NSCI 314

LIFE IN THE COSMOS

8 – SEARCHING FOR LIFE IN OUR SOLAR SYSTEM

- GENERAL CONSIDERATIONS- LIFE ON THE INNER PLANETS?

Dr. Karen KolehmainenDepartment of Physics

CSUSB

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

HOW TO SEARCH FOR LIFE WITHIN OUR SOLAR SYSTEM

OBSERVATIONS WITH TELESCOPES, ETC.– LIGHT-GATHERING (MAKE FAINT OBJECTS BRIGHTER)– MAGNIFY OR ENLARGE IMAGE– PICK OUT DETAILS IN IMAGE (IMPROVE RESOLUTION)– CAN USE A VARIETY OF WAVELENGTHS (NOT JUST VISIBLE LIGHT)– CAN DO SPECTROSCOPIC ANALYSIS

• SPLIT LIGHT INTO COLORS

• ANALYZE BRIGHTNESS AT VARIOUS WAVELENGTHS

• INDICATES PRESENCE OF VARIOUS MATERIALS VISITS BY SPACECRAFT

– FLYBY (ALL PLANETS, PLUS MANY MOONS)– ORBITER (EARTH'S MOON, VENUS, MARS, JUPITER, SATURN)– PROBE DESCENDS INTO ATMOSPHERE (JUPITER)– LANDER (EARTH'S MOON, VENUS, MARS, SATURN'S MOON TITAN) – SAMPLE RETURN (EARTH'S MOON)– HUMAN VISITS (EARTH'S MOON)

TO ESTIMATE HOW EASY IT WOULD BE FOR US TO FIND LIFE (IF IT EXISTS) ON ANOTHER PLANET IN OUR SOLAR SYSTEM, TURN THE QUESTION AROUND:

HOW COULD A HYPOTHETICAL ALIEN CIVILIZATION (WITH TECHNOLOGY SIMILAR TO OURS) ON A NEARBY PLANET (IN OUR SOLAR SYSTEM) TELL THERE IS LIFE ON EARTH?– SPECTROSCOPIC DETECTION OF GASES IN THE

ATMOSPHERE THAT ARE PRODUCED BY LIVING ORGANISMS: OXYGEN AND MAYBE METHANE

– INFRARED OBSERVATIONS CAN DETECT SEASONAL CHANGES IN VEGETATION (DIFFICULT)

HOW COULD AN ALIEN ON A NEARBY PLANET TELL THERE IS A TECHNOLOGICALLY ADVANCED CIVILIZATION ON EARTH? LIGHTS FROM CITIES VISIBLE AT NIGHT

TV AND FM RADIO BROADCASTS ESCAPE INTO SPACE

SPECTROSCOPIC DETECTION OF GASES IN THE ATMOSPHERE THAT ARE PRODUCED BY TECHNOLOGY (e.g., CFCs)

EXTRATERRESTRIAL LIFE IN OUR SOLAR SYSTEM? NEED:

ELEMENTS LIKE CARBON (OR SILICON?), HYDROGEN, OXYGEN, NITROGEN – ENOUGH ALMOST EVERYWHERE

SIMPLE ORGANIC MOLECULES – PROBABLY ENOUGH IN MANY LOCATIONS

SOURCE OF ENERGY – SUNLIGHT (MORE AVAILABLE CLOSER TO SUN)– HEAT FROM INSIDE PLANET OR MOON– CHEMICAL SOURCES

PROTECTED ENVIRONMENT– ATMOSPHERE – OCEANS– UNDERGROUND

LIQUID SOLVENT (WATER OR SOMETHING ELSE?)– REQUIRES CORRECT TEMPERATURE RANGE

WHAT SHOULD A LIQUID SOLVENT DO?

