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CSUSB NSCI 314 - suitable stars and planets

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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57NSCI 314LIFE IN THE COSMOS13 - WHERE TO SEARCH FOR LIFE OUTSIDE OUR SOLAR SYSTEM:SUITABLE STARS AND PLANETSAND EXTRASOLAR PLANETSDr. Karen KolehmainenDepartment of Physics, CSUSBhttp://physics.csusb.edu/~karen/SEARCHING FOR LIFE IN OTHER SOLAR SYSTEMSWE WILL TAKE A CONSERVATIVE APPROACH: -WE WILL CONSIDER ONLY LIFE THAT IS BASED ON THE ELECTROMAGNETIC INTERACTION(IS MADE OF ATOMS AND MOLECULES). - WE WILL ONLY CONSIDER LIFE THAT USES CARBON-BASED CHEMISTRY. - WE WILL ONLY CONSIDER LIFE THAT USES WATER AS ITS LIQUID SOLVENT. - IGNORE POSSIBILITY OF “EXOTIC LIFE,” SUCH AS LIFE THAT USES A LIQUID SOLVENT OTHER THAN WATER, SILICON-BASED LIFE, OR LIFE BASED ON THE STRONG FORCE.–THEREFORE CONSIDER ONLY EARTH-LIKE PLANETS (OR LARGE MOONS) WITH LIQUID WATER.–IF EXOTIC LIFE CAN EXIST, THEN LIFE MAY EXIST IN A LARGER RANGE OF LOCATIONS AND BE MORE COMMON THAN WHAT WE WILL ESTIMATE.PROPERTIES OF A PLANET THAT IS SUITABLE FOR LIFE1. - RELATIVELY LARGE ABUNDANCES OF CARBON, NITROGEN, AND OXYGEN (PLUS TRACE AMOUNTS OF HEAVIER ELEMENTS)•IN ORDER TO HAVE SUFFICIENT QUANTITIES OF ELEMENTS HEAVIER THAN HYDROGEN AND HELIUM, THE PLANET MUST ORBIT A FAIRLY YOUNG (POPULATION I) STAR2. - NOT NEAR A SITE OF COSMIC VIOLENCE•IN CERTAIN LOCATIONS, SUCH AS NEAR THE CENTER OF A GALAXY, A PLANET MIGHT BE BOMBARDED BY FREQUENT COMETARY IMPACTS OR HAVE HIGH LEVELS OF DAMAGING RADIATIONPROPERTIES OF A PLANET THAT IS SUITABLE FOR LIFE1. - ROCKY PLANET - SOLID SURFACE•PROBABLY THIS WILL USUALLY BE THE CASE IF THE PLANET IS LOCATED IN THE INNER PART OF THE SOLAR SYSTEM ORBITING A RELATIVELY YOUNG (POPULATION I) STAR2. - MASSIVE ENOUGH TO RETAIN A REASONABLY DENSE ATMOSPHERE •IF THE ATMOSPHERE ESCAPES INTO SPACE, THERE CAN BE NO LIQUID WATER (OR ANY OTHER LIQUID) ON THE SURFACE•REMEMBER THAT THIS IS THE PROBLEM WITH MARS IN OUR SOLAR SYSTEMPROPERTIES OF A PLANET THAT IS SUITABLE FOR LIFE1. - CORRECT TEMPERATURE RANGE FOR LIQUID WATER (SOLVENT)•THIS REQUIRES A PLANET TO HAVE A NEARLY CIRCULAR ORBIT AROUND ITS STAR WITHIN THE “HABITABLE ZONE,” OR TO HAVE A SOURCE OF INTERNAL HEAT (SUCH AS TIDAL HEATING)2. - STABLE ENVIRONMENT FOR SEVERAL BILLION YEARS (TIME NEEDED ON EARTH FOR “ADVANCED” LIFE FORMS TO EVOLVE)HABITABLE ZONESPHERICAL SHELL SURROUNDING STAR IN WHICH ANY ORBITING PLANETS WILL HAVE THE RIGHT TEMPERATURE FOR LIQUID WATERINNER EDGE OF ZONE IS WHERE AVERAGE TEMPERATURE = 100oCOUTER EDGE OF ZONE IS WHERE AVERAGE TEMPERATURE = 0oCWHERE IS THE HABITABLE ZONE FOR FOR OUR SUN?OUR SUN’S HABITABLE ZONEINNER EDGE: ABOUT 0.85 - 0.95 AU FROM SUNOUTER EDGE: ROUGHLY 1.4 - 1.7 AU FROM SUN–EXACT VALUES DEPENDS ON DETAILS OF GREENHOUSE EFFECTHABITABLE ZONE MOVES OUTWARD WITH TIME, AS SUN BRIGHTENS SLIGHTLY–WHEN SOLAR SYSTEM FIRST FORMED, INNER EDGE AT 0.65 – 0.80 AU AND OUTER EDGE AT 1.1 – 1.5 AU CONTINUOUSLY HABITABLE ZONE (FOR FIRST FEW BILLION YEARS AFTER SOLAR SYSTEM FORMED)–INNER EDGE AT 0.85 TO 0.95 AU–OUTER EDGE AT 1.1 TO 1.5 AUOUR SUN’S HABITABLE ZONEWHERE ARE PLANETS RELATIVE TO SUN’S HABITABLE ZONE?EARTH IS AT 1 AU – WITHIN CONTINUOUSLY HABITABLE ZONE (OBVIOUSLY!)VENUS IS AT 0.72 AU – TOO CLOSE NOW, BUT MAY HAVE BEEN BARELY HABITABLE VERY EARLY IN ITS HISTORY.MARS IS AT 1.52 AU – PROBABLY WITHIN HABITABLE ZONE NOW, BUT POSSIBLY NOT EARLIER IN ITS HISTORY.