due to the migration of water to higher latitudes and bombardment of the ice by plasma. The presence of a magnetic field on Ganymede results in more intense charged particle bombardment of its surface in the unprotected polar regions; sputtering then leads to redistribution of water molecules, with frost migrating to locally colder areas within the polar terrain.

Ganymede has a tenuous oxygen atmosphere that includes O, O2, and possibly O3 (ozone). But, the atmosphere is far too thin to support life as we know it. Another minor constituent of the Ganymedian atmosphere is atomic hydrogen. Ganymede probably formed by an accretion in Jupiter’s disk of gas and dust surrounding Jupiter after its formation. The accretion of Ganymede probably took about 10,000 years, much shorter than the 100,000 years estimated for Callisto. Ganymede formed closer to Jupiter then Callisto, where the disk was denser, which explains its shorter formation timescale. Several probes (Pioneer 10 and 11, Voyager 1 and 2, and Galileo) flying by or orbiting Jupiter have explored Ganymede. The next planned mission to the Jovian system is the Jupiter Icy Moon Explorer (JUICE), due to launch in 2022. After flybys of the other three Galilean moons, the probe is planned to enter orbit around Ganymede in 2032.

Image Credit: NASA/JPL The Galilean Moons of Jupiter The Galilean Moons of Jupiter Summary: Jupiter has more than 60 known moons, but understanding the geology of its four largest will hopefully lead to some groundbreaking discoveries. Sections: The Galilean Moons Each of the Jovian planets has a number of moons, although Jupiter has the most with more than 60 catalogued to date. Jupiter's 4 largest moons exhibit some of the most interesting geology in the solar system. They were discovered by Galileo Galilei and are known as the Galilean moons. Jupiter's largest moon, Ganymede, is larger than Mercury while the other three are larger than Pluto. Outward from Jupiter: Io: Volcanoes and All Jupiter's Moon Io The Voyager spacecraft took the first close-up images of Io more than 300 years after the moon's discovery. The images showed a surface with no signs of craters from past impacts. What we saw instead was a surface almost entirely covered with large volcanoes. Cameras on Voyager actually captured volcanic eruptions in progress.

The frequency of these sulfuric eruptions has filled in almost all of the impact craters and left Io with one of the youngest looking surfaces in the solar system. Io Close-Up (click to enlarge) Close-up photos of eruptions in progress show powerfully hot lava glowing orange and red. Photos taken on the night side of Io show not only the hot volcanic vents, but also a thin sulfur dioxide atmosphere produced by constant outgassing. Io's unusual red and orange colors come primarily from sulfur, which condenses on the surface after being outgassed by the volcanoes. Although there is no direct evidence of tectonic activity on Io, scientists feel confident it exists since the processes that fuel volcanism also fuel tectonics. The volcanic eruptions are so frequent and cover the surface so thoroughly that any clear evidence of tectonic activity is likely to be buried. Europa: What Lies Beneath? Europa Europa's surface and crust are made almost entirely of water ice, and its bizarre, fractured appearance is proof enough that tidal heating has acted there. The icy surface is nearly devoid of impact craters and may be only a few million years old.

Europa's Interior Observations made by the Galileo spacecraft show that Europa has a metallic core and a rocky mantle. Surrounding the rocky interior appears to be an icy layer 100 kilometers thick, the top few kilometers of which seem to be frozen solid. The stretching and squeezing of tidal friction should provide enough heat to melt some of this into liquid water beneath a thin ice shell. If it does, then Europa may have an ocean with more than twice as much liquid water as all of Earth's oceans combined. Analyzing Europa's Cracked Surface Close-up photos of the surface of Europa support the idea of a liquid ocean beneath the surface. These photos, taken by the Galileo spacecraft, show what appears to be icebergs stuck in a layer of ice. Other evidence comes from double-ridged cracks on the surface. Tidal flexing that allows water to well up and build ridges may create these cracks. Ganymede: Largest Moon in the Solar System Two Regions of Ganymede's Surface (click to enlarge) The surface of Ganymede shares many similarities with Europa. Ganymede's surface is also made of water ice, but unlike Europa's surface, it shows signs of varying age.

