1781: Uranus Discovered. The Outer Worlds. 1846: Neptune Discovered. Distance Comparison. Uranus Rotates Sideways. Exaggerated Seasons On Uranus

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1 The Outer Worlds 1781: Discovered (accidentally!) by William Herschel using a 6 inch telescope [he thought it was a comet!] 2 Draft 12/03/2006 Updated May 05, : Discovered Le Verrier: proposed that another planet was creating deviations in orbit of. Predicts position. John Couch Adams: independently does same Johann Gottfried Galle: (student of Encke) using Le Verrier s prediction, observes planet. 3 Sun Jupiter 12 year orbit Distance Comparison 1 AU 5.2 AU 9.6 AU 19.2 AU 30.1 AU 3.7% Saturn 29 year orbit 1.1% 86 year orbit 0.3% 165 year orbit 0.1% 4 Exaggerated Seasons On s axis of rotation lies nearly in the plane of its orbit, producing greatly exaggerated seasonal changes on the planet 5 Rotates Sideways 6 Seasons are 42 years long! This unusual orientation may be the result of a collision with a planetlike object early in the history of our solar system. Such a collision could have knocked on its side 1

2 Size Comparison 7 Density Comparison Item Jupiter Saturn 8 51,118 km (4.0 D E ) 49,528 km (3.8 D E ) Mass (earth masses) Density (kg/m 3 ) ,536 km (9.4 D E ) Albedo Temp Masses determined from orbits of their moons 12,757 km (1 D E ) 142,984 km (11 D E ) & are much higher density than expected, implies more heavier elements (INCONSISTENT with theories of planet formation which predict outer planets would be lighter in density) Temperatures of & are nearly the same! 1977 Rings Discovered Voyager 2 Probe 1986 Encounter 1989 Encounter 10 Sees thin, dark rings 11 Voyager at and Significant differences from Jupiter and Saturn bluish color very bland faint belts and zones and also a few storms much smaller (and less massive) than Jupiter and Saturn 12 2

3 : Atmosphere Nearly featureless, though recent Hubble images show some small storms 82.4%H, 15.2% He, 2.3 % CH 4 (methane) The blue tint is caused by methane Too cold for ammonia or water ice clouds, so any clouds are also methane Does not emit excess heat 13 Recent Hubble Pictures As the vernal equinox approaches, is becoming stormy: Heating of northern hemisphere produces storms, made visible by clouds of methane. 14 : Atmosphere Similar composition as (80% H, 19% He, 2% CH4) More storms and clouds Also belts and zones why? less should mean less active atmosphere =>, like Jup and Sat, emits more heat than it receives. This internal heat must drive atmospheric activity 15 s Clouds Much more cloud activity is seen on than on This is because lacks a substantial internal heat source 16 s atmosphere is being warmed from below by internal heat. 17 & : Winds Both and winds blow west at equator and east at N and S poles and mid-latitudes Not understood why s winds do not follow belts and zones like on Jupiter and Saturn Rotation: 17 Hours, 16 Hours 18 This extra heat drives large circular storms, like the Great Dark Spot seen above. 3

4 & : Magnetic Fields No metallic layer in interior fields generated by ionized liquid ammonia and water Rotated large amounts from spin vectors and offset from center perhaps currently undergoing reversal, does perhaps very large impact knocked them off line 19 & : Interior Structure Rocky core ~ size of Earth Liquid mantle probably NH 3 and H 2 O or related material Liquid molecular H and He with some liquid methane Thin atmosphere 20 +Rings+Moons 21 Some of s satellites show evidence of past tidal heating 22 has five satellites similar to the moderatesized moons of Saturn, plus at least 22 more small satellites. Biggest is 1600 km (i.e. half our moon s) Oberon (outermost moon) 23 Titania (next closer) 24 Old, heavily cratered, and icy surface. The LARGEST moon little evidence of internal activity other than some unknown dark material that apparently covers the floors of many craters. Has a few large impact basins, but is generally covered with small craters and very rough rocks. image shows several large impact craters towards the center of the image. On the limb, a high mountain rises 6 kilometers (4 miles) above its surroundings. There are bright rays similar to those seen on Jupiter's moon Callisto. Long 1,600 km trench large double walled crater can be seen towards the top of the image. many faults indicating there has been internal forces molding its surface. 4

5 Umbriel 25 Ariel 26 Brightest of the Uranian moons Darkest of the Uranian moons It is about the same size as Ariel and has about the same density. The surface appears to be old with large craters and does not change much from one location to another. Near the top is a puzzling bright ring called the fluorescent cheerio. It is probably the floor of a crater. It is about the same size as Umbriel and has about the same density. The surface is pock-marked with craters long rift valleys stretching across the entire surface. Canyons much like the ones on Mars appear in the pictures. The canyon floors appear as though they have been smoothed by a fluid. The fluid could not have been water because water acts like steel at these temperatures. The flow marks might have been made by ammonia, methane or even carbon monoxide Miranda 27 Miranda 28 Gigantic Scarp! huge fault canyons as deep as 20 kilometers Such a small moon should not have had any significant internal heating or evolution, so the features were quite a surprise. scientists believe that Miranda may have been shattered as many as five times during its evolution has 13 known moons. 12 are small (< 500 km across) and irregular. One is the giant moon Triton Proteus Triton Nereid 5

6 Triton is a frigid, icy world with a young surface and a tenuous atmosphere 31 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 s gravity into a retrograde orbit Triton has a tenuous nitrogen atmosphere Triton: 38K, frozen methane & nitrogen 32 Triton has craterfree plains; perhaps the frozen calderas of extinct ice volcanoes? Density of Triton = 2100 km/m 3 ; ice mantle over rocky core. 35 Triton has geysers 5 miles high driven by vaporized nitrogen. 36 Plumes are swept downwind in the very tenuous nitrogen atmosphere. 6

7 Triton is on a tilted retrograde orbit around It has most likely been captured by. Tidal forces are moving Triton toward. In 100 million years, Triton will enter the Roche limit. A farewell to the Solar System: Voyager 2 looks back at and Triton. Notes Polar caps are frozen nitrogen 7