The Moons of the Gas Giants

The Moons of the Gas Giants

Astronomy 311Professor Lee

CarknerLecture 20

Why do the rings of Uranus and Neptune look dark?

a) They are made of small silicate particlesb) They receive very little light from the sunc) They only radiate light at ultraviolet

wavelengths d) They are covered with carbon soote) The rings are blocked by a screen of dust

The blue and white colors we see in the atmospheres’ of Uranus and Neptune are due to,a) gaseous helium and water cloudsb) ammonia clouds and sulfur cloudsc) gaseous methane and methane

clouds d) gaseous methane and carbon dioxide

cloudse) the fact that light is sometimes absorbed

and sometimes scattered off ice crystals in the atmosphere

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

The Galilean Moons

The 1st, 3rd, 4th and 6th largest

moons in the solar system

Made from rock and ice

Orbits of the Galilean Moons

1 rotation on its axis per 1 revolution around Jupiter

This is due to the small separation between the inner moons

Formation of the Galilean Moons

The inner parts of the nebula were hotter than the outer The inner satellites (Io and Europa) formed mostly from

rock

The inner 3 satellites experienced tidal heating and differentiated into a rocky core and an icy crust Much of the energy that powers the large moons of

the solar system comes from tidal heating

The Interiors of the Galilean

Moons

Galileo Visits the Galilean Moons

Made several passes by each moon

Galileo refused to die and kept taking data up to Sept 2003 deliberate crash into Jupiter

Galileo has achieved imaging resolutions up to 50 times better than Voyager

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

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

Callisto shows few signs of interior or surface activity

Large impact basin Valhalla

3000 km in diameter impact occurred about 4 billion years ago

Titan

Most distant planet sized solid body Thick atmosphere make the surface

impossible to see

Titan is large enough to have a reasonably strong gravitational field

Titan’s Atmosphere Titan has a thicker atmosphere than the Earth

Titan’s atmosphere may have originally been

composed of ammonia (NH3) and methane (CH4)

90% of the atmosphere is N2

Much of the rest is methane

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 maybe lakes

Titan is very cold (95 K=-288 F) and so it would be difficult for life to form

Triton

It is probably a captured Kuiper belt object 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 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

Ganymede 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

Titan 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