MUST BE ABUNDANT MUST BE ABLE TO DISSOLVE A LOT OF

DIFFERENT MATERIALS IN IT SHOULD REMAIN LIQUID OVER A LARGE

TEMPERATURE RANGE TEMPERATURE RANGE OVER WHICH SOLVENT

IS LIQUID SHOULDN’T BE TOO HIGH OR TOO LOW– IF TEMPERATURE RANGE IS TOO LOW,

INTERACTIONS PROCEED TOO SLOWLY– IF TEMPERATURE RANGE IS TOO HIGH, MOLECULES

ARE BROKEN APART TOO EASILY MIGHT BE BENEFICIAL IF IT HELPS ORGANISMS

REGULATE THEIR INTERNAL TEMPERATURE

SPECIFIC AND LATENT HEAT SPECIFIC HEAT = THE AMOUNT OF ENERGY

THAT NEEDS TO BE ADDED TO 1 GRAM OF MATERIAL TO RAISE ITS TEMPERATURE BY 1oC

LATENT HEAT OF VAPORIZATION = THE AMOUNT OF HEAT THAT NEEDS TO BE ADDED TO BOIL ONE GRAM OF LIQUID MATERIAL (ASSUMING IT IS ALREADY AT THE APPROPRIATE TEMPERATURE, i.e., THE “BOILING POINT”)

SPECIFIC HEAT AND LATENT HEAT ARE DIFFERENT FOR DIFFERENT MATERIALS

SPECIFIC AND LATENT HEAT A MATERIAL WITH A LARGE SPECIFIC HEAT DOESN’T

UNDERGO EXTREME VARIATIONS IN TEMPERATURE. SINCE LARGE AMOUNTS OF ENERGY MUST BE ADDED (REMOVED) TO INCREASE (DECREASE) THE TEMPERATURE VERY MUCH, THE TEMPERATURE DOESN'T CHANGE MUCH.

IF A LIQUID WITH A LARGE LATENT HEAT

EVAPORATES, IT CARRIES A LOT OF HEAT AWAY WITH IT.

IF A LIQUID SOLVENT HAS A LARGE SPECIFIC HEAT AND A LARGE LATENT HEAT, ORGANISMS THAT USE IT WILL BE ABLE TO MAINTAIN A CONSTANT TEMPERATURE MORE EASILY.

ADVANTAGES OF WATER ABUNDANT (2ND MOST COMMON MOLECULE IN

INTERSTELLAR SPACE)

DISSOLVES MANY MATERIALS (BECAUSE H2O MOLECULE IS “POLAR”)

STAYS LIQUID OVER A LARGE TEMPERATURE RANGE

VERY LARGE SPECIFIC HEAT AND LATENT HEAT – KEEPS TEMPERATURE FROM VARYING TOO MUCH

LARGE SURFACE TENSION – DROPS FORM EASILY, MAY BE IMPORTANT FOR THE ORIGIN OF LIFE (FORMATION OF CELL MEMBRANES)

ADVANTAGES OF WATER EXPANSION UPON FREEZING

– COULD BE AN ADVANTAGE BECAUSE:• ICE FLOATS ON LIQUID WATER• THIS PREVENTS BODIES OF WATER FROM

FREEZING OVER COMPLETELY, WHICH WOULD KILL ORGANISMS THERE

– COULD BE A DISADVANTAGE BECAUSE:• CELLS RUPTURE WHEN THEY FREEZE

– COULD BE NEUTRAL IF TEMPERATURE NEVER GETS LOW ENOUGH FOR FREEZING

OTHER SOLVENTS? CONSIDER AMMONIA (NH3), METHANE (CH4), AND

ETHANE (C2H6):– ALL ARE RELATIVELY ABUNDANT.

– NOT POLAR MOLECULES - CAN’T DISSOLVE AS MANY MATERIALS AS WATER.

– LOW SURFACE TENSION - HARDER TO FORM DROPS.

– ETHANE IS LIQUID OVER A LARGE TEMPERATURE RANGE, METHANE AND AMMONIA ARE NOT.

– ALL ARE LIQUID AT LOW TEMPERATURES (LOWER THAN WATER) – METABOLIC PROCESSES WOULD BE SLOW.

– SMALL LATENT HEAT AND/OR SPECIFIC HEAT (EXCEPT AMMONIA).

– NONE EXPAND UPON FREEZING. MOST OTHER POSSIBLE LIQUID SOLVENTS AREN’T

VERY ABUNDANT.

