Lecture 27: Jupiter and Saturn cont.

Overview of Jupiter and Saturn

  • Study Chapter 6 (The Giant Planets) in detail.
  • Review online resources:

Thermal Emission and Energy Balance

  • Jupiter and Saturn emit radiation similar to a black body.
  • Total energy emitted by these planets is greater than the energy they receive from the Sun.
  • Both planets appear warmer than expected based on their distance from the Sun, suggesting internal heat sources.

Differentiation and Internal Heat

  • Differentiation leads to a planet's layered structure, with denser materials sinking.
  • This process releases gravitational potential energy, converted into heat.
  • Jupiter: Helium and hydrogen currently undergoing differentiation, causing helium to separate and settle, releasing further energy.

Helium and Hydrogen Behavior

  • Inside Jupiter and Saturn, helium and hydrogen exist as two immiscible liquids, forming an emulsion-like state.
  • As helium droplets sink, gravitational energy is released, potentially explaining the depletion of neon in Jupiter’s atmosphere.

Atmospheric Dynamics of Jupiter

  • Jupiter’s atmosphere shows a clear banding structure due to convection:
    • Warm air rises, cools, and condenses, forming clouds.
  • Rapid rotation (9.9-hour day) disrupts convection, causing alternating wind systems and impacting storm dynamics (e.g., Great Red Spot).
  • Equatorial wind speeds can reach approximately 150extm/s150 ext{ m/s} or 540extkm/hr540 ext{ km/hr}.

Cloud Bands and Composition

  • Cloud Layers: Two main types of bands –
    • Zones: Light-colored due to high altitudes and ammonia concentration.
    • Belts: Darker areas where ammonia clouds dissipate, revealing deeper layers made of ammonium hydrosulfide ice.

The Great Red Spot

  • A long-lived anti-cyclone located in the southern hemisphere, characterized by its vast size (over twice the diameter of Earth).
  • First recorded in 1665 and still evolving, demonstrating dynamic atmospheric changes.

Coriolis Effect and Storm Systems

  • The Coriolis effect causes rotation patterns in atmospheric systems:
    • Low pressure systems (cyclones) spin counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.
    • High-pressure zones show the opposite spin.

Saturn’s Characteristics and Exploration

  • Saturn appears less colorful than Jupiter, with less pronounced cloud bands.
  • Major insights into Saturn came from the Cassini-Huygens mission, launched in 1997 and orbiting Saturn from 2004 to 2017.

Energy Sources for Space Probes

  • RTGs (radioisotope thermoelectric generators) are used for spacecraft power, notably in Cassini, which used plutonium pellets to generate electricity.

Magnetic Fields of Jupiter and Saturn

  • Jupiter’s magnetic field is tilted; Saturn’s field is closely aligned with its rotation axis.
  • Both planets emit radio waves related to their magnetic fields and rotation, which can vary across regions.

Differential Rotation in Saturn

  • Saturn shows slight differences in its rotation rate measurements, illustrating the complexity of planetary dynamics.
    • Variations may be influenced by atmospheric plasma interactions with the magnetic field.

Dynamic Atmosphere of Saturn

  • Like Jupiter, Saturn possesses a dynamic, banded atmosphere, frequently changing due to storm activity driven by convection.

Overview of Galilean Moons of Jupiter

  • Discovered by Galileo Galilei in 1610, the four largest moons (Io, Europa, Ganymede, Callisto) exhibit diverse features:
    • Callisto: Heavily cratered, suggesting inactivity and possible differentiation with a rocky core.
    • Ganymede: Fully differentiated with a layered structure and potentially a subsurface ocean beneath ice.

Differentiation Factors in Ganymede and Callisto

  • Ganymede's greater differentiation likely arises from faster accretion rates and increased tidal heating compared to Callisto.

Future Study Directions

  • Further exploration into icy moons and their potential subsurface oceans, as well as volcanic activity, is suggested for next meetings.
    • Study related articles on Moons of Jupiter (EUROPA, IO, GANYMEDE) and their implications.

Useful References