1. THE JOVIAN PLANETS
Giants of the Solar System
Observations of Jupiter and Saturn
The Discoveries of Uranus and Neptune
The Jovian Planets In Bulk
Jupiter’s Atmosphere
The Atmosphere of the Outer Jovian Worlds
•Interior Structure
•Internal Heating
Jovian Magnetosphere
Interlude-A Planetary Impact
3. Jovian planets are also known as gas giants. There are four Jovian planets: Jupiter, Saturn,
Uranus, and Neptune. These four planets also comprise the outer planets. The term Jovian came
from Jupiter, describing the other gas giants in our Solar System as Jupiter-like. Despite
common belief, gas giants are not composed entirely of gas. A rocky core exists somewhere
within these balls of gas, but it is difficult if not impossible as of yet, to determine where this
center is. Because of the intense high temperatures in the middle of these planets, the rocky core
of a gas giant is actually believed to be liquid heavy compounds, such as nickel. Thus, it is
sometimes misleading when astronomers refer to the rocky core of these planets. The Jovian
planets are larger than the other planets of the Solar System and have dozens of moons.
4. THE DISCOVERIES OF URANUS AND NEPTUNE
• The five planets visible with the unaided eye are Mercury, Venus, Mars, Jupiter
and Saturn. If you know where to look, you can’t miss them, even in light
polluted skies. But there are two planets, Uranus and Neptune, which are a
little harder to find. You’ll need a telescope to even see them.
• Both Uranus and Neptune were discovered after the invention of the telescope.
Galileo first pointed his crude telescope at the heavens, but other astronomers
actually discovered Uranus and Neptune. Uranus was found in 1781 by
William Herschel, and Neptune was found in 1846 based on calculations by
John Couch Adams in England and Urbain Le Leverrier in France.
5. THE JOVIAN PLANETS IN BULK
• Most of the masses of Jupiter and Saturn, and about half those of Uranus and
Neptune, are made up of hydrogen and helium—light gases on Earth (having
densities 0.08 and 0.16 kg/m3, respectively, at room temperature and sea level),
but compressed enormously by these planets’ strong gravitational fields. The
abundance of hydrogen and helium on these worlds is itself a consequence of the
strong Jovian gravity. The Jovian planets are massive enough to have retained even
the lightest gas, hydrogen, and very little of their original atmospheres have
escaped since the birth of the solar system 4.6 billion years ago. At the heart of
each Jovian planet lies a dense, compact core many times more massive than
Earth.
• None of the Jovian planets has a solid surface of any kind. Their gaseous
atmospheres just become denser with depth because of the pressure of the
overlying layers, eventually becoming liquid in the interior. The surface we see
from Earth is simply the top of the outermost layer of atmospheric clouds.
6. JUPITER’S ATMOSPHERE
• The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System. It is
mostly made of molecular hydrogen and helium in roughly solar proportions; other
chemical compounds are present only in small amounts and include methane, ammonia,
hydrogen sulfide and water. Although water is thought to reside deep in the atmosphere,
its directly measured concentration is very low. The oxygen, nitrogen, sulfur, and noble
gas abundances in Jupiter's atmosphere exceed solar values by a factor of about three.
• The Jovian atmosphere shows a wide range of active phenomena, including band
instabilities, vortices (cyclones and anticyclones), storms and lightning.The vortices reveal
themselves as large red, white or brown spots (ovals). The largest two spots are the Great
Red Spot(GRS) and Oval BA which is also red. These two and most of the other large spots
are anticyclonic. Smaller anticyclones tend to be white. Vortices are thought to be relatively
shallow structures with depths not exceeding several hundred kilometers. Located in the
southern hemisphere, the GRS is the largest known vortex in the Solar System. It could
engulf several Earths and has existed for at least three hundred years. Oval BA, south of
GRS, is a red spot a third the size of GRS that formed in 2000 from the merging of three
white ovals.
7. THE ATMOSPHERE OF THE OUTER JOVIAN WORLDS
• The atmospheres of Jupiter and Saturn are made almost entirely of hydrogen and helium,
although there is some evidence they contain hydrogen compounds. Uranus and Neptune are
made primarily of hydrogen compounds, with smaller traces of hydrogen, helium, metal and
rock. The most common hydrogen compounds are methane (CH4), ammonia (NH3), and water
(H2O).
• The farther away a planet is from the Sun, the cooler its atmosphere will be. This means that
the same gases will condense to form clouds at different altitudes on different planets because
the condensation of a gas requires a specific amount of pressure and temperature. Ammonia,
ammonium hydrosulfide and water make up the 3 cloud layers of Jupiter and Saturn. You can
see from the graph to the right that these condense at lower altitudes in Saturn's atmosphere
than they do in Jupiter's atmosphere.
