The Jovian Planets, Part III Uranus and Neptune

URANUS The God of the Heavens

Physical Data n Discovered by William Herschel in 1781 n Diameter: 51,118 km (4.01 D earth ) n Mass: 8.69x10 25 kg (14.54 M earth ) n Density: 1.24 g/cm 3 n Rotation Period: hours n Tilt of Axis: 98 o (retrograde rotation!) n Surface Temperature: 52 K (-366 o F)

Physical Data n Orbital Semi-Major Axis: AU n Orbital Period: years n Orbital Inclination: 0.8 o n Orbital Eccentricity: n Surface Gravity: Earth gravity n Satellites: 27 as of 2011 n Magnetic Field: yes

Uranus’ Interior ATMOSPHERE MOLECULAR HYDROGEN ICE ROCK

The Discovery of Uranus n First discovered planet even though at its closest to earth it can be seen with the naked eye n Was recorded 22 times as a star on star charts before W. Herschel discovered it as a planet in 1781 m

Uranus’ Motions N N N N S S S S SUN n Uranus rotates on its side, producing strange seasons and day-night patterns

Uranus’ Atmosphere COMPOSITION: n 85% Hydrogen n 15% Helium n Traces of Methane CLOUDS: n Mostly made of methane ice n Featureless cloudtops (inconspicous bands)

Uranus’ Magnetic Field n Magnetic dipole is offset 31% from the center of the planet n Tilted -59 o from rotational axis n Comparable in strength to Earth’s (0.74 Earth’s) n Uranus has aurora and radio emissions

Uranus’ Rings n Found from star occultations in 1977 n Thought to be made of stone n Uranus also has partial rings called “ring arcs” n Also has sheperd satellites

Uranus’ Moons n All are named after William Shakespeare and Alexander Pope characters n There are 15 known moons

Uranus’ Moons MIRANDA: n Surface is a weird mix of old and new terrain n It has been proposed than it was shattered and reassembled in this way n There was not enough heat to fuse it smoothly together m

Uranus’ Moons ARIEL: n Youngest surface of the Uranian Satellites n There is evidence of tectonic activity n It has faults over 10 km deep

Uranus’ Moons TITANIA: n Largest of Uranus’ moons n Has faults up to 100 km across n Has a heavily cratered surface

NEPTUNE GOD OF THE SEA

Physical Data n First observed in 1846 by Johann Galle n Diameter: 49,500 km (3.89 D earth ) n Mass: 1.030x10 26 kg (17.23 M earth ) n Density: 1.61 g/cm 3 n Rotation Period: hours n Tilt of Axis: o n Surface Temperature: 57 K (-357 o F)

Physical Data n Orbital Semi-Major Axis: AU n Orbital Period: years n Orbital Inclination: 1.8 o n Orbital Eccentricity: n Surface Gravity: 1.19 Earth’s gravity n Satellites: 13 as of 2011 n Magnetic Field: yes

The Discovery of Neptune n It’s existence was calculated before it was observed from variations of Uranus’ orbit from what was predicted n Calculations were made by U.J. Leverrier, sent to Johann Galle at Berlin Observatory, and he found Neptune after searching for 30 minutes n Galileo actually recorded Neptune twice in 1612 and 1613 in his notebooks as a background star in his drawings of Jupiter

Neptune’s Interior ATMOSPHERE MOLECULAR HYDROGEN ICE ROCK Similar to Uranus

Neptune’s Atmosphere n 75% Hydrogen n 25% Helium n Small amounts of: Methane, Ammonia & Acetylene n There are three majors cloud-top features: The Great Dark Spot Dark Spot 2 Scooter

Neptune’s Atmosphere The Great Dark Spot: n Anti-cyclone with a circulation period of 16 days n About the size of Earth n In southern hemisphere

Neptune’s Atmosphere Dark Spot 2: n Smaller cyclone in S. hemispere Scooter: n Fast rotating n Rapidly changes shape Great Dark Spot Scooter Dark Spot 2

Neptune’s Magnetic Field n Magnetic dipole is offset 55% from center of Neptune n Tilted -47 o with respect to rotational axis n Has a field strength of 0.4x Earth’s at the equator n Has aurora and radio emissions

Neptune’s Rings n Discovered in 1981 n Brighter areas are ring arcs n There is a total of 5 rings, all very thin

Neptune’s Moons TRITON: n Has thin atmosphere, geysers, and strange “cantaloupe terrain” n Diameter: 3000km

Neptune’s Moons Proteus: n Second largest moon of Neptune discovered by Voyager n Surprisingly, Neried, Neptune’s third largest moon was discovered from the ground before Proteus