* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Uranus and Neptune Uranus Saturn Neptune
Document related concepts
Uranus and Neptune Uranus: The god of the heavens—The son and husband of Gaia—he hated his sons which angered Gaia. She fashioned a sickle which Saturn, his son, used to castrate him. Neptune: The god of the sea— brother of Jupiter and Pluto The Solar System CHAPTER 14 Uranus, Neptune, Pluto & TNO’s What We Learn About Uranus, Neptune, Pluto & TNO’s How Uranus and Neptune were discovered The unusual properties of the axis, orbit and atmosphere of Uranus What gives Neptune’s clouds and atmosphere their distinctive appearance The internal structures of Uranus and Neptune The unique orientations of the magnetic fields of Uranus and Neptune Why the rings of Uranus and Neptune are hard to see What We’ve Learned About Uranus, Neptune, Pluto & TNO’s What could have powered geologic activity on Uranus’s moderate-sized moons Why Neptune’s satellite Triton is destined to be torn apart How Pluto came to be discovered What shapes the orbits of Pluto and the thousands of other objects that orbit beyond Neptune What TNO’s are and why Pluto, Charon, and Triton are part of this population. Note: Orbit of Uranus Uranus—Voyager 2, 1986 False Color True Color South Pole Hubble Image 2004 Ultraviolet, Visible, infrared composite Springtime on Uranus Uranus’ Structure Atmosphere: H2 , He, CH4 Outer Mantle: Liquid H2, He ≈ 4 ME Inner Mantle: Liquid H2O, NH3, CH4 ≈ 11 ME Core: Fe, Ni and Mg silicates ≈ 1 ME Discovery of Uranus’ Rings–1977 Stellar Occultation Uranus Rings • Rings are thin and dark • Typically 0.1–10 m size • larger particles than Saturn’s rings • Methane ice— undergoes radiation darkening Uranus rings Hubble Image of Rings • Short exposure to reveal planet and inner rings • Long exposure to reveal outer rings How were the rings of Uranus discovered? A.By Galileo who originally saw them but thought the looked like ‘ears’ sticking out on the sides of Uranus, which he mistakenly thought were moons. B.By a Cornell astronomer who hoped to measure the size of Uranus during an anticipated stellar occultation in 1977, when he surprisingly observed that light from the target star blinked on and off before and after it was actually occulted by Uranus. C.By Voyager I, when its electronics failed as it passed through Uranus’ rings. D.By Voyager II, during its 1986 flyby. Uranus’ Major Moons Uranus Rings and Small Moons Miranda Miranda Mosaic Surface of Miranda Miranda initially in resonance orbit with Umbriel Tidal heating melted Miranda causing differentiation Differentiation failed to complete when tidal heating ceased Neptune Neptune Data Discovered by Johann Gotfried Galle Sept 23, 1846 Mass (Earth = 1) 17.135 Equatorial radius (Earth = 1) 3.8799 Mean density (gm/cm 3)1.64 Mean distance from the Sun (Earth = 1) 30.0611 Rotational period (hours) 16.11 Orbital period (years) 164.79 Orbital eccentricity 0.0097 Tilt of axis (degrees)29.56 Orbital inclination (degrees) 1.774 Equatorial surface gravity (m/sec 2) 11.0 Albedo 0.41 (Magnitude 7.84) Mean cloud temperature -193 to -153°C Atmospheric pressure (bars) 1-3 Atmospheric composition Hydrogen 85%, Helium 13%, Methane 2% When the English student, John Couch Adams, and the French astronomer, Urbain Le Verrier, independently predicted the existence of Neptune on the basis of measured irregularities of Uranus’ orbital motion, what factor ultimately led to Neptune’s discovery by Johann Galle at Berlin Observatory rather than by James Challis at Cambridge, England, even though Challis was told of the prediction much earlier than Galle? A. better eyesight B. Galle used photography, while Challis had to rely on eye observation C. The Berlin Observatory had better star charts and Galle took LeVerrier seriously while Challis and Sir George Biddell Airy failed to take Adams seriously D. less cloud cover Neptune Structure Atmosphere: H2 , He, CH4 ≈ 2 ME Mantle: Liquid H2O, NH3, CH4 ≈ 14 ME Core: Fe, Ni and Mg silicates, ≈ 1 ME Magnetic Fields of Jovian Planets Neptune Storms Neptune Rings Jovian Planet Differences Triton and Neptune • Triton in retrograde orbit • Orbit inclined 23o from Neptune’s equatorial plane • How does satellite co-form this way? • Diameter 2706 km • Largest captured satellite Triton and Neptune Absence of large craters—why? Triton Volcanic Surface Frozen ‘lakes’— calderas of extinct volcanoes? Triton initially in highly elliptical orbit Tidal flexing as on Io until orbit ‘circularized’ Triton’s Surface • Pink material— N2 frost? What future awaits Triton, the largest satellite of Neptune? A.eventual escape from Neptune as it gradually spirals outward B.tidal breakup as it slowly spirals closer to Neptune and falls within its Roche limit C.probable destruction when it eventually collides with Pluto D.vaporization as it eventually falls into the Sun Pluto and Charon Pluto: The god of the Underworld—brother of Neptune Charon: The ferryman who carried the doomed souls across the River Styx into Hell Discovery of Pluto—1930 Pluto shifts about 1 arcmin/day relative to background stars Pluto and Charon Charon discovered in 1978, James Christy Pluto and Charon “He gave way to the queer, savage feeling that sometimes takes by the throat a husband twenty years’ married, when he sees, across the table, the same face of his wedded wife, and knows that, as he has sat facing it, so must he