Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 19uranusneptune5s
Document related concepts
Exploration of Io wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Planet Nine wikipedia , lookup
Exploration of Jupiter wikipedia , lookup
Triton (moon) wikipedia , lookup
Kuiper belt wikipedia , lookup
Definition of planet wikipedia , lookup
Scattered disc wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Jumping-Jupiter scenario wikipedia , lookup
Transcript
Uranus and Neptune Astronomy 311 Professor Lee Carkner Lecture 19 Uranus -- God of the Sky He gives his name to Urania, the Greek muse of astronomy Discovery of Uranus The other planets can only be seen with a telescope Uranus was discovered in 1781 by William Herschel while surveying the sky Herschel had built a very high quality telescope and was systematically observing the brighter stars when he found Uranus Observing Uranus Most of our information about Uranus comes from Voyager 2 and HST No future missions planned Uranus Facts Size: Orbit: 19.22 AU Description: blue-green, featureless, tilted on its side The Rotation of Uranus The tilt of Uranus’s axis is 98 degrees Extreme tilt may be due to a large impact when Uranus was forming The large tilt produces seasons where half of the planet is in sunlight and half in darkness for long periods of time Seasons on Uranus Composition of Atmosphere Hydrogen: 84 % Helium: 14 % Methane (CH4): 2% The large amount of methane gives Uranus its bluish color Structure of Atmosphere Ammonia, Ammonium hydrosulfide and water have frozen out in the lower atmosphere where we can’t see them Careful observations have determined that Uranus does not have alternating zones and bands Winds mostly blow east Uranus’s Rings As Uranus moved past a star, the star dimmed several times before being occulted by the planet Rings are composed of dark material They reflect very little light and are difficult to observe at optical wavelengths The Moons of Uranus Uranus has 5 major moons and 22 minor moons Moons are composed of mixture of ice and rock Two of the moons shepherd the Epsilon ring The other rings may also have shepherd moons that are too small to see Radiation Darkening Why are the moons and rings of Uranus (and Neptune) so dark? Impacts by high energy electrons from the magnetosphere break off the carbon atoms Carbon soot builds up on the ice making it dark Magnetic Fields Fields on Uranus and Neptune May be formed by motions of a liquid water mantle containing ions The centers of the magnetic fields are offset from the center of the planet How can the dynamo effect produce an offcentered field? Rotation and Magnetic Axis Determining Mass How are the masses of planets determined? We can measure the period and the orbital radius of a moon or spacecraft The relationship between them depends on mass Neptune -- God of the Sea The name is appropriate due to Neptune’s bluegreen color The Discovery of Neptune Was an undiscovered planet altering the orbit? In 1846 J. G. Galle used Le Verrier’s calculations to find Neptune after a 30 minute search Observing Neptune Neptune shows no detail from groundbased telescopes Best images from Earth from the Hubble Space Telescope Neptune Facts Size: ~4 Earth diameters Orbit: 30.11 AU Description: more distant, cloudier Uranus Neptune’s Atmosphere Neptune has visible storms like Jupiter, but they appear to be short lived The white features in Neptune’s atmosphere are high altitude methane clouds All seem to be moving east rather than in opposite directions Composition and Heating 84 % Hydrogen 14 % Helium 2 % Methane Neptune may be still contracting The Rings of Neptune But stars were dimming by different amounts Caused by the gravity of a near-by moon Inner narrow ring has shepherd moons The Moons of Neptune Triton’s orbit is unstable, in 100 million years it will be inside of the Roche limit giving Neptune a spectacular ring system Triton may be a captured Kuiper Belt object Interiors We can model each planet with a similar interior Mantle of water and ammonia (Windex) The two planets have relatively more heavy elements and less hydrogen than Jupiter and Saturn They also do not have enough gravity to produce liquid metallic hydrogen The Interiors of Uranus and Neptune The Formation of Uranus and Neptune At 20-30 AU the planetesimals were fewer and more widely dispersed than at 5-10 AU By the time they formed much of the hydrogen and helium was dispersed Next Time Read Chapter 11.5 and 12.5 Summary Information comes from Voyager and HST Blue-green in color with white clouds Caused by methane Radiation darkening produces dark, soot colored rings and moons Interior composed of rocky core, water and ammonia mantle and hydrogen atmosphere Offset magnetic field Formed more slowly than Jupiter and Saturn and so captured less gas Summary: Uranus Discovered by survey (1781) Faint cloud patterns Due to low internal heat Tilted on its axis Causing non-uniform solar illumination Summary: Neptune Discovered through use of Newton’s laws (1846) Most distant gas giant Has more internal heat and stronger cloud features than Uranus
