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 32NSCI 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/SUITABLE 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 (e.g., CARBON-BASED, USES WATER AS LIQUID SOLVENT)WHAT PROPERTIES MUST A STAR POSSESS IN ORDER TO BE A SUITABLE STAR?SUITABLE STARSA SUITABLE STAR MUST BE:1. MAIN SEQUENCE2. SPECTRAL TYPES K, G, AND SOME F3. POPULATION I (ENOUGH HEAVY ELEMENTS)4. NOT TOO NEAR GALACTIC CENTER5. SINGLE STARS (NOT BINARY OR MULTIPLE)?IN OUR MILKY WAY GALAXY (OR A SIMILAR SPIRAL GALAXY), THIS LIMITS US TO ABOUT 5 TO 10% OF STARS (MORE IF WE ALLOW SOME BINARIES).NUMBER OF SUITABLE STARSLIMITATIONS ON SEARCH TIMES(WE'LL TALK ABOUT HOW TO SEARCH LATER)OUT TO 100 LY: OUT TO 1,000 LY:20,000 SUITABLE STARS 20 MILLION SUITABLE STARS200,000 STARS 200 MILLION STARSSEARCH RATE:1 PER DAY1 PER HOUR1 PER MINUTE1 PER SECONDOUT TO 100 LY:55 YEARS2.3 YEARS14 DAYS6 HOURSOUT TO 1000 LY:55,000 YEARS2,300 YEARS38 YEARS230 DAYSPROPERTIES OF A SUITABLE PLANETA SUITABLE PLANET IS A PLANET ON WHICH LIFE COULD BE FOUNDPROPERTIES:–MUST ORBIT A SUITABLE STAR–TEMPERATURE MUST BE IN THE CORRECT RANGE FOR LIQUID WATER VIA EITHER:•MUST ORBIT ITS STAR WITHIN THE HABITABLE ZONE, PLUS ORBIT MUST BE NEARLY CIRCULAR SO THAT IT IS ENTIRELY WITHIN THE HABITABLE ZONE, OR•MUST HAVE A SIGNIFICANT SOURCE OF INTERNAL HEAT (PERHAPS ON A LARGE MOON EXPERIENCING SIGNIFICANT TIDAL FORCES FROM THE PLANET IT ORBITS)–MUST BE ROCKY, HAVE A SOLID SURFACE–MUST BE MASSIVE ENOUGH TO RETAIN A REASONABLY THICK ATMOSPHEREHELPFUL (BUT MAYBE NOT CRUCIAL) FEATURES FOR A SUITABLE PLANETPRESENCE OF A LARGE MOON–PRODUCES TIDES (TIDEPOOLS ARE A POSSIBLE PLACE FOR THE ORIGIN OF LIFE)–STABILIZES ROTATION AXIS (PREVENTS SEASONAL CHANGES FROM VARYING DRAMATICALLY WITH TIME)PLATE TECTONICS –PROVIDES A VARIETY OF ENVIRONMENTS–PLAYS A ROLE IN CO2 CYCLE ON EARTH, WHICH HELPS REGULATE CLIMATE–MAY BE INEVITABLE FOR A SUFFICIENTLY MASSIVE ROCKY PLANET (STILL HOT INSIDE)HELPFUL (BUT MAYBE NOT CRUCIAL) FEATURES FOR A SUITABLE PLANETIMPACTS NOT TOO FREQUENT–A SUFFICIENTLY LARGE IMPACT COULD WIPE OUT ALL LIFE ON THE PLANET–FREQUENCY OF IMPACTS MAY DEPEND ON POSITIONS OF LARGE PLANETS WITHIN SOLAR SYSTEM•THEIR GRAVITATIONAL EFFECTS EXPEL COMETS TO OORT CLOUD•JUPITER MAY PROTECT EARTH IN THIS RESPECTBUT OCCASIONAL IMPACTS MAY BE HELPFUL FOR EVOLUTION OF ADVANCED LIFE FORMS–IMPACTS CAUSE MASS EXTINCTIONS (E.G., DINOSAURS)–MASS EXTINCTIONS OPEN UP ECOLOGICAL NICHES FOR NEW SPECIESHELPFUL (BUT MAYBE NOT CRUCIAL) FEATURES FOR A SUITABLE PLANETOCCASIONAL MAJOR CLIMATE CHANGES MAY BE HELPFUL FOR EVOLUTION OF ADVANCED LIFE FORMS- THESE CAN “STIMULATE” EVOLUTION BY OPENING UP NEW ECOLOGICAL NICHES FOR A VARIETY OF SPECIES.- THE END OF THE “SNOWBALL EARTH” STAGE IN THE EARTH'S HISTORY (A VERY SEVERE GLOBAL ICE AGE) HAPPENED ABOUT THE SAME TIME AS THE “CAMBRIAN EXPLOSION,” A MAJOR INCREASE IN THE DIVERSITY OF LIFE FORMS ON EARTH, AND THE ORIGIN OF “ADVANCED” ORGANISMS.