continue to sit until the day of its death or his own.” Rudyard Kipling Pluto Data Discovered by Clyde W. Tombaugh, Feb 18, 1930 Mass (kg)1.27 x 10 22 (Earth = 1) 2.125 x 10 -3 Radius (km) 1,137 (Earth = 1) 0.1783 Mean density (gm/cm -3) 2.05 Mean distance from the Sun (Earth = 1) 39.5294 Rotational period (days) 6.3872 Orbital period (years) 248.54 Orbital eccentricity 0.2482 Tilt of axis (degrees) 122.52 Orbital inclination (degrees )17.148 Equatorial surface gravity (m/sec2) 0.4 Albedo 0.3 (Magnitude 15.12) Atmospheric composition Nitrogen Methane Pluto, Charon and (Hydra and Nix) HST discovery of Nix and Hydra—2005 Pluto…Light & Dark Regions Mercator Map of Pluto New Horizons … 2015 The orbital and rotational periods of the Pluto-Charon system bear what relationship (if any) to each other? A.Charon and Pluto orbit each other’s common center of mass with identical orbital and rotational periods. B.Charon orbits Pluto twice, while Pluto orbits Charon once. C.There is no relationship between rotation period of Pluto and orbital period of Charon. D.Charon orbits Pluto once each month. Kuiper Belt and Oort Cloud • Kuiper Belt extends from about 30 to 60 AU • Oort cloud, a spherical distribution, extends to about 100,000 AU! ‘Kuiper Belt’ Around HD 139664 57 Ly Away Known KBO’s • Green–main belt • Orange–scattered objects TNO Distribution KBO Resonances Mauna Kea—Site of CFHT Simulations Orbits before Jupiter Saturn 2:1 resonance note: Neptune formed closer in than Uranus Orbits after Jupiter/Saturn 2:1 resonance resonance causes Uranus & Neptune to migrate outward Neptune scatters primordial planetesimals into TNO’s (Kuiper Belt, etc) Largest (TNO’s) Eris … The Largest Dwarf Eris was named after the Greek goddess of discord and strife. She stirs up jealousy and envy to cause fighting and anger among men. At the wedding of Peleus and Thetis all the gods were invited with the exception of Eris, and, enraged at her exclusion, she spitefully caused a quarrel among the goddesses that led to the Trojan war. Orbit of Eris – Largest TNO The Kuiper Belt consists _______. A.very soft leather used by Gerard Kuiper to make designer belts. B.asteroids that pass closer to the Sun than Earth's orbital distance. C.a region in the asteroid belt where all the Kuiper family objects orbit the Sun. D.mostly of small, icy planetesimals that formed just beyond Jupiter and were scattered outward just beyond the orbit of Neptune by gravitational forces exerted on them by the Jovian planets. Key Ideas Discovery of the Outer Planets: Uranus was discovered by chance. Neptune’s existence was predicted via Newtonian mechanics. Pluto was discovered after a long search. Atmospheres of Uranus and Neptune: Uranus and Neptune have atmospheres composed of hydrogen, helium, and a small percentage of methane. Methane absorbs red light, giving Uranus and Neptune their greenish-blue color. No white ammonia clouds are seen on Uranus or Neptune. Low temperatures caused ammonia to precipitate into planetary interiors. Clouds are composed of methane. Key Ideas Much more cloud activity is seen on Neptune than on Uranus. Uranus lacks a substantial internal heat source. Interiors and Magnetic Fields of Uranus and Neptune: Uranus and Neptune have rocky cores surrounded by a mantle of water and ammonia. Electric currents in these mantles generate the magnetic fields of the planets. The magnetic axes of both Uranus and Neptune are steeply inclined from their axes of rotation. The magnetic and rotational axes of all the other planets are more nearly parallel. The magnetic fields of Uranus and Neptune are also offset from the centers of the planets. Key Ideas Uranus’s Unusual Rotation: Uranus’ axis of rotation lies nearly in the plane of its orbit, producing greatly exaggerated seasonal changes on the planet. This unusual orientation may be the result of a collision with a planet-like object early in the history of our solar system. Such a collision could have knocked Uranus on its side. Ring Systems of Uranus and Neptune: Uranus and Neptune are both surrounded by systems of thin, dark rings. The low reflectivity of the ring particles may be due to radiation-darkened methane ice. Key Ideas Satellites of Uranus and Neptune: Uranus has five satellites similar to the moderate-sized moons of Saturn, plus at least 22 more small satellites. Neptune has 13 satellites, one of which (Triton) is comparable in size to our Moon or the Galilean satellites of Jupiter. Triton has a young, icy surface indicative of tectonic activity. The energy for this activity may have been provided by tidal heating that occurred when Triton was captured by Neptune’s gravity into a retrograde orbit. Triton has a tenuous nitrogen atmosphere. Key Ideas Pluto and Charon: Pluto and its moon, Charon, move together in a highly elliptical orbit steeply inclined to the plane of the ecliptic. They are rocky, icy worlds that belong to a class of objects called Trans Neptunian Objects (TNO’s) Key Ideas Beyond Neptune: Trans-Neptunian Objects (TNO’s) are icy worlds that mostly lie in a band called the Kuiper belt that extends from 30 to 50 AU from the Sun. The Kuiper Belt and the Oort Cloud contain billions of small, icy, rocky objects in orbit around the Sun More than a thousand icy worlds have been discovered beyond Neptune. Pluto and Charon are part of this population. Neptune’s gravity shapes the orbits of objects within the Kuiper belt.