MARSDIAMETER: 53% EARTHMASS: 11% EARTHDENSITY: 3.9 gm/cm

SUNLIGHT: 43% OF EARTHTEMP: 140 TO 280 K (-130 TO 7oC OR 200 TO 45oF)

ATMOSPHERE: 95% CO2, 3% N2, 2% Ar, H2O & CO2 CLOUDS,

SEASONS ON MARSSEASONS SIMILAR TO EARTHMARS' AXIS IS TILTED BY 25O, ALMOST THE SAME DEGREE OF TILT AS THE EARTH'S AXIS EACH SEASON LASTS TWICE AS LONG, SINCE THE YEAR IS TWICE AS LONGHOWEVER, UNLIKE EARTH, MARS' ORBIT IS SUBSTANTIALLY ELLIPTICALMARS IS CLOSER TO THE SUN IN NORTHERN HEMISPHERE WINTER, SOUTHERN HEMISPHERE SUMMERMARS IS FARTHER FROM THE SUN IN NORTHERN HEMISPHERE SUMMER, SOUTHERN HEMISPHERE WINTERA PLANET MOVES FASTER IN ITS ORBIT WHEN IT IS CLOSER TO THE SUN

SEASONS ON MARSTHE RESULT IS:IN THE NORTHERN HEMISPHERE:WINTER IS WARM AND SHORTSUMMER IS COOL AND LONGIN THE SOUTHERN HEMISPHERE:WINTER IS COLD AND LONG SUMMER IS HOT AND SHORTREMEMBER THAT WARM AND HOT ARE USED RELATIVELY. MARS IS MUCH COLDER THAN EARTH OVERALL.IN MID-DAY ON A WARM DAY IN THE SUMMER NEAR THE EQUATOR ON MARS, THE TEMPERATURE MIGHT REACH 60OF

SEASONS ON MARSPOLAR CAPS:WATER ICE ALL YEAR ROUNDFROZEN CO2 (DRY ICE) IN WINTER CAP1/3 OF THE TOTAL CO2 IN THE ATMOSPHERE MOVES FROM ONE POLAR CAP TO THE OTHER POLAR CAP AS THE SEASONS CHANGE.THE RESULT IS VERY STRONG WINDS BLOWING FROM THE SUMMER POLAR CAP TO THE WINTER POLAR CAP.WINDS CAUSE HUGE DUST STORMS, WHICH OFTEN OBSCURE SURFACE DETAILS.

EVIDENCE FOR LIQUID WATER ON THE SURFACE OF MARSIN THE DISTANT PAST (2-3 BILLION YEARS AGO):DRY RIVER CHANNELSERODED FEATURESPRESENCE OF CERTAIN TYPES OF ROCKS THAT COULD HAVE FORMED ONLY IN THE PRESENCE OF WATERSALTY OCEAN?

EVIDENCE FOR LIQUID WATER ON THE SURFACE OF MARSMORE RECENTLY?SOME DRAINAGE FEATURES LOOK YOUNG AND UNERODED. IF THEY WERE OLDER, DUST SHOULD HAVE COVERED THEM UP BY NOW.IN A FEW CASES, PHOTOGRAPHS TAKEN SEVERAL YEARS APART SHOW CHANGES.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.

HISTORY OF WATER ON MARSLONG AGO, WHEN MARS HAD LIQUID WATER, IT MUST HAVE BEEN WARMER AND HAD A THICKER ATMOSPHERE (TO PREVENT WATER FROM BOILING).ORIGINALLY MARS OUTGASSED ENOUGH CO2 FROM VOLCANOES TO HAVE 400 x AS MUCH AS IT HAS TODAY.THIS WOULD HAVE PRODUCED A SIGNIFICANT GREENHOUSE EFFECT, WARMING MARS TO TEMPERATURES HIGH ENOUGH FOR LIQUID WATER.

