The Moons of the Gas Giants Astronomy 311 Professor Lee Carkner Lecture 20

Jupiter’s Lovers Ganymede was Jupiter’s cup bearer Titan is so named because Saturn was the king of the Titans Triton was Neptune’s son

Galileo Visits the Galilean Moons Made several passes by each moon Galileo refused to die and kept taking data up to its Sept 2003 deliberate crash into Jupiter Galileo has achieved imaging resolutions up to 50 times better than Voyager

Formation of the Galilean Moons The inner parts of the nebula were hotter than the outer The outer satellites (Ganymede and Callisto) formed from rock and ice Much of the energy that powers the large moons of the solar system comes from tidal heating Need close, elliptical orbit

The Interiors of the Galilean Moons

Io Io has an elliptical orbit, so the tidal forces on it vary with time The hot interior produces massive volcanism and a differentiated interior Io has a iron core surrounded by a molten rocky mantle

Volcanism on Io Io has no impact craters Volcanoes produce plumes of material that extend up to 280 km above the surface Volcanoes can be very long lived Some have been observed for 20 years

Io’s Plasma Torus Ions are atoms that have lost an electron giving them a net electrical charge As Jupiter rotates its changing magnetic field produces an electrical current through the torus and interior of Io

Gravity and Energy An object of mass (m) launched off of the surface of a planet has kinetic energy: When it reaches its maximum height (h) it has potential energy equal to Where g is the acceleration of gravity for the planet where M is the mass of the planet, R is the radius of the planet and G = 6.67X10-11 (in units of m3 kg-1 s-2) KE = PE Note that all distances are in meters and masses are in kilograms

Europa Under the ice is water or warm fluid ice Tidal heating produces the internal energy Tidal flex may also crack the surface

Evidence for Warm Oceans on Europa Galileo has imaged faults where the ice has pulled apart and water as flowed up Galileo magnetometer measurements indicate that Europa has a variable magnetic field On Earth simple life forms evolved under water at warm deep ocean vents Could something similar have happened on Europa?

Models for the Interior of Europa

Ganymede Ganymede is the largest moon in the solar system Slightly larger than Mercury But, Ganymede shows evidence for surface alteration Did it once have a more eccentric orbit?

The Surface of Ganymede Old dark terrain Dark due to the ice being covered with dust from meteoroid impacts New bright terrain Bright due to fracturing of the icy surface

Callisto It has experienced the least tidal heating Fairly uniform mixture of ice and rock Covered with craters Large impact basin Valhalla impact occurred about 4 billion years ago

Titan Only moon with an atmosphere Why does Titan have an atmosphere? Most distant planet sized solid body Only moon with an atmosphere Why does Titan have an atmosphere? Titan is cold enough so that the gas in the atmosphere is slow moving

Titan’s Atmosphere 200 km deep with a surface pressure of 1.5 atmospheres Much of the ammonia was disassociated by UV light from the Sun and the hydrogen escaped 90% of the atmosphere is N2

Chemicals in Titan’s Atmosphere Titan’s atmosphere also contains hydrocarbons (composed of H and C) and polymers (long chains of H, N and C) Methane can rain from atmosphere and form streams and lakes Titan is very cold (95 K=-288 F) and so it would be difficult for life to form

Triton Triton is in a decaying, highly inclined (23 degrees), retrograde orbit Triton shows evidence of geologic activity Few craters Plumes of outgassing material When Triton was first captured it was probably in a highly eccentric orbit which resulted in tidal heating

Triton’s Atmosphere Triton is very cold (37 K) and thus nitrogen is mostly frozen on the surface A little bit of nitrogen evaporates to produce the atmosphere

Next Time Read Chapter 14.3

Summary The six large moons of the gas giants resemble the terrestrial planets of the inner solar system They can have volcanoes, atmospheres, and evidence of resurfacing In general they are cold and have rocky interiors and icy exteriors Some produce internal energy through tidal heating Europa and Titan may possibly have the conditions for life to exist

Summary: Io and Europa Io Europa Strong tidal heating produces massive volcanism Volcanism produces powerful outgassed plumes, sulfurous surface and plasma torus of ions Europa Icy surface shows evidence for water flowing up from interior May have a warm subsurface ocean due to tidal heating

Summary: Ganymede and Callisto Shows both old dark terrain and bright new terrain Must have had more internal heat to drive geologic activity in the past Callisto No tidal heating results in no differentiation Fairly uniform mixture of icy and rock with many craters

Summary: Titan and Triton Large size and low temperatures results in an thick atmosphere Atmosphere composed of nitrogen, methane, hydrocarbons and polymers Triton Has a decaying, inclined retrograde orbit Thin atmosphere and surface activity