NSCI 314 LIFE IN THE COSMOS 11 - SEARCHING FOR LIFE IN OUR SOLAR SYSTEM: THE OUTER PLANETS AND THEIR MOONS Dr. Karen Kolehmainen Department of Physics CSUSB

JUPITER DIAMETER: 11 X EARTH MASS: 318 X EARTH = MORE THAN REST OF SOLAR SYSTEM (EXCLUDING THE SUN) COMBINED DENSITY: 1.3 gm/cm³ SUNLIGHT: 4% OF EARTH TEMP: 125 K (–150 o C OR –235 o F) AT CLOUD TOPS, BUT WARMER DEEP IN ATMOSPHERE ATMOSPHERE: 86% H, 14% He, TRACES of CH 4, NH 3,H 2 O, HIGH WINDS & STORMS SURFACE: ONLY ATMOSPHERE IS VISIBLE STRUCTURE: SMALL ROCKY CORE, COVERED BY A LAYER OF METALLIC HYDROGEN, THEN A LAYER OF LIQUID HYDROGEN, THEN THE ATMOSPHERE

SATURN DIAMETER: 9.5 X EARTH MASS: 95 X EARTH DENSITY: 0.7 gm/cm³ SUNLIGHT: 1% OF EARTH TEMP: 90 K (-185 o C or -300 o F) AT CLOUD TOPS, WARMER DEEPER DOWN ATMOSPHERE: 86% H, 14% He, TRACES of CH 4, NH 3, H 2 O, HIGH WINDS & STORMS SURFACE: ONLY ATMOSPHERE IS VISIBLE STRUCTURE: SMALL ROCKY CORE, COVERED BY LAYERS OF METALLIC HYDROGEN AND LIQUID HYDROGEN, THEN ATMOSPHERE RINGS: LARGEST RING SYSTEM OF ANY PLANET, COMPOSED MOSTLY OF CHUNKS OF WATER ICE

URANUS DIAMETER: 4 X EARTH MASS: 15 X EARTH DENSITY: 1.2 gm/cm³ SUNLIGHT: 0.3% OF EARTH TEMP: 64 K (-210 o C OR –345 o F) AT CLOUD TOPS, WARMER DEEPER DOWN ATMOSPHERE: 84% H, 14% He, 2-3% CH 4 (NH 3 & H 2 O FROZEN), BLUE COLORS DUE TO METHANE SURFACE: ONLY ATMOSPHERE VISIBLE STRUCTURE: SMALL ROCKY CORE, COVERED BY LAYER OF WATER, METHANE, AND AMMONIA, THEN ATMOSPHERE

NEPTUNE DIAMETER: 3.9 X EARTH MASS: 17 X EARTH DENSITY: 1.7 gm/cm³ SUNLIGHT: 0.1% OF EARTH TEMP: 50 K(-220 o C OR –370 o F) AT CLOUD TOPS, WARMER DEEPER DOWN ATMOSPHERE: 84% H, 14% He, 2-3% CH 4 (NH 3 & H 2 O FROZEN), BLUE COLORS DUE TO METHANE SURFACE: ONLY ATMOSPHERE VISIBLE STRUCTURE: SMALL ROCKY CORE, COVERED BY LAYER OF WATER, METHANE, AND AMMONIA, THEN ATMOSPHERE

LIFE ON THE OUTER PLANETS? DEEP ENOUGH DOWN IN THE ATMOSPHERE, IT IS WARM ENOUGH FOR LIQUID WATER DROPS. SIMPLE ORGANIC MOLECULES HAVE BEEN FOUND IN THE ATMOSPHERES. SUGGESTION: PERHAPS BLIMP-LIKE LIFE FORMS COULD FLOAT OR FLY IN THE ATMOSPHERE. IF THESE EXIST, JUPITER IS THE MOST LIKELY SITE. IT IS THE WARMEST OF THE OUTER PLANETS, AND THEREFORE HAS THE MOST ACTIVE CHEMISTRY. PROBLEM: STRONG CIRCULATION PATTERNS IN THE ATMOSPHERE MIGHT PREVENT COMPLEX ORGANIC MOLECULES FROM FORMING, SO HOW COULD LIFE GET STARTED?

