Ganymede 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, 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.
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. Atomic
hydrogen is a minor atmospheric constituent.
Whether the satellite has an ionosphere associated
with its atmosphere is unresolved.
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,
due to launch in 2022. After flybys of all
three icy Galilean moons the probe is planned
to enter orbit around Ganymede.
Discovery and naming
On January 7, 1610, Galileo Galilei observed
what he believed were three stars near Jupiter,
including what turned out to be Ganymede,
Callisto, and one body that turned out to
be the combined light from Io and Europa;
the next night he noticed that they had moved.
On January 13, he saw all four at once for
the first time, but had seen each of the moons
before this date at least once. By January
15, Galileo came to the conclusion that the
stars were actually bodies orbiting Jupiter.
He claimed the right to name the moons; he
considered "Cosmian Stars" and settled on
"Medicean Stars".
The French astronomer Nicolas-Claude Fabri
de Peiresc suggested individual names from
the Medici family for the moons, but his proposal
was not taken up. Simon Marius, who had originally
claimed to have found the Galilean satellites,
tried to name the moons the "Saturn of Jupiter",
the "Jupiter of Jupiter", the "Venus of Jupiter",
and the "Mercury of Jupiter", another nomenclature
that never caught on. From a suggestion by
Johannes Kepler, Marius once again tried to
name the moons:
"... Then there was Ganymede, the handsome
son of King Tros, whom Jupiter, having taken
the form of an eagle, transported to heaven
on his back, as poets fabulously tell ...
the Third, on account of its majesty of light,
Ganymede ..."
This name and those of the other Galilean
satellites fell into disfavor for a considerable
time, and were not in common use until the
mid-20th century. In much of the earlier astronomical
literature, Ganymede is referred to instead
by its Roman numeral designation as Jupiter
III or as the "third satellite of Jupiter".
Following the discovery of moons of Saturn,
a naming system based on that of Kepler and
Marius was used for Jupiter's moons. Ganymede
is the only Galilean moon of Jupiter named
after a male figure — like Io, Europa,
and Callisto, he was a lover of Zeus.
Chinese astronomical records report that in
365 BC, Gan De detected what appears to have
been a moon of Jupiter, probably Ganymede,
with the naked eye.
Orbit and rotation
Ganymede orbits Jupiter at a distance of 1,070,400 km,
third among the Galilean satellites, and completes
a revolution every seven days and three hours.
Like most known moons, Ganymede is tidally
locked, with one side always facing toward
the planet. Its orbit is very slightly eccentric
and 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. The ranges of
change are 0.0009–0.0022 and 0.05–0.32°,
respectively. These orbital variations cause
the axial tilt to vary between 0 and 0.33°.
Ganymede participates in orbital resonances
with Europa and Io: for every orbit of Ganymede,
Europa orbits twice and Io orbits four times.
The superior conjunction between Io and Europa
always occurs when Io is at periapsis and
Europa at apoapsis. The superior conjunction
between Europa and Ganymede occurs when Europa
is at periapsis. The longitudes of the Io–Europa
and Europa–Ganymede conjunctions change
with the same rate, making the triple conjunctions
impossible. Such a complicated resonance is
called the Laplace resonance.
The current Laplace resonance is unable to
pump the orbital eccentricity of Ganymede
to a higher value. The value of about 0.0013
is probably a remnant from a previous epoch,
when such pumping was possible. The Ganymedian
orbital eccentricity is somewhat puzzling;
if it is not pumped now it should have decayed
long ago due to the tidal dissipation in the
interior of Ganymede. This means that the
last episode of the eccentricity excitation
happened only several hundred million years
ago. Because the orbital eccentricity of Ganymede
is relatively low—0.0015 on average—the
tidal heating of this moon is negligible now.
However, in the past Ganymede may have passed
through one or more Laplace-like resonances
that were able to pump the orbital eccentricity
to a value as high as 0.01–0.02. This probably
caused a significant tidal heating of the
interior of Ganymede; the formation of the
grooved terrain may be a result of one or
more heating episodes.
