Lecture 33 - Moons of the Solar System

ASTR 1210 (Exam 3)

Jupiter’s Bands

• Primary component of Jovian planets is not actually gaseous - we just see the gaseous clouds forming on top of Jupiter 

• Jupiter has different cloud layers and bands 

• Earth’s clouds form thru convection in the troposphere

• Jupiter water clouds also form thru convection 

• Jupiter is hotter near its interior, colder near the top 

• Brighter at infrared wavelengths, the hotter it is in that region - looking deeper into the core 

Jupiter’s Great Red Spot

• Multi-century old hurricane

• Shrinking in size 

• now 2 times the size of the Earth 

• Raging for centuries - these winds contribute to Coriolis effect that drives those banded structures very long on Jupiter

• Winds are going to interact and change a lot of the appearance because the winds are stronger and faster rotations 

Swirling storms at Jupiter’s pole

• Energy is getting transferred to the poles - gas to rise near the equator of the Earth and sink near the poles = one large convection cell

• Jupiter’s rotation complicates easterly and westerly winds - making it way more banded

• Winds are spinning up the hurricane

• Places where atmosphere is moving - no mountains to stop it

• Great Red Spot is shrinking

Wind Patterns on the Jovian Planets

• Three bands in the North and three bands in the South - easterly and westerly

• More banded than the Earth is

• Uranus and Neptune are a little simpler because sunlight drives a lot of wind

• Creates some notable storms 

Saturn’s Hexagon 

• Hexagonal storm in the polar region of Saturn

• Seems to be some wind structure to create this hexagonal shape

• Has to do with the interactions of different wind features forming it

• Need to send a spacecraft to Saturn to see it - picture was taken by the Cassini spacecraft

• Storms on Uranus - visible in the infrared

• Neptune’s Great Dark Spot 

Jovian Planet’s Rings 

• Saturn’s rings will change

• Huygens Drawings of Saturn (1655) — had to conclude this

What Are Saturn’s Rings Like?

• Made up of numerous, tiny individual particles

• Orbit around Saturn’s equator

• Very thin 

• RIng system forms in what we would call the ecliptic plane of the Sun

• made out of millions of tiny particles - none of the bigger than a giant boulder 

Saturn’s Changing Ring Appearance

• Cassini Gap 

• Ring Plane Crossing - rings are thin 

• Gets into a view where rings disappear from us 

Artist’s Conception of Rings Close-Up

• Biggest rocks are about the size of cars

Gap Moons

• Some small moons create gaps within the rings - shepherding moons

• Daphnis clears a gap of those tiny particles and supplying the ring material 

Shepherd Moons

Pair of moons pulling along the rings

Jovian Ring Systems 

• All four Jovian planets have ring systems

• Others have smaller, darker ring particles than Saturn

Origins of the Jovian Rings

• Likely formed from dust created by impacts on moons orbiting those planets

• Rings aren’t leftover from planet formation because particles are too small to have survived for so long

• Must be continuous replacement of tiny particles

• Most likely source is impacts with Jovian moons 

Which planets has most currently confirmed moons in the Solar System?

• Saturn 

• Jupiter SHOULD have the most moons 

• What do you define a moon to be? 

What is a moon? 

Natural satellites which orbit another body - can be orbiting a planet, asteroid, comet, etc

• More than 200 observed moons in our solar system

• 20 of them large enough to be gravitationally spherical

• Most massive objets are spherical 

• Inner planets have almost no moons

• Each of the gas giants have > 10 moons currently observed

Phobos and Deimos

• Small moons

• tiny and lumpy

• not spherical

• Likely captured asteroids

• Perturbed in the asteroid belt and now part of Mars’s orbit

• Phobos is getting so close to Mars that it might get pulled apart

• Orbital dynamics of moons

Roche limit

Limit where tidal forces (pull object in one direction and compress it in another direction) are so strong, it can tear Phobos apart

What Kinds of Moons Orbit the Jovian Planets? 

• Four of the biggest moons -

  • Ganymede - a little bit bigger than Mercury

  • Europa

  • Io

  • Callisto

• Large moons of the solar system - ongoing geological activity

Moons of the Jovian Planets

• Small Moons

  • No geological activity

• Medium-sized moons

  • Geological activity in the past

• Large moons

  • Ongoing geological activity

Medium and Large Moons

• Enough self-gravity to be spherical

• Have substantial amounts of ice

• Formed in orbit around Jovian planets

• Circular orbits in same direction as planet rotation

Io’s Volcanoes

• Volcanoc eruptions continue to change Io’s surface

• Tidal heat from tidal stresses

• Receives greatest tidal heating because it is closest to Jupiter

Europa: Waterworld?

• Europa, Io, and Ganymede are in resonant orbit

• For every two times Io orbits, Europa orbits once. 4:1 for Ganymede

• Forces stack up over time - making tidal forces stronger and stronger

• Europa is heated very significantly from the inside out

• Has a huge amount of water ice

• Might have a lot of liquid water beneath the surface

• Tidal Stresses Crack Europa’s surface ice

Europa may have more water than Earth 

• Everywhere we find liquid water, we have life

• Maybe there’s life swimming underneath Europa 

If Ganymede is larger than Mercury, why isn’t it designated as a planet?

• Ganymede primarily orbits Jupiter - not the Sun

• sometimes called a satellite planet - large sphere orbiting a planet

Saturn’s Moon - Titan

• Only moon in solar system to have a THICK atmosphere, consisting of mostly nitrogen with argon, methane, and ethane

• Has a cycle similar to the water cycle we have on Earth

Titan’s Surface

• Lake of methane 

• Found liquid methane and ice made of rocks 

Which large-sized moon of a Jovian planet is the most similar to Earth?

• Titan

• Has erosion, atmospheres, equivalent of liquid