INNER (TERRESTRIAL) PLANETS

MERCURY, VENUS, EARTH & MARS

WARMER, CLOSER TO SUN

RELATIVELY LOW MASS

DENSE, ROCKY, FEW LIGHT ELEMENTS

FEW OR NO MOONS

NO RINGS

OUTER (JOVIAN) PLANETS JUPITER, SATURN, URANUS, NEPTUNE

COLDER, FARTHER FROM SUN

HIGH MASS

LOW DENSITY, MOSTLY GASEOUS, LOTS OF LIGHT ELEMENTS

LOTS OF MOONS (LIKE MINIATURE SOLAR SYSTEMS)

ALL HAVE RINGS

CHARACTERISTICS OF PLANETS

Planet Diameter(Earth=1)

Mass(Earth=1)

AverageDensity

(gm/cm³)

OrbitalPeriod(Years)

DistanceFrom the Sun

(AU or Earth=1)

MercuryVenusEarthMars[Asteroids]JupiterSaturnUranusNeptune

0.380.951.000.53

-11.29.54.03.9

0.060.811.000.11

-318951517

5.45.35.54.0-

1.30.71.31.6

0.240.621.001.88

-122984

165

0.390.721.001.52

[Avg. = 2.77]5.29.51930

1. FLAT SHAPE (PLANETARY ORBITS ARE IN THE SAME PLANE)•EXPLAINED BY CONSERVATION OF ANGULAR MOMENTUM

•NEBULA FLATTENS AS IT CONTRACTS

2. COMMON DIRECTION OF PLANETARY ORBITAL MOTION, MOST PLANETS’ ROTATIONS, & ORBITS OF MOST MOONS•EXPLAINED BY CONSERVATION OF ANGULAR MOMENTUM

•DIRECTION OF ROTATION IS THE SAME AS THAT OF ORIGINAL NEBULA

3. ORIGIN OF COMETS AND ASTEROIDS•LEFTOVER PLANETESIMALS THAT DIDN'T GET INCORPORATED INTO PLANETS

1. SOLAR SYSTEM PROPERTIES AS EXPLAINED BY THE NEBULAR THEORY OF FORMATION

1. - OUTER PLANETS ARE MUCH LARGER AND MORE MASSIVE THAN INNER PLANETS.

2. - INNER PLANETS ARE MADE OF ROCKY MATERIALS.

3. - OUTER PLANETS ARE MADE MOSTLY OF GAS.

4. - MOONS OF OUTER PLANETS ARE MADE MOSTLY OF ICE.

•FAST-MOVING GAS MOLECULES ESCAPED THE GRAVITY OF PLANETS IN THE HOTTER INNER SOLAR NEBULA. SLOWER MOVING GAS PARTICLES WEREN'T ABLE TO ESCAPE THE GRAVITY OF PLANETS IN THE COOLER OUTER NEBULA. ICE PARTICLES CONDENSED IN THE COOL OUTER NEBULA, BUT IT WAS TOO HOT IN THE INNER NEBULA.

5. - ALSO RECALL THAT LARGER PLANETS AND MOONS COOL MORE SLOWLY THAN SMALL ONES, AND THEREFORE ARE STILL HOTTER INSIDE.

1. SOLAR SYSTEM PROPERTIES AS EXPLAINED BY THE NEBULAR THEORY OF FORMATION - DIFFERENCES BETWEEN INNER AND OUTER PLANETS

LOOSE ENDS PLUTO AND NEW “PLANET” (AND THEIR MOONS)

ARE MOST PROPERLY THOUGHT OF AS KUIPER BELT OBJECTS

SEVERAL MOONS ARE PROBABLY CAPTURED KUIPER BELT OBJECTS – TRITON (NEPTUNE) – RETROGRADE ORBIT

SEVERAL MOONS ARE PROBABLY CAPTURED ASTEROIDS– PHOBOS AND DEIMOS (MARS)

