The Jovian Planets€¦ · water ice, etc… →Dense core: required to account for gravitational...
Transcript of The Jovian Planets€¦ · water ice, etc… →Dense core: required to account for gravitational...
The Jovian PlanetsSaturn
• Small “Core”/Atmosphere Ratio• Rings• Lots of Satellites
Jupiter
Uranus Neptune
Spacecraft Missions to the Jovian PlanetsThree Major Missions• Pioneers 10 & 11 (launched 1972)• Voyagers 1 & 2 (launched 1977)• Galileo (launched 1989)
Difficulties with sending probes to Jovian planets• Energy source: solar panels + internal radioactive
generators needed• Distance from Earth: autonomous• Destruction of spacecraft by debris: asteroids, rocks, etc.• Trajectory: gravity assisted
Flight Paths of Voyager Spacecraft
• Gravity-assisted Trajectories
Trajectory video – Cassini Spacecraft (arrival date to Saturn –2004)
Where are the Voyager Spacecraft?
Deep Space Network – Antenna locations
• Voyager 1 & 2 continue to transmit signals back to Earth• They are continuously monitored by the Deep Space
Network
• Present mission – Find the edge of the Solar System (Video)
The Jovian Planets• How do we determine the nature of their interiors?→ Mass, radius, rotation rate, heat balance, atmospheric
composition, gravitational effects on moons• Composition→ Primarily Hydrogen & Helium, plus methane, ammonia,
water ice, etc…→ Dense core: required to account for gravitational field;
composed of things denser than Hydrogen & Helium (Silicon, metals, heavy volatiles?)
• Note: The behavior of Hydrogen & Helium at high temperatures & pressures is not well understood
Sizes of Jovian planets compared to the Earth
14 Mearth317 Mearth 90 Mearth 17 Mearth
Properties of Jupiter• Composition: 75%
hydrogen, 24% helium + methane, ammonia, water ice…
• Average Distance from the Sun: 0.7 light hours
• Rotation Rate
• Orbital Period: 11.9 Earth years
• Axis Tilt: 3.1°• Number of Moons: ~ 61
9h55m30s – Magnetic Field9h50m30s – Equatorial Clouds9h55m41s – High Latitude CloudsNote: Hydrogen and Helium
are colorless.
Moons are being found at a regular rate around the Jovian planets
Technique is similar toKuiper Belt search
The moon Io and Jupiter
Properties of Saturn• Average Distance from
the Sun: 1.3 light hours• Rotation Rate
• Orbital Period: 29.5 Earth years
• Axis Tilt: 27° (i.e., Seasons: UV + Methane → Ethane in the Summer
• Number of Moons: ~ 31• Equator is 10% wider than
pole-to-pole
10h39m24s – Magnetic Field10h14m – Equatorial Clouds10h40m – High Latitude Clouds
Note: tan “smog” that overliesclouds below gives Saturn itscolor.
The Jovian planets have equatorial bulges
• Rotation Rates ~ 10-17 hours• Gravity makes planets spherical• Rotation makes planets bulge at the equator(Note: This keeps rings/satellites aligned with equator)
Jupiter & Saturn are about as large as planets can be
Internal Heat SourcesJupiter & Saturn radiate twice as much heat as they receive
from the Sun• Earth radiates 0.005% as much energy as it receives
from the Sun
Source of heat from Jupiter is the slow contraction of the planet
• Gravitational potential energy → kinetic energy →thermal energy
Source of heat from Saturn is Helium rain• At lower temperature & pressure of Saturn, liquid helium
does not dissolve with liquid hydrogen• Deficit of Helium relative to Hydrogen has been
measured in the outer atmosphere of Saturn
Probing Jupiter’s Atmosphere – The Galileo Probe (video)
1995: Galileo probe dropped into Jupiter’s atmosphere
cold enough for water tocondense, etc…
Troposphere: turbulent clouds due to the Greenhouse effect
(UV)
JovianAtmosphere Comparison
Internal structure of Jupiter
Belts & Zones• Strong Coriolis forces
divide circulation cells into bands
• Convection results in bands of different color
→ Zones: rising, cooling air out of which ammonia condenses into clouds
→ Belts: falling air depleted in clouds; allows clouds below to be seen
The Great Red Spot
• Storm that has persisted for at least 300 years
• Size: twice as wide as the Earth
• Why are such storms so long-lived?
→ No solid surface to sap away energy (as happens on the Earth)
Magnetic Fields
Auroras of Jupiter
Flux tube connecting satellites to Jupiter
Ultraviolet
Rings• Composition: mixture of
rocks of varying sizes comprised mostly of water ice (high albedo)
• Dimensions of Saturn’s rings: 270,000 km x 10s of meters
• Roche zone: tidal forces ~ binding gravitational forces
• Note: smaller rocks are held together by gravitational & electrostatic forces, & thus can survive
Jupiter’s Rings• Jupiter’s rings are less
prominent than Saturn’s• Why? Smaller particles
Features in Rings• Gaps are present in the
rings. They are created by Gap Moons that nudge particles out of particular orbits
• Spokes: particles levitated out of ring plane by forces associated with the magnetic fields
Origin of Rings• Moon that strayed too
close• Tidal forces prevented a
Moon from ever forming there
Formation of Jovian Planets & Satellites
• Ice & Rock cores build→ Mass ~ 10 Earth Masses
• Hydrogen & Helium from surrounding solar nebulae were gravitationally captured
→ Planets that are massive & cold enough can retain hydrogen & helium
• Solid grains in surrounding nebula form satellites