# Wikijunior:Solar System/Jupiter

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!♃.svg "♃"){width="80"} **Jupiter Facts**:

-   Due to its magnetic field trapping particles from the Sun, Jupiter
    is surrounded by very powerful radiation belts which would kill
    anyone who entered them.
-   Jupiter\'s moon Europa is thought to have a giant ocean below its
    surface.
-   Jupiter\'s moon Ganymede is the largest moon in the solar system.
-   Jupiter is the third brightest object in the night sky, second being
    Venus and first being the Earth\'s moon.
-   Jupiter has more than twice the mass of all the other planets in the
    solar system combined.
-   Jupiter is considered an almost-star. The smallest red dwarf star
    was only 30% bigger than Jupiter.
-   Jupiter\'s red spot and the Earth are close to the same size. That
    means that there is a storm going on in Jupiter that is as big as
    the Earth!
-   *Jovian* in English means anything relating to Jupiter --- the god
    or the planet. Sometimes the four outer planets are called the
    Jovian planets.

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**Jupiter** is by far the largest planet in our Solar System: two and a
half times larger than all of the other planets put together. It is the
fifth planet from the Sun and one of the brightest planets as seen from
Earth. Jupiter, along with Saturn, Uranus and Neptune, is sometimes
called a \"gas giant\" because most of these planets are made up of
liquid and gas.

## How big is the planet?

!Comparing the sizes of the Sun, Jupiter, Earth, and the Moon. Notice
the red spot is about the size of the Earth!

Jupiter is 142,984 km or about 11 Earths in diameter at the **equator**.
That makes it about one tenth as big in diameter as the Sun! You could
fit about 1,400 Earths into the volume of Jupiter. It is 133,709 km or
10 Earths in diameter from pole to pole. Jupiter\'s rapid **rotation**
(it spins around in under ten hours compared with 24 hours for Earth)
makes it bulge out at the equator.

Jupiter\'s magnetic field is the largest single planetary thing in the
Solar System. It is 26 million kilometers across, making it about 20
times bigger than the Sun. It has a tail that extends past Saturn\'s
orbit. If it could be seen from Earth, it would appear to be five times
the size of the full moon.

## What is the surface like on Jupiter ?

!Jupiter\'s
atmosphere The
surface we see is not solid. This enormous planet has a relatively small
solid and rocky core. Liquids and gases surround this core and blend
with the atmosphere.

Jupiter is a cloudy, windy and stormy planet. It is always covered by a
layer of clouds, and wind speeds of 600 km/h are not uncommon. The
storms are visible as swirls, bands and spots. A particularly violent
storm, about three times Earth\'s diameter, is known as the Great Red
Spot. This storm has been in existence since at least 1831, and maybe
since 1665. If the storm has existed since 1665, that would make it more
than 300 years old!

The layer of clouds is divided into several bands. The lighter colored
bands are called **zones** and the darker bands are called **belts**.
The colors are caused by small changes in the temperature and chemistry.
Each band rotates in the opposite direction from its neighbors. Along
the edges where the bands meet, these winds collide and create swirling
patterns.

The stormy atmosphere of Jupiter has flashes of lightning just like on
Earth. However, while Earth\'s lightning strikes may be hotter than
50,000 °C, Jupiter\'s lightning strikes may go over 5,000,000 °C, which
is a hundred times more than Earth lightning, and is more than the
temperature of the sun\'s corona. The lightning is made by water near
the tops of the clouds.

## What are its rings like?

!The rings of Jupiter as seen by the Voyager 2
spacecraft
Jupiter\'s rings are dark and hard to see. They are made of tiny
particles that meteors knocked off Jupiter\'s small inner moons and
debris left over from comets and other objects that came close to the
surface of Jupiter. In fact, until the Voyager spacecraft arrived near
Jupiter and took closeup pictures of the rings of Jupiter, scientists
didn\'t even know that it even had rings at all. Two rings are clearly
from material that can be associated with two sets of the inner moons of
the planet.

These are the names of the rings and their sizes:

  Ring Name          Inner Radius   Outer Radius
  ------------------ -------------- --------------
  Halo               100,000 km     122,000 km
  Main               122,000 km     129,000 km
  Gossamer (inner)   129,000 km     182,000 km
  Gossamer (outer)   182,000 km     225,000 km

  : **Rings of Jupiter**

Gossamer means in English anything that is delicate, light, and flimsy.

{{  }}

## What is the planet\'s atmosphere made of?

!Jupiter as seen by the space probe *Cassini*. This is the most
detailed color portrait of Jupiter ever
assembled.
In the outermost layer of Jupiter lie frozen Ammonia crystals. (Ammonia
is a compound of hydrogen and nitrogen; its scientific designation is
NH~3~.) crystals.

Jupiter\'s atmosphere is mainly made of **hydrogen**(H~2~). Near the
surface, there is almost 90% hydrogen. Apart from this, the atmosphere
has helium(He). Because of the high pressure, helium becomes a liquid
further down in the planet. In addition, Jupiter has
methane(CH~4~)(0.3%), hydrogen deuteride(HD)(0.003%),
ethane(C~2~H~6~)(0.0006%), and least of all, water(H~2~O)(0.0004%).

Jupiter\'s temperature is very high. Because of this, scientists cannot
tell all the materials the planet is made of. The outer core of Jupiter
has hydrogen. The pressure present can make the gas solid. However,
because of the very high temperature, the gas melts, and becomes liquid.

