NSCI 314

LIFE IN THE COSMOS

9 - SEARCHING FOR LIFE IN OUR SOLAR SYSTEM: THE INNER PLANETS

Dr. Karen KolehmainenDepartment of Physics

CSUSB

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

EARTH’S MOON DIAMETER: 27% EARTH

MASS: 1.2% EARTH

DENSITY: 3.3 gm/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. THE MOON WAS ORIGINALLY ROTATING FASTER, BUT

AS IT ROTATED, THE SHAPE WAS CONTINUALLY DISTORTED TO KEEP THE BULGE POINTED TOWARED THE EARTH.

THE RESULTING FRICTION SLOWED DOWN THE MOON’S 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 (MOON AND MERCURY HAVE TOO LOW A MASS, 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 RADIATION 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 ALL WATER ON VENUS EVAPORATED

H20 VAPOR IS A GREENHOUSE GAS AND INCREASED TEMPERATURE FURTHER

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

NO OCEANS 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)

MARS DIAMETER: 53% EARTH MASS: 11% EARTH DENSITY: 3.9 gm/cm³

SUNLIGHT: 43% OF EARTH TEMP: 180 TO 280 K (-90 TO 7oC OR –135 TO 45oF)

ATMOSPHERE: 95% CO2, 3% N2, 2% Ar, H2O & CO2 CLOUDS, <1% OF EARTH PRESSURE

WATER: POLAR ICE CAPS, SUB-SURFACE PERMAFROST(?), LARGE AMOUNTS (?) OF LIQUID WATER ON SURFACE WHEN PLANET WAS YOUNG

SURFACE: ROCKY, CRATERED, FORMER (BUT MAYBE NOT CURRENT?) GEOLOGICAL ACTIVITY

January 1997

October 1996 March 1997

EVIDENCE FOR WATER ON MARS

IN THE DISTANT PAST:– DRY RIVER CHANNELS– ERODED FEATURES– PRESENCE OF CERTAIN TYPES OF ROCKS THAT

PROBABLY FORMED IN WATER– SALTY OCEAN?

MORE RECENTLY?– SOME DRAINAGE FEATURES LOOK YOUNG AND

UNERODED.– PERHAPS THERE IS STILL SUB-SURFACE WATER,

AND OCCASIONALLY A LANDSLIDE ON THE SIDE OF A CLIFF (OR SOME SIMILAR EVENT) FREES SOME WATER TO RUN OUT BRIEFLY ONTO THE SURFACE.

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CHALLENGES THAT LIFE ON MARS WOULD FACE

LOW ATMOSPHERIC PRESSURE

NO LIQUID WATER ON SURFACE (ATMOSPHERE IS TOO THIN – WATER WOULD BOIL)

COLD

LARGE DAILY TEMPERATURE VARIATION

ULTRAVIOLET BOMBARDMENT OF SURFACE (NO OZONE LAYER)

VIKING LANDER EXPERIMENTS: TESTS FOR LIFE

CARBON ASSIMILATION: MARTIAN SOIL EXPOSED TO RADIOACTIVELY LABELED (14C) CO2 AND CO GAS, LOOK FOR 14C IN SOIL (PRESUMABLY WOULD HAVE GOTTEN THERE VIA METABOLIC PROCESSES IN ORGANISMS)

• RESULTS: FOUND 14C IN SOIL, BUT…• HEAT-STERILIZED SOIL GAVE SAME RESULTS • CAN BE EXPLAINED NON-BIOLOGICAL CHEMICAL REACTIONS

LABELED RELEASE: RADIOACTIVELY LABELED (14C) NUTRIENTS DRIPPED ON SOIL, LOOK FOR 14C IN GAS ABOVE (RELEASED VIA METABOLIC PROCESSES)

• RESULTS: FOUND 14C LABELED GAS, BUT…• CAN BE EXPLAINED BY INTERACTION OF BROTH AND

PEROXIDES (NON-ORGANIC CHEMICALS) IN SOIL, PRODUCING CO2

VIKING LANDER EXPERIMENTS: TESTS FOR LIFE

GAS EXCHANGE: ADD MARTIAN SOIL TO NUTRIENT BROTH; LOOK FOR O2, CO2, N2, H2, OR CH4 ADDED TO GAS ABOVE – RESULTS: O2 PRODUCED, BUT… – ALSO PRODUCED WHEN DONE IN DARKNESS– ALSO PRODUCED WHEN SOIL WAS HEAT-STERILIZED– ALSO PRODUCED WHEN WATER REPLACED BROTH – CAN RESULT FROM CHEMICAL (NOT BIOLOGICAL)