There are two hypotheses for the origin of
the Laplace resonance among Io, Europa, and
Ganymede: that it is primordial and has existed
from the beginning of the Solar System; or
that it developed after the formation of the
Solar System. A possible sequence of events
for the latter scenario is as follows: Io
raised tides on Jupiter, causing its orbit
to expand until it encountered the 2:1 resonance
with Europa; after that the expansion continued,
but some of the angular moment was transferred
to Europa as the resonance caused its orbit
to expand as well; the process continued until
Europa encountered the 2:1 resonance with
Ganymede. Eventually the drift rates of conjunctions
between all three moons were synchronized
and locked in the Laplace resonance.
Physical characteristics
Composition
The average density of Ganymede, 1.936 g/cm3,
suggests a composition of approximately equal
parts rocky material and water, which is mainly
in the form of ice. The mass fraction of ices
is between 46–50%, slightly lower than that
in Callisto. Some additional volatile ices
such as ammonia may also be present. The exact
composition of Ganymede's rock is not known,
but is probably close to the composition of
L/LL type ordinary chondrites, which are characterized
by less total iron, less metallic iron and
more iron oxide than H chondrites. The weight
ratio of iron to silicon is 1.05–1.27 in
Ganymede, whereas the solar ratio is around
1.8.
Ganymede's surface has an albedo of about
43%. Water ice seems to be ubiquitous on the
surface, with a mass fraction of 50–90%,
significantly more than in Ganymede as a whole.
Near-infrared spectroscopy has revealed the
presence of strong water ice absorption bands
at wavelengths of 1.04, 1.25, 1.5, 2.0 and
3.0 μm. The grooved terrain is brighter
and has more icy composition than the dark
terrain. The analysis of high-resolution,
near-infrared and UVspectra obtained by the
Galileo spacecraft and from the ground has
revealed various non-water materials: carbon
dioxide, sulfur dioxide and, possibly, cyanogen,
hydrogen sulfate and various organic compounds.
Galileo results have also shown magnesium
sulfate and, possibly, sodium sulfate on Ganymede's
surface. These salts may originate from the
subsurface ocean.
The Ganymedian surface is asymmetric; the
leading hemisphere is brighter than the trailing
one. This is similar to Europa, but the reverse
is true for Callisto. The trailing hemisphere
of Ganymede appears to be enriched in sulfur
dioxide. The distribution of carbon dioxide
does not demonstrate any hemispheric asymmetry,
although it is not observed near the poles.
Impact craters on Ganymede do not show any
enrichment in carbon dioxide, which also distinguishes
it from Callisto. Ganymede's carbon dioxide
gas was probably depleted in the past.
Internal structure
Ganymede appears to be fully differentiated,
consisting of an iron sulfide–iron core
and a silicate mantle. The precise thicknesses
of the different layers in the interior of
Ganymede depend on the assumed composition
of silicates and amount of sulfur in the core.
Subsurface oceans
NASA scientists, in the 1970s, first suspected
a thick ocean in Ganymede between just two
layers of ice, one on the top and one on the
bottom. In the 1990s, NASA's Galileo mission
flew by Ganymede, confirming the moon's ocean.
An analysis published in 2014, taking into
account the 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. Water–rock contact may
be an important factor in the origin of life.
Core
Ganymede has the lowest moment of inertia
among the solid Solar System bodies. The existence
of a liquid, iron-rich core provides a natural
explanation for the intrinsic magnetic field
of Ganymede detected by Galileo spacecraft.
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 5.5–6 g/cm3
and the silicate mantle is 3.4–3.6 g/cm3.
The radius of this core may be up to 500 km.
The temperature in the core of Ganymede is
probably 1500–1700 K and pressure up to
10 GPa.
Surface features
The Ganymedian surface is a mix of two types
of terrain: very old, highly cratered, dark
regions and somewhat younger, lighter regions
marked with an extensive array of grooves
and ridges. The dark terrain, which comprises
about one-third of the surface, contains clays
and organic materials that could indicate
the composition of the impactors from which
Jovian satellites accreted.
The heating mechanism required for the formation
of the grooved terrain on Ganymede is an unsolved
problem in the planetary sciences. The modern
view is that the grooved terrain is mainly
tectonic in nature. Cryovolcanism is thought
to have played only a minor role, if any.