MOONS OF OUTER PLANETS MIXTURE OF ICE AND ROCK LOTS OF THEM EACH PLANET WITH ITS MOONS RESEMBLES A MINIATURE SOLAR SYSTEM SMALL MOONS ARE IRREGULARLY SHAPED, WITH NO ATMOSPHERES, NOT GOOD CANDIDATES FOR LIFE LARGER ONES ARE SPHERICAL, SOME HAVE ATMOSPHERES OR ARE INTERESTING IN OTHER WAYS

CHARACTERISTICS OF LARGE MOONS PlanetName Density (g/cm 3 )‏ Mass (Moon=1)‏ Diameter (Moon=1)‏ Earth Jupiter Saturn Neptune Moon Io Europa Ganymede Callisto Titan Triton (Pluto)‏

TIDAL FORCES AND MOONS THE SIDE OF THE MOON CLOSEST TO ITS PLANET EXPERIENCES A STRONGER GRAVITATIONAL PULL FROM THE PLANET THAN DOES THE SIDE OF THE MOON FARTHEST FROM THE PLANET. THIS PULLED THE MOON INTO AN ELONGATED SHAPE. AS THE MOON ROTATED ON ITS OWN AXIS, ITS SHAPE KEPT CHANGING TO KEEP THE BULGES ON A LINE FACING THE PLANET. THIS CAUSED FRICTION INSIDE THE MOON, WHICH SLOWED ITS ROTATION. JUST LIKE WITH THE EARTH’S MOON, THIS HAS LOCKED THE MOON INTO “SYNCHRONOUS ROTATION” WITH THE PLANET. ONE SIDE OF THE MOON ALWAYS FACES TOWARDS THE PLANET, AND THE OTHER SIDE FACES AWAY FROM THE PLANET.

TIDAL FORCES AND MOONS AS THE ORIGINAL ROTATION OF THE MOON WAS SLOWING (BEFORE IT WAS LOCKED INTO SYNCHRONOUS ROTATION), INTERNAL FRICTION HEATED THE MOON ENOUGH TO MELT IT, LEADING TO A DIFFERENTIATED (LAYERED) STRUCTURE. TIDAL FORCES ALSO AFFECTED ORBITS OF MOONS AROUND THEIR PLANETS, LOCKING THEM INTO “RESONANCES.” –EXAMPLE: MOON FARTHER OUT ORBITS IN TWICE THE TIME OF ONE CLOSER IN. ORBITS ARE ELLIPTICAL (NOT CIRCULAR), SO SHAPE OF MOON VARIES SLIGHTLY THROUGHOUT ITS ORBIT AROUND ITS PLANET. –MORE ELONGATED WHEN CLOSER TO PLANET –MORE SPHERICAL WHEN FARTHER AWAY –THIS LEADS TO CONTINUING INTERNAL FRICTION, HEATING THE INTERIOR OF THE MOON.

TIDAL EFFECTS ON MOONS AS A RESULT, THE INTERIORS OF THE LARGE MOONS OF THE OUTER PLANETS ARE WARMER THAN WE WOULD EXPECT BASED ON THEIR DISTANCE FROM THE SUN AND THEIR SIZE. (THEY'RE SMALL, SO THEY LOST HEAT RAPIDLY). THE LARGER THE MOON AND THE CLOSER IT IS TO ITS PLANET, THE GREATER THE AMOUNT OF TIDAL HEATING. THIS EFFECT MAKES SOME MOONS WARM ENOUGH TO BE POSSIBLE CANDIDATES FOR LIFE!

MAJOR MOONS OF JUPITER (IN ORDER OUT FROM JUPITER, THEREFORE HOTTEST TO COLDEST)‏ IO EUROPA GANYMEDE CALLISTO

IO CLOSEST MOON TO JUPITER, SO TIDAL EFFECTS ARE LARGEST HIGHEST DENSITY - ROCKIER THAN OTHER MOONS, TOO HOT INSIDE FOR ICE HOT ENOUGH TO BE COMPLETELY MOLTEN INSIDE LOTS OF SULFUR ON SURFACE MANY ACTIVE VOLCANOES ERUPTING CONSTANTLY MORE VOLCANOES THAN ANY OTHER OBJECT IN THE SOLAR SYSTEM NOT A GOOD PROSPECT FOR LIFE: NO WATER, LITTLE OR NO ATMOSPHERE, AND LARGE TEMPERATURE EXTREMES