The darker regions are heavily cratered, suggesting they are billions of years old. The lighter regions show no signs of craters and it is thought that eruptions of water covered the surface before freezing over. These areas are geologically younger than the darker regions. If liquid water occasionally makes its way to the surface to fill in craters, could that suggest a liquid ocean similar to the one that might exist on Europa? Callisto: The Outermost Galilean Moon Callisto Callisto is the stereotypical outer solar system satellite. It is one of the largest and most heavily cratered satellites in the solar system. The surface is very icy and dates back four billion years. Beneath the icy crust is possibly a salty ocean supported by a deeper rocky interior. Callisto's Surface Callisto doesn't have any large mountains, show evidence of volcanic or tectonic activity or have any appreciable level of internal heat. Nonetheless, observations of Callisto's magnetic field may cause scientists to add the large moon to the list of possible worlds with subsurface salty oceans.

Space Today Online - Exploring Jupiter - JIMO - Jupiter Icy Moons Orbiter - the moon Ganymede The Jupiter Icy Moons Orbiter: Ganymede is the Largest Solar System Moon Jupiter's moon Ganymede Ganymede is not only the largest natural satellite of Jupiter, but also the largest moon in our Solar System. It's diameter is 3,280 miles. Ganymede could be classified as a planet if it orbited the Sun instead of the planet Jupiter. In fact, it's bigger than the planets Mercury and Pluto and almost as big as Mars. It's nearly half as big as Earth, which has a diameter of 7,926 miles. MOON DIAMETERS Ganymede would be the second moon explored by the Jupiter Icy Moons Orbiter, after Callisto. Above the surface. Until recently, scientists thought Ganymede has no atmosphere. Recently, however, the Hubble Space Telescope detected ozone at the surface of the big moon. Of course, the amount of ozone is small when compared to Earth. The ozone probably is produced when charged particles trapped in Jupiter's magnetic field fall on the moon's surface.

As the particles penetrate the ice, particles of water are disrupted leading to a chemical process generating ozone. If that assumption is correct, Ganymede probably has a thin oxygen atmosphere similar to that detected on the moon Europa. On the surface. Ganymede has mountains, valleys, craters and lava flows. It shows both dark and light regions. In the dark regions, the moon is more heavily cratered, which suggests an ancient origin. In the bright regions, the terrain is grooved with ridges and troughs. The ridges reach heights of several hundred feet and the grooves run for thousands of miles in complex patterns. The grooves probably were formed more recently than the dark cratered areas indicating Ganymede has had a complex geological history. Beneath the surface. Ganymede may be like Callisto with a crust of rock and ice, a water-ice mantle, and a rocky core. The moon has a low density, which suggests the core takes up about half of the satellite's diameter. The crust probably is a thick layer of water ice, and the mantle probably is ice and silicates. At some places the crust has spread and separated.

Surface of the moon Ganymede click to enlarge Galileo image A view of the surface. The NASA photo at right shows the surface of Jupiter's icy moon Ganymede as recorded by the Galileo spacecraft in 1996. The background image, behind the two panels, is a photo of Ganymede made in 1979 by the Voyager 2 spacecraft. The area shown in the Galileo photo is the Uruk Sulcus region of Ganymede. The picture covers about 75 by 68 miles, and was taken at a distance of 4,628 miles from Ganymede. The photo reveals the parallel ridges and troughs that are the principal features in the brighter regions of Ganymede's ice-rich surface. Resolution of the Galileo images is 243 feet per pixel, while resolution of the Voyager image is 4,224 feet per pixel. That means the Galileo photos are relatively high-resolution and the Voyager picture is low-resolution. Thus, the Voyager picture in the background appears fuzzy. Pixel is an abbreviation for the term picture element. A pixel is the smallest picture element of a digital image.

