Space Science---------Ganymede: Facts About Jupiter's Largest Moon

Ganymede:Facts About Jupiter's Largest Moon 

Ganymede (Jupiter III) is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively. It has a diameter of 5,268 km (3,273 mi), 8% larger than that of the planet Mercury, but has only 45% of the latter's mass. Its diameter is 2% larger than that of Saturn's Titan, the second largest moon. It also has the highest mass of all planetary satellites, with 2.02 times the mass of the Earth's moon.

Enhanced-color Galileo spacecraft image of Ganymede's trailing hemisphere.The crater Tashmetum's prominent rays are at lower right, and the large ejecta field of Hershef at upper right. Part of dark Nicholson Regio is at lower left, bounded on its upper right by Harpagia Sulcus.

Ganymede is composed of approximately equal amounts of silicate rock and water ice. It is a fully differentiated body with an iron-rich, liquid core, and it might have ice and oceans stacked up in several layers.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 is not fully known, but was likely the result of tectonic activity brought about by tidal heating.

Ganymede is the only moon in the Solar System known to possess a magnetosphere, likely created through convection within the liquid iron core.The meager magnetosphere is buried within Jupiter's much larger magnetic field and would show only as a local perturbation of the field lines. The satellite has a thin oxygen atmosphere that includes O, O2, and possibly O3 (ozone).Atomic hydrogen is a minor atmospheric constituent. Whether the satellite has an ionosphere associated with its atmosphere is unresolved.

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).

Ganymede's discovery is credited to Galileo Galilei, who was the first to observe it on January 7, 1610.The satellite's name was soon suggested by astronomer Simon Marius, for the mythological Ganymede, cupbearer of the Greek gods and Zeus's lover. Beginning with Pioneer 10, spacecraft have been able to examine Ganymede closely.The Voyager probes refined measurements of its size, whereas the Galileo craft discovered its underground ocean and magnetic field. The next planned mission to the Jovian system is the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022. After flybys of all three icy Galilean moons the probe is planned to enter orbit around Ganymede.

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.

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 km). It takes Ganymede about seven Earth days to orbit Jupiter.

Size: Ganymede’s mean radius is 1,635 miles (2,631.2 km). Due to its size, Ganymede can be viewed with the naked eye. Early Chinese astronomical records show the discovery of a moon of Jupiter, mostly likely the first observation of Ganymede. Although Ganymede is larger than Mercury it only has half its mass, classifying it as low density.

Temperature: Daytime temperatures on the surface average -171F to -297F, and night temperatures drop to -193C. It is unlikely that any living organisms inhabit Ganymede.
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).

The Discovery 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.

Ganymede’s Name

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.

Exploration of Ganymede

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.

Pioneer 10 approached in 1973 and Pioneer 11 in 1974, and they returned information about the satellite.This included more specific determination on physical characteristics and resolving features to 400 km (250 mi) on its surface.Pioneer 10's closest approach was 446,250 km.

Voyager 1 and Voyager 2 were next, passing by Ganymede in 1979. They refined its size, revealing it was larger than Saturn's moon Titan, which was previously thought to have been bigger.The grooved terrain was also seen.

Size comparison of Earth, the Moon, and Ganymede.

In 1995, the Galileo spacecraft entered orbit around Jupiter and between 1996 and 2000 made six close flybys to explore Ganymede.These flybys are G1, G2, G7, G8, G28 and G29.During the closest flyby—G2—Galileo passed just 264 km from the surface of Ganymede.During a G1 flyby in 1996, the Ganymedian magnetic field was discovered,[86] while the discovery of the ocean was announced in 2001.Galileo transmitted a large number of spectral images and discovered several non-ice compounds on the surface of Ganymede.The most recent spacecraft to explore Ganymede up close was New Horizons, which passed by in 2007 on its way to Pluto. New Horizons made topography and composition maps of Ganymede as it sped by.

Mission concepts

The Europa Jupiter System Mission (EJSM), had a proposed launch date in 2020, and was a joint NASA and ESA proposal for exploration of many of Jupiter's moons including Ganymede. In February 2009 it was announced that ESA and NASA had given this mission priority ahead of the Titan Saturn System Mission.EJSM consisted of the NASA-led Jupiter Europa Orbiter, the ESA-led Jupiter Ganymede Orbiter, and possibly a JAXA-led Jupiter Magnetospheric Orbiter. ESA's contribution faced funding competition from other ESA projects but on 2 May 2012 the European part of the mission, renamed Jupiter Icy Moon Explorer (JUICE), obtained a L1 launch slot in 2022 with a Ariane 5 in the ESA's Cosmic Vision science programme.The spacecraft will orbit Ganymede and conduct multiple flyby investigations of Callisto and Europa.

The Russian Space Research Institute is currently evaluating the Ganymede Lander (GL) mission, with emphasis in astrobiology.The Ganymede Lander would be a partner mission for JUpiter ICy moon Explorer (JUICE).If selected, it would be launched in 2024, though this schedule might be revised and aligned with JUICE.

A Ganymede orbiter based on the Juno probe was proposed in 2010 for the Planetary Science Decadal Survey.Possible instruments include Medium Resolution Camera, Flux Gate Magnetometer, Visible/NIR Imaging Spectrometer, Laser Altimeter, Low and High Energy Plasma Packages, Ion and Neutral Mass Spectrometer, UV Imaging Spectrometer, Radio and Plasma Wave sensor, Narrow Angle Camera, and a Sub-Surface Radar.

Another canceled proposal to orbit Ganymede was the Jupiter Icy Moons Orbiter. It was designed to use nuclear fission for power, ion engine propulsion, and would have studied Ganymede in greater detail than previously.However, the mission was canceled in 2005 because of budget cuts.Another old proposal was called The Grandeur of Ganymede.

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.

The Laplace resonances of Ganymede, Europa, and Io.

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 has 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.

Forty percent of the surface of Ganymede is covered by highly cratered dark regions, and the remaining sixty percent is covered by a light grooved terrain, which forms intricate patterns across Ganymede.

It is believed that Ganymede has a saltwater ocean 124 miles below its surface, compared to Europa, which has an extensive ocean closer to the surface.

Ganymede’s Atmosphere

Ganymede has a thin oxygen atmosphere – too thin to support life. It 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.

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