Transcript Day_32
ASTR-1010 Planetary Astronomy Day - 32 Jupiter Course Announcements Homework Chapter 9: Due Wednesday April 13. Exam 3: Will be returned on Monday. The last 1st Quarter moon observing nights are: Tuesday (April 20) & Thursday (April 22) 8:00 pm both nights. Jupiter rotates faster at the equator than at the poles Polar Rotation Period 9 hr 55 min 41 sec Equatorial Rotation Period 9 hr 50 min 28 sec Models of the Interior • Temperatures and pressures have been measured only in the outer layers. • Models are used to calculate interior conditions. • Giant planets have rocky cores and hot, dense interiors. • Jupiter/Saturn (gas giants) have more hydrogen and helium. • Uranus/Neptune (ice giants) have more water and ices (ammonia, methane). Planetary Interiors Density / Compression • Density is a clue to composition. • In an uncompressed state – Hydrogen/helium (lowest density) – Water/ices – Rock – Metals (highest density) • Density can also be increased by compression from weight of upper layers. • Interiors are extremely hot and dense. Origins • Jupiter / Saturn formed from accretion disk while hydrogen / helium still present. • Solar wind later blew out these gases. • Uranus / Neptune formed later, by merger of icy smaller bodies. • All four possess a rocky core. • Many details still not understood. Magnetic Fields • Magnetic fields are generated by the motion of electrically charged materials. • Like having a large bar magnet in the planet. • Magnets have N and S poles. • Orientation of these at an angle to the rotation axis. • Orientations differ from planet to planet, and are not understood. Magnetic Fields Magnetospheres • Magnetospheres are huge (Jupiter’s 6 AU). • They interact with the solar wind. – Auroras (“Northern lights” on the Earth). – Produce strong radio waves. • Radio waves come from synchrotron emission: electrons on spiral motions in the magnetic fields. Jupiter has an enormous magnetosphere The Liquid Metallic Hydrogen creates the intense magnetic field Saturn’s Magnetosphere is not as strong as Jupiter’s The magnetic fields of Uranus & Neptune are highly tilted and off centered Concept Quiz – Heat How do we know Jupiter has a significant amount of internal heat? A. It emits strong radio waves. B. Its atmosphere is mainly hydrogen and helium. C. It is hotter than expected at its distance from the Sun. Concept Quiz – Composition Which two giant planets have a larger fraction of water than the other two? A. B. C. D. E. Jupiter and Saturn Uranus and Neptune Jupiter and Neptune Saturn and Neptune Uranus and Jupiter Concept Quiz – Density You discover a giant planet around another star. It is as big as Jupiter, but much more dense. What does the density tell you? A. It has less hydrogen and helium than Jupiter. B. It has a lower mass than Jupiter. C. Like Jupiter, it is probably hot inside. The facts on Jupiter Shoemaker-Levy 9 was a “String of Pearls” comet SL9’s impact in 1994 dredged up material from deep inside SL9 A Impact Sequence SL9 G Impact If the G-fragment had hit Earth… SL9 Impacts gave Jupiter a Black eye The facts on Saturn A Saturnian Year Ring Nomenclature The Ring Structure The rings of Uranus were discovered by occultation Uranus has thin rings and several moons Neptune has rings, too The Jovian system is a mini solar system