Jupiter 1
Data
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Name – The planet Jupiter is named after the king of the gods in Roman mythology.
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Size 2 – Jupiter is the largest planet in the solar system, measuring 88,850 miles in
diameter.
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Location – Jupiter is the fifth planet from the Sun, with an average distance of
approximately 484 million miles.
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Orbital period – 11.86 years.
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Rotational period – 9.83 hours.
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Number of Satellites – 67 known moons.
Atmosphere
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Composition – Jupiter’s atmosphere is primarily composed of hydrogen (88-92%)
and helium (8-12%).
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Trace Constituents – Jupiter’s atmosphere also contains trace amounts of
methane, ammonia, hydrogen deuteride, ethane, water, carbon, hydrogen sulfide,
neon, oxygen, phosphine, sulfur, and silicon-based compounds. Traces of
hydrocarbons (hydrogen-carbon compounds), such as acetylene and benzene have
also been found. The Sun’s ultraviolet radiation breaks down the methane in
Jupiter’s atmosphere to form these hydrocarbons. This process, known as
photochemistry, is also responsible for the formation of the Earth’s ozone layer,
the sulfuric acid clouds of Venus, and the trace constituents within the
atmospheres of Saturn, Uranus, and Neptune. In addition, lightning (up to a
thousand times more powerful than lightning on Earth) observed within the
clouds of Jupiter may contribute to the formation of hydrocarbons.
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Hydrogen-Helium Rich Atmosphere – Because of Jupiter’s strong gravitational
force and the cold temperatures (-150º F) associated with the planet’s distance
from the Sun, the retention of a hydrogen-helium rich atmosphere is possible.
(The atmospheres of Saturn, Uranus and Neptune are also hydrogen-helium rich
for the same reasons.)
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Circulation – The structure of Jupiter’s atmosphere is related to its circulation.
Jupiter exhibits a constantly shifting pattern of clouds, but its overall appearance is
characterized by a fairly constant pattern of alternating bright and dark bands 3. The
formation and stability of these bands are due to the planet’s high rotation rate and
lack of a solid (obstructive) surface. (These reasons also apply to bands found within
the atmospheres of Saturn, Uranus, and Neptune.) The variation in their brightness is
associated with the boundaries of convection cells. The bright bands, referred to as
zones, are associated with the upwelling portions of the convection cells, while the
dark bands, referred to as belts, are associated with the downwelling portions 4.
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Colored Clouds 5 – Jupiter’s atmosphere consists of layers of clouds of varying color.
Temperature, pressure, gas composition and abundances determine the characteristics
of these clouds. Moreover, many of the color differences may be the result of
observing to varying depths. Specifically, clouds composed of ammonia-ice crystals
characterize the upper, colder levels of Jupiter’s atmosphere. At deeper, warmer
levels, sulfur compounds may be responsible for the yellow, beige and dark brown
colored clouds.
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Brown Ovals 6 – Brown ovals observed in Jupiter’s atmosphere could be openings
in the upper cloud deck where warmer cloud levels may exist. Features of this
type have an average lifetime of one to two years.
Storms 7 – The most striking feature of Jupiter’s atmosphere is the Great Red Spot.
First observed over 350 years ago, it appears to be a hurricane-like storm, with wind
speeds up to 400 miles/hour 8. The Great Red Spot most likely originated from an
eddy between counter-flowing eastward and westward winds, called zonal jets 9. Its
dimensions are about 16,000 by 9,000 miles, making it large enough to accommodate
two planets the size of our Earth side-by-side 10. The chemicals responsible for the
reddish color of the Great Red Spot are unknown. However, red phosphorous,
complex organic compounds, and sulfur compound have been considered. In 1938,
three smaller storms referred to as white ovals 11 were discovered within Jupiter’s
atmosphere. By 2000, they merged to form a single storm (Earth-size), increasing in
intensity, and changing color from white to red. Though formally named Oval BA, it
has been nicknamed “Red Spot Jr.” 12.
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Longevity – Why are storms on Jupiter so long-lived? On Earth, powerful storms
such as hurricanes dissipate when they traverse land. Without the condensation of
water vapor (condensation releases energy) that comes from the oceans, these
storms lose their energy. On Jupiter, there are no continents, and once these
storms grow large enough to overcome the effects of encounters with smaller
systems, they can persist for long periods of time. Moreover, internal heat
(discussed later) may be a source of power for Jupiter’s atmospheric winds and
storms.