HISTORY OF WATER ON MARSWHAT HAPPENED TO CHANGE MARS?MOST CO2 AND H2O ESCAPED INTO SPACEMARS IS SO LIGHT THAT ITS GRAVITY ISN'T STRONG ENOUGH TO HOLD ONTO FAST-MOVING GAS MOLECULESSOME GAS MAY HAVE BEEN BLASTED AWAY BY IMPACTSSOME GAS MOLECULES STRIPPED OUT OF ATMOSPHERE BY SOLAR WINDMAGNETIC FIELD WOULD HAVE PROTECTED EARLY MARS FROM SOLAR WINDAS MARS COOLED, CORE SOLIDIFIED AND MAGNETIC FIELD WEAKENED, ALLOWING SOLAR WIND TO GET INUV LIGHT FROM SUN DISSOCIATED H2O MOLECULES, H ESCAPED TO SPACE, O COMBINED WITH ROCKS (--> RUST)

CHALLENGES THAT LIFE ON MARS WOULD FACEVERY 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)

MARS VIKING LANDER EXPERIMENTS: TESTS FOR LIFECARBON ASSIMILATION: MARTIAN SOIL WAS SCOOPED UP AND EXPOSED TO RADIOACTIVELY LABELED (WITH 14C) CO2 AND CO GAS (BROUGHT FROM EARTH). THEN THE SOIL WAS ANALYZED TO LOOK FOR 14C. IF THERE WERE MARTIAN ORGANISMS THAT ABSORB CO2 OR CO LIVING IN THE SOIL, THE 14C COULD HAVE GOTTEN INTO THE SOIL VIA METABOLIC PROCESSES IN THE MARTIAN ORGANISMS.RESULTS: FOUND 14C IN SOIL, BUTHEAT-STERILIZED SOIL GAVE SAME RESULTS. CAN BE EXPLAINED NON-BIOLOGICAL CHEMICAL REACTIONS.

MARS VIKING LANDER EXPERIMENTS: TESTS FOR LIFEGAS EXCHANGE: MARTIAN SOIL WAS SCOOPED UP AND ADDED TO A NUTRIENT BROTH (BROUGHT FROM EARTH). THEN THE GAS ABOVE THE SOIL WAS ANALYZED FOR THE PRESENCE OF O2, CO2, N2, H2, OR CH4IF THE SOIL CONTAINED MARTIAN ORGANISMS, THEIR METABOLIC PROCESSES MAY HAVE RELEASED ONE OR MORE OF THESE GASES.RESULTS: O2 PRODUCED, BUT ALSO PRODUCED WHEN DONE IN DARKNESSALSO PRODUCED WHEN SOIL WAS HEAT-STERILIZEDALSO PRODUCED WHEN WATER REPLACED BROTH CAN RESULT FROM CHEMICAL (NOT BIOLOGICAL) INTERACTION WITH WATER IN BROTH

MARS VIKING LANDER EXPERIMENTS: TESTS FOR LIFELABELED RELEASE: RADIOACTIVELY LABELED (WITH 14C) NUTRIENTS WERE DRIPPED ONTO SCOOPED-UP MARTIAN SOIL. THEN THE GAS ABOVE THE SOIL WAS EXAMINED FOR THE PRESENCE OF 14C. IF THERE WERE MARTIAN ORGANISMS LIVING IN THE SOIL, THEY MIGHT HAVE ABSORBED THE NUTRIENTS AND THEN RELEASED GASES CONTAINING THE 14C.RESULTS: FOUND 14C LABELED GAS, BUTCAN BE EXPLAINED BY INTERACTION OF BROTH AND PEROXIDES (NON-ORGANIC CHEMICALS) IN SOIL, PRODUCING CO2

VIKING LANDER EXPERIMENTS: TESTS FOR LIFEGAS CHROMATOGRAPH - MASS SPECTROMETER MEASUREMENTS: SCOOPED-UP MARTIAN SOIL WAS BAKED UNTIL VOLATILES (EASILY VAPORIZED MATERIALS) OUTGAS. THE RESULTING GAS WAS ANALYZED, LOOKING FOR ORGANIC MOLECULES.

