Life on Jovian Moons Astrobiology Chapter 9 Day_23

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

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? 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  2 nd 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 features No pooling of liquids Huygens landing site – dry Cassini – evidence of lakes & rivers

Cassini - Huygens Cassini – evidence of lakes & rivers Liquid 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 C 6 H 12 O O 2 6 CO H 2 O + energy Possible reactions on other worlds: 2 Fe +2 + ½ O H + 2 Fe +3 + H 2 O Redox reactions produce energy which may be utilized by microbes. Iron and Sulfur are important.