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Chapter 11

Astronomy & Astrophysics
Course Code
Stefan Mochnacki

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Chapter 11 – Jovian planet Systems
11.1: A Different kind of Planet
Remember: we need to know angular size and distance to calculate an objects true size
Jovian Planet Composition:
Jupiter and Saturn are made almost entirely of hydrogen and helium. (Small percentage
of their mass in the form of hydrogen compounds, and even less in the form of rock and
Uranus and Neptune much smaller in size and are made up of hydrogen compounds like:
water, methane and ammonia, with small amounts of rock and metal
Jovian planets formed in the outer solar system so it was cold enough for hydrogen
compounds to condense into ices, thus increasing in size because of the abundance of
these compounds. Once they were big enough, their gravity brought in the gases.
At greater distances, it took longer for hydrogen compounds to condense into ice
planetismals. Thus, Jupiter was the first one to become large enough to start drawing in
gases followed by Saturn, Uranus, and Neptune.
The solar wind blew away the remaining gas , and because all the Jovian planets stopped
accreting at the same time, the distant planets had less time to capture the gases resulting
in smaller sizes
Density Differences:
Why is Jupiter denser then Uranus and Neptune even though Jupiter is made of hydrogen
and helium?
Jupiter is probably the maximum size a Jovian planet can be. If more gas was added to
Jupiter, its weight would actually compress the gas more making it smaller.
Jovian Planet Rotation and Shape:
To determine a Jovian planets rotation speed we must observe the movement of clouds.
What can be observes is that they do not rotate like solid balls. (equatorial regions
complete rotation in less time than polar regions)
Rapid rotation affects their shapes. Gravity would make them into spherical masses, but
the speed of the rotation makes the material bulge outward.

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Size of the bulge depends on the balance between the strength of gravity and rare to
rotation. Bulges also exert an extra gravitational pull that keeps moons and rings aligned
with the equator.
Has immense temperature and pressure making it hard for planetary exploration
Although there is no surface, they do not differ much in layer composition. They differ
however in the phase (liquid or gas) of their hydrogen.
Layers of Jupiter:
Cloud Tops Gaseous Hydrogen Liquid Hydrogen Metallic Hydrogen Core
Note that the core is made up of rock, metals, and hydrogen compounds. It is similar to
the size of the earth but more massive because is it compressed to such high density.
Comparing Jovian Interiors:
Saturn is the most similar to Jupiter; it has the same four layers except they differ from
Jupiter’s because of its weaker gravity and lower mass. Thicker layers of gaseous and
liquid hydrogen and thinner layers of metallic hydrogen
Uranus and Neptune only have a thick layer of gaseous hydrogen surrounding it core of
hydrogen compounds, metals, and rocks. Core maybe liquid making unusual oceans
Cores of Neptune and Uranus are lager then the cores of Jupiter and Saturn. This is
because they are less compressed by their layers. This allowed for differentiation to
occur, so hydrogen compounds reside in a layer around a center of rock and metals
Internal Heat:
Jupiter’s large size means it loses heat very slowly even though it loses twice as much
heat as it gets from the sun.
Accretion, differentiation, and radioactive decay are factors that heat Jupiter, but the real
explanation for the excess heat is the fact the planet is contracting which converts
gravitational potential energy to thermal energy

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Saturn also loses twice as much heat as it gains but it is too small for the planet to gain
heat by contracting, instead helium condenses into liquid form and the helium droplets
slowly rain down representing a form of differentiation. (Higher density materials are still
sinking to the core.
Uranus emits virtually no energy. Neptune however is more mysterious because like
Jupiter and Saturn it loses twice as much as it gains. The only reasonable explanation for
this is that the planet is still contracting
Atmospheric Structure and Clouds:
Temperature structure of Jupiter is similar to earths. Jupiter has a thermosphere, a
stratosphere, and a troposphere.
In the troposphere, warmer temperatures drive convection, and this is responsible for the
thick clouds that enshroud Jupiter. Jupiter has three primary cloud layers: water,
ammonium hydrosulfide, and ammonia
The atmospheric structure of the other three planets are similar except the atmospheres
get progressively cooler with increasing distance from the sun causing the cloud layers to
be at different positions.
Ex. Saturn has the same set of cloud layers except they are at a lower altitude because of
the lower overall temperature
Uranus and Neptune are so cold that if there were similar cloud layers to Saturn and
Jupiter, it would be buried to deep for us to see so we don’t know if these clouds even
exist in Uranus and Neptune. However we can see a cloud layer made by methane snow.
Clouds and Layers:
Different types of clouds reflect light of different colours.
The mid layer clouds of Jupiter and Saturn reflect brown and red light which gives Saturn
and Jupiter its distinct colour.
Uranus and Neptune are blue in colour because of the fact that methane effectively
absorbs red light and reflects blue light
Global Winds and Storms on Jupiter
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