The Jovian Planets Jovian Planets •  More massive than the terrestrial planets –  Formed outside the Frost line •  Dominated by their atmospheres •  Many satellites Jovian Planets •  More massive than the terrestrial planets –  Formed outside the Frost line •  Dominated by their atmospheres •  Many satellites Composi:ons Formed outside the Frost line •  Jupiter and Saturn –  Mostly H/He, few % H compounds, liCle metal (%) –  Similar to Sun –  “Failed star”? •  Uranus and Neptune –  H/He less than ½ mass –  H compounds dominate (CH4, H2O, NH3) –  Small amounts of metal/rock Explaining the Composi:ons •  Jovian planet cores made of ices + rock –  Leading theory: all 4 formed ~ 10 M⊕ icy/rocky cores •  What causes the difference in composi:on? –  Jupiter/Saturn captured a lot of H/He –  Icy core is now only a small frac:on of mass –  Uranus/Neptune captured less H/He –  Longer :me needed for cores of Uranus/Neptune to form—less :me to capture H/He Forma:on scenarios •  Accre:on •  like the terrestrial planets •  Gas collapse •  like star forma:on Densi:es •
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Jupiter: 1.33 gm cm-­‐3 Saturn: 0.70 gm cm-­‐3 Uranus: 1.27 gm cm-­‐3 Neptune: 1.64 gm cm-­‐3 High density of Jupiter due to large mass/
compression of core Between Planets and Stars Jupiter: ~0.001 M¤ •  <13 MJ (0.013 M¤): planets •  0.013 < M/M¤ < 0.076: Brown Dwarfs –  Fuse Deuteriumè 3He •  M > 0.076 M¤: stars –  Fuse H è 4He Note: M stars (<0.2 M¤), BDs, Jupiter ~ same radius Jovian Planet Rota:on Fast! •  Not rigid rotators •  How do you measure rota:on? –  Period of clouds? (wind?) –  La:tude dependence –  Magnetosphere rota:on •  Coupled to interior •  Jupiter/Saturn: ~10 hours •  Uranus/Neptune: ~16-­‐17 hours Centripetal forces è equatorial bulges Saturn -­‐ not Round! Internal Structure •  Gas Giants –  High pressure → gas is not like anything on earth •  How do we determine structure? –  Modeling/lab experiments (this is how science works) –  Measurements of g and B –  Models give size, density, atm. composi:on, shapes, ... •  Lab experiments help us understand H/He at high P •  Jupiter may have solid H2 core Jupiter T,P increase with depth No solid surface Dis:nct layers Most are s:ll H/He Metallic H Conducts electricity B field generated here Core Much denser than Earth Not differen:ated Internal Structure Jovian planet cores ~ same mass/composi:on; Interior differences due to H/He layers Saturn similar to Jupiter Uranus/Neptune: lower mass Lower Pressure No liquid or metallic H Simpler structure: gaseous H layer core of H compounds, rock, and metal Core differen:ated : H compounds above rock/metal Internal Heat Internal heat affects atmospheric dynamics •  Jupiter –  Emits 2x energy it receives from Sun •  Earth's internal heat only 0.005% what it gets from Sun –  Cooling via radia:on –  S:ll contrac:ng (not “finished” forming) •  Contrac:on too small to measure –  Over 4.5 billion years, cooled significantly •  Saturn –
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Emits 2x the energy it receives from the Sun Too small to generate heat from contrac:ng P + lower T = helium rain Outer atmosphere depleted in He •  Uranus/Neptune –  No He rain, accre:on, ... –  Internal heat should have stopped (true for Uranus) –  Neptune emits 2x what it receives Jupiter And its moons Proper7es •  Composi:on: 75% H, 24% He + methane, ammonia, water ice… •  Average distance from Sun: •  5.2 AU •  0.7 light hours •  Rota:on Rate •  9h55m30s – Magne:c Field •  9h50m30s – Equatorial Clouds •  9h55m41s – High La:tude Clouds •  Orbital Period: 11.9 years •  Axis Tilt: 3.1° •  Number of Moons: ~ 63 The Atmosphere of Jupiter •  Jovian atmosphere: por:on of the planet we see –  Winds, weather, storms –  Mostly H/He + some H compounds •  H compounds –  Auer H/He: O, C, and N most abundant –  Compounds formed: CH4, NH3, and H2O –  Smaller amounts of hydro-­‐carbons: C2H2, C2H6, C3H8 –  Compounds responsible for colors, clouds The Atmosphere of Jupiter •  Galileo probe (1995) descended through atmosphere •  Similar structure to Earth –  Thermosphere (heat source?) –  Stratosphere (what causes UV absorp:on?) –  Troposphere heated from below (Jupiter's heat + solar energy) •  Clouds form in troposphere –  Different compounds at different al:tudes •  Three primary cloud layers: –  H20 –  Ammonium hydrosulfide (NH4SH) –  NH3 Clouds Cloud Tops in 2015 Seeing through the Clouds IR Visual Belts and Zones Jovian Weather 4 Hadley cells + Convec:on = Weather Jovian Weather 300 yr old storm 2x width of Earth High-­‐pressure center Why are such storms so long-­‐lived? •  Color due to chemicals (tholines?) •
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3 Storms Jovian Winds 1 Oct – 9 Dec 2000. 168 rota:ons. 751 nm. Cassini Flyby Polar Winds Cassini Flyby Oct-­‐Dec 2000 Jupiter’s Magne:c Field Strongest in the Solar System; 20,000 x Earth’s Io Torus Jovian Aurora Polar images: UV light from the HST ç Op:cal IR ê Jupiter’s Ring IR Op:cal (New Horizons) The Moons of Jupiter
Ganymede
Callisto
Io
The 4 Galilean moons
There are at least 59 others
Europa
Discovery of
the Galilean
Satellites
Orbital Resonances
Io
• The size of Luna
• Sulfur surface
produces the
orange, yellow, and
black colors.