EUROPA NEXT LARGE MOON OUT FROM JUPITER WARM INTERIOR, NOT AS HOT AS IO COMPOSITION: –ROCKY AND/OR METALLIC CORE –SURROUNDED BY LIQUID WATER OCEAN (?) 50 TO 150 KM DEEP –COVERED BY CRUST OF CRACKED ICE 20 TO 25 KM THICK –NO ATMOSPHERE, BUT ICE CRUST PREVENTS WATER FROM BOILING INTO SPACE FEW CRATERS

EVIDENCE FOR OCEAN ON EUROPA FEW IMPACT CRATERS –IMPACT BREAKS THROUGH ICE, WATER FROM BELOW FILLS IN CRATER AND FREEZES CHAOTIC TERRAIN –PATCHWORK RIDGED PATTERN OF ICEBERGS FROZEN IN PLACE STAINS ON CRUST INDICATE UPWELLING OF WATER CONTAINING DISSOLVED (ORGANIC?) MATERIALS MAGNETIC FIELD –IMPLIES PRESENCE OF ELECTRICALLY CONDUCTING LIQUID MATERIAL (SALT WATER)‏

LIFE ON EUROPA? NO ATMOSPHERE, BUT ICE PREVENTS WATER FROM BOILING AND PROVIDES UV PROTECTION ENERGY SOURCE: –HYDROTHERMAL VENTS? –UNDERSEA VOLCANOES? –RADIOACTIVE DECAY IN INTERIOR OF MOON? –PHOTOSYNTHESIS COULD OCCUR IN POCKETS OF WATER DIRECTLY UNDER THINNER ICE? (BUT NOT MUCH SUNLIGHT)‏ –HIGH ENERGY ELECTRICALLY CHARGED PARTICLES ARE ACCELERATED BY JUPITER'S MAGNETIC FIELD AND HIT ICE AT HIGH SPEEDS –UV PHOTONS FROM SUN HIT ICE

LIFE ON EUROPA? PROBABLY NO COMPLEX LIFE, BUT MAYBE SIMPLE LIFE FORMS –PROBABLY NOT ENOUGH ENERGY TO SUPPORT LARGE AND COMPLEX ECOSYSTEM SPACECRAFT MISSION PLANNED, FUNDING CUT –WILL DRILL THROUGH ICE AND RELEASE SUBMARINE IF WE DO FIND EVEN SIMPLE LIFE ON EUROPA (OR ANYWHERE ELSE IN OUR SOLAR SYSTEM), IT WILL MAKE US MUCH MORE OPTIMISTIC ABOUT FINDING EXTRATERRESTRIAL LIFE IN GENERAL.

GANYMEDE NEXT LARGE MOON OUT FROM JUPITER LARGEST MOON IN SOLAR SYSTEM (BIGGER THAN MERCURY)‏ ICE CRUST WITH A MIXTURE OF: –LIGHTER YOUNGER GROOVED TERRAIN (SIMILAR TO EUROPA), AND –DARKER OLDER CRATERED TERRAIN MAY BE AN OCEAN UNDER THE ICE, BUT EVIDENCE IS WEAKER THAN FOR EUROPA –MAGNETIC FIELD –OCCASIONAL FLOODING AND FREEZING HAS FILLED IN CRATERS IN SOME AREAS COLDER THAN EUROPA, SO ICE IS THICKER

CALLISTO COLDEST OF JUPITER’S MAJOR MOONS SOME EVIDENCE FOR AN OCEAN UNDER THE ICE –MAGNETIC FIELD –WEAKER EVIDENCE THAN EITHER EUROPA OR GANYMEDE MORE HEAVILY CRATERED, SO LESS FLOODING OF SURFACE BY WATER HUGE IMPACT CRATER VALHALLA –IMPACT MELTED ICE TEMPORARILY –WAVES SPREADING OUT FROM IMPACT WERE FROZEN IN PLACE –NO BULGE ON OPPOSITE SIDE SUGGESTS LIQUID INTERIOR PRESENT TO ABSORB SHOCK

MOONS OF SATURN MOST ARE SMALL BODIES CONSISTING OF A MIXTURE OF ICE AND ROCK, WITH NO ATMOSPHERES. TITAN IS AN EXCEPTION: A LARGER ICE/ROCK BODY WITH A THICK ATMOSPHERE.

