1Class 24Uranus, Neptune and minor bodies Uranus and Neptune Structure and atmospheres of the planets Rings and Moons Minor bodies Asteroids Trans-Neptunian Objects Comets2I : Uranus and Neptune Discovery… Uranus discovered by chance in 1781 by Herschel Careful observations revealed perturbations in orbitof Uranus… was suggested that gravity of an 8thplanet was responsible Neptune discovered by Galle in 1846 Principal features Higher proportion of heavier elements comparedwith Jupiter and Saturn Have distinct blue appearance due to methane inatmosphere Uranus… no internal heat source, so little weather Neptune… still undergoing gravitational contractionwhich drives active weather system Possess dark rings (radiation darkened)3456Satellites of Uranus (+ 11 smaller bodies)7II : Asteroid belt Asteroid belt can be thought of as a “ring”around the Sun If not for Jupiter, another terrestrial planet wouldprobably have formed here But Jupiter disturbed/ejected the planetesimals inthe early solar system and prevented such a planetfrom forming… left the asteroid belt Resonances with Jupiter leave gaps (Kirkwood gaps) Largest asteroid is Ceres (1000km diameter)…most are much smaller Most asteroids are in Asteroid Belt, but someare on orbits that cross that of the otherplanets… eventually strike one of the planet8910III : TNOs, Oort Cloud and Comets There are two places where we havelarge icy bodies orbiting the Sun(“Trans-Neptunian Objects”)… Kuiper Belt… ring of icy objects orbiting Sunbeyond Neptune… most famous is Pluto Oort Cloud… a distant spherical “cloud” oficy bodies surrounding the Sun If icy objects are disturbed from theirorbits, can fall into inner solar systemand become a comet111213Painting by William Hartmann400km from ground-zeroPainting by William Hartmann60km from ground-zero14151617Geological anomalies at the K-T boundary18The K-T impact… Initial impact of a 10km asteroid or comet Atmosphere has almost no effect on incoming object…strikes surface at full speed. Explosion yield of approximately 100 million megaton TNTequivalent Impacting asteroid and approx 100km3 of Earth rock arevaporized and thrown 100km into the atmosphere Intense fireball and blast wave flattens and igniteseverything for few x 1000 km across Molten debris rains down across planet, seeding massivewildfires – 90% of all plant life burns. Huge earthquakes cause massive Tsunamis… devastatecoastlines around the globe. Next 10-1000 years… Atmospheric debris and smoke completely blocks theSun from reaching the surface Temperature plummets (like “nuclear winter”). Photosynthesis stops and most plants die Food chain collapses Eventually, debris settles out of atmosphere and theSun starts to shine again… But then there’s dramatic global warming… Carbon dioxide from fires causes a greenhouseeffect… temperature rises and planet becomes toohot! This lasts for an unknown length of time… Few species survive this