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Interior
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Model – Since Jupiter lacks a solid surface, seismic data cannot be obtained to reveal
properties of the planet’s interior. However, it is possible to construct a plausible
model of Jupiter’s interior from data derived from remote surveys. The distribution
and state of matter inside of Jupiter can be determined from information such as
density (1.31 g/cm3), mass, radius, rotation rate, heat balance, and atmospheric
composition.
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Composition and Structure 13 – Jupiter’s interior has no well-defined boundaries.
Instead, with increasing depth, there is fairly gradual transition of the materials that
make up its interior. Although Jupiter is differentiated, these changes are primarily
related to an increase of pressure and temperature.
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Liquid Molecular Hydrogen – Below Jupiter’s atmosphere the pressure is high
enough to cause molecular hydrogen gas to be liquefied, and therefore produce a
layer referred to as liquid molecular hydrogen (H2).
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Liquid Metallic Hydrogen – Eventually, with increasing depth, the pressure and
temperature become high enough to cause electrons to break free of the hydrogen
nuclei, thus forming ionized hydrogen (atoms missing electrons so that they have
net positive charge). The liquid hydrogen then has the conductivity of metals,
producing a layer referred to as liquid metallic hydrogen.
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Magnetic Field – Jupiter has a strong magnetic field, with an intrinsic strength
19,000 times greater than the Earth. The origin of Jupiter’s magnetic field is
the liquid metallic hydrogen layer. This layer has the necessary properties for
the formation of a planetary magnetic field – metallic, liquid phase, and
convective processes (a dynamo) generated by Jupiter’s high rotation rate.
Core – It is speculated that Jupiter’s core is 10 to 20 times the mass of the Earth,
and mainly composed of silicate rock and ice. The rock may include some nickeliron and the ice may be a mixture of water, ammonia and methane. Although, the
temperature within the core is calculated to be about 50,000 F, the pressure
(about 100 million bars) is so high that the core material remains in a solid state.
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Liquid Planets – Although Jupiter and the other Jovian planets are often referred to as
the gas giants, in actuality they are mainly composed of material in a liquid state.
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Internal Energy – Jupiter radiates twice as much energy as it receives from the Sun.
However, this energy is released as infrared radiation (heat energy), not visible light.
The source of this energy is derived from the planet’s continuing contraction (referred
to as the Kelvin-Helmholtz mechanism) from a protoplanetary phase. In other words,
Jupiter’s mass is moving inward under the influence of gravity, and the resulting
energy of motion (kinetic energy) is transformed into heat. This process results in the
planet shrinking by about 2 cm each year.
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Ring System
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Discovery and Observations – Although the ring system of Jupiter was discovered by
the Voyager mission in 1979, data derived from the Pioneer mission in 1974
suggested the possibility of its existence. Jupiter’s rings can be seen by ground-based
telescopes, but only barely. Because of their tenuous nature, most probe images of
the rings were acquired by forward-scattering light (light redirected slightly by
diffraction off its path from the Sun) rather than reflected light 14.
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Composition and Structure 15 – Jupiter’s ring system is mainly composed of dark
silicate dust (about the size of cigarette smoke particles), and is divided into three
components: main ring, halo, and gossamer ring.
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Origin – The origin of Jupiter’s ring system is the result of the ejection of dust from
the surfaces of some of the planet’s minor moons by a combination of small impacts
and the blasting by atomic particles of Jupiter’s magnetosphere. Because of the small
size of the ring particles, they easily acquire a small electrical charge from interaction
with Jupiter’s magnetosphere, and the mutual repulsive force of these charge particles
lifts them out of the ring plane. As a result, dust is continuously swept away, but is
replenished by new particles eroded from the small satellites.