TITAN LARGEST MOON OF SATURN SECOND LARGEST MOON IN THE SOLAR SYSTEM (AFTER GANYMEDE)‏ SURFACE TEMPERATURE IS 93 K (- 180 o C OR -290 o F)‏ –NOT AS MUCH TIDAL HEATING AS JUPITER'S LARGE MOONS –FARTHER FROM THE SUN THAN JUPITER AND ITS MOONS ROCKY CORE SURROUNDED BY ICY MANTLE? (H 2 0, CH 4 AND NH 3 ICES)

TITAN HAS A THICK ATMOSPHERE –90% N 2, ALSO Ar (ARGON), CH 4 (METHANE), C 2 H 6 (ETHANE), AND MORE COMPLEX HYDROCARBONS (SMOG)‏ – HAZY CLOUDS OBSCURE SURFACE –200 KM THICK –1.5 x PRESSURE OF EARTH’S ATMOSPHERE –ONLY MOON IN THE SOLAR SYSTEM WITH A THICK ATMOSPHERE –PROBABLY CH 4 (METHANE) AND NH 3 (AMMONIA) BUBBLED OUT OF CRUST WHEN TITAN WAS YOUNG AND WARM, UV LIGHT FROM SUN CAUSED CHEMICAL REACTIONS TO PRODUCE OTHER MOLECULES

TITAN HUYGENS PROBE LANDED ON SURFACE IN 2004 FEW IMPACT CRATERS RIVERS AND LAKES OF LIQUID METHANE AND ETHANE ONLY BODY BESIDES EARTH KNOWN TO HAVE LIQUID ON THE SURFACE LIQUID METHANE/ETHANE RAIN METHANE CONTINUES TO LEAK INTO ATMOSPHERE –ICE VOLCANOES OR SLOWER SUBLIMATION? “SAND” DUNES PRODUCED BY WIND –“SAND” IS MADE OF PIECES OF HYDROCARBON ICE NO EVIDENCE OF LIFE

LIFE ON TITAN? PLENTY OF ORGANIC MOLECULES ENERGY SOURCE? –CHEMICAL REACTIONS IN ATMOSPHERE –ICE VOLCANOES? PLENTY OF LIQUID METHANE AND ETHANE –RECALL THAT NEITHER OF THESE IS AS GOOD A LIQUID SOLVENT AS WATER IS MAY BE A SUB-SURFACE OCEAN OF LIQUID WATER AND AMMONIA LOW TEMPERATURE WOULD MEAN THAT CHEMICAL REACTIONS, AND THUS METABOLIC RATES, ARE VERY SLOW PROBABLY TOO COLD FOR LIFE, BUT INTERESTING ORGANIC CHEMISTRY

ENCELADUS SMALL TO MEDIUM-SIZED MOON OF SATURN MIXTURE OF ICE AND ROCK FEW IMPACT CRATERS SATURN'S TIDAL FORCE CAUSES INTERNAL WARMING HAS ICE VOLCANOES –SOME REGIONS NEAR THE SOUTH POLE ARE WARMER THAN THE REST OF THE SURFACE –CRACKS IN ICY CRUST, MATERIAL CAN SPEW UP FROM BELOW –FOUNTAINS OF ICE PARTICLES AND WATER VAPOR –SOME ORGANIC MOLECULES FOUND

IAPETUS MEDIUM-SIZED MOON OF SATURN HEAVILY CRATERED LEADING HEMISPHERE IS DARK, TRAILING HEMISPHERE IS LIGHT DARK MATERIAL IS ORGANIC MAY BE COLLECTED FROM SPACE AS IAPETUS MOVES IN ITS ORBIT

TRITON LARGEST MOON OF NEPTUNE RETROGRADE ORBIT - PROBABLY CAPTURED KUIPER BELT OBJECT INTERIOR OF ICE AND ROCK FEW IMPACT CRATERS SURFACE CONTAINS NITROGEN ICE AND METHANE ICE ACTIVE SURFACE (ICE MAY COVER LAKES OR OCEAN OF NITROGEN, METHANE, AMMONIA, AND/OR WATER?)‏ LIQUID GEYSERS OR ICE VOLCANOES OCCASIONALLY ERUPT VERY THIN NITROGEN ATMOSPHERE PROBABLY WAY TOO COLD FOR LIFE