Europa
• 2nd of the Galilean satellites
• Smoothest surface in SS
• Surface appears to be water ice
• Surface looks like Arctic Ocean
• Iceberg-like structures
• Dark lines appear to be cracks
in the ice
• No craters è < 30 million year
old surface
• Severe radiation environment
Ganymede
• 3rd of the Galilean satellites
• Bigger than Mercury
• Differentiated, iron core
• Complex surface
• dark cratered regions
• light grooved regions
• The grooved terrain:
• 60% of the surface
• Faulted
• Few craters è young
Callisto
• Most distant of the
Galilean satellites
• Density è rock and ice
• Moment of inertia
èundifferentiated
• Tidal forces have not
heated its interior.
• Heavily cratered, very
old surface
Internal Structures
Small Inner Moons Thebe Amalthea Me:s Lessons from Jupiter •  Raw materials are abundant outside the frost line •  Jupiter/Galilean moons form a miniature solar system •  Weather is simpler in a gas planet Saturn
Saturn •  Average Distance from the Sun: –  9.5 AU –  1.3 light hours •  Rota:on Rate –  10h39m24s – Magne:c Field –  10h14m – Equatorial Clouds –  10h40m – High La:tude Clouds •
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Orbital Period: 29.5 years Axis Tilt: 27° (i.e., seasons) Number of Moons: ~ 60 Equator is 10% wider than pole-­‐to-­‐pole Rhea, Enceladus, & Dione Telesto
Titan
Prometheus
Dione
Titan
Rings The Roche Limit •  Where :dal stresses overwhelm forces holding the body together •  Depends on mass, composi:on, radius Daphnis (8 km) in Keeler Gap Aurorae on Saturn HST images 2 days apart. UV + op:cal Titan
The second-largest moon in the Solar System
The only moon with a substantial atmosphere
90% N2 + some CH4, Ar, C2H6, C3H8, C2H2, HCN, CO2
1.5 bars; 95K
Enceladus
Mimas
Closest of
the large
moons.
Prometheus 148 x 100 x 68 km Uranus •  Composi:on: –  84% H, 14% He, 2% methane (CH4) + others •  Average density 1.3 g/cm3 •  Average Distance from the Sun: –  19.2 AU –  2.7 light hours •  Rota:on Rate (retrograde) –  7.2h – Magne:c Field •  Orbital Period: 84 years •  Axis Tilt: 98° •  Number of Moons: ~ 27 •  Clouds: methane Uranus •  1986: no bands seen •  Recently, bands and storms seen –  Due to extreme axial :lt? –  North pole becoming illuminated Why are Uranus and Neptune blue? Uranus from HST 4 years of imaging Moons Ariel and its Shadow 5 classical moons: Titania, Oberon, Ariel, Umbriel, Miranda Densi:es suggest ice + rock Neptune •  Composi:on: ~84% H, ~14% He, 2% methane + others •  Average density 1.6 g/cm3 •  Average Distance to Sun: –  30.1 AU –  4.2 light hours •  Rota:on Rate –  16.1h – Magne:c Field •  Orbital Period: 165 years •  Axis Tilt: 27° (seasons) •  Number of Moons: ~ 13 Neptune •  Dark spot: lasted about 6 years High Clouds on Neptune Seasons on Neptune Triton
•  Retrograde orbit
•  Tidally heated?
Lessons from the Jovian Planets •  Lots of atmosphere + rota:on -­‐> weather •  Rings and moons are ubiquitous •  The moons can rival the terrestrial planets –  Densi:es suggest rock + ice composi:ons