Life Outside the Habitable Zone? Astrobiology Workshop June 27, 2006 Astrobiology Workshop June 27, 2006

Terrestrial Planet Region: Quick Review  MERCURY  MOON  VENUS  MARS X Terrible Extremes of Temperature No Atmosphere, UV, Cosmic Rays Little or No Volatiles, No Liquids Terrible Extremes of Temperature No Atmosphere, UV, Cosmic Rays Little or No Volatiles, No Liquids Been There, Done That X Absurdly High Temperatures No or Little Water Young Surface  No Fossil Record X ? Evidence for Liquid Water in Past Possible Environments for Life to Survive? Volatiles and Water Present Now

Gas and Ice Giant Planets: Interiors Gas Giant Planets Ice Giant Planets

Jupiter’s Interior: More Detail XXXXX

Gas and Ice Giant Planets: Atmospheres

Gas and Ice Giant Planets: Prospects for Life? Prospects for Life? There are ingredients for organic chemistry, and Atmospheric layers exist with roughly Earth-like Temperature & Pressure; But veryUranus NeptuneBut there are no solid surfaces (except ice crystals) and no liquid water (except very deep in Uranus and Neptune), Violent winds and convective turbulence would mix any life-bearing gas quickly over extremes of T & P. Although the sunlight is very weak, Internal heat is available. veryThey are very difficult to explore!

What about Moons of Planets? For instance, the Galilean Satellites of Jupiter Io Europa Ganymede Callisto

Moons of the Outer Solar System: Jupiter’s Io

Moons of the Outer Solar System: Jupiter’s Europa

Moons of the Outer Solar System: Io and Europa Jupiter’s Io ost volcanic  Is the most volcanic object in the Solar System due to  Tidal heating  Tidal heating caused by the gravitational tug of war it experiences from Jupiter and its sister Galilean satellites. Jupiter’s Europa weaker tidal heating,  Has similar but weaker tidal heating, water ice crust  Has a young cracked water ice crust perhaps only a few kilometers thick, and warm ocean of liquid water  May have a warm ocean of liquid water below the crust. life?  Could there be life?

Tidal forces are difference forces. Tidal Forces: Tides Raised on Earth by the Moon The misaligned bulges exert a small force on the Moon that increases the size of its orbit, while friction in the bulges slows the Earth’s rotation.

Tidal Heating of a Moon: Tides Raised by a Planet on its Moon Tidal heating occurs because Io and Europa’s orbits are Eccentric. The orbits stay eccentric due to a three-way orbital resonance among the three moons Io, Europa, and Ganymede.

Effects of Tidal Interactions Rotation synchronized  Rotation of moons become synchronized with their orbits.  They keep the same face toward the planet.  The rotation of the planet is slowed down.Orbits outward  Orbits of moons mostly evolve outward. Internal “Tidal Heating”  Eccentric orbits lead to periodic flexing of the moon’s shape which heats the interior.  Orbital resonances tidal heating  Orbital resonances with other moons can maintain eccentric orbits and tidal heating.

Roche Radius Roche Radiusabout 2 Planet Radii  Objects held together by their own gravity are shattered inside the Roche Radius (about 2 Planet Radii).  This is where most giant planet rings are.  Comet SL9tidally disrupted  Comet SL9 was tidally disrupted within the Roche Radius of Jupiter and destroyed Why doesn’t the Space Shuttle get disrupted? Why don’t we get disrupted?

Tidal Disruption: Comet Shoemaker Levy 9

Moons of the Outer Solar System: Saturn’s Enceladus Saturn’s Enceladus 500 km  Small icy moon (500 km) in diameter  Young, crater-free surface regions with like those on Europa  Orbit resonance with Dione  South polar hot spot and ice plumes  Thin “atmosphere” of water vapor  Subsurface ocean!?

Moons of the Outer Solar System: Saturn’s Enceladus Surface Temperatures on Enceladus Ice Plumes from Enceladus

Moons of the Outer Solar System: Saturn’s Titan Saturn’s Titan denser than Earth’s 100K  The atmosphere is denser than Earth’s but very cold (100K) and mostly CH 4 and N 2 smog-like clouds  It is completely enshrouded in smog-like clouds  Methane  Methane acts like water there.  There are few craters on the surface.  Surface eroded by liquids but no oceans.

Moons of the Outer Solar System: Titan’s Atmosphere

Moons of the Outer Solar System: Saturn’s Titan

Moons of the Outer Solar System: Movie of Huygen’s Decent Show the movie outside the ppt if there is time:

Moons of the Outer Solar System: “The Dunes of Titan”

Moons of the Outer Solar System: Neptune’s Triton Neptune’s Triton < 40K icy volcanism.  Extremely cold (< 40K) objects made from volatile materials produce icy volcanism.  Huge geysers of nitrogen!  Pluto and the Kuiper Belt Objects may look and act similarly.

Comparative Planetology: Lessons Learned Surfaces of Planets (or Moons)  Location, location, location…  Size matters (for retaining an atmosphere).  The star matters. Overall, However  There is an incredible diversity of worlds!!! outside Habitable Zone  Warm pockets or oceans of liquids plus organics may exist in a variety of environments outside the classic Habitable Zone.  Even on Earth not all life requires starlight for an energy source. Sources of potentially life-giving energy may exist even in the cold outer reaches of our own and other planetary systems.

Beyond the Solar System Do We Live in a “Life-Friendly” Universe?  Water and Carbon Chemistry are Everywhere! Hydrogen, Oxygen, Carbon, Nitrogen –1st, 3rd, 4th, and 6th most abundant elements Organic Chemistry is found in –Interstellar gas clouds, comets, meteorites, outer planet and moon atmospheres  Physical Laws Copasetic Time Scales –Expansion rate of the Universe & stellar lifetimes compatible with time to evolve complex life Abundant Materials –Even small changes in physical constants would cause little hydrogen or carbon to exist Huge Diversity of Environments