Great God! I'd rather be A Pagan suckled in a creed outworn; So might I, standing in this pleasant lea, Have glimpses that would make me less forlorn; Have sight of Proteus rising from the sea; Or hear old Triton blow his wreathed horn. William Wordsworth, The World Is Too Much With Us

Assignment: Read in Explorations, pp. 307-313 Sign up for Observing Lab #3

In Class: Question to Ponder Saturn's moon Titan has a substantial atmosphere while larger objects such as Ganymede and Callisto and even Mars don't because a) Titan is made of gas-rich material. b) Titan has a higher density. c) Titan has recently been volcanically active. d) the temperature of Titan's atmosphere is really cold. Uranus Substantially smaller than Jupiter and Saturn, but still much larger than Earth. Much farther away -- Saturn is only halfway to Uranus. Big deal is that the rotation axis of Uranus is tipped over. Most planets' rotation axes are tilted by 0-25 degress compared to their orbital axes. Uranus' tilt is 90 degrees. Hard to figure out how it could've formed this way. Maybe it was hit early on by a large planetesmal that knocked it over. Moons: five major ones. Rings: three thin wispy ones. Neptune We really know very little about this planet. Similar in size and mass to Uranus. "Only" another 10 A.U. further from the Sun. Two interesting outer moons: Triton and Nereid. Both moons orbits suggest that they're capture products and did not form with Neptune. Triton Relatively big moon (bigger than Pluto, not quite as big as our Moon). Icy surface, but density suggests rocky core -- differentiated. Atmosphere is mostly nitrogen. Nitrogen freezes out in winter, sublimates back into the atmosphere in summer. Springtime "vents" or "volcanoes" are present as nitrogen goes back into gas form. Pluto Similar in composition to Triton -- maybe both were once little outer planets. Has moon Charon. We really don't know much about this planet -- no spacecraft visits. More Plutos? Kuiper Belt is a region betyond Neptune's orbit filled with objects like Pluto Most are much smaller, but a few are comparable, and one --- 2003 UB313 -- is larger than Pluto. Some consider that Pluto really shouldn't be a planet -- just one of the largest of the Kuiper Belt objects.