- SIMILAR, BUT LESS SEVERE, CLIMATE CHANGES MAY HAVE PROMPTED THE EVOLUTION OF HUMANS.WE HAVE ALREADY EXAMINED THE SUITABILITY OF PLANETS IN OUR SOLAR SYSTEM (ORBITING OUR SUN).HOW COMMON DO WE THINK SUITABLE PLANETS ARE IN OTHER SOLAR SYSTEMS?LET’S EXAMINE:–METHODS FOR DETECTING EXTRASOLAR PLANETS (PLANETS OUTSIDE OUR SOLAR SYSTEM, i.e., ORBITING OTHER STARS) –WHAT WE HAVE DISCOVERED ABOUT EXTRASOLAR PLANETS–NOTE: WE DO NOT HAVE THE ABILITY TO SEND SPACECRAFT OVER INTERSTELLAR DISTANCES (i.e., TO OTHER SOLAR SYSTEMS) TO LOOK FOR EXTRASOLAR PLANETS.METHODS FOR DETECTING EXTRASOLAR PLANETSDIRECT OBSERVATION TRANSITSGRAVITATIONAL LENSINGASTROMETRYDOPPLER EFFECT (MOST SUCCESSFUL)DIRECT OBSERVATION(USING EITHER VISIBLE LIGHT OR INFRARED RADIATION)PROBLEMS:PLANET IS MUCH FAINTER THAN THE STAR IT ORBITSEXAMPLE: USING VISIBLE LIGHT, THE SUN IS 1 BILLION TIMES BRIGHTER THAN JUPITER, SEEN FROM THE SAME DISTANCE. USING INFRARED, THE SUN IS “ONLY” 100,000 TIMES BRIGHTER THAN JUPITER.RESOLUTION - ABILITY TO SEE SEPARATELY TWO OBJECTS THAT ARE CLOSE TOGETHERWITH CURRENT GENERATION TELESCOPES (EVEN THE HUBBLE SPACE TELESCOPE), THE IMAGE OF A PLANET WOULD APPEAR BLENDED TOGETHER WITH THE IMAGE OF THE STAR IT ORBITS.FAINTNESS AND RESOLUTION COMBINED MAKE THE PROBLEM EVEN WORSE.DIRECT OBSERVATIONCURRENT TECHNOLOGY CANNOT DETECT EXTRASOLAR PLANETS VIA DIRECT IMAGING.FUTURE IMAGING TECHNOLOGY (WITHIN THE NEXT FEW YEARS TO DECADES):-TELESCOPES IN EARTH ORBIT-WILL USE INTERFEROMETRY (COMBINATION OF IMAGES FROM SEVERAL TELESCOPES TO IMPROVE RESOLUTION) -MAY BE ABLE TO DETECT CHANGES IN BRIGHTNESS DUE TO CLOUD COVER OR SEASONAL CHANGES-SPECTROSCOPIC ANALYSIS WILL BE ABLE TO DETECT COMPOSITION OF ATMOSPHERETRANSITSA PLANET PASSES IN BETWEEN US AND THE STAR IT ORBITS.THE PLANET PARTIALLY BLOCKS LIGHT FROM THE STAR, CAUSING A TEMPORARY DECREASE IN THE STAR’S BRIGHTNESS.BRIGHTNESS DIPS REPEATEDLY, ONCE PER ORBIT OF THE PLANET. THIS WORKS ONLY IF ORBIT IS SEEN EDGE-ON (SMALL FRACTION OF SOLAR SYSTEMS).NO EXTRASOLAR PLANETS HAVE BEEN DISCOVERED THIS WAY, BUT IT WAS USED TO VERIFY THE EXISTENCE OF SEVERAL PLANETS THAT HAD BEEN ALREADY DISCOVERED VIA THE DOPPLER EFFECT.GRAVITATIONAL LENSINGLIGHT FROM A DISTANT OBJECT PASSES BY SOME NEARER OBJECT (AN EXTRASOLAR PLANET IN OUR CASE) ON ITS WAY TO US.GRAVITATIONAL EFFECTS OF NEARER OBJECT BEND THE PATH OF THE LIGHT.AS A RESULT, THE DISTANT OBJECT APPEARS SHIFTED IN POSITION OR IN MULTIPLE IMAGES.PROBLEM: PLANETS AREN’T MASSIVE ENOUGH TO CAUSE SIGNIFICANT BENDING.NO EXTRASOLAR PLANETS HAVE BEEN DISCOVERED THIS WAY, BUT THIS TECHNIQUE MAY WORK IN THE FUTURE.THIS WORKS BETTER WHEN A MORE MASSIVE OBJECT (E.G., A STAR OR GALAXY) IS BENDING THE LIGHT. THIS HAS BEEN OBSERVED.ORBITSAN UNDERSTANDING OF THIS IS NEEDED TO DISCUSS THE TWO REMAINING TECHNIQUES – ASTROMETRY AND THE DOPPLER EFFECT.OBJECT A