The forces that caused the strong stresses
in the Ganymedian ice lithosphere necessary
to initiate the tectonic activity may be connected
to the tidal heating events in the past, possibly
caused when the satellite passed through unstable
orbital resonances. The tidal flexing of the
ice may have heated the interior and strained
the lithosphere, leading to the development
of cracks and horst and graben faulting, which
erased the old, dark terrain on 70% of the
surface. The formation of the grooved terrain
may also be connected with the early core
formation and subsequent tidal heating of
Ganymede's interior, which may have caused
a slight expansion of Ganymede by 1–6% due
to phase transitions in ice and thermal expansion.
During subsequent evolution deep, hot water
plumes may have risen from the core to the
surface, leading to the tectonic deformation
of the lithosphere. Radiogenic heating within
the satellite is the most relevant current
heat source, contributing, for instance, to
ocean depth. Research models have found that
if the orbital eccentricity were an order
of magnitude greater than currently, tidal
heating would be a more substantial heat source
than radiogenic heating.
Cratering is seen on both types of terrain,
but is especially extensive on the dark terrain:
it appears to be saturated with impact craters
and has evolved largely through impact events.
The brighter, grooved terrain contains many
fewer impact features, which have been only
of a minor importance to its tectonic evolution.
The density of cratering indicates an age
of 4 billion years for the dark terrain,
similar to the highlands of the Moon, and
a somewhat younger age for the grooved terrain.
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 both overlay and
are crosscut by the groove systems, indicating
that some of the grooves are quite ancient.
Relatively young craters with rays of ejecta
are also visible. Ganymedian craters are flatter
than those on the Moon and Mercury. This is
probably due to the relatively weak nature
of Ganymede's icy crust, which can flow and
thereby soften the relief. Ancient craters
whose relief has disappeared leave only a
"ghost" of a crater known as a palimpsest.
One significant feature on Ganymede is a dark
plain named Galileo Regio, which contains
a series of concentric grooves, or furrows,
likely created during a period of geologic
activity.
Ganymede also has polar caps, likely composed
of water frost. The frost extends to 40°
latitude. These polar caps were first seen
by the Voyager spacecraft. Theories on the
formation of the caps include the migration
of water to higher latitudes and bombardment
of the ice by plasma. Data from Galileo suggests
the latter is correct. 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.
Atmosphere and ionosphere
In 1972, a team of Indian, British and American
astronomers working at Java and Kavalur claimed
that they had detected a thin atmosphere around
the satellite during an occultation, when
it and Jupiter passed in front of a star.
They estimated that the surface pressure was
around 0.1 Pa. However, in 1979 Voyager 1
observed an occultation of a star during its
flyby of the planet, with differing results.
The occultation measurements were conducted
in the far-ultraviolet spectrum at wavelengths
shorter than 200 nm; they were much more
sensitive to the presence of gases than the
1972 measurements in the visible spectrum.
No atmosphere was revealed by the Voyager
data. The upper limit on the surface particle
number density was found to be 1.5 × 109
cm−3, which corresponds to a surface pressure
of less than 2.5 µPa. The latter value is
almost five orders of magnitude less than
the 1972 estimate.
Despite the Voyager data, evidence for a tenuous
oxygen atmosphere on Ganymede, very similar
to the one found on Europa, was found by the
Hubble Space Telescope in 1995. HST actually
observed airglow of atomic oxygen in the far-ultraviolet
at the wavelengths 130.4 nm and 135.6 nm.
Such an airglow is excited when molecular
oxygen is dissociated by electron impacts,
evidence of a significant neutral atmosphere
composed predominantly of O2 molecules. The
surface number density probably lies in the
1.2 × 108–7 × 108 cm−3 range, corresponding
to the surface pressure of 0.2–1.2 µPa.
These values are in agreement with the Voyager's
upper limit set in 1981. The oxygen is not
evidence of life; it is thought to be produced
when water ice on Ganymede's surface is split
into hydrogen and oxygen by radiation, with
the hydrogen then being more rapidly lost
due to its low atomic mass. The airglow observed
over Ganymede is not spatially homogeneous
like that over Europa. HST observed two bright
spots located in the northern and southern
hemispheres, near ± 50° latitude, which
is exactly the boundary between the open and
closed field lines of the Ganymedian magnetosphere.
