ASTR 380 Possibilities for Life in the Outer Solar System

Possibility of Life in the Inner Solar System The Moon, Mercury, and the Moons of Mars Deimos NO LIFE NOW or EVER This is a 98% conclusion! Phobos Moon Mercury

Possibility of Life in the Inner Solar System The Venus versus our checklist: chemical building blocks: Earth-like origin. Lots of C, N, O. But currently low on water! energy: reasonable sunlight. Hot temperatures a problem for Earth type complex molecules liquid: No. Too hot for water stability: Very hot and dry now. Surface may have episodes of extreme volcanic activity. Very poor chance for current life. Small chance of life in the past.

Possibility of Life in the Inner Solar System The Mars versus our checklist: chemical building blocks: Earth-like origin. Lots of C, N, O. energy: reasonable sunlight. Temperature on the cold side. liquid: Not at the present but water ice. Strong evidence for liquid water in the distant past. stability: currently stable but not at the best conditions Poor chance for current life best possibilities are at the ice caps and underground. Reasonable chance of life in the past depending on how long the water lasted!

ASTR 380 Possibilities for Life in the Outer Solar System Let s first consider the large gas planets: Jupiter, Saturn, Uranus and Neptune Planets to scale with Sun in background

ASTR 380 Possibilities for Life in the Outer Solar System History of Exploration of the Outer Solar System Spacecraft Closest approach Jupiter close approach Planets visited (dwarf planet) Pioneer 10 December 3, 1973 130,000 km Jupiter Pioneer 11 December 4, 1974 34,000 km Jupiter, Saturn Voyager 1 March 5, 1979 349,000 km Jupiter, Saturn Voyager 2 July 9, 1979 570,000 km Jupiter Saturn, Uranus, Neptune Ulysses February 1992 409,000 km Jupiter February 2004 240,000,000 km Jupiter Cassini December 30, 2000 10,000,000 km Saturn New Horizons February 28, 2007 2,304,535 km Jupiter, Pluto

Jupiter

Jupiter motion of bands centered red Red Spot

Jupiter aurora at pole

Jupiter magnetic field

Saturn

Saturn band structure close up

Saturn thermal emission Showing different temperatures in bands

Saturn pole and rotation

Uranus

Neptune

Neptune dark spot

Neptune upper level clouds

ASTR 380 Possibilities for Life in the Outer Solar System

ASTR 380 Possibilities for Life in the Outer Solar System Structure of Jupiter s interior and atmosphere

ASTR 380 Possibilities for Life in the Outer Solar System Composition of Jupiter s atmosphere

ASTR 380 Possibilities for Life in the Outer Solar System Composition of Jovian atmosphere

ASTR 380 Possibilities for Life in the Outer Solar System Structure of atmospheres of Saturn SATURN URANUS

ASTR 380 Possibilities for Life in the Outer Solar System Temperature in the atmospheres of the jovian planets Planet Jupiter Saturn Uranus Neptune Temperature at 0.1 bar at 1.0 bar at 10 bar 112 K 84 K 53 K 50 K 165 K 134 K 85 K 74 K 320 K 250 K 175 K All of the jovian planets radiate significantly more energy than they receive from the Sun! Internal heating so temperature increases inward.??

ASTR 380 Possibilities for Life in the Outer Solar System Water and/or water ice likes exist at places in the atmospheres of the jovian planets --- but at pressures of a few to many 10 s of bar Pressure and Temperature Planet in region of water or water ice pressure temperature Jupiter Saturn Uranus Neptune 5 bar 12 bar 60 bar?? 270 K 240 K 275 K??

ASTR 380 Possibilities for Life in the Outer Solar System The atmospheres of jovian planets have strong winds which circulate around the planet and strong convection which moves gas up and down a big problem for life?

Possibility of Life in the Outer Solar System The Jovian Planets versus our checklist: chemical building blocks: Low C, N, O concentration due to abundant H and He. Very low in other elements. energy: weak sunlight, almost no sunlight in areas where water could be present. But internal heat so warm. liquid: Perhaps water or ice suspended in atmosphere but no solid surfaces other than ice particles. stability: stable but very strong winds. Any life might be carried by winds through good and bad conditions. Only reasonable place is at 3-20 bars into atmosphere Chances are poor but largely unknown!

ASTR 380 Possibilities for Life in the Outer Solar System The many moons of the outer planets.. Most of the moons are very small 1 to a few hundred km in diameter. Too small to hope to hold an atmosphere or surface liquid. Planet Number of moons Jupiter 63 Saturn 60 Uranus 27 Neptune 13 The largest moons Planet Satellite Luna masses Io 1.2 Jupiter Europa 0.6 Ganymede 2.0 Callisto 1.6 Saturn Titan 1.5 Uranus Titania 0.05 Oberon 0.04 Neptune Triton 0.3