Moons of the Jovian Planets: Satellites of Ice and Rock · What kinds of moons orbit the jovian planets? · What makes Jupiter's Galilean moons unusual? · What makes Saturn©s moon Titan different from other moons? · Why are small icy moons more geologically active than small rocky planets? What kind of moons orbit the jovian planets? · Two kinds: Medium and large moons: mostly formed at the same time as their planets (nearly circular orbits, all in the same direction). Small moons: mostly captured asteroids and comets (mildly to extremely elliptical orbits, even retrograde ones). Medium & large moons · L o ts o f ic e · Active resurfacing in the past (some moons even today) · Enough self- gravity to be spherical: young, Ámolten© moon rock and ice ran Ádownhill© [like water on Earth] until it made a sphere [on which there is no more Ádownhill©] What makes Jupiter's Galilean moons unusual? IO EUROPA Ganymede Callisto Io's Volcanoes Io is the solar system©s most volcanic world. Tidal stress cracks Europa's surface ice, which floats to new positions on a subsurface ocean of water or slush. Interiors of Io & Europa are warmed by tidal heating. What makes Saturn©s moon Titan different from other moons? What makes Saturn©s moon Titan different from other moons? · Only moon with an atmosphere: 90% nitrogen, plus argon, methane, hydrocarbons (smog!). · Methane & ethane are greenhouse gases. · Still cold: 93 K (-180 degrees C) · Chemical reactions on Titan produce organic, chemicals (hydrocarbons, etc.) · Cassini spacecraft images show a young surface (few craters) but with evidence of hydrocarbon lakes only at the poles. · Possibly a captured Neptune's Moon Triton K u i p e r b e l t o b j e c t : orbiting Neptune opposite Neptune's direction of rotation · Neptune©s tidal bulges (caused by Triton) are pulling backwards on Triton, slowing it down into a future crash into Neptune. · Smaller than Earth's Moon, yet has recent geological activity (nitrogen geysers). Uranus' small moon Miranda shows huge cliffs & tectonic activity, and few craters. Why are small icy moons more geologically active than small rocky planets? · Hot interiors needed for geological activity. · Ice deforms more easily than solid rock ± Less internal heat is required ± Smaller objects can be geologically active. · Tidal heating important for some icy moons, but not for rocky planets (example: the Moon©s tides are slowing down the Earth, but not heating it up by any significant amount). What have we learned? · What kinds of moons orbit the jovian planets? · We can categorize the more than 100 known moons as small, medium-size, or large. · Most medium-size and large moons probably formed with their planet in the disks of gas that surrounded the young jovian planets. · Small moons are most often captured asteroids or comets. · What makes Jupiter's Galilean moons unusual? What have we learned? · Io is the most volcanically active object in the solar system. Europa may have a deep, liquid water ocean under its icy crust. Ganymede also thought to have a subsurface ocean. · What makes Titan different from other moons? · Titan is the only moon in our solar system with a thick atmosphere. It has a young surface with lots of contrasting features, but we don©t yet know what they are. What have we learned? · Why are small icy moons more geologically active than small rocky planets? · Ices deform and melt at much lower temperatures than rock, allowing icy volcanism and tectonics at surprisingly low temperatures. .