Friday March 17:

● Assignment #1 will be handed back at end of today (also next week). Average: 14/18 = 78%

● Assignment #1 solutions now on WebCT

● Assignment #2 due Friday, Mar 31

● Monday March 20: Guest lecture from Dr. Martin Duncan, on “The Kuiper Belt and Outer Solar System”

Outer Planets and Moons Continued

Motivation:

● Outer moons contain very exciting possibilities for life, especially Europa, Enceladus, and Titan

● If life found in the outer solar system, it extends the habitable zone, and the range of domains for which to search for life

● Titan may tell us a lot about what conditions were like when the Earth was young

● Extrasolar planets are all “hot Jupiters”, so we should learn more about these big planets

Exploration of the Outer Planets

● Pioneer 10/11 (1970s)

Jupiter, Saturn

● Voyager 1/2 (1977-1989):

Jupiter, Saturn, Uranus, Neptune

● Galileo (1995-2003):

Jupiter and its moons

● Cassini/Huygens (2004-Present):

Saturn and its moons

Life On (in?) Jupiter and Saturn

Pro

● Organic chemistry very likely producing simple organic compounds.

-- could more complex organic compounds also be produced? e.g. to explain cloud colours?

● There is a region in atmosphere where temperature (27 C) and pressure (few times Earth) allows liquid water to exist as clouds

-- Jupiter has internal sources of heat, so temperatures not so cold as one might think

-- water is available

Con

● Ammonia toxic to most (but not all) LAWKI

● No solid surfaces to help concentrate and polymerize organics

● Deep convection mixes upper and lower atmosphere on 300 year (or shorter) time scales

-- extreme climate change on short time scales

-- proto-life environs mixed down to much different environment (higher T, different chemicals)

Summary:

● If life exists in/on Jupiter, it's probably in upper atmosphere, where there are water clouds, reasonable temperatures and pressures.

● Maybe there are “floaters”, balloon life-forms drifting through the clouds? (Carl Sagan)

● Neither Jupiter or Saturn are seriously considered as possible sites for life

Lynette Cook

Saturn's Moons

Titan

● Titan is Saturn's largest moon, like Ganymede in size and composition. It's bigger than Mercury.● Titan has a dense atmosphere, ~1.5x denser than Earth!

-- even though Titan 45x less massive than Earth, it's cold enough (85K) to retain an atmosphere against thermal escape● Very interesting atmosphere! 97-98% N

2, 1-2% CH

4, traces

of H2, CO, C

2H

6, C

2H

4, C

2H

2, H

2O, CO

2

-- Many complex chemical reactions happening

-- Photochemical reactions: Solar UV photons break up CH4

and produce other hydrocarbons in atmosphere

-- Photochemical Smog: long-chain hydrocarbons

● Could even more complex organics be present? HCN is starting point for some components of DNA; CO and CO

2 makes

formation of amino acids possible

● Could have rain or snowfall of organic material onto surface

● There could be oceans of methane and ethane! Methane and ethane would both be liquid at pressure and temperature (95K) of Titan's surface

● However: -- Earth-based radar data rule out deep, global oceans

-- Huygens did not see any evidence for liquid (later)

● No evidence for surface liquid at present time (but probably in the past-- later)

-- but still pretty exciting, and possibility of life in an ocean!

● This is very interesting organic chemistry even though it's not LAWKI: organic compounds and maybe liquid solvent ...

Cassini-Huygens Mission to Saturn and Titan● Arrived July 2004, to spend 4 years studying Saturn and moons

● In Dec 2004, Huygens probe dropped onto Titan

● Both Cassini and Huygens studying surface, atmosphere of Titan with several instruments

Cassini InstrumentsOptical Remote Sensing

Composite Infrared SpectrometerImaging Science SubsystemUltraviolet Imaging SpectrographVisible & IR Mapping Spectrometer

Fields, Particles and Waves

Cassini Plasma SpectrometerCosmic Dust AnalyzerIon and Neutral Mass SpectrometerMagnetometerMagnetospheric Imaging InstrumentRadio & Plasma Wave Science

Microwave Remote Sensing

RadarRadio Science

Huygens Instruments

Atmospheric Structure Instrument

Doppler Wind Experiment

Descent Imager/Spectral Radiometer

Gas Chromatograph Mass Spectrometer

Aerosol Collector and Pyrolyser

Surface-Science Package

Titan Pictures

Titan Science Results: Nature, Vol. 438, 8 Dec 2005

Titan's Atmosphere

● N2 and CH

4 confirmed as main species

● Must be geological source to replenish CH

4

● 12C/13C ratios show no evidence for biota

● Trace organic species (e.g. cyanogen/ethane) found on surface

● 14N depleted-- loss of 5x present atmosphere

● Detection of N-containing organic compounds (amino groups?)

Titan's Atmosphere: The Big Picture

Titan's Surface

● Huygens landed on “soft, solid surface” like damp sand-- probably mix of ice chips, precipitated aerosols, and liquid methane.

●So methane cycle of rain and evaporation!

● No evidence from Cassini or Huygens for large amounts of liquid on the surface, but spectacular images of river networks and drainage channels.

●So liquid methane has flowed on the surface in the past-- how recently?

●Could be water ice on the surface-- unclear

Titan's Surface

Titan Summary

Chances for life on Titan are small:

●very cold on surface (95 K)

●little water

●what energy source? Not much sunlight penetrates clouds

●no evidence for biota

But:

●complex organic chemistry on surface and in atmosphere

●evidence for liquid methane (and ethane?) on surface

●methane could be locked in ice covering ocean of water and ammonia (methane released by cryovolcanism)

Saturn's Moon Enceladus:Science, Vol 311, 10 Mar 2006

“Tiger Stripes”

Enceladus● Very active: south polar hot spot, deep canyons and thick flows on surface, and plume of H

2O, CO

2, CH

4, N

2

● Heat source: likely tidal heating and heat retention

● Source of plume: deep, gas-saturated ocean or deep crustal pocket of water?

● Life habitat? Would be hard, as on Titan ...

EnceladusMovie

Triton

● Triton is Neptune's largest moon, similar to Pluto in composition, about half size of Titan, probably captured

● Surface temperature only 37K (-235C)! Damn cold

● Frozen Methane and either liquid/solid Nitrogen on surface

● There is also a very thin atmosphere, about 16 millionths that of Earth. The pinkish color of Triton, plus haze and clouds in atmosphere tell us there is organic chemistry happening on the surface (like in atmospheres of Jupiter and Titan)

● Triton also very active: young surface, geysers up to 8km high: cryovolcanism

●So quite intriguing with this chemistry and activity: but must be too cold to be a good candidate for finding life.

Summary of Outer Planets

● No definite evidence for life on any of the outer planets or their moons, similar to Mars

● However, some really interesting possibilities: -- Jupiter's moon Europa-- Saturn's moons Titan and Enceladus

-- Neptune's moon Triton (?)-- and possibly atmosphere of Jupiter itself (maybe

Saturn?)

● Further exploration will be very exciting. Any signs of life in the outer solar system will extend the habitable zone in size, and will have huge implications for life on planets around other stars