Life in the Terrestrial Planet Region X MERCURY

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Life in the Terrestrial Planet Region: X – MERCURY Terrible Extremes of Temperature, No

Life in the Terrestrial Planet Region: X – MERCURY Terrible Extremes of Temperature, No Atmosphere, UV, Cosmic Rays, Little or No Volatiles, No Liquids X Very High Temperatures, No or Little Water Young Surface No Fossil Record – MOON – VENUS – MARS ? Evidence for Liquid Water in Past Possible Environments for Life to Survive? Volatiles and Water Present Now

Moving Outwards

Moving Outwards

Gas and Ice Giant Planets: Prospects for Life? – Ingredients for organic chemistry –

Gas and Ice Giant Planets: Prospects for Life? – Ingredients for organic chemistry – Atmospheric layers with roughly Earth-like Temperature & Pressure; – But no solid surfaces (except ice crystals) and no liquid water (except very deep in Uranus and Neptune), Neptune – Violent winds and convective turbulence would mix any lifebearing gas quickly over extremes of temperasture & pressure. – Although the sunlight is very weak, internal heat is available. – They are very difficult to explore!

Life on Jupiter? • All the basic molecular ingredients are present in the atmospheres

Life on Jupiter? • All the basic molecular ingredients are present in the atmospheres • But convection will ultimately (and quickly) bring any organic molecules down to regions where T~ 700 C (over 1200 F!) where they will be destroyed Sagan & Salpeter “speculations” “floaters” “hunters”

Life on Moons of Planets? For instance, the Galilean Satellites of Jupiter Io Europa

Life on Moons of Planets? For instance, the Galilean Satellites of Jupiter Io Europa Ganymede Callisto

Medium & large moons • Enough self-gravity to be spherical • Are, or were,

Medium & large moons • Enough self-gravity to be spherical • Are, or were, geologically active. • Have substantial amounts of ice. • Roughly circular, equatorial orbits in same direction as planet rotation.

Small moons • • • Far more numerous than the medium and large moons.

Small moons • • • Far more numerous than the medium and large moons. Not enough gravity to be spherical: “potato-shaped” Captured asteroids, so orbits do not follow patterns. Orbits can be tilted, elliptical, and even backwards! No atmospheres or liquid water – not suitable for life

Focus on the large & medium sized moons

Focus on the large & medium sized moons

Sizes and orbits Earth’s Moon Diameter Orbit Period (km) (days) comments 3, 474 28

Sizes and orbits Earth’s Moon Diameter Orbit Period (km) (days) comments 3, 474 28 orbit stabilizes Earth’s tilt & seasons Io (Jupiter) 3, 640 1. 77 orbit perturbed by Ganymede, Europa, eccentric irregular orbit, extremely variable tidal force Europa (Jupiter) 3, 130 3. 55 eccentric orbit Ganymede (Jupiter) 5, 268 7. 15 Callisto (Jupiter) 4, 806 16. 69 Enceladus (Saturn) 494 1. 37 Titan (Saturn) 5, 150 15. 94 Largest in solar system, substantial atmosphere

What about… - a source of energy (Sun is too faint)? - presence of

What about… - a source of energy (Sun is too faint)? - presence of liquid water?

Tidal Forces Because the gravitational force decreases with (distance)2, the attractive force experienced by

Tidal Forces Because the gravitational force decreases with (distance)2, the attractive force experienced by one object (e. g. , the Earth) due to the gravitational field of a second object (e. g. , the Moon) varies with position (closest parts attracted most strongly). Tidal forces are difference forces.

Synchronous Rotation • …is when the rotation period of a moon, planet, or star

Synchronous Rotation • …is when the rotation period of a moon, planet, or star equals its orbital period about another object. • Tidal friction on the Moon (caused by Earth) has slowed its rotation down to a period of one month. • The Moon now rotates synchronously. – We always see the same side of the Moon. • Tidal friction on the Moon has ceased since its tidal bulges are always aligned with Earth.

 • All of the large moons in the solar system are in synchronous

• All of the large moons in the solar system are in synchronous rotation.

Tidal Heating in Jovian Moons The four inner moons of Jupiter - Io, Europa,

Tidal Heating in Jovian Moons The four inner moons of Jupiter - Io, Europa, and Ganymede - all show evidence of geological activity - indicators of molten interiors. The heat source is tidal heating. Moons have elliptical orbit and synchronous rotation - one side always faces Jupiter - as Ganymede completes one orbit, Europa completes exactly two orbits, and Io completes exactly four orbits - moons periodically line up - causes orbital ellipticity. - tidal bulges are constantly being flexed in different directions - generates friction inside

Effects of Tidal Interactions • Rotation – Rotation of moons become synchronized with their

Effects of Tidal Interactions • Rotation – 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 – 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 with other moons can maintain eccentric orbits and tidal heating

Jupiter’s Galilean Satellite’s Io Europa Ganymede Callisto

Jupiter’s Galilean Satellite’s Io Europa Ganymede Callisto

Io

Io

Io’s Volcanoes Io is the most volcanically active world in the solar system.