INTERACTION WITH WATER IN BROTH GAS CHROMATOGRAPH - MASS SPECTROMETER

MEASUREMENTS: BAKE SOIL UNTIL VOLATILES OUTGAS, LOOK FOR ORGANIC MOLECULES– RESULTS: NONE FOUND

MARTIAN METEORITE ALH84001 ONE OF 19 KNOWN METEORITES OF MARTIAN

ORIGIN MARTIAN ORIGIN DETERMINED BY

– COMPOSITION: VOLCANIC ROCK– ISOTOPIC ABUNDANCES– TRAPPED BUBBLES OF GAS CONSISTENT WITH

KNOWN COMPOSITION OF MARTIAN ATMOSPHERE HOW DID IT GET HERE?

– BLASTED OFF MARS IN AN IMPACT 16 MILLION YEARS AGO

– ORBITED THE SUN FOR NEARLY 16 MILLION YEARS– COLLIDED WITH EARTH 13,000 YEARS AGO– FOUND IN ANTARCTICA IN 1984

CONTENTS OF ALH84001 CARBONATE GLOBULES

– INDICATE PAST PRESENCE OF LIQUID WATER– HAVE A LAYERED STRUCTURE THAT LIVING

ORGANISMS CAN PRODUCE– BUT THERE ARE NON-BIOLOGICAL WAYS OF

PRODUCING LAYERING AS WELL

MAGNETITE CRYSTALS – SIMILAR TO THOSE PRODUCED BY

TERRESTRIAL BACTERIA– BUT MAY HAVE A NON-BIOLOGICAL ORIGIN

CONTENTS OF ALH84001 POLYCYCLIC AROMATIC HYDROCARBONS

(PAHs) – ORGANIC MATERIALS USUALLY PRODUCED BY

DECAY OF ORGANISMS ON EARTH– BUT COULD BE PRODUCED IN NON-BIOLOGICAL

WAYS, OR BE A RESULT OF CONTAMINATION AFTER LANDING IN ANTARCTICA

TINY (100 NM) ROD-SHAPED STRUCTURES– RESEMBLE FOSSIL ANAEROBIC EARTH BACTERIA– BUT MUCH SMALLER – PROBABLY TOO SMALL TO BE REAL FOSSILS– COULD BE NON-BIOLOGICAL STRUCTURES OF THE

SAME SHAPE SOME TERRESTRIAL BACTERIA

– PROOF OF CONTAMINATION

PROSPECTS FOR LIFE ON MARS

NO KNOWN EARTH LIFE FORM (NOT EVEN EXTREMOPHILES) COULD SURVIVE ON THE SURFACE OF MARS.

SOME TERRESTRIAL EXTREMOPHILES MIGHT BE ABLE TO SURVIVE UNDERGROUND ON MARS.

IT’S DIFFICULT TO IMAGINE HOW LIFE COULD ARISE UNDER CURRENT MARTIAN CONDITIONS.

BUT 3.5 BILLION YEARS AGO, THERE WAS A THICKER ATMOSPHERE AND LIQUID WATER.

COULD LIFE HAVE EVOLVED ON MARS THEN? IF SO, MARS MAY HAVE SEEDED EARTH WITH

LIFE ??

PROSPECTS FOR LIFE ON MARS COULD LIFE HAVE EVOLVED 3.5 BILLION

YEARS AGO (OR EARLIER), AND SINCE EVOLVED TO ADAPT TO HARSH CONDITIONS?

IF SO, IT MAY STILL SURVIVE– UNDERGROUND (WATER, UV PROTECTION)– AT EDGE OF POLAR CAPS

WE NEED TO GO THERE AND CHECK!

SUMMARY THERE IS DEFINITELY NO COMPLEX LIFE ON

MARS

SIMPLE LIFE FORMS MAY HAVE EVOLVED LONG AGO ON MARS, AND THEN EITHER BECAME EXTINCT OR ADAPTED TO SURVIVE UNDERGROUND AND/OR IN SPECIALIZED LOCATIONS

WHAT WENT WRONG?– MARS IS TOO LIGHT, GRAVITY IS TOO WEAK,

COULDN’T HOLD ONTO ITS ATMOSPHERE – ATMOSPHERIC LOSS HELPED BY IMPACTS

AND/OR SOLAR WIND