Moons
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Galilean Satellites 16 – One of Galileo’s telescopic discoveries was the four major
moons of Jupiter. They are known collectively as the Galilean satellites, in honor of
their discoverer. In order of increasing distance from Jupiter, they are: Io, Europa,
Ganymede, and Callisto 17. The Galilean satellites most likely originated from the
coalescence of a disk of gas and dust (referred to a protosatellite nebula) surrounding
Jupiter very early in its history. Their diameters range from about 1900 miles to
nearly 3300 miles. Ganymede is not only the largest moon of Jupiter, but also the
largest moon in the solar system, exceeding the size of Mercury. The density of the
four moons decreases with distance from Jupiter. Specifically, Io’s density (3.53
g/cm3) is intermediate between rock and iron, whereas Callisto’s density (1.83 g/cm3)
is intermediate between ice and rock. Evidence indicates that Callisto is partially
differentiated. In contrast, the interiors of Io, Europa, and Ganymede appear to be
differentiated. The current model is that these three moons experience tidal heating
(discussed later) as a result of Jupiter’s gravitational field. Moreover, the nearer the
moon is to Jupiter, the hotter the interior. In all but Callisto, this will have melted the
interior ice, allowing rock and iron to sink to the interior and water to cover the
surface. In Ganymede a thick and solid ice crust then formed. In warmer Europa a
thinner more easily broken crust formed. In Io the heating is so extreme that all the
rock has melted and all the water has long ago boiled out into space.
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Io 18 – With over 400 active volcanoes, Io is the most volcanically active object in
the solar system. No impact craters have been observed on the moon, indicating
that the surface is very young (probably less than one million years old). Io is
capable of erasing its craters as fast as they are formed. Unlike the Earth, Io’s
main source of internal heat comes from tidal flexing rather than radioactive
isotope decay. Because of Jupiter’s strong gravitation, Io has developed a large
tidal bulge. In addition, gravitational interactions in the satellite system have
made Io’s orbit eccentric, thus varying the distance between Jupiter and Io and
thereby causing the height of the tidal bulge to fluctuate by about 300 feet. As Io
orbits Jupiter, the bulge moves, flexes the crust, and heats Io's interior (like a
paper clip bent rapidly back and forth), providing abundant molten material for
the intense volcanic activity associated with the moon.
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Color 19 – The surface of Io exhibits a variety of colors. The yellow, red,
black, and green are most likely attributed to allotropes (elemental sulfur,
which has the property of taking on many colored forms depending on its
temperature and the way it is cooled from the liquid state) and sulfur
compounds. The white areas on Io most likely originate from the ejected gas
of plumes, which freezes when released into the cold of space and falls back
onto Io’s surface as sulfur dioxide frost.
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Plume Eruptions 20, 21 – The largest volcanic events on Io are the plume
eruptions. Similar to geysers on Earth, plume eruptions spray about 100,000
tons of material each second, enough to alter the color of an area of thousands
of square miles in a few weeks. Plume eruptions take place when lava flows
encounter the thick deposits of frozen sulfur dioxide. They are similar to the
explosive eruptions that sometimes occur when terrestrial lava flows meet
bodies of ice or water. However, on Io, where the temperatures are lower and
there is almost no atmosphere, the plumes can shoot up to tremendous heights
(up to 300 miles).
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Paterae 22 – Io’s surface is dotted with volcanic depressions known as paterae.
Resembling terrestrial calderas, paterae generally have flat floors bounded by
steep walls. However, they do not lie at the peak of volcanoes and are
typically larger. The formation mechanism of paterae is unclear, but may
relate to volcanic sills – layers of subsurface molten rock.
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Lava Flows 23 – Lava flows represent another major volcanic feature on Io.
Magma erupts onto the surface from vents on the floors of paterae or on the
plains from fractures. Earth-based infrared studies and measurements from
the Galileo spacecraft indicate that these flows are composed of basaltic lava.
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Mountains 24 – Io has more than 100 mountains, some of which are taller than
Mount Everest. Most of these mountains are tectonic structures, and form as
the result of compressive stresses on the base of the lithosphere, which uplift
and tilt chunks of Io’s crust. A handful of mountains on Io appear to have a
volcanic origin, resembling small shield volcanoes.
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Europa 25 – Europa’s surface is extremely smooth with few features exceeding a
few hundred feet in height. It is the brightest of any of the Galilean satellites,
composed of relatively pure water-ice. Moreover, there are very few craters on
Europa; only three craters larger than about 3 miles in diameter have been
observed. These characteristics suggest a continuing process that resurfaces the
moon with fresh material below. Like Io, Europa is subjected to tidal heating, but
because Europa is further from Jupiter than Io the tidal effect is less dramatic.
Specifically, the effect of the tides induced by Jupiter heats the interior of Europa
sufficiently to keep the surface soft. Therefore, no vertical relief features can
survive for long on Europa's surface, explaining its smoothness.
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Chaos Terrain 26 – Although Europa mainly consists of smooth terrain, a few
percent of the moon’s surface has been subjected to geological deformation.
