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NSCI 314LIFE IN THE COSMOS
11 - SEARCHING FOR LIFE IN OUR SOLAR SYSTEM:
MOONS OF THE OUTER PLANETS
PLUS: WHY IS PLUTO NO LONGER CNSIDERED A PLANET?
Dr. Karen KolehmainenDepartment of Physics
CSUSBhttp://physics.csusb.edu/~karen/
DIAMETER: 20% OF EARTH MASS: 0.2% OF EARTH DENSITY: 2.1 gm/cm³
SUNLIGHT: 0.06% OF EARTH TEMP: 45 K (-230 oC OR –380 oF) ATMOSPHERE: VERY THIN, METHANE (CH4) ICE
CRYSTALS SURFACE: ICE AND ROCK, METHANE (CH4) ICE MOON: ONE LARGE ONE (CHARON), PLUS TWO
SMALL ONES NOTE: PLUTO IS NO LONGER CONSIDERED TO BE
A PLANET. IT IS JUST A LARGE KUIPER BELT OBJECT.
PLUTO
PLUTO AND CHARON PLUTO IS SMALLER THAN ANY PLANET IN THE
SOLAR SYSTEM - ONLY 2/3 SIZE OF EARTH’S MOON
MOON (CHARON) IS HALF THE SIZE OF PLUTO BOTH ARE ICY/ROCKY BODIES BOTH IN SYNCHRONOUS ROTATION SIZE AND COMPOSITION SIMILAR TO MOONS OF
OUTER PLANETS OR LARGEST KUIPER BELT OBJECTS (COMETS)
WAY TOO COLD FOR LIFE (NO WARMER AREAS LIKE GAS GIANT PLANETS DEEP DOWN IN ATMOSPHERE)
NO OFFICIAL NAME YET UNOFFICIALLY CALLED XENA BY SOME, BUT THIS IS
UNLIKELY TO BE THE OFFICIAL NAME DIAMETER: 20 TO 25% OF EARTH (A LITTLE LARGER
THAN PLUTO) MASS: PROBABLY 0.2 TO 0.3% OF EARTH DENSITY: PROBABLY ABOUT 2 gm/cm³ SUNLIGHT: 0.01% OF EARTH TEMPERATURE: ABOUT 3O K (-245 oC OR –405 oF) ATMOSPHERE: ?? (NOT MASSIVE ENOUGH TO HOLD
ONTO MUCH OF ONE) SURFACE: ICE AND SOME ROCK, METHANE (CH4) ICE MOON: HAS ONE (NOT NAMED YET EITHER)
NEW LARGE KUIPER BELT OBJECT
THIS OBJECT AND PLUTO ARE SIMILAR. BOTH ARE:•SMALLER THAN ALL 8 PLANETS (MERCURY THROUGH NEPTUNE)•MOSTLY ICE, SOME ROCK•ORBITS AREN'T AS CIRCULAR AS THOSE OF THE 8 PLANETS•ORBITS ARE TIPPED SLIGHTLY RELATIVE TO THE DISK FORMED BY THE PLANE OF THE 8 PLANETS
SEEM MORE LIKE BIG KUIPER BELT OBJECTS •RECALL THAT THE KUIPER BELT IS THE INNER GROUP OF COMETS IN OUR SOLAR SYSTEM. (THE OORT CLOUD IS THE OTHER GROUP OF COMETS FARTHER FROM THE SUN.)
NEW LARGE KUIPER BELT OBJECT
THE DISCOVERY OF THIS OBJECT PROMPTED RECONSIDERATION OF THE DEFINITION OF A PLANET. •THERE MAY BE MANY KUIPER BELT OBJECTS THIS LARGE WAITING TO BE DISCOVERED. •DO WE WANT TO CALL THEM ALL PLANETS?•IF NOT, THEN TO BE CONSISTENT, PLUTO SHOULDN'T BE CALLED A PLANET EITHER.
OFFICIAL DECISION (RECENT): NEITHER PLUTO NOR THIS OBJECT ARE PLANETS. INSTEAD, THEY ARE LARGE KUIPER BELT OBJECTS (COMETS).
THE RULES ASTRONOMERS HAVE ESTABLISHED FOR NAMING PLANETS ARE DIFFERENT THAN FOR NAMING OTHER OBJECTS, SO NO DECISION ON THE NAME OF THE RECENTLY DISCOVERED OBJECT WAS MADE BEFORE THE DEFINITION OF A PLANET WAS DECIDED UPON.
NEW LARGE KUIPER BELT OBJECT
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 THE MOONS OF JUPITER
THE SIDE OF THE MOON CLOSEST TO JUPITER EXPERIENCES A STRONGER GRAVITATIONAL PULL FROM JUPITER THAN DOES THE SIDE OF THE MOON FARTHEST FROM JUPITER.
JUST LIKE WITH THE EARTH’S MOON, THIS HAS LOCKED THE MOON INTO “SYNCHRONOUS ROTATION” WITH JUPITER. ONE SIDE OF THE MOON ALWAYS FACES TOWARDS JUPITER, AND THE OTHER SIDE FACES AWAY FROM JUPITER.
AS THE ORIGINAL ROTATION OF THE MOON WAS SLOWING (BEFORE THEY WERE LOCKED INTO SYNCHRONOUS ROTATION), INTERNAL FRICTION HEATED MOONS ENOUGH TO MELT THEM, LEADING TO A DIFFERENTIATED (LAYERED) STRUCTURE.
TIDAL EFFECTS ON JUPITER’S MOONS
TIDAL FORCES ALSO AFFECTED ORBITS, 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 JUPITER.– MORE ELONGATED WHEN CLOSER TO JUPITER– MORE SPHERICAL WHEN FARTHER AWAY– THIS LEADS TO CONTINUING INTERNAL FRICTION,
HEATING THE INTERIOR OF THE MOON. AS A RESULT, JUPITER'S LARGE MOONS ARE WARMER
THAN WE WOULD EXPECT BASED ON DISTANCE FROM THE SUN.
THE LARGER THE MOON IS AND THE CLOSER IT IS TO JUPITER, THE GREATER THE AMOUNT OF TIDAL HEATING.
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 5 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 DECAYIN INTERIOR OF MOON?– PHOTOSYNTHESIS COULD OCCUR IN POCKETS OF
WATER DIRECTLY UNDER THINNER ICE? (BUT NOT MUCH SUNLIGHT)
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
GANYMEDE NEXT LARGE MOON OUT FROM JUPITER LARGEST MOON IN SOLAR SYSTEM 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
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 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 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 ROCKY CORE SURROUNDED BY ICY
MANTLE? (H20, CH4 AND NH3 ICES) HAS A THICK ATMOSPHERE
– 90% N2, 6% Ar, 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
TITAN HUYGENS PROBE LANDED ON
SURFACE IN JANUARY 2004 RIVERS AND LAKES OF LIQUID
METHANE AND/OR ETHANE (BUT PROBABLY NOT OCEANS)
LIQUID METHANE/ETHANE RAIN? NO EVIDENCE OF LIFE PROBABLY TOO COLD FOR LIFE, BUT
INTERESTING ORGANIC CHEMISTRY
IAPETUS SMALL 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 ACTIVE ICY SURFACE (ICE COVERS LAKES
OR OCEAN OF NITROGEN, METHANE, AMMONIA, AND/OR WATER?)
LIQUID GEYSERS OCCASIONALLY ERUPT VERY THIN NITROGEN ATMOSPHERE PROBABLY WAY TOO COLD FOR LIFE