Astronomy 340 Fall 2005 3 November 2005 Class

Astronomy 340 Fall 2005 3 November 2005 Class #18

Announcements & Review n EMW gone next week Paper assignment ready n Composition of giant planets n q q n How do we measure this? what are the salient results? Interior structure of giant planets q How do we have any clue about the interior structure of a gas ball?

Satellites of the Outer Planets Mercury Earth Pluto Moon Io Europa Ganymede Callisto Titan Triton 2440 6378 1150 1738 1821 1565 2634 2403 2575 1353 5. 43 5. 52 2. 0 3. 34 3. 53 2. 97 1. 94 1. 85 1. 88 2. 05

Questions n n n Do satellite systems act as miniature solar systems? How do satellites form? Orbital mechanics resonances and wacky orbits Relationship to ring systems Special cases tidal heating/volcanism Note discovery of Jovian satellites weakened geocentric cosmology

Jovian system vs solar system n n Prograde orbits in common plane Mass of Jovian satellites ~ MMars Mass of jovian satellites ~ 1% of heavy element abundance of Jupiter (similar to Sun) Jovian system extends ~30 RJ, while solar system extends ~200 RSun might just be a feeding zone question

Formation issues n Timescales q q n Compare predicted accretion timescales with planetary cooling times Callisto must have formed slowly (rapid accretion more melting) Taccretion ~ few Myr Orbits q “regular” satellites in circular, prograde orbits in planet’s equatorial plane

Io n n n No evidence of water ice unlike other Jovian satellites Net heat flow ~ 2. 5 W m-2 Tidal forces q q Recall tides circularize orbits 108 yrs Synchronicity minimizes tides, unless orbit is noncircular eccentricity gives rise to tides

Io n Slightly eccentric orbit (e=0. 004), proximity to Europa tidal forces stretch interior q q q n n Internal heating. Enough to yield volcanism Surface age ~ few 100, 000 yrs Impact on environment sulphur

Europa - Questions n n Does it have a subsurface ocean? What accounts for the linear features on surface? Chemical composition? Energy flux?

Subsurface Ocean (e. g Moore et al 2001 Icarus 151 93) n n n Surface spectroscopy – H 2 O ice plus impurities Tidal effects (6% effect); interior should be warm enough to melt ice Young surface – only 10 -20 Myr Weak (but existence) magnetic field Surface features q q q Cracks/ridges reflect stretched lithosphere Similar to behavior of terrestrial ice Regions of rough terrain – weak ice collapses, liquid boils up, refreezes, generates chaotic terrain

Europa n n Heat flow – 0. 2 W m-2 Conduction vs convection q q n Thickness = k (ΔT/F) ~ 3 km, where k = thermal conductivity 3. 5 W m 1 K-1 ΔT ~ 173 K (based to surface) Galileo gravity measurements q Differentiated with 80 -200 km

Commensurate Orbits n Io: Europa: Ganymede 1: 2: 4, three of them never all on same side of J at the same time.