## What are its moons like?

!A simulation of the orbit paths of the moons of
Jupiter.
Jupiter has 95 known moons. There are four major moons that were
discovered by Galileo in 1610, the first moons ever discovered around
another planet. Those moons are Io, Europa, Ganymede and Callisto; they
are named from characters in mythology closely associated with Jupiter.
They are called the Galilean moons. There are often **eclipses** on
Jupiter\'s cloud tops by the Galilean moons.

### Amalthea Group

There are four small moons **orbiting** inside Io\'s orbit. That group
is called the Amalthea group because Amalthea is the largest one. They
are all small and potato shaped. Amalthea is very red. The material of
Jupiter\'s rings came from meteors knocking it off of those moons.
Amalthea(Greek:Ἀμάλθεια) in Greek mythology is a foster mother of Zeus.

### Io

!The four largest moons of Jupiter. From left to right with increasing
distance: Io, Europa, Ganymede,
Callisto..tif "The four largest moons of Jupiter. From left to right with increasing distance: Io, Europa, Ganymede, Callisto.")
Io (pronounced EYE-oh) is Jupiter\'s closest major moon. It is 3643.2 km
across, slightly larger than Earth\'s Moon. It has the most spectacular
**volcanoes** in the solar system and molten **sulfur** lakes. Any
craters formed by asteroids hitting the surface are quickly covered up
by the volcanic activity. Io\'s core is made of molten **iron** and is
surrounded by a rock shell. Unlike Jupiter\'s other moons, there is very
little water on Io. Scientists think that when Jupiter was forming, it
was hot enough to dry out Io, but not the other major moons. In Roman
mythology, Io(Ancient Greek:Ἰώ) was a beautiful young nymph(Nymphs are
divine spirits that animate nature and generally portrayed as beautiful
young women.) that Zeus loved.

### Europa

Europa (pronounced *Eurṓpē*) is 3,121.6 km across, about 10% smaller
than Earth\'s Moon. It is made of silicates and has a layer of smooth
water ice 10 to 30 km thick. The ice has long cracks in it and very few
craters. It looks like the sea ice on Earth. The ice has slid around at
the cracks. We believe there is liquid water under the ice as much as
100 km below the surface. There are also some large spots on the
surface. In Roman mythology Europa was courted by Jupiter in the form of
a bull. Europa (Ancient Greek:Ευρώπη) in Greek mythology was a
Phoenician noblewoman who was abducted by Zeus to Crete (An island of
Greece).

### Ganymede

!Jupiter and its four largest moons, as seen through a
telescope.
Ganymede is 5262.4 km across, making it 380 km wider than Mercury. It is
Jupiter\'s largest moon and the largest moon in the Solar System. It has
**plate tectonics** like Earth. There are older, darker regions and
newer areas with grooves where the plates have moved. Newer craters have
bright rays around them from material thrown up by impacts. Older
craters look flat and faded because the icy surface does not hold the
shape of the crater as well as rock does over long periods of time.
Ganymede may have an iron and sulfur core with a silicate **mantle** and
an icy shell. It may be similar to Io except with a layer of ice on it.
In Roman mythology Ganymede was a beautiful young man who Jupiter
kidnapped and made cupbearer to the gods on Mt. Olympus.

### Callisto

!The orbit paths of the 4 largest
moons.
Callisto is 4820.6 km across, about the same size as Mercury. It has
many craters. Like craters on Ganymede, the older craters have faded.
The largest crater is *Valhalla*. It has a bright center 600 km across
with rings around it up to 3000 km across. Callisto is made of silicates
and ice. There is a 200 km thick icy **crust** with a liquid water sea
under it. In Roman mythology Callisto was turned into a bear by
Jupiter\'s jealous wife Juno. Later Jupiter placed her in the stars as
The Great Bear.

### Other moons

The other moons are smaller in several groups outside the orbits of the
major moons. There is also a small moon, Themisto and four groups of
small moons that orbit very far from Jupiter.

## How long is a day on this planet?

One Jupiter day is about 10 Earth hours long. You have to say \"about\"
because different parts of Jupiter rotate about its axis at different
speeds. This is caused by the fact that Jupiter is mostly gases that are
in constant motion and sometimes going in different directions. Some
efforts have been made to try and measure the rotation speed of the
inner rocky core of Jupiter, but that has proved to be quite difficult
to accomplish due to the magnetic fields that surround Jupiter and the
very active radio energy that is generated by the atmosphere of Jupiter,
which interferes with measuring techniques like radar that has been used
to measure the surface of Venus and Mars.

## How long is a year on Jupiter?

!The Great Red
Spot !Jupiter
Eclipses One year
on Jupiter is 4,335 Earth days or 11.87 Earth years long.

A Jupiter year is about equal to four-tenths (or two-fifths) of a Saturn
year. Thus after every two Saturn years, Jupiter has completed five full
orbits about the Sun. So after 59 years, Saturn and Jupiter will be back
in nearly the same position. When the orbits of two planets are simple
ratios of each other like this, it is called a **resonance**.\

## How much would Jupiter\'s gravity pull on me?

If someone were floating close to the cloud tops of Jupiter, it would
pull them down with a force about two and a half times as strong as the
force of Earth\'s gravity.

Jupiter\'s rapid rotation causes the equator to bulge out. This would
also cancel out about 10 percent of gravity\'s force on them if they
were at the equator. The amount of this counteraction becomes lower the
closer they get to the poles.

## Who is it named after?

!Statue of Zeus (Jupiter) in Olympia,
Greece in Olympia, Greece")

Jupiter (Latin *Iuppiter*) is named after the king of the Roman gods,
also called Zeus in ancient Greece. The god Jupiter was known for
causing lightning strikes on Earth. He is associated with the eagle and
the oak tree.

Next Topic: Saturn

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