Astronomy 171
Solar System Astronomy
Prof. Paul Martini

Lecture 35: Massive Jupiter

Key Ideas:

Jupiter is the largest of the Planets: Prototype Gas Giant Planet
Jupiter has many moons and a faint ring
Atmosphere and Clouds: Colored belts and zones; Great red spot; Gaseous atmosphere of Hydrogen and Helium
Internal Structure: Radiates more energy than it gets from the Sun; Rocky inner core, liquid metallic outer core

Spacecraft to Jupiter

Fly-bys:: Pioneer 10 and 11 (1973 and 1974); Voyager 1 and 2 (1979); Ulysses (1992); Cassini (2001, while enroute to Saturn)
Orbiters:: Galileo (arrived Dec 1995, deliberately crashed into Jupiter in 2003); Dropped an atmospheric probe in Dec 1995

Jupiter is a Giant Gas Planet

No solid surface: Deep, heavy hydrogen and helium atmosphere; Rock and ice core
Rapidly rotating: Rotates once every 9 hours and 50 minutes; Measured using its magnetic field
Flattened at the poles:: Equatorial Radius: 71,492 km; Polar Radius: 66,854 km (6.5% flattening)

63 Moons of Jupiter

Jupiter's Dusty Rings

Jupiter has faint, dusty rings:: Made of micron-sized dark dust particles; Total mass is < 10^-12 M_Earth
Ring material may have been knocked off the moons of Jupiter or captured from comets

Atmosphere of Jupiter

Composition:: 86.4% H₂ (Molecular Hydrogen); 13.6% He (Helium); <0.1% H₂O (Water); 0.21% CH₄ (Methane); 0.07% NH₃ (Ammonia); 0.008% H₂S (Hydrogen Sulfide)

Atmospheric Probe

Released by the Galileo mission in December 1995
Survived 200km into the atmosphere, until crushed by high pressure
Relatively constant wind speed
Measured the chemistry of the atmosphere: Surprisingly little water; High abundance of Xe, Ar, Kr

Clouds of Jupiter

What we see are the tops of the clouds: Crystals of ammonia, methane, and water ices; Average temperatures is 100 - 140 K
Atmosphere is divided into latitudinal bands:: Dark Belts; Bright Zones; Cyclonic and Anti-Cyclonic storms
The detailed chemistry of the colorful clouds is still not well understood

Belts and Zones of Jupiter

Belts: high pressure and low temperature: Gaps in high clouds, view lower atmosphere; Colors due to complex organics and polysulfides
Zones: low pressure, low temperature: Regions of cold, high ice clouds

Cyclonic Storms?

Strong winds at the belt/zone boundaries:: Wind speeds up to 400 km/hr; Blow east-to-west or west-to-east, alternating between belts/zones; Some storms persist for centuries

Internal Energy

Jupiter radiates 2.5x more energy than it receives from the Sun: Slowly contracts under its own weight; Releases gravitational energy that heats up the interior; Explains constant wind speed in lower atmosphere
This heat powers Jupiter's weather

Jupiter's Magnetic Field

Circulating currents in the metallic hydrogen "mantle" of Jupiter generates a powerful magnetic field: Strongest planetary magnetic field; Tilted by ~9.6 degrees from the rotation axis; Co-rotates with the planet's interior (~9 hours, 56 minutes); Generates energetic radio emission (one of the brightest radio sources in the sky); Ionized gas torus linked to the moon Io

Jupiter is not a failed star

Jupiter resembles the Sun in composition, but it is not a "failed star": Formed from a rocky core that gathered hydrogen, helium, and volatiles from the surrounding proto-solar nebula; Inner core is solid (rock and ice)
Had a very different formation history than that of a small star
The smallest stars are 12x larger

See A Note about Graphics to learn why some of the graphics shown in the lectures are not reproduced with these notes.