nsci 314 life in the cosmos 9 - searching for life in our solar system: the inner planets dr. karen...
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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