Life on Jovian Moons

AstrobiologyChapter 9Day_23

Announcements

HW – Chapter 9: Due Tuesday 4/12 1, 5, 16, 24, 25, 28, 36, 41, 47, 48

1st Quarter moon observing nights Monday 4/12 – 7:30pm Tuesday 4/13 - 7:30pm

Jovian Planets

Jovian planets: Jupiter, Saturn, Uranus, Neptune

Sunlight is too weak to provide much energy J, S, N all have internal energy production All have massive magnetic fields Surface gravities – Appendix E (pg A-15) Densities – light materials

Jovian Moons

All have moons: Table E-3 (~150 and growing) Big moons: these are the interesting ones (for us) Small moons: just so much space junk

1610 – Galileo – discovered 4 bodies orbiting Jupiter (the Galilean moons)

1656 – Huygens – discovered Titan at Saturn By 1700 – Cassini – 4 more at Saturn

Jupiter

Galileo's observing notes - 1610

Galilean Moons Today

Big Moons

G, Titan are larger than Mercury

E, C, I, and Triton are larger than Pluto

Our Moon is #4, Between E & I in size

Orbit planet in “proper” direction. (mini-SS).

Formation Formed in the

proto-planetary nebula, along with host planet.

Gives: Orbit direction composition

Small Moons

Irregular shapes High inclination orbits

Some retrograde Highly elliptical orbits

Suggest captured asteroids or KBOs or TNOs

Triton

Composition Ices could condense

Rock and ice – found Low average densities Variation within systems

Temp. gradient in P-PN Jupiter – water ice

Probably nothing else Outer planets

Water, methane, other

Rotation

Nearly all show synchronous rotation Keep same side toward host planet

Results from tidal forces Tidal drag Europa – very slight deviation

Earth

Tidal friction lengthens the day by 1 second in about 50,000 years.

Earth

Tidal friction lengthens the day by 1 second in about 50,000 years (Earth spin slows).

Conservation of angular momentum requires that the moon move farther away.

Io

Tidal heating – 1979 – Voyager 1 – volcanoes Close to Jupiter – strong tidal forces Slightly elliptical orbit – large changes in tidal force

Orbital Resonance

4:2:1 (I:E:G) Moving out toward

Callisto (not currently in resonance orbit).

Other Heat Sources

Radioactive decay Internal generation

Iapetus May have had liquid

or soft interior at one time.

Life on Galilean Moons

Io – extreme tidal heating, no water => no life Callisto – no tidal heating (not in resonant orbit) Ganymede, Europa – tidal heating, but might be

a good thing for these.

Europa

Liquid water ocean? 1979 – Voyager

Differentiation – water Smooth surface Ice covered

Galileo s/c – long term monitoring Subtle variations Internal structure

Galileo spacecraft view

Europa - ocean

Lack of impact craters, brittle icy crust? 80-170 km crust Liquid underneath – gravitometer measurements 1996 – magnetic field – opposes Jupiter's

Chaotic terrain

Recent water breakout?

Evidence for Ocean

Small number of craters – young surface Surface features – suggest water from below Magnetic field – something conducts electricity Tidal heating supplies enough heat to melt ice.

Proof: Europa mission Long-wave radar Laser altimeter

Life on Europa

3 key elements for life Source of elements/molecules to build living organisms Source of energy for metabolism & growth Liquid medium for transporting molecules

Good, indirect evidence of liquid water ocean. Expect elements for life in ocean and on floor. Possible energy sources, but small wrt Earth.

Energy question But, how do you use it? To use warm water

energy, you have to have a cold sink.

How wide spread could life be? On Earth, very little life

derives its energy & material directly from volcanic vents.

Ganymede

Largest in solar system Has old and young

surfaces Intrinsic magnetic field Variation of field with

Jupiter rotation – liquid High-density ice forms

Types of Ice

Callisto

Farthest out of the four. Old surface. Evidence of ice

sublimation (powder) Magnetic field – ocean? Much less energy

Saturn and Beyond Titan

2nd largest moon in SS Thick atmosphere

1.5 X Earth pressure Cold -180C 90% Nitrogen, 0 Oxygen Methane, Argon, Ethane Lower impact velocities

Cassini - Huygens

Coastline-like featuresNo pooling of liquids Huygens landing site – dryCassini – evidence of

lakes & rivers

Cassini - Huygens

Cassini – evidence of lakes & riversLiquid methane lakes near pole?

Wind blown dunes?

Life on Titan?

Solid ice, no liquid water Other liquid hydrocarbons (methane)

Slower chemical reaction rates UV produces a lot of organic molecules in the

atmosphere. These should settle out and build on the surface.

Energy sources? Cryovolcanoes? Acetylene reactions

Enceladus Several of Saturn's moons

show evidence of past geological activity.

Enceladus - current activity. Fresh ice Ice spray – water? Subsurface ocean

ammonia/water mix Tidal heating

Triton Backwards orbit

Suggests captured KBO Resurfacing actions Internal heat source

Tidal heating Radioactive decay?

Cryovolcano activity

Chemical Energy

For life, need “disequilibrium” Redox reactions

C6H

12O

6 + 6 O

26 CO

2 + 6 H

2O + energy

Possible reactions on other worlds:

2 Fe+2 + ½ O2 + 2 H+ 2 Fe+3 + H

2O

Redox reactions produce energy which may be utilized by microbes.

Iron and Sulfur are important.