Referred to as chaos terrain, these areas formed when the ice crust was broken
into pieces (hundreds of feet to a few miles across), and then rotated or tilted
as if they were icebergs floating in an ocean. However, these icebergs are not
free-floating today, but embedded within younger ice.
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Lineae 27 – Europa’s most striking surface features are a series of dark,
reddish-brown streaks (possibly colored by sulfur compounds) crisscrossing
the entire globe, called lineae (English: lines). Lineae may have been
produced by a series of eruptions of warm ice as the Europa’s crust spread
open to expose warmer layers beneath. The effect would have been similar to
that seen in Earth’s oceanic ridges. Furthermore, studies of Voyager and
Galileo images have revealed evidence of subduction on Europa’s surface,
suggesting that, just as the lineae are analogous to ocean ridges of diverging
plates, so these areas are analogous to converging plates. It has been proposed
that heat from tidal flexing, which causes the ocean to remain liquid, also
drives geological activity similar to plate tectonics.
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Life? – Evidence suggests that there is a large ocean of liquid water below
Europa’s ice crust 28. A global ocean and an internal heat source have made
Europa a target of prime interest in the search for extraterrestrial life. Like
life associated with hydrothermal vents on the Earth’s ocean floor, life on
Europa would need to extract its energy from chemical reactions that take
place from the heating of its interior. Further exploration of Europa will be
necessary to answer this question. Specifically, missions that will include
vehicles capable of melting through the ice crust to explore the subsurface
liquid zone. (The idea has been raised that life may also exist in oceans under
the surfaces of Ganymede and Callisto.)
Ganymede 29 – Ganymede has a combination of a dark terrain that probably dates
back to the early history of the solar system, and a younger, brighter terrain
(sometimes referred to as the bright grooved terrain) that once experienced
extensive tectonic activity. In addition, Ganymede is the only satellite in the solar
system known to possess a magnetosphere, likely created through convection
within the liquid iron core.
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Dark Terrain – Ganymede’s dark terrain is heavily cratered, suggesting a
surface age about 4 billion years. The dark coloration is most likely the result
of the accumulation of meteoritic dust, which covers a brighter, ice sub-layer.
Evidence of this sub-layer is seen where impacts ejected fresh ice onto the
surface 30.
Bright Grooved Terrain – The forces that caused the strong stresses in the
Ganymede’s ice crust necessary to initiate the tectonic activity, and thus the
formation of the bright grooved terrain, may be connected to the tidal heating
in the past. Specifically, the tidal heating “flexed” the ice crust causing the
development of cracks and horst and graben faulting – a horst represents a
block of crust pushed upward by the faulting, and a graben is a block of crust
that has dropped due to the faulting. The term “sulcus”, meaning a groove or
burrow, is often used to describe the grooved features. For example, Uruk
Sulcus 31.
Palimpsest 32 – A palimpsest is an ancient crater whose features have
disappeared due to “relaxation” of the icy surface or subsequent cryovolcanic
outpourings, leaving a circular feature, perhaps with a “ghost” of a rim.
Callisto 33 – Callisto has the most heavily cratered, and hence the oldest surface of
the Galilean satellites (very little to no tectonic activity has occurred on this
moon). Like Ganymede’s dark terrain, Callisto’s surface overall is dark due to
the contamination of the icy surface by meteoritic material. However, bright
spots are widespread, formed by young impacts ejecting fresh ice onto the
surface.
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Craters – Over most of Callisto’s surface, craters are nearly as densely packed
as those in the lunar highlands. These craters were most likely formed early
in the moon’s history during a time of higher cratering rates. Like Ganymede,
Callisto has palimpsests.
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Multi-ringed Structures 34 – Multi-ring structures probably originated as a
result of a post-impact concentric fracturing of the lithosphere lying on a layer
of soft or liquid material, possibly an ocean. Also, these impacts blasted deep
into Callisto’s interior, ejecting fresh ice onto the surface and causing the
central portions of these structures to appear brighter than the surrounding
regions. The largest of multi-ringed structure is Valhalla, spanning a length
equivalent to the contiguous United States.
Minor Moons 35 – Jupiter has 63 minor satellites, which range in diameter from less
than 10 miles to about 170 miles. They are irregularly shaped objects, with dark
surfaces similar to primitive asteroids found within the main asteroid belt. In fact,
with the exception of four of these moons forming with Jupiter, the rest may have
been initially asteroids, captured by Jupiter’s strong gravity.
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