Rings of the Jovian Planets Module 5

Module 5

Rings of the Jovian Planets

  • All four Jovian planets have rings.

  • Materials in the rings consist of tiny particles to small "moonlets."

  • Formation theories:

    • May form when a moon(s) is destroyed.

    • Composed of material that couldn’t form a moon.

  • Strong gravity of the Jovian planets allow large bodies to be torn apart by tidal forces, resulting in smaller particles remaining intact.

Discovery of Saturn’s Rings

  • 1610: Galileo observes Saturn with "ears."

  • 1655: Christaan Huygens posits that Saturn is surrounded by a solid ring.

  • 1676: Giovanni Cassini discovers a gap in the rings, named the Cassini Division.

  • The main rings extend from 7,000 km to 80,000 km (4200-48000 miles) above Saturn's equator, with a thickness of only 10 meters (32 feet).

  • Composed of 99.9% pure water ice.

  • Ring particles vary in size from 1 cm to 10 m.

Saturn’s Rings

  • Visible from Earth: Three main rings – A, B, C

    • Ring A: Farthest; second brightest

    • Ring B: Brightest

    • Ring C: Translucent, closest to the planet

  • Small Encke gap in A ring and Cassini Division (dark gap) present.

  • Rings D-F not visible from Earth.

Formation of Saturn’s Rings

  • Characteristics: Rings may be relatively young, potentially only 50 million years old.

  • Factors influencing formation:

    • Waves, collisions, or interactions with moons can create and replenish ring material.

    • Recent catastrophic events could lead to moons being torn apart by gravity or impacts.

  • Example: Saturn's ring mass could result from a 250 km diameter satellite.

  • Triton, a moon of Saturn, is expected to eventually create a ring system.

Saturn’s Rings – Variations by Season

  • Seasonal changes occur due to Saturn's tilted axis and orbit.

  • Brightness of rings changes with axial tilt:

    • North/South pole towards the sun: Bright appearance.

    • Spring and fall: Rings appear edge-on, becoming hard to see.

Changing Aspects of Saturn's Rings

  • Changes observed as Earth and Saturn orbit the Sun, which takes 29.457 Earth years.

  • Images from the Hubble Space Telescope show Saturn's appearance changes.

Roche Limit

  • How rings form:

    • A small moon approaches Saturn and becomes stretched by gravity tidal forces until it’s torn apart.

    • Pieces spread into individual orbits, forming rings.

  • Roche limit: Minimum distance from a planet where a space object will be torn apart.

    • Approximately 2.4 times the planet radius.

    • Not applicable to smaller space objects held together by interatomic/electromagnetic forces rather than gravity.

Details of Saturn’s Rings

  • Voyager 2: Discovered main rings contain tens of thousands of ringlets.

  • Ringlet characteristics:

    • Ring particles come together and disperse; contain narrow gaps.

    • Presence of moonlets (10-20 km across) which impact particles.

Cassini Division

  • Caused by the gravity of the moon Mimas, which deflects ring particles into new orbits, clearing the division.

F-ring

  • Discovered by Pioneer 11 in 1979.

  • Appears as a braided strand and is thin.

  • Is maintained by shepherd satellites, such as Pandora.

D-ring

  • Faint and located inside the C-ring, closer to cloud tops.

  • Contains few dark particles, making it invisible from Earth.

E-ring

  • Located outside the main rings, comprised of diffuse dust.

Discovery of Jupiter’s Rings

  • Voyager found a faint ring around Jupiter, located inside the inner moon orbit.

  • Consists of dark rock fragments and dust, resulting from chipped-up moons by meteorites.

  • The ring is thin, measuring only several tens of kilometers thick.

Jupiter's Rings

  • Rings are faint and challenging to see.

  • Enhanced images display a gossamer appearance composed of:

    • Main Ring

    • Halo

    • Amalthea, Adrastea, Metis, Thebe

Uranus's Ring System

  • First discovered in 1977; it has 11 thin rings.

  • The rings are dark, narrow, and widely spaced, exhibiting a very thin structure.

Neptune’s Rings

  • Comprises four dark rings, including three that are narrow and one broad/diffuse ring.

  • The outer rings exhibit clumping; some areas are too thin.

  • Clumping may be attributed to shepherd satellites.