While individual pixels are too small to notice, together they make up an entire picture. Source: NASA Jet Propulsion Laboratory Diameters of the Largest Satellites and the Planets Jupiter's Moon Ganymede Has a Salty Ocean with More Water than Earth Jupiter's Moon Ganymede Has a Salty Ocean with More Water than Earth By Miriam Kramer, Space.com Staff Writer | March 12, 2015 01:50pm ET MORE In this artist’s conceptual illustration, the moon Ganymede orbits giant planet Jupiter. NASA’s Hubble Space Telescope detected auroras on the moon controlled by Ganymede's magnetic fields. Image released March 12, 2015. Credit: NASA/ESA A salty ocean is lurking beneath the surface of Jupiter's largest moon, Ganymede, scientists using the Hubble Space Telescope have found. The ocean on Ganymede — which is buried under a thick crust of ice — could actually harbor more water than all of Earth's surface water combined, according to NASA officials. Scientists think the ocean is about 60 miles (100 kilometers) thick, 10 times the depth of Earth's oceans, NASA added.

The new Hubble Space Telescope finding could also help scientists learn more about the plethora of potentially watery worlds that exist in the solar system and beyond. "The solar system is now looking like a pretty soggy place," Jim Green, NASA's director of planetary science, said during a news teleconference today (March 12). Scientists are particularly interested in learning more about watery worlds because life as we know it depends on water to thrive. [ See amazing photos of Ganymede ] Scientists have also found that Ganymede's surface shows signs of flooding. Young parts of Ganymede seen in a video map may have been formed by water bubbling up from the interior of the moon through faults or cryo-volcanos at some point in the moon's history, Green said. NASA Hubble Space Telescope images of Ganymede's auroral belts (colored blue in this illustration) lie on top of a Galileo orbiter image of the moon. The amount of rocking of the moon's magnetic field supplied evidence that the moon possesses a subsurface saltwater ocean. Image released March 12, 2015.

Credit: NASA/ESA Scientists have long suspected that there was an ocean of liquid water on Ganymede — the largest moon in the solar system, at about 3,273 miles (5,268 kilometers) across — has an ocean of liquid water beneath its surface. The Galileo probe measured Ganymede's magnetic field in 2002, providing some data supporting the theory that the moon has an ocean. The newly announced evidence from the Hubble telescope is the most convincing data supporting the subsurface ocean theory yet, according to NASA. Scientists used Hubble to monitor Ganymede's auroras, ribbons of light at the poles created by the moon's magnetic field. The moon's auroras are also affected by Jupiter's magnetic field because of the moon's proximity to the huge planet. When Jupiter's magnetic field changes, so does Ganymede's. Researchers were able to watch the two auroras "rock" back and forth with Hubble. Ganymede's aurora didn't rock as much as expected, so by monitoring that motion, the researchers concluded that a subsurface ocean was likely responsible for dampening the change in Ganymede's aurora created by Jupiter.

"I was always brainstorming how we could use a telescope in other ways," Joachim Saur, geophysicist and team leader of the new finding, said in a statement. "Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon's interior." Hunting for auroras on other worlds could potentially help identify water-rich alien planets in the future, Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy, said during the teleconference. Scientists might be able to search for rocking auroras on exoplanets that could potentially harbor water using the lessons learned from the Hubble observations of Ganymede. This cross-sectional illustration shows the interior of Jupiter's largest moon Ganymede, based on theoretical models, in-situ observations by NASA's Galileo orbiter, and Hubble Space Telescope observations of the moon’s magnetosphere. Image released March 12, 2015. Credit: NASA, ESA, and A.

Feild (STScI) Astronomers might be able to detect oceans on planets near magnetically active stars using similar methods to those used by Saur and his research team, Hammel added. "By monitoring auroral activity on exoplanets, we may be able to infer the presence of water on or within an exoplanet," Hammel said. "Now, it's not going to be easy — it's not as easy as Ganymede and Jupiter, and that wasn't easy. It may require a much larger telescope than Hubble, it may require some future space telescope, but nevertheless, it's a tool now that we didn't have prior to this work that Joachim and his team have done." Jupiter's moons are popular targets for future space missions. The European Space Agency is planning to send a probe called JUICE — short for JUpiter ICy moons Explorer — to Jupiter and its moons in 2022. JUICE is expected to check out Europa, Callisto and Ganymede during its mission. NASA also has its eye on the Jupiter system. Officials are hoping to send a probe to Europa by the mid-2020s.

