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Table of Contents Uranus Introduction Uranus' RingsUranus StatisticsAnimations of UranusViews of UranusRings of UranusUranus Moon Summary Satellites of Uranus Ariel, Belinda, Caliban, Cordelia, Cressida, Desdemona, Juliet, Miranda, Oberon, Ophelia, Portia, Puck, Rosalind, Sycorax, Titania, Umbriel, New Moons of Uranus Uranus Science Uranus Science Summary Uranus Exploration Chronology Hubble Uncovers Smallest Moons Yet Seen Around Uranus Uranus Image/Animation Gallery Other Resources The Uranian Ring System Uranus is the seventh planet from the Sun and is the third largest in the solar system. It was discovered by William Herschel in 1781. It has an equatorial diameter of 51,800 kilometers (32,190 miles) and orbits the Sun once every 84.01 Earth years. It has a mean distance from the Sun of 2.87 billion kilometers (1.78 billion miles). It rotates about its axis once every 17 hours 14 minutes. Uranus has at least 22 moons. The two largest moons, Titania and Oberon, were discovered by William Herschel in 1787. The atmosphere of Uranus is composed of 83% hydrogen, 15% helium, 2% methane and small amounts of acetylene and other hydrocarbons. Methane in the upper atmosphere absorbs red light, giving Uranus its blue-green color. The atmosphere is arranged into clouds running at constant latitudes, similar to the orientation of the more vivid latitudinal bands seen on Jupiter and Saturn. Winds at mid-latitudes on Uranus blow in the direction of the planet's rotation. These winds blow at velocities of 40 to 160 meters per second (90 to 360 miles per hour). Radio science experiments found winds of about 100 meters per second blowing in the opposite direction at the equator. Uranus is distinguished by the fact that it is tipped on its side. Its unusual position is thought to be the result of a collision with a planet-sized body early in the solar system's history. Voyager 2 found that one of the most striking influences of this sideways position is its effect on the tail of the magnetic field, which is itself tilted 60 degrees from the planet's axis of rotation. The magnetotail was shown to be twisted by the planet's rotation into a long corkscrew shape behind the planet. The magnetic field source is unknown; the electrically conductive, super-pressurized ocean of water and ammonia once thought to lie between the core and the atmosphere now appears to be nonexistent. The magnetic fields of Earth and other planets are believed to arise from electrical currents produced in their molten cores. Uranus' Rings In 1977, the first nine rings of Uranus were discovered. During the Voyager encounters, these rings were photographed and measured, as were two other new rings and ringlets. Uranus' rings are distinctly different from those at Jupiter and Saturn. The outermost epsilon ring is composed mostly of ice boulders several feet across. A very tenuous distribution of fine dust also seems to be spread throughout the ring system. There may be a large number of narrow rings, or possibly incomplete rings or ring arcs, as small as 50 meters (160 feet) in width. The individual ring particles were found to be of low reflectivity. At least one ring, the epsilon, was found to be gray in color. The moons Cordelia and Ophelia act as shepherd satellites for the epsilon ring. Uranus Statistics Discovered by William Herschel Date of discovery 1781 Mass (kg) 8.686e+25 Mass (Earth = 1) 1.4535e+01 Equatorial radius (km) 25,559 Equatorial radius (Earth = 1) 4.0074 Mean density (gm/cm^3) 1.29 Mean distance from the Sun (km) 2,870,990,000 Mean distance from the Sun (Earth = 1) 19.1914 Rotational period (hours) -17.9 Orbital period (years) 84.01 Mean orbital velocity (km/sec) 6.81 Orbital eccentricity 0.0461 Tilt of axis (degrees) 97.86 Orbital inclination (degrees) 0.774 Equatorial surface gravity (m/sec^2) 7.77 Equatorial escape velocity (km/sec) 21.30 Visual geometric albedo 0.51 Magnitude (Vo) 5.52 Mean cloud temperature -193°C Atmospheric pressure (bars) 1.2 Atmospheric composition HydrogenHeliumMethane 83%15%2% Animations of Uranus Historical background: Discovery of Uranus. Magnetic field of Uranus. Core & magnetic field of Uranus. Views of Uranus Uranus The greenish color of it atmosphere is due to methane and This view of Uranus was acquired by Voyager 2 on January 10, 1986. The blue-green appearance of its atmosphere results from methane and high-altitude photochemical smog. This gas absorbs red wavelengths from the incoming sunlight, leaving the predominant bluish color seen here. Towards the bottom of the image a few clouds can be seen. This image is one of the few Voyager pictures that shows this type of cloud. (Copyright Calvin J. Hamilton) The Interior of Uranus Our knowledge of the internal structure of Uranus is inferred from the planet's radius, mass, period of rotation, the shape of its gravitational field and the behavior of hydrogen, helium, and water at high pressure. Its internal structure is similar to that of Neptune except for the fact that it is less active in terms of atmospheric dynamics and interior heat flow. This cut-away view shows Uranus composed of an outer envelope of molecular hydrogen, helium and methane roughly the mass of one to two Earths. Below this region Uranus appears to be composed of a mantle rich in water, methane, ammonia, and other elements. These elements are under high temperatures and pressures deep within the planet. The mantle is equivalent to 10 to 15 earth masses. Uranus's core is composed of rock and ice, and is likely no more than one Earth mass. (Copyright Calvin J. Hamilton) Uranus with its Rings This is the highest resolution image of Uranus with its rings ever assembled. Four separate images were mosaicked together to create the picture of Uranus. The rings were made from two high resolution images of Uranus's rings in which a strip was cut out and projected for a full 360 degrees. The rings and planet are to scale