–BUT THE REAL PROBLEM IS THAT MARS IS TOO LIGHT, SO IT LOST MOST OF ITS ATMOSPHERE.PROPERTIES OF MAIN SEQUENCE STARSSPECT. TYPEBRIGHTNESS (SUN=1)NUMBER OF STARS (IN MW)PERCENT OF TOTALO BAFGKM100,0005001020.90.20.00580,000360 MILLION2.4 BILLION12 BILLION28 BILLION60 BILLION290 BILLION0.00002%0.09%0.6%3%7%15%73%COLORBLUEBLUEWHITEYELLOWYELLOWORANGEREDHABITABLE ZONES AROUND OTHER STARSFOR BRIGHTER STARS:–HABITABLE ZONE IS FARTHER FROM STAR AND LARGER IN EXTENT (E.G., 5 TO 20 AU FOR AN A-TYPE MAIN SEQUENCE STAR)FOR FAINTER STARS:–HABITABLE ZONE IS CLOSER TO STAR AND SMALLER IN EXTENT (E.G., 0.02 TO 0.06 AU FOR AN M-TYPE MAIN SEQUENCE STAR)–HABITABLE ZONE MAY BE SO SMALL THAT IT IS UNLIKELY THAT ANY PLANETS ARE FOUND WITHIN IT–IF PLANET IS TOO CLOSE TO STAR, OTHER POSSIBLE PROBLEMS INCLUDE:•SOLAR FLARES •PLANET’S ROTATION MAY BE TIDALLY LOCKED (MIGHT BE OK IF ATMOSPHERE CAN SPREAD HEAT AROUND ENOUGH)STABLE ENVIRONMENTSTAR MUST NOT CHANGE TOO MUCH IN TEMPERATURE OR BRIGHTNESS FOR SEVERAL BILLION YEARSTHIS REQUIRES A MAIN SEQUENCE STAR THAT IS COOLER/REDDER/FAINTER THAN MID-F SPECTRAL TYPE –MAIN SEQUENCE LIFETIME IS TOO SHORT FOR HOTTER/BLUER/BRIGHTER STARS–THIS REQUIREMENT ELIMINATES ONLY A FEW PERCENT OF ALL MAIN SEQUENCE STARSPROPERTIES OF MAIN SEQUENCE STARSSPECT. TYPEBRIGHTNESS (SUN=1)LIFETIME (YEARS)# OF STARS (IN MW)PERCENT OF TOTALO BAFGKM100,0005001020.90.20.0055 MILLION10 MILLION500 MILLION1 BILLION10 BILLION100 BILLION1 TRILLION80,000360 MILLION2.4 BILLION12 BILLION28 BILLION60 BILLION290 BILLION0.00002%0.09%0.6%3%7%15%73%COLORBLUEBLUEWHITEYELLOWYELLOWORANGEREDSUITABLE STARSDEFINED AS STARS AROUND WHICH PLANETS THAT ARE SUITABLE FOR LIFE MIGHT BE ORBITING.REMEMBER THAT WE ARE RESTRICTING OUR ATTENTION TO LIFE SIMILAR TO THAT ON THE EARTH (CARBON-BASED, USES WATER AS LIQUID SOLVENT)WHAT PROPERTIES MUST A STAR POSSESS IN ORDER TO BE A SUITABLE STAR?PROPERTIES OF SUITABLE STARSMAIN SEQUENCE - MOST NON-MAIN SEQUENCE STARS (RED GIANTS & WHITE DWARFS) AREN’T STABLE ENOUGH IN BRIGHTNESS AND TEMPERATURE OVER A LONG ENOUGH TIME - 90% OF STARS ARE MAIN SEQUENCESUFFICIENTLY LONG MAIN SEQUENCE LIFETIME- AT LEAST SEVERAL BILLION YEARS - SPECTRAL TYPES M, K, G, AND SOME F - 97% OF MAIN SEQUENCE STARS ARE OF THESE SPECTRAL TYPESPROPERTIES OF SUITABLE STARSSUFFICIENTLY LARGE LUMINOSITY - REASONABLY LARGE HABITABLE ZONE THAT ISN’T TOO CLOSE TO THE STAR - SPECTRAL TYPE M TOO FAINT, HABITABLE ZONE TOO SMALL AND TOO CLOSE TO STARLOCATION IN SPIRAL ARMS OR DISK OF A SPIRAL GALAXY, OR IN AN IRREGULAR GALAXY- STARS HERE ARE YOUNGER (POPULATION I) AND THUS HAVE SUFFICIENT ABUNDANCE OF HEAVY ELEMENTS -


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