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A Look at Our Solar System: The Sun, the planets and more by Firdevs Duru U R A N U S N E P T U N E Uranus and Neptune Uranus discovered by William Hershel in 1781. Deviations of the Uranus’ orbit from the simple elliptical orbit lead to the discovery of Neptune. John Adams (1845) and Urbain Leverrier (1846) determined the mass and the orbit of the new planet. Johanne Galle found the new planet within a few degrees of the predicted position. Uranus’ tilt It’s spin axis is nearly in its orbital plane. Each pole: 42 years darkness, 42 years sunlight. Not dramatic temperature differences, due to dense atmosphere, very far away from the Sun. Atmospheres 84 % H, 14 % He, 3 % methane on Neptune 84 % H, 14 % He, 2 % methane on Uranus Ammonia not seen. Blue color: due to methane Weather Few clouds in Uranus’ cold upper atmosphere Winds with speeds between 200 to 500 km/s More atmospheric features are visible in Neptune than in Uranus. Due to extra warmth, Neptune’s stratospheric haze is thinner and cloud layers are less dense. Numerous methane clouds Largest storm: The Great Dark Spot Interior Uranus and Neptune have Earth-size cores. Rocky cores. 85 % of the mass of these two planets is contained in a thick layer of rock and ice. Outer envelope is made of H, He, water, methane, ammonia. Internal energy Neptune has excess energy as Jupiter. Uranus does not have the heat flowing out. Magnetic fields and Magnetospheres Populated largely by electrons and protons. Magnetic fields are not aligned with the planets’ rotational axes and are significantly offset from the planets’ centers. Could be due to the fact that the fields are generated by currents within icy fluids far from the centers of the planets. Rings - Uranus Ring system of Uranus is discovered in 1977. They are dark, narrow, and widely spaced. A few tens of meters thick. Made of carbon mostly. Large particles. Rings - Neptune Neptune surrounded by four dark rings. Extremely dark and faint. First three are narrow, fourth one is broad and more diffused. Space between them are filled with dust. Made mostly of microscopic particles. Triton 4.5 billion km from the Sun. Has an icy surface. Temperature is 37 K. Very thin nitrogen atmosphere and solid and frozen surface (primarily of water ice). Relatively high density (2050 kg/m3) à 75 % rock and 25 % ice. In retrograde orbit around the parent planet. It spirals slowly inward. Evidence of internal activity and resurfacing. Has plumes. Trans-Neptunian Objects (TNOs) Large number of relatively small, icy bodies in the region beyond Neptune. Pluto: Percival Lowell tried, Clyde Tombaugh found it. About 40 AU from the Sun on average. At perihelion, Pluto crosses Neptune’s orbit. Has a satellite named Charon (1978), which provided the mass of the Pluto (just 0.0021 Earth mass) to great accuracy. Very reflective surface, due to ice material (frozen nitrogen, small amounts of frozen carbon monoxide and methane). Pluto: Not a planet anymore! Defini&on of a planet: • Orbits a star • Massive enough for its gravity to give it nearly a round shape • Has cleared the neighborhood around its orbit Pluto and Eris are dwarf planets! Other TNOs More than 1200 TNOs are known. Most of them orbit Kuiper belt (lie between 40 and 50 AU). Plutoids: Pluto and other dwarf planets (Ceres, Eris) beyond Neptune. SMALL SOLAR SYSTEM BODIES A meteor is a sudden streak of light in the sky caused by friction between air molecules in the Earth’s atmosphere and incoming piece of asteroid, meteoroid or comet. A given meteor shower occurs about the same date each year. Earth crosses the orbit of the meteoroids responsible for that shower on the same date each year. Three main kinds: Stony meteorites: 94%. Most of them are chondrites. They contain spheres of silicate rock. Iron meteorites: 5%. Pure alloys of iron and nickel. Stony-iron meteorites: 1%. Mixtures of silicate rock and metal. Asteroids Asteroeides : like a star. Asteroids are the multitude of rocky bodies that orbit the Sun within the planetary system. Sizes: A few km à 1000 km. Almost all of them orbit the Sun in the same direction as the Earth does. Orbits change in shape and size, but are more eccentric than the planets. Location Most of them are found in the region known as the asteroid belt, located between Mars and Jupiter (between 2.1 and 3.3 AU from the Sun). Largest are Pallas and Vesta. They are in the asteroid belt. Two other groups of asteroids share Jupiter’s orbit. Known as Trojan asteroids, located 60° ahead and behind Jupiter. Most of the asteroids always remain between the orbits of Mars and Jupiter. There are thousands that have orbits that cross Earth’s orbit: They may have been deflected into the inner solar system due to gravitational fields of Mars and Jupiter. Comets Small icy bodies in orbit around the Sun. They shine by reflected light. Anatomy Nucleus: Main frozen solid body. A few km in diameter. Mostly made of frozen water. Also has frozen CO, CO2 and formaldehyde, with microscopic particles trapped in it. Coma (halo): A ball of outflowing gas and dust around the nucleus. Tail: can be as big as 1 AU Tail Ion tail (plasma tail): Made of ions and electrons. Blue due to ionized carbon monoxide. Dust tail: Broad, diffuse and gently curved. White or yellow. Rich in microscopic dust particles that reflect sunlight. Both tails are directed away from the solar wind. Comet Orbits Long-period comets: Periods longer than 200 years. Could go as much as 100000 AU away from the Sun. Highly elliptical orbits. Orbits exhibit all inclinations and orientations with respect to the ecliptic plane, both prograde and retrograde. The swarm of long-period comets is called the Oort cloud. Short-period comets: Periods shorter than 200 years. Less frequent. Prograde and lie on the ecliptic plane. Originated in the Kuiper belt. Nearly circular orbits. What happens to comets? On each passage near the Sun, part of the outer dust and ice layer of the comet is lost. When all the ice is gone, the nucleus cannot produce a coma or a tail. Only the swarm of dust stays, which forms the meteoroids. The comets with rocky cores become asteroids.