Io’s Volcanoes Io is the most volcanically active world in the solar system.

Io Jupiter’s tidal forces flex Io like a ball of silly putty. - friction

Io Jupiter’s tidal forces flex Io like a ball of silly putty. - friction generates heat - interior of Io is molten Volcanoes erupt frequently. - sulfur in the lava accounts for yellow color - surface ice vaporizes and jets away -Thin atmosphere made up mainly of sulfur dioxide, produced by volcanic activity and temporarily retained by the moon’s gravity. Evidence of tectonics and impact cratering is covered.

Volcanic Plumes

Volcanic Plumes

Lava fountain - active lava hot enough to cause "bleeding" in Galileo's camera -

Lava fountain - active lava hot enough to cause "bleeding" in Galileo's camera - overloading of camera by the brightness of the target Newly erupted hot lava flow. Dark, "L" -shaped lava flow marks the location of the November 1999 eruption.

Gas and Dust Plume A broad plume of gas and dust about 80 km

Gas and Dust Plume A broad plume of gas and dust about 80 km high above a lava flow

Europa

Europa

Jupiter’s Europa – Has similar but weaker tidal heating, – Has a young cracked

Jupiter’s Europa – Has similar but weaker tidal heating, – Has a young cracked water ice crust perhaps only a few kilometers thick, and – May have a warm ocean of liquid water below the crust. – Could there be life?

Europa Icy surface - “fresh” almost no craters

Europa Icy surface - “fresh” almost no craters

Ocean under the ice? • Evidence – Gravity measurements: central metallic core surrounded by

Ocean under the ice? • Evidence – Gravity measurements: central metallic core surrounded by 80 170 km of water/ice – Lack of craters ice tectonics liquid below (but could be “fluid” ice, like glaciers) – Chaotic terrain: like arctic ice pack, with separating pieces – Magnetic field: conducting liquid for internal dynamo & metallic core too cold brine ocean – Tidal heating: computations show it can do the job • Estimated size – Crust depth: 5 25 km, based on flooded impact crater – Ocean 50 150 km deep (< 11 km on Earth)

Surface of Jupiter’s Moon: : Europa Fractures in Floating Icebergs

Surface of Jupiter’s Moon: : Europa Fractures in Floating Icebergs

Evidence of a Subsurface ocean Jumbled crust with icebergs and surface cracks with double-ridged

Evidence of a Subsurface ocean Jumbled crust with icebergs and surface cracks with double-ridged pattern caused by tidal flexing of thick layer of ice on top of liquid ocean of water.

Europa’s interior also warmed by tidal heating Salty - Europa has a magnetic

Europa’s interior also warmed by tidal heating Salty - Europa has a magnetic

Sub-Crust Ocean . . . Hydrogen-Carbon compounds likely: Amino acids Life in the Ocean?

Sub-Crust Ocean . . . Hydrogen-Carbon compounds likely: Amino acids Life in the Ocean? First New Ocean Since Balboa

Missions to Europa http: //www. jpl. nasa. gov/europaorbiter/

Missions to Europa http: //www. jpl. nasa. gov/europaorbiter/

Ganymede

Ganymede

Ganymede • Largest moon in the solar system • Clear evidence of geological activity

Ganymede • Largest moon in the solar system • Clear evidence of geological activity • Tidal heating expected - but is it enough?

Ganymede Wrinkles due to tectonic movement in ice crust in (distant) past possible water

Ganymede Wrinkles due to tectonic movement in ice crust in (distant) past possible water deep below?

Ganymede • Cratering – Dark areas: cratering upon cratering several byr old – Bright

Ganymede • Cratering – Dark areas: cratering upon cratering several byr old – Bright areas: far fewer craters and grooves – Explanation: “lava” (i. e. , water) eruptions followed by freezing • Ocean? – Magnetic field convecting core – Part of magnetic field varies with Jupiter’s rotation electrically conducting interior (brine? ) – Salts found on the surface • Heat source – Less tidal heating than Europa (larger distance from Jupiter) – Large mass more radioactivity – Much less heat than in Europa thick crust (>150 km? ) Much harder to prove the existence of life never mind finding it

Callisto

Callisto

 • “Classic” cratered iceball. • No tidal heating no orbital resonances. • But

• “Classic” cratered iceball. • No tidal heating no orbital resonances. • But it has magnetic field !? Callisto

Callisto Scarp close up Possible water deep?

Callisto Scarp close up Possible water deep?

Callisto • Cratering – Heavily cratered everywhere no water gushing to the surface •

Callisto • Cratering – Heavily cratered everywhere no water gushing to the surface • Gravity – Undifferentiated: mix of ice and rock throughout • Induced magnetic field – Exists underground ocean? • Heat source? – Does not participate in the tidal resonance – Radioactive decay: only possibility

Life on Galilean Moons? • Io X • Europa Very active volcanically. Hostile environment

Life on Galilean Moons? • Io X • Europa Very active volcanically. Hostile environment ? • Ganymede Subsurface saline ocean, hydrothermal vents? ? Subsurface saline ocean? hydrothermal vents? • Callisto saline ? ? Subsurface ocean?