EVIDENCE OF COLLISIONS– ORIGIN OF EARTH'S MOON

EVIDENCE OF NEAR-COLLISIONS– VENUS HAS RETROGRADE ROTATION– URANUS’ ROTATION AXIS IS TIPPED SIDEWAYS

COMETS “DIRTY SNOWBALLS” – WATER ICE, CO2 ICE,

SIMPLE ORGANIC MOLECULES

NUCLEUS IS A FEW KM TO A FEW HUNDRED KM ACROSS, IRREGULARLY SHAPED

MOST ORBITS ARE HIGHLY ELLIPTICAL – VERY CLOSE TO SUN AT ONE END & VERY FAR FROM SUN AT THE OTHER END

ORBITS CAN BE IN ANY PLANE

LEFTOVER ICY PLANETESIMALS FROM FORMATION OF SOLAR SYSTEM

SOURCES OF COMETS OORT CLOUD

– SPHERICAL RESERVOIR OF COMETS

– HUGE - RADIUS OF APPROXIMATELY 1 LY (60,000 AU)

– PLANETESIMALS THAT WERE EJECTED OUTWARD

– COMETS HERE CAN BE SHIFTED INTO NEW ORBITS BY PASSING STARS

KUIPER BELT – SMALLER DISK-SHAPED RESERVOIR OF COMETS

– RADIUS OF APPROXIMATELY 50 AU

– INCLUDES PLUTO AND NEW “PLANET” AS LARGEST OBJECTS

– PLANETESIMALS THAT WERE NOT EJECTED OUTWARD

– COMETS HERE CAN BE SHIFTED INTO NEW ORBITS BY MASSIVE PLANETS

NEW ORBIT CAN BRING COMET INTO INNER SOLAR SYSTEM, WHERE WE SEE IT

COMETS WHEN NEAR THE SUN ICE SUBLIMATES (SOLID GAS), RELEASING

DUST GRAINS FROM NUCLEUS

RELEASED GAS & DUST FORM A CLOUD CALLED COMA (CAN BE LARGER THAN THE SUN)

GAS IS IONIZED BY SUNLIGHT AND PUSHED DIRECTLY AWAY FROM SUN BY PRESSURE OF PHOTONS, FORMING BLUE GAS TAIL

DUST LAGS BEHIND COMET IN ORBIT, FORMING YELLOWER DUST TAIL

ASTEROIDS ROCKY OBJECTS

UP TO FEW HUNDRED KM ACROSS

MOST ARE IRREGULARLY SHAPED, NOT SPHERICAL

ORBIT THE SUN, MOST BETWEEN THE ORBITS OF MARS AND JUPITER

LEFTOVER ROCKY PLANETESIMALS THAT DIDN’T FORM A PLANET (PROBABLY BECAUSE OF JUPITER’S GRAVITY)

METEORS, METEOROIDS, AND METEORITES METEOROIDS: SMALL ROCKY OBJECTS

ORBITING THE SUN – SMALLER THAN ASTEROIDS

METEORS: METEOROIDS THAT HAVE ENTERED EARTH’S ATMOSPHERE, USUALLY VAPORIZE DUE TO FRICTIONAL HEATING, “SHOOTING STARS” OR “FALLING STARS”

METEORITES: METEORS THAT HAVE PARTIALLY SURVIVED ATMOSPHERIC PASSAGE AND HIT THE GROUND

METEORITES TYPES (BASED ON COMPOSITION):

– METALLIC (IRON, NICKEL, ETC.)– STONY-IRON– STONY

• CARBONACEOUS CHONDRITES

CARBONACEOUS CHONDRITES CONTAIN WATER AND ORGANIC COMPOUNDS, INCLUDING 74 AMINO ACIDS (50% L, 50% R), ALL 5 GENETIC BASES, FATTY ACIDS, ETC.

ADVANTAGES OF PLANETS AND LARGE MOONS FOR LIFE

CONDUCIVE TO CHEMISTRY (ATOMS COMBINING AND RECOMBINING TO FORM MOLECULES)

MANY PROVIDE A RELATIVELY STABLE AND PROTECTED ENVIRONMENT

– ATMOSPHERE PROVIDES PROTECTION FROM UV AND OTHER HIGH ENERGY PHOTONS AND FROM COSMIC RAYS

SMALL VARIATIONS IN ENVIRONMENT

– TEMPERATURE VARIATIONS – POSSIBLE INTERFACES BETWEEN LAND,

OCEANS, AND ATMOSPHERE

LIFE ON SOLAR SYSTEM BODIES OTHER THAN PLANETS & LARGE MOONS?