The bright spots are probably polar auroras,
caused by plasma precipitation along the open
field lines.
The existence of a neutral atmosphere implies
that an ionosphere should exist, because oxygen
molecules are ionized by the impacts of the
energetic electrons coming from the magnetosphere
and by solar EUV radiation. However, the nature
of the Ganymedian ionosphere is as controversial
as the nature of the atmosphere. Some Galileo
measurements found an elevated electron density
near Ganymede, suggesting an ionosphere, whereas
others failed to detect anything. The electron
density near the surface is estimated by different
sources to lie in the range 400–2,500 cm−3.
As of 2008, the parameters of the ionosphere
of Ganymede are not well constrained.
Additional evidence of the oxygen atmosphere
comes from spectral detection of gases trapped
in the ice at the surface of Ganymede. The
detection of ozone bands was announced in
1996. In 1997 spectroscopic analysis revealed
the dimer absorption features of molecular
oxygen. Such an absorption can arise only
if the oxygen is in a dense phase. The best
candidate is molecular oxygen trapped in ice.
The depth of the dimer absorption bands depends
on latitude and longitude, rather than on
surface albedo—they tend to decrease with
increasing latitude on Ganymede, whereas O3
shows an opposite trend. Laboratory work has
found that O2 would not cluster or bubble
but dissolve in ice at Ganymede's relatively
warm surface temperature of 100 K.
A search for sodium in the atmosphere, just
after such a finding on Europa, turned up
nothing in 1997. Sodium is at least 13 times
less abundant around Ganymede than around
Europa, possibly because of a relative deficiency
at the surface or because the magnetosphere
fends off energetic particles. Another minor
constituent of the Ganymedian atmosphere is
atomic hydrogen. Hydrogen atoms were observed
as far as 3,000 km from Ganymede's surface.
Their density on the surface is about 1.5 × 104 cm−3.
Magnetosphere
The Galileo craft made six close flybys of
Ganymede from 1995–2000 and discovered that
Ganymede has a permanent magnetic moment independent
of the Jovian magnetic field. The value of
the moment is about 1.3 × 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. Its north
pole lies below the orbital plane. The dipole
magnetic field created by this permanent moment
has a strength of 719 ± 2 nT at Ganymede's
equator, which should be compared with the
Jovian magnetic field at the distance of Ganymede—about
120 nT. The equatorial field of Ganymede
is directed against the Jovian field, meaning
reconnection is possible. The intrinsic field
strength at the poles is two times that at
the equator—1440 nT.
The permanent magnetic moment carves a part
of space around Ganymede, creating a tiny
magnetosphere embedded inside that of Jupiter;
it is the only moon in the Solar System known
to possess the feature. Its diameter is 4–5 RG.
The Ganymedian magnetosphere has a region
of closed field lines located below 30° latitude,
where charged particles are trapped, creating
a kind of radiation belt. The main ion species
in the magnetosphere is single ionized oxygen—O+—which
fits well with Ganymede's tenuous oxygen atmosphere.
In the polar cap regions, at latitudes higher
than 30°, magnetic field lines are open,
connecting Ganymede with Jupiter's ionosphere.
In these areas, the energetic electrons and
ions have been detected, which may cause the
auroras observed around the Ganymedian poles.
In addition, heavy ions continuously precipitate
on Ganymede's polar surface, sputtering and
darkening the ice.
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. The main difference is the
speed of plasma flow—supersonic in the case
of Earth and subsonic in the case of Ganymede.
Because of the subsonic flow, there is no
bow shock off the trailing hemisphere of Ganymede.
In addition to the intrinsic magnetic moment,
Ganymede has an induced dipole magnetic field.
Its existence is connected with the variation
of the Jovian magnetic field near Ganymede.
The induced moment is directed radially to
or from Jupiter following the direction of
the varying part of the planetary magnetic
field. The induced magnetic moment is an order
of magnitude weaker than the intrinsic one.
