Saturns Satellites Discussion What does the density of Saturns satellites tell you about their composition? Discussion Why dont the satellites of Saturn show a density gradient like the Galilean satellites of Jupiter? Epimetheus Janus Mimas Enceladus Enceladus backlit South pole composite image Heat map of South pole region Geysers Tethys Telesto & Calypso Dione Helene Rhea Titan Hyperion Iapetus Leading side Trailing side Discussion Can you think of a reason why one side of Iapetus should be so much brighter than the other? Tenuous ring near Phoebe Equatorial ridge 10 km high equatorial mountain Phoebe Titan Methane absorption lines Reflected light spectrum from Titan Discussion How can Titan have an atmosphere, whereas the more massive Mercury does not? Voyager 1 Composition: 90% nitrogen 1.5 atm With trace amounts of methane (CH 4 ), argon, hydrogen, carbon monoxide, ethane (C 2 H 6 ), acetylene (C 2 H 2 ), propane (C 2 H 8 ), hydrogen cyanide (HCN). Discussion Why does Titan have hydrogen in its atmosphere? I thought hydrogen couldnt be held by anything less massive than a Jovian sized planet. Discussion With all the flammable gasses in Titans atmosphere why doesnt the satellite explode? Why does Titan still have methane in its atmosphere? At the present rate of destruction, all of the methane now in Titans atmosphere should be gone in a few million years. Thus, there must be some source of methane such as comets, volcanoes, or underground springs. Discussion Why is there no carbon dioxide in Titans atmosphere? Hint: surface temperature on Titan is -180 C Discussion Why doesnt Ganymede have an atmosphere? Escape velocity 2.7 km/s Surface temperature 110 K about the same as on Titan Discussion Why does the atmosphere around Titan appear blue? The aerosols cannot stay suspended forever As the polymers grow longer they will precipitate out of the atmosphere and onto the surface. Titan may have bodies of liquid ethane on its surface. Huygens probe Earth Sand dunes Titan Frozen ethane dunes? Ice Giants Discussion Both Uranus and Neptune have about the same size, 4 times the radius of the Earth, but Neptune has more mass than Uranus, 17.2 M e and 14.5 M e respectively. What does this tell you about Neptune? Atmospheres Both planets have about the same atmospheric composition: UranusNeptune Hydrogen82.5%80% Helium15.2%19% Methane2.3%2% And the same temperature at their cloud tops -360 F or 55 K. Discussion How can Uranus and Neptune both have the same temperature, when Neptune is much farther from the Sun? Differences Neptune is denser and has a significant internal heat source while Uranus does not. Neptunes atmosphere has belts, storms and high clouds, while Uranuss atmosphere is bland and featureless. Uranus Neptune Discussion The blue/green color of Uranus and Neptune are caused by methane. What do you think happens when ultraviolet light breaks up this methane? Discussion Why is Uranuss atmosphere so plain compared to Neptunes? Uranus Discussion How do you think we got the previous plot of the density profile of Uranuss atmosphere? Uranus and the seasons Uranus false color Uranus HST infrared image Neptune HST infrared image