Lecture 32 - The Jovian Planets

ASTR 1210 (Exam 3)

Are Jovian Planets All Alike?

• Jupiter is next largest sphere in the solar system

• 10 Earth diameters across Jupiter’s diameter

• 1000 Earths in Jupiter

• 1000 Jupiters in the Sun

Jupiter

• Alternating red/brown and white bands — white bands are water clouds

  • Each cloud gives insight into composition of Jupiter

• Relatively large moons

  • Jupiter has over 100 moons

  • Has 4 LARGE moons 

  • Largest moon slightly bigger than Mercury (Ganymede)

• Significant weather features

  • Great Red Spot — giant hurricane 

  • Other dots are weather patterns 

• Looks like a dot from the Earth - a wandering star

• Next most explored planet, besides the Earth

JWST Image of Jupiter

• Looks at infrared

• Different bands corresponds to different heights —> different temperatures

• See rings and tiny moons and Auroras in infrared wavelengths 

Saturn

• Dull yellow color - clouds 

• Hints of bands 

• Masses of planets alter cloud tops 

• Has enormous moons - second largest moon that is bigger than Mercury — Titan

  • Titan has clouds

  • Rivers, lakes, and oceans made of methane

JWST Image of Saturn 

• Gap in the rings

• Cassini gap - astronomer Cassini 

Uranus and Neptune

• Smaller than both Jupiter and Saturn but still much larger than the Earth

• Significantly more blue in color

  • Uranus is a light blue

  • Neptune is a dark blue

    • Great Dark spot

    • Weather - not as much as Saturn or Jupiter 

• Less banded than Jupiter and Saturn but still weather clearly on the outer atmosphere

Jovian Planet Composition 

• Jupiter and Saturn

  • Mostly H and He - what the solar nebular is made of 

  • Large planetesimals pulling in H and He from the solar nebula

• Uranus and Neptune

  • Mostly hydrogen compounds: water, methane, ammonia — color

  • Some H, He, and rock 

Density Differences 

• Uranus and Neptune are denser than Saturn because they have less H/He proportionately

• But why is Jupiter more dense on average?

If you added more gas around the current atmosphere of the Earth, how would you expect the density of material at the surface of change?

• Density will increase at the surface

• Adding mass to a jovian planet compresses the underlying gas layers

• Greater densities can change characteristics of gases at each layer

Sizes of Jovian Planets

• Jupiter and Saturn are the same size, but Jupiter has more gas, compressing on it, giving it more mass

• Greater compression is why Jupiter is NOT MUCH LARGER than Saturn even though it is three times more massive - Jupiter just kinda shrunk

• Jovian planets with even more mass can be smaller than Jupiter

Interiors of Jovian Planets 

• No solid surface

• Layers under high pressures and temperatures

• Cores (~10 Earth masses) made of hydrogen compounds, metals, and rock

• The layers are different for the different planets 

• H and He under intense pressure and temperature 

Inside Jupiter

• High pressures inside Jupiter cause phase changes of H w/ depth

• Layers include

  • Gaseous H

  • Liquid H

  • Metallic H

    • Electrons free to move around - share their charges freely and act like iron/nickel 

• Rocky core of Jupiter are under extreme pressures and temperatures

  • 20,000 K compared to 3,000 K on Earth

• What we call rock is different in Jovian world - a fuzzy rock

• Cloud top layer creates so much pressure that the gaseous H becomes liquid H

  • Beneath liquid H, there’s a metallic H (special type of liquid H) 

• Primary composition of gas giants is liquid, not gas 

• We see “gas” - but is actually liquid 

Phase Changes of Water 

• Pressure can change composition, shape of matter

Jupiter does not have a large metal core like the Earth. How can it have a magnetic field?

• It has metallic hydrogen inside, which circulates and makes a magnetic field

• Charges need to move and the planet needs to move

• Jupiter’s Magnetosphere - Auroras - strong magnetic field

• All jovian planets have substantial magnetospheres, but Jupiter’s is the largest by far

Comparing Jovian Interiors

• All Jovian planets have similar compositions - Jupiter and Saturn

• Neptune and Uranus don’t have enough mass to create metallic hydrogen core - but they still have a magnetic field

  • Maybe they have molten rocky core similar to Earth generating that magnetic field

Rotation of the Jovian planets 

• Jupiter is fastest spinning planet - Jupiter spun faster due to angular momentum during collapse of solar nebula 

Rotation and Shape

• Planets will compress because of fast rotation - not perfect spheres (oblateness)

• Jupiter and Saturn

• Impact density structure

Bands of Jupiter

• Each color corresponds to clouds of different composition - reflect light differently

• Hydrogen compounds in Jupiter form clouds

• Different cloud layers correspond to freezing points of different H compounds

Jovian Planet Atmospheres 

• Other Jovian planets have cloud layers similar to Jupiter’s 

• Different compounds make clouds of different colors 

• Because red clouds are more distant from yellow, we only see yellow ones in Saturn

• Uranus and Neptune is cold enough for methane clouds to form 

Jupiter’s Great Red Spot

Great Red Spot is older than UVA

• Storm twice as wide as Earth

• Existed for at least three hundred centuries

• Shrinking in size