Astronomy 340 Fall 2005 15 November 2005 Class
Astronomy 340 Fall 2005 15 November 2005 Class #19
Organizational n n n I’m back!!! HW #3&4 is due on Thursday – hope you’re making progress “Paper” is due on the same day as the final. Remember, you need to get approval for your topic
Review n Europa q q q Surface spectroscopy H 2 O ice Tidal effects interior should be warm enough for liquid water Young surface (10 -20 Myr) Weak magnetic field some sort of conductive layer Distinctive surface features n n Cracks/ridges indicative of stretching (same behavior in terrestrial ice) Rougher terrain localized heating/melting
Europa cont’d n Internal heating q q n Heat flow ~ 0. 2 W m-2 L = k(ΔT/F) = 3 km if ΔT ~ 173 K (273 K 100 K) Gravity q q Differentiated with 80 -200 km ice/liquid H 2 O shell over silicate/metal mantle Core?
Commensurate Orbits n Io: Europa: Ganymede 1: 2: 4 (orbital periods) q q n 1 -3 n 2 +2 n 3 = 0 n = mean motion or average angular speed Three moons never line up on the same side of jupiter
Titan n n Discovered in 1655 by Huygens 2 nd largest moon q q n R = 2575 km Density = 1. 9 gm cm-3 Orbital properties q q 4: 3 resonance with Hyperion Somewhat eccentric effect of tidal forces?
Titan’s Surface
Titan’s Atmosphere n n 1 st detected 1944 Composition (pre-Cassini) q q q n CH 4 plus some C 2 H 6, CH 3 D, C 2 H 2, HCN Voyager detected N 2 98% N 2 Pressure comparable to Earth’s CH 4 cycle q q q Liberated from ethane/methane oceans Some migrates upwards Dissociation & photolysis H 2 + hydrocarbons n n n H 2 may escape Cx. Hy haze/clouds remain Possible methane/ethane snow/rain
Titan’s Clouds (Griffith et al. 2000) n Techniques q q Variations in brightness = variation in albedo = presence of clouds Spectral windows = different depths n n Stratosphere reflects at 2. 17 -2. 4 μm Deep into atmosphere, but not surface 2. 12 -2. 17 μm Surface 2. 0 -2. 11 μm Results q q q Variations in brightness in 2. 12 -2. 17 μm window Low covering factor (<5%) Altitude ~ 25 -30 km
Titan’s Clouds (Samuelson et al 1983) n Effects of surface temperature variation Tsurf ~90 -95 K, lows ~70 K, highs ~180 K n Atmospheric processes n q q q Greenhouse effect Absorption via hydrocarbons Photolysis of CH 4 reservoirjj
Titan’s Surface – Radar Mapping
Titan’s Surface
Titan’s Surface Note variation in color variation in surface features Bright spot is of particular interest CO 2 ice?
Titan’s Surface
- Slides: 14