SMALL MOONS, ASTEROIDS, COMETS, ETC.?– BIG PROBLEM: NO ATMOSPHERE

• TEMPERATURE EXTREMES BETWEEN DAY AND NIGHT

• NO LIQUIDS - THEY BOIL INTO SPACE• NO UV PROTECTION

SUN (OR STARS IN GENERAL)?– TOO HOT FOR COMPLEX MOLECULES TO FORM

INNER (TERRESTRIAL) PLANETS

MERCURY, VENUS, EARTH & MARS

WARMER, CLOSER TO SUN

RELATIVELY LOW MASS

DENSE, ROCKY, FEW LIGHT ELEMENTS

FEW OR NO MOONS

NO RINGS

EARTH DIAMETER: 1 EARTH

MASS: 1 EARTH

DENSITY: 5.5 g/cm³

SUNLIGHT: 1 EARTH

TEMP: 210 to 320 K (-60 to 50 oC or –80 to 120 oF)

ATMOSPHERE: 78% N2, 21% O2, 1% Ar, 0.03% CO2; H20 CLOUDS

WATER: COVERS 71% OF SURFACE, BUT ONLY 0.02% OF TOTAL MASS, OCEANS 3.6 KM DEEP ON AVERAGE

SURFACE: ROCKY, WITH OCEANS, ICE CAPS, VOLCANOES, PLATE TECTONICS, LIFE TO ~5 KM DEPTH

EARTH’S MOON DIAMETER: 27% EARTH

MASS: 1.2% EARTH

DENSITY: 3.3 g/cm³

SUNLIGHT: 1 EARTH

TEMP: 160 to 400 K (-110 to 130 oC or –170 to 260 oF)

ATMOSPHERE: NONE

WATER: NO LIQUID WATER, BUT PERMANENT ICE IN A FEW CRATERS NEAR THE POLES THAT NEVER GET SUNLIGHT

SURFACE: ROCKY, HEAVILY CRATERED, SMOOTHER MARIA (FORMED VIA LAVA FLOODING BASINS AFTER LARGE IMPACTS), NO CURRENT GEOLOGICAL ACTIVITY (COOL SOLID INTERIOR)

TIDAL FORCES THINK ABOUT THE GRAVITATIONAL FORCE OF THE MOON

PULLING ON THE EARTH. THE SIDE OF THE EARTH THAT IS CLOSEST TO THE MOON

EXPERIENCES A STRONGER FORCE THAN DOES THE SIDE OF THE EARTH THAT IS FARTHEST FROM THE MOON.

THE DIFFERENCE BETWEEN THE FORCES ON DIFFERENT SIDES OF THE EARTH CAUSES TIDES. (OCEANS CAN ALTER SHAPE MORE EASILY THAN ROCK.)

EARTH ROTATES INSIDE TIDAL BULGES, PRODUCING TWO HIGH TIDES PER DAY.

FRICTION BETWEEN WATER AND OCEAN BOTTOM IS SLOWING DOWN EARTH’S ROTATION.

TIDAL FORCES EARTH ALSO EXERTS TIDAL FORCES ON THE MOON. THE MOON HAS NO OCEANS, BUT THE ROCK ITSELF IS

DISTORTED INTO AN ELONGATED SHAPE. WHEN THE MOON FIRST FORMED, IT WAS ROTATING

MORE QUICKLY. AS IT DID SO, THE TIDAL FORCES KEPT CHANGING THE MOON'S SHAPE.

FRICTION SLOWED DOWN THE MOON’S ORIGINAL ROTATION UNTIL IT NOW ROTATES ONLY ONCE PER ORBIT.

SYNCHRONOUS ROTATION: THE MOON NOW KEEPS ONE SIDE FACING THE EARTH.

THIS HAS ALSO HAPPENED WITH MOST MOONS OF OUTER PLANETS.