RESULTS: NONE FOUND

BOTTOM LINE RESULTS OF ALL EXPERIMENTS: RESULTS INTERESTING, BUT INCONCLUSIVE

METHANE IN MARTIAN ATMOSPHERE?DISCOVERED BY EUROPEAN SPACECRAFT IN 2004 VERIFICATION STILL NEEDEDMETHANE CAN BE PRODUCED BY LIFE, VOLCANOES, OR LARGE COMETARY IMPACTSMETHANE LASTS ONLY A FEW CENTURIES IN THE ATMOSPHERE NO RECENT LARGE COMETARY IMPACTCOLD BE VOLCANIC IN ORIGIN, BUT THAT IS STILL EXCITINGCURRENT GEOLOGICAL ACTIVITY WOULD IMPLY POCKETS OF WARMTH BELOW THE SURFACE

MARTIAN METEORITE ALH84001

ONE OF 30 OR 40 KNOWN METEORITES OF MARTIAN ORIGINMARTIAN ORIGIN DETERMINED BY ISOTOPIC ABUNDANCESTRAPPED BUBBLES OF GAS CONSISTENT WITH KNOWN COMPOSITION OF MARTIAN ATMOSPHEREHOW DID IT GET HERE?BLASTED OFF MARS IN AN IMPACT 16 MILLION YEARS AGOORBITED THE SUN FOR NEARLY 16 MILLION YEARSCOLLIDED WITH EARTH 13,000 YEARS AGOFOUND IN ANTARCTICA IN 1984

CONTENTS OF ALH84001CARBONATE GLOBULES INDICATE PAST PRESENCE OF LIQUID WATERHAVE A LAYERED STRUCTURE THAT LIVING ORGANISMS CAN PRODUCEBUT THERE ARE NON-BIOLOGICAL WAYS OF PRODUCING LAYERING AS WELL

MAGNETITE CRYSTALS SIMILAR TO THOSE PRODUCED BY TERRESTRIAL BACTERIABUT MAY HAVE A NON-BIOLOGICAL ORIGIN

CONTENTS OF ALH84001POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) ORGANIC MATERIALS USUALLY PRODUCED BY DECAY OF ORGANISMS ON EARTHBUT COULD BE PRODUCED IN NON-BIOLOGICAL WAYS, OR BE A RESULT OF CONTAMINATION AFTER LANDING IN ANTARCTICATINY (100 NM) ROD-SHAPED STRUCTURESRESEMBLE FOSSIL ANAEROBIC EARTH BACTERIABUT MUCH SMALLER PROBABLY TOO SMALL TO BE REAL FOSSILSCOULD BE NON-BIOLOGICAL STRUCTURES OF THE SAME SHAPESOME TERRESTRIAL BACTERIA PROOF OF CONTAMINATION

PROSPECTS FOR LIFE ON MARSNO 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.ITS 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?

PROSPECTS FOR LIFE ON MARSCOULD LIFE HAVE EVOLVED 3.5 BILLION YEARS AGO (OR EARLIER), AND SINCE EVOLVED TO ADAPT TO HARSH CONDITIONS?

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

FUTURE SPACECRAFT MISSIONS WILL CONTAIN ADDITIONAL EXPERIMENTS TO LOOK FOR LIFE.

SUMMARYTHERE IS DEFINITELY NO COMPLEX LIFE ON MARS.SIMPLE LIFE MAY HAVE EVOLVED LONG AGO ON MARS, AND THEN IT EITHER BECAME EXTINCT OR ADAPTED TO SURVIVE UNDERGROUND AND/OR IN SPECIALIZED LOCATIONS.WHAT WENT WRONG?MARS IS TOO SMALL, GRAVITY IS TOO WEAK, COULDNT HOLD ONTO MUCH OF AN ATMOSPHERE. ONCE ATMOSPHERE WAS MOSTLY LOST, LIQUID WATER COULDNT EXIST ON SURFACE.

MOONS OF MARSTWO SMALL MOONS PHOBOS AND DEIMOSSUCH LOW MASS THAT GRAVITY ISN'T STRONG ENOUGH TO PULL THEM INTO SPHERICAL SHAPEPROBABLY CAPTURED ASTEROIDSRECALL THAT MOST ASTEROIDS ARE FOUND BETWEEN THE ORBITS OF MARS AND JUPITER. THUS, MANY ASTEROIDS COME CLOSE TO MARS, AND MARS' GRAVITY COULD CAPTURE THEM.