Saturn’s Satellites
Discussion What does the density of Saturn’s satellites tell you about their composition?
Discussion Why don’t 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 couldn’t be held by anything less massive than a Jovian sized planet.
Discussion With all the flammable gasses in Titan’s atmosphere why doesn’t the satellite explode?
Why does Titan still have methane in its atmosphere? At the present rate of destruction, all of the methane now in Titan’s 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 Titan’s atmosphere? Hint: surface temperature on Titan is -180 C
Discussion Why doesn’t 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. Neptune’s atmosphere has belts, storms and high clouds, while Uranus’s 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 Uranus’s atmosphere so plain compared to Neptune’s?
Uranus
Discussion How do you think we got the previous plot of the density profile of Uranus’s atmosphere?
Uranus and the seasons
Uranus false color
Uranus HST infrared image
Neptune HST infrared image