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
Why is Jupiter denser then Uranus and Neptune even though Jupiter is made of hydrogen
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.