NASA will also celebrate the Hubble telescope's 25th anniversary this year. "This discovery marks a significant milestone, highlighting what only Hubble can accomplish," John Grunsfeld, assistant administrator of NASA's Science Mission, said in the same statement . "In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system. A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth." Jupiter's largest moon has an ocean, say scientists - CSMonitor.com Jupiter's largest moon has an ocean, say scientists Latest News In this artist’s conceptual illustration, the moon Ganymede orbits giant planet Jupiter. NASA’s Hubble Space Telescope detected auroras on the moon controlled by Ganymede's magnetic fields. Image released March 12, 2015. NASA/ESA View Caption of A salty ocean is lurking beneath the surface of Jupiter 's largest moon, Ganymede, scientists using the Hubble Space Telescope have found. The ocean on Ganymede — which is buried under a thick crust of ice — could actually harbor more water than all of Earth's surface water combined, according to NASA officials.

Scientists think the ocean is about 60 miles (100 kilometers) thick, 10 times the depth of Earth's oceans, NASA added. The new Hubble Space Telescope finding could also help scientists learn more about the plethora of potentially watery worlds that exist in the solar system and beyond. "The solar system is now looking like a pretty soggy place," Jim Green , NASA's director of planetary science, said during a news teleconference today (March 12). Scientists are particularly interested in learning more about watery worlds because life as we know it depends on water to thrive. [ See amazing photos of Ganymede ] Recommended: Could you pass Astronomy 101? Take the quiz! Scientists have also found that Ganymede's surface shows signs of flooding. Young parts of Ganymede seen in a video map may have been formed by water bubbling up from the interior of the moon through faults or cryo-volcanos at some point in the moon's history, Green said.

Photos of the Day Photos of the Day 01/17 Scientists have long suspected that there was an ocean of liquid water on Ganymede — the largest moon in the solar system, at about 3,273 miles (5,268 kilometers) across — has an ocean of liquid water beneath its surface. The Galileo probe measured Ganymede's magnetic field in 2002, providing some data supporting the theory that the moon has an ocean. The newly announced evidence from the Hubble telescope is the most convincing data supporting the subsurface ocean theory yet, according to NASA. Scientists used Hubble to monitor Ganymede's auroras, ribbons of light at the poles created by the moon's magnetic field. The moon's auroras are also affected by Jupiter's magnetic field because of the moon's proximity to the huge planet. When Jupiter's magnetic field changes, so does Ganymede's. Researchers were able to watch the two auroras "rock" back and forth with Hubble.

Ganymede's aurora didn't rock as much as expected, so by monitoring that motion, the researchers concluded that a subsurface ocean was likely responsible for dampening the change in Ganymede's aurora created by Jupiter. "I was always brainstorming how we could use a telescope in other ways," Joachim Saur, geophysicist and team leader of the new finding, said in a statement. "Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon's interior." Hunting for auroras on other worlds could potentially help identify water-rich alien planets in the future, Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy, said during the teleconference. Scientists might be able to search for rocking auroras on exoplanets that could potentially harbor water using the lessons learned from the Hubble observations of Ganymede.

Astronomers might be able to detect oceans on planets near magnetically active stars using similar methods to those used by Saur and his research team, Hammel added. "By monitoring auroral activity on exoplanets, we may be able to infer the presence of water on or within an exoplanet," Hammel said. "Now, it's not going to be easy — it's not as easy as Ganymede and Jupiter, and that wasn't easy. It may require a much larger telescope than Hubble, it may require some future space telescope, but nevertheless, it's a tool now that we didn't have prior to this work that Joachim and his team have done." Jupiter's moons are popular targets for future space missions. The European Space Agency is planning to send a probe called JUICE — short for JUpiter ICy moons Explorer — to Jupiter and its moons in 2022. JUICE is expected to check out Europa, Callisto and Ganymede during its mission. NASA also has its eye on the Jupiter system. Officials are hoping to send a probe to Europa by the mid-2020s. NASA will also celebrate the Hubble telescope's 25th anniversary this year.

"This discovery marks a significant milestone, highlighting what only Hubble can accomplish," John Grunsfeld, assistant administrator of NASA's Science Mission, said in the same statement . "In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system. A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth."

Question: Ganymede is the largest moon of which planet?
Answer: Jupiter