The field strength of the induced field at
the magnetic equator is about 60 nT—half
of that of the ambient Jovian field. 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.
Given that Ganymede is completely differentiated
and has a metallic core, its intrinsic magnetic
field is probably generated in a similar fashion
to the Earth's: as a result of conducting
material moving in the interior. The magnetic
field detected around Ganymede is likely to
be caused by compositional convection in the
core, if the magnetic field is the product
of dynamo action, or magnetoconvection.
Despite the presence of an iron core, Ganymede's
magnetosphere remains enigmatic, particularly
given that similar bodies lack the feature.
Some research has suggested that, given its
relatively small size, the core ought to have
sufficiently cooled to the point where fluid
motions and a magnetic field would not be
sustained. One explanation is that the same
orbital resonances proposed to have disrupted
the surface also allowed the magnetic field
to persist: with Ganymede's eccentricity pumped
and tidal heating increased 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.
Origin and evolution
Ganymede probably formed by an accretion in
Jupiter's subnebula, a 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. The Jovian subnebula
may have been relatively "gas-starved" when
the Galilean satellites formed; this would
have allowed for the lengthy accretion times
required for Callisto. In contrast Ganymede
formed closer to Jupiter, where the subnebula
was denser, which explains its shorter formation
timescale. This relatively fast formation
prevented the escape of accretional heat,
which may have led to ice melt and differentiation:
the separation of the rocks and ice. The rocks
settled to the center, forming the core. In
this respect, Ganymede is different from Callisto,
which apparently failed to melt and differentiate
early due to loss of the accretional heat
during its slower formation. This hypothesis
explains why the two Jovian moons look so
dissimilar, despite their similar mass and
composition. Alternative theories explain
Ganymede's greater internal heating on the
basis of tidal flexing or more intense pummeling
by impactors during the Late Heavy Bombardment.
After formation, the Ganymedian core largely
retained the heat accumulated during accretion
and differentiation, only slowly releasing
it to the ice mantle like a kind of thermal
battery. The mantle, in turn, transported
it to the surface by convection. Soon the
decay of radioactive elements within rocks
further heated the core, causing increased
differentiation: an inner, iron–iron sulfide
core and a silicate mantle formed. With this,
Ganymede became a fully differentiated body.
By comparison, the radioactive heating of
undifferentiated Callisto caused convection
in its icy interior, which effectively cooled
it and prevented large-scale melting of ice
and rapid differentiation. The convective
motions in Callisto have caused only a partial
separation of rock and ice. Today, Ganymede
continues to cool slowly. The heat being released
from its core and silicate mantle enables
the subsurface ocean to exist, whereas the
slow cooling of the liquid Fe–FeS core causes
convection and supports magnetic field generation.
The current heat flux out of Ganymede is probably
higher than that out of Callisto.
Coordinate system
A crater named Anat provides the reference
point for measuring longitude on Ganymede.
By definition, Anat is at 128 degrees longitude.
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.
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 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.
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, 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, 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,
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 mission, with
emphasis in astrobiology. The Ganymede Lander
would be a partner mission for JUpiter ICy
moon Explorer. 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.
See also
Jupiter's moons in fiction
List of craters on Ganymede
List of geological features on Ganymede
Lunar and Planetary Institute
Notes
References
External links
Ganymede Profile at NASA's Solar System Exploration
site
Ganymede page at The Nine Planets
Ganymede page at Views of the Solar System
Ganymede Crater Database from the Lunar and
Planetary Institute
Images of Ganymede at JPL's Planetary Photojournal
Movie of Ganymede's rotation from the National
Oceanic and Atmospheric Administration
Ganymede map from Scientific American article
Ganymede map with feature names from Planetary
Photojournal
Ganymede nomenclature and Ganymede map with
feature names from the USGS planetary nomenclature
page
Paul Schenk's 3D images and flyover videos
of Ganymede and other outer solar system satellites
"Terraforming Ganymede with Robert A. Heinlein",
article by Gregory Benford, 2011
Part 2
Ganymede Orbiter Concept
Global Geologic Map of Ganymede
