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Lecture #26: Jupiter• Jupiter:

– General properties.– Atmosphere.– Interior.– Origin and evolution.

• Readings: 7.1 (Jupiter), 11.1

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The Main Point

Jupiter is the largest planet in the solar system by far, and is made almost entirely

of the same “stuff” as the Sun.

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The Jovian Planets

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Basic Properties of Jupiter• Average Distance from Sun: 778,000,000 km (a=5.20 AU).• Orbital period: 11.86 years; eccentricity: 0.048.• Period of Spin around axis: ~10 hours (varies with latitude).• Tilt of Jovian spin axis: 3.1° (no real seasons).• Mass: 1.9x1027 kg = 317 ME ; Radius: 71,400 km = 11 RE. • Density = 1.3 g/cm3 (mostly gaseous, small "rocky" core?)• No "surface" like the terrestrial planets: only clouds visible.• Gravity = 24.8 m/sec2 (2.5 times Earth's).• Cloud-top temperature: 125 K (-148°C).• Atmosphere: Mostly H, He (plus CH4, NH3, H2O, NH4HS, ...).• Moons: 63 presently known (48 have been named).• Rings: Jupiter has an elegant set of thin dark rings.

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Observations• Jupiter is a prominent object in the night

sky for many months out of each year.• Through even a small telescope, Jupiter's clouds

appear yellow, red, & brown.• And features can be seen:

– Belts of red clouds.– Zones of white clouds.– Oval-shaped storms.

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Space Missions

• 8 robotic spacecraft have flown past Jupiter.Mission Dates Goals and Results Pioneer 10 1973 First Jupiter flyby; studied magnetic field, clouds.Pioneer 11 1974 Flyby; studied magnetic field, atmosphere.Voyager 1 1979 Flyby; high resolution imaging and other studies.Voyager 2 1979 Flyby; high resolution imaging and other studies.Ulysses 1992 Flyby (gravity assist); solar wind & magnetic field.Galileo 1995- Orbiter; imaging, spectroscopy, magnetic fields,

and atmospheric entry probe.Cassini 1999 Flyby (gravity assist); imaging, spectroscopy.New Horizons 2007 Flyby (gravity assist); imaging, spectroscopy.

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Grand Tour of the Voyager Spacecraft

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Jupiter's Dynamic Atmosphere• The zones, belts, and storms change with time.

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Belts & ZonesKnowledge of the composition and temperature allows astronomers to create a model to explain the distribution and colors of the belts and zones.

Zones: rising air forms white ammonia clouds.Belts: falling air forms no white clouds and reveals red clouds below.

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Atmospheric Circulation

The most famous storm, the Great Red Spot, has been around at least since 1610.

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Atmospheric Composition• Determined by spectroscopy from

telescopes and spacecraft.• Directly by the Galileo probe.

Name Symbol % Volume Hydrogen H2 86Helium He 13.6 Methane CH4 1.8 x 10-3

Ammonia NH3 2.6 x 10-4

Ethane C2H6 6 x 10-6

Deuterated Hydrogen HD 5 x 10-5

Water vapor H2O <=6 x 10-4

Deuterated Methane CH3D 3 x 10-5

Phosphine PH3 1 x 10-6

Carbon monoxide CO 1 x 10-7

Germanium Tetrahydride GeH3 ? 1 x 10-7

The composition of Jupiter is very close to the composition of the Sun.

Galileo Probe Mission

Release Date: 7/13/95 Entry into Jupiter: 12/7/95Entry Speed: 106,000 mphProbe Data Return:

59 min3.5 megabits

Penetration depth 200 km (124 mi)

Astro 102/104 12Atmospheric Structure: Direct measurements from the Galileo entry probe in 1995.

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Probe Results:• Composition close to (but not

exactly) solar.• Cloud structure close to that

predicted.• Circulation is “deep” rather than

“shallow”.• H2O is distributed very non-

uniformly.• Complex hydrocarbon molecules

more scarce than predicted.Astro 102/104 14

• How can we know?– Orbits of inner moons.– Trajectories of spacecraft.– Shape of the planet ("oblateness").– Interior rotation rate (from magnetic field).

• Models:– Solar composition.– Phase diagram of H, He (gas, liquid, "metal").

Jupiter's Interior ??

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Jupiter's Interior

Interior structure is inferred from models and extrapolation of data from the upper cloud layers...

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Internal vs. External Heat Sources• Energy Balance:

– Energy in = Energy out.– Solar heat absorbed = Outgoing planetary heat.

• But for Jupiter: Outgoing = 1.8 × Incoming.• Jupiter has a strong internal heat source:

– Heat stored from planetary contraction?• This has a strong influence on atmospheric

circulation and “climate”.

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Giant Planet or Failed Star?

• Calculations suggest that Jupiter is about 80 times less massive than needed to initiate hydrogen fusion reactions in its core and become a star.

• Some people have called Jupiter a “failed star” for this reason, but it might better be thought of as a very successful planet.

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Jupiter's Magnetic Field• One of the largest planetary structures in the

solar system (apparent size > the full Moon).• Jupiter's magnetic field is

about 20,000 times stronger than Earth's.

• The solar wind is deflected in a huge zone around the planet.

• Evidence for the magnetic field can be seen in telescope and spacecraft images of aurorae.

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Jupiter's Magnetic Field• Field is tilted slightly

relative to the spin axis.• Intense toroidal zone of

charged particles coming from Io's volcanoes.

• Extended "sheet" of plasma along magnetic equator.

• Entire structure oscillates at Jupiter's spin rate.

Jupiter L Burst Jupiter S BurstAstro 102/104 20

Satellites & Rings• Galileo discovered the 4 large moons of

Jupiter (the Galilean satellites) in 1610.• 12 other smaller rocky/icy

bodies found from 1872-1979.• 51 more very small, outer moons

discovered in 1999-2005.• Many more details in Lectures 30 & 31.

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Summary

• Jupiter is a gas giant planet, composed mostly of H and He in the same relative abundances as the Sun.

• Jupiter has vigorous atmospheric circulation that manifests itself as long-lived belts, zones, & storms.

• Jupiter's interior consists of liquid and metallichydrogen, at enormous temperatures and pressures.

• Jupiter has a very large magnetic field that interacts strongly with the satellites and the solar wind.

• Jupiter has 63 known satellites…Astro 102/104 22

Next Lecture...

• Saturn:– General properties.– Atmosphere.– Interior.– Origin and evolution.

•• Readings: 7.1 (Saturn), 11.1 Readings: 7.1 (Saturn), 11.1