MERCURY

DIAMETER: 38% EARTH

MASS: 5% EARTH

DENSITY: 5.4 gm/cm³

SUNLIGHT: 6.5 X EARTH

TEMP: 100 to 700 K (-170 to 430 oC or –280 to 800 oF)

ATMOSPHERE: NONE

WATER: NONE

SURFACE: ROCKY, HEAVILY CRATERED, NO CURRENT GEOLOGICAL ACTIVITY

LIFE ON EARTH’S MOON OR MERCURY? PROBABLY NOT PROBLEMS:

– NO ATMOSPHERE (MASSES OF MOON AND MERCURY ARE SO LOW THAT THEIR GRAVITY CAN'T HOLD ONTO LIGHT GAS MOLECULES)• NO PROTECTION FROM UV BOMBARDMENT OR

COSMIC RAYS• NO LIQUID WATER (OR ANY OTHER LIQUID THAT

COULD SERVE AS A SOLVENT)• LARGE TEMPERATURE EXTREMES (ESPECIALLY ON

MERCURY)

VENUS DIAMETER: 95% EARTH

MASS: 82% EARTH

DENSITY: 5.3 gm/cm³

SUNLIGHT: 2 X EARTH

TEMP: 730 K (460 oC or 850 oF), NOT MUCH VARIATION

ATMOSPHERE: 97% CO2 , 3% N2, 90 X EARTH PRESSURE, SULFURIC ACID CLOUDS

WATER: NONE

SURFACE: ROCKY, CRATERED, RECENT LAVA FLOWS, UNCLEAR WHETHER ANY CURRENT GEOLOGICAL ACTIVITY

GREENHOUSE EFFECTSUNLIGHT ABSORBED BY PLANET’S SURFACE

ENERGY RE-RADIATED FROM GROUND AS INFRARED

INFRARED ABSORBED BY ATMOSPHERIC GREENHOUSE GASES: CO2 ,H2O, CH4, OTHERS

ATMOSPHERE WARMS, RADIATES EXCESS HEAT TO SPACE (AS BLACKBODY)

EVENTUALLY EQUILIBRIUM IS REACHED SO THAT ENERGY ABSORBED = ENERGY RADIATED, AND TEMPERATURE STABILIZES

- EARTH 40K (OR 72 oF) HOTTER- MARS 5K (OR 9 oF) HOTTER- VENUS 400K (OR 720 oF)HOTTER

WHY ISN’T THE GREENHOUSE EFFECT MORE IMPORTANT ON EARTH? LIMESTONE ROCKS (CALCIUM CARBONATE OR CaCO3)

FORMED IN OCEANS.

MOST CO2 (170,000 x MORE THAN IN OUR ATMOSPHERE) IS DISSOLVED IN SEA WATER AND LOCKED UP IN LIMESTONE.

IF IT WEREN’T, GREENHOUSE EFFECT WOULD BE MUCH MORE SEVERE.

HUMAN INDUSTRIAL ACTIVITY IS ADDING GREENHOUSE GASES TO ATMOSPHERE, RESULTING IN GLOBAL WARMING.

WHY IS THE GREENHOUSE EFFECT SO IMPORTANT ON VENUS?

TEMPERATURE ON PRE-GREENHOUSE VENUS WOULD HAVE BEEN ~350 TO 400 K, TOO HOT FOR LIQUID WATER

THEREFORE VENUS' WATER EVAPORATED, OCEANS NEVER FORMED

H20 VAPOR IS A GREENHOUSE GAS AND INCREASED TEMPERATURE FURTHER

MOST H20 WAS PHOTODISSOCIATED, H ESCAPED TO SPACE, O COMBINED WITH OTHER ELEMENTS

NO OCEANS, THEREFORE NO CARBONATE ROCKS TO ABSORB CO2, SO IT REMAINS IN ATMOSPHERE

LIFE ON VENUS? PROBABLY NOT

PROBLEMS:

– WAY TOO HOT DUE TO RUNAWAY GREENHOUSE EFFECT

– NO LIQUID WATER (OR ANY OTHER LIQUID THAT COULD SERVE AS A SOLVENT)

– ATMOSPHERIC PRESSURE VERY HIGH (ALTHOUGH NO HIGHER THAN AT SOME HYDROTHERMAL VENTS ON EARTH)