NSCI 314

LIFE IN THE COSMOS

10 - SEARCHING FOR LIFE IN OUR SOLAR SYSTEM:

THE OUTER PLANETS AND THEIR MOONSDr. Karen KolehmainenDepartment of Physics

CSUSB

http://physics.csusb.edu/~karen/

JUPITERDIAMETER: 11 X EARTHMASS: 318 X EARTH = MORE THAN REST OF SOLAR SYSTEM (EXCLUDING THE SUN) COMBINEDDENSITY: 1.3 gm/cm³

SUNLIGHT: 4% OF EARTHTEMP: 125 K (–150oC OR –235oF) AT CLOUD TOPS, BUT WARMER DEEP IN ATMOSPHERE

ATMOSPHERE: 86% H, 14% He, TRACES of CH4, NH3,H2O, HIGH WINDS & STORMS

SURFACE: ONLY ATMOSPHERE IS VISIBLESTRUCTURE: 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 oC or –300 oF) AT CLOUD TOPS,

WARMER DEEPER DOWN

ATMOSPHERE: 86% H, 14% He, TRACES of CH4, NH3, H2O, 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 oC OR –345 oF) AT CLOUD TOPS,

WARMER DEEPER DOWN

ATMOSPHERE: 84% H, 14% He, 2-3% CH4 (NH3 & H2O 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 oC OR –370 oF) AT CLOUD TOPS,

WARMER DEEPER DOWN

ATMOSPHERE: 84% H, 14% He, 2-3% CH4 (NH3 & H2O 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

Planet NameDensity (g/cm3)

Mass (Moon=1)

Diameter(Moon=1)

Earth

Jupiter

Jupiter

Jupiter

Jupiter

Saturn

Neptune

Moon

Io

Europa

Ganymede

Callisto

Titan

Triton

(Pluto)

3.3

3.5

3.0

1.9

1.9

1.9

2.1

2.1

1

1.2

0.7

2.0

1.5

1.8

0.3

0.17

1

1.1

0.9

1.5

1.4

1.5

0.8

0.65

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 SIZES (SMALL, SO 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,

TEMPERATURE IS TOO HIGH 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 (-180oC OR -

290oF)– 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?

(H20, CH4 AND NH3 ICES)

TITAN HAS A THICK ATMOSPHERE – 90% N2, ALSO Ar (ARGON), CH4 (METHANE), C2H6

(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 CH4 (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 JANUARY

2004 RIVERS AND POSSIBLY LAKES OF LIQUID METHANE

AND POSSIBLY ETHANE

– BUT NOT OCEANS LIQUID METHANE/ETHANE RAIN? METHANE CONTINUES TO LEAK INTO ATMOSPHERE

– ICE VOLCANOES OR SLOWER SUBLIMATION? “SAND” DUNES PRODUCED BY WIND

– “SAND” IS PIECES OF HYDROCARBON ICE NO EVIDENCE OF LIFE

LIFE ON TITAN? PLENTY OF ORGANIC MOLECULES ENERGY SOURCE?

– CHEMICAL REACTIONS IN ATMOSPHERE– ICE VOLCANOES?

NO LIQUID WATER, BUT THERE IS LIQUID METHANE AND MAYBE ETHANE– RECALL THAT NEITHER OF THESE IS AS GOOD A LIQUID

SOLVENT AS WATER IS 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 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 WATOR 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

OTHER MOONS OF SATURN SMALL TO MEDIUM-SIZED

ICE AND ROCK

HEAVILY CRATERED

SOME SHOW SIGNS OF GEOLOGICAL ACTIVITY IN THE PAST (CRACKS, RIDGES, ETC.)

TRITON LARGEST MOON OF NEPTUNE RETROGRADE ORBIT - PROBABLY CAPTURED KUIPER

BELT OBJECT INTERIOR OF ICE AND ROCK FEW IMPACT CRATERS ACTIVE ICY SURFACE (ICE COVERS 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