LIFE IN THE UNIVERSE
LIFE IN THE UNIVERSE AST 2037
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This 37 page Class Notes was uploaded by Ms. Adrian Buckridge on Friday September 18, 2015. The Class Notes belongs to AST 2037 at University of Florida taught by Stephen Robert Kane in Fall. Since its upload, it has received 14 views. For similar materials see /class/206977/ast-2037-university-of-florida in Astronomy at University of Florida.
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Date Created: 09/18/15
Search for ExtraSolar Planets Stephen Eikenberry 27 March 2008 AST 2037 Planets Around Other Stars None known prior to 1992 l In 1992 Alex Wolczan discovered 2 now 3 I Ianets around a neutron star But those seemed weird rronamy supernova Iettover bits In 1995 Michel Mayor amp Didier Queloz discover a planet around 51 Pegasi how Kepler s Laws Kepler described 3 laws of planetary motion for our solar system Kel ler did not have a h sical basis for the laws ie Newton s laws of motion He just found patterns in the motions of planets and used them to develop 3 guidelines that provided a good matching description Newton later used his physical laws of motion to show WHY Kepler s rules for planet motion worked O Kepler s Flrst Law Planet orbits are ELLIPSES what s that The sunstar is at one focus of the ellipse Both the planet and the star orbit the center of mass The distance from center to focus is the eccentricity Circles are elli ses with eccentricit 0 both foci at center 9 Kepler s Second Law Planet motion sweeps out equal areas of the ellipse in equal time Meaning planet moves faster when it is closer to the star and slower when it is farther away Kepler s Third Law asPz Mtot a semimajor axis of the ellipse AU P period of the orbit years Mtot total mass of the system solar masses Orbital Re ex Motion For a starplanet system the planet does most of the moving Its low mass means it is farthest from the center of mass Same period larger distance means higher velocity what is it for Earth For Jupiter But you can t see it too faint Star moves VERY little High mass means small distance from COM what is it for SunEarth SunJupiter But we can SEE the star Doppler Shift due to Stellar Wobble g m Radial Velocitv Planet Searches Howto with movie 0 h iii Clix r quotm1j n m i f39wi gf w Take a spectrum with a big telescope and very precise and STABLE spectrograph Radial Velocitv Information Jupiter has biggest re ex velocity effect on the Sun but this velocit is still small 39 period is long 7400 i i i i i i Information we get 500 w ll 2 3 Period how 7600 1 g i l i in 3 0 Orbit distance 3 7700 f i i Glow 0 Eccentricity b 7800 i Planet mass note sin 900 l i uncertainty 71000 f 400 500 800 moo 1200 1400 1600 JD 7 2 45npoo Radial Velocity Information Jupiter has blggesi reflex velocity effect on the Sun 39 but thls velocity is still small period is long Information we get Pvrlod how Orbit dl ance how Eccentricity Flam man not umdnty Really planet MINIMUM mass Faceon Mlnlmum Doppler Signature Edgeon Maxlmum Doppler Signamm 51 Pegasi In 1995 Mayor amp Queloz announce the discovery of an orbital signature with amplitude 50 ms In a 423 dny period around star 51 Pegasi 39 Mass 05 MN 9 First extrasolar phnet quot lm A The Great Square of Pegasus Phnm hm Sewers Arum Planevanum amp Aslmnnmy Mmaum 39 3 I Jupiter Planet Bonanza Geoff Marcy amp Paul Butler quickly con rmed 51 Pegasi They had lots of archival data from searches for J upiter type planets periods gt10 years so they were still in progress No on even thought to look for shortperiod MASSIVE planets why would they be easier Found many Hot Jupiters most extra solar planets Known toaay are not Jupters ESPlanet Population As of this morning 228 planets are now known to orbit other stars I All of this has happened in about 10 years someone currently nds a new planet every couple of weeks or less These planets are NOT generally like our Solar System objects WHY Next time properties of ExtraSolar Planets and implications for Life in the Universe ExtraSolar Life Habitable Zones Stephen Eikenberry 25 March 2008 AST 2037 Life in the Solar System Mcrcu ryVenus too hot Earth just right Mars was OK once but now cold Jupiter Saturn Uranus Neptune too cold though some moons may be OK Life Ingredients The ingredients 0fEarthlike life are all common H20 C etc So are many possible alternatives to them ie Si NH3 etc Why are these so common If they are so common why isn t there life on ALL the planets Optimal Temperature Range It s not unique but H20 is our favorite solvent It s not unique but we prefer it as a liquid This means T gt 0 C 0 T lt100 C We need to nd temperatures in this range at least part ofthe time How common is that What Sets Planet Temperatures Lots of factors such as Temperature Balance Assume that the dominant factor is stellar radiation Fluxemitted Fluxradiated Show balance solve for T Show range in distance The Enlar System s Habitable Zane d N Mara Habitable logesz Other Stars Henzsprung Russell Diagram again Scaling for other stars same balance now lry distance versus luminosity Iumnos y solar unns 1 F 1 000 0000 6000 surlace lemperawre KeMn How Manv Other Stars Stars within 4 pc 5 WC stars 5 K stars 25 M stars The number of K stars is about equal to the U u no number of O B A F and G stars TOGETHER The number of M stars is greater than the TOTAL of all the other stars combined In other words Most stars are M stars Even excluding M stars about 12 of all the rest of stars are K stars Q Habitable Zane Mars Earth 5 a m a jquot IL I z E I I L I39 1 H1 u D ll l m E E 1 m I I Radius of rlrit r lative tu Earth39s 7 Ftype star Mtype M Star Problems Habitable zone is VERY close to the star Gravitationaltidal forces are much stronger here so we expect tidal locking may develop this close Why is that not good for life gt To dwm Humming mm M Star Problems I M stars have very actin magnetuspheric storms and ares Why it that not good for life39 Why is being close a particular problem Habitable Zones OB stars Show on board Range in distance from the star is huge We expect many planets in this range But lifetime issue How long does an 0 stars live How about a B star An A star So What Stars What stars are the likeliest targets in searching for extraterrestrial life Late F stars F5 G stars yeah us K stars Where around these stars do we look The Habitable Zone Is this the whole storv What about Venus Venus is MUCH hotter by about 60K than we expect Due to its thick atmosphere and greenhouse gases So thick atmosphere can ruin a planet in the close end of the HZ Alternately it can keep a planet just outside the distant end of the HZ warm Is this the whole storv What about EuropaEnceladus These moons seem to have liquid water potentially in VERY large quantities Why Both are WAY outside the nominal HZ So there are other effects other heating sources which can create habitable niches as well HIPL allhe Slmsmom galaxy are mualv ylars 5AM c mmm q nmurm Munrva summme Summary Ingredients for life are everywhere f a big it we assume that liquid water is important for life then there is a limited volume of any stellar system where that might exist the Habitable Zone If we assume temperature is dominated by sunstar light then the HZ can be calculated for any given star Likely star types for life are F G and K stars bigger stars die fast M stars have tiny HZs and other issues Multiple stars are not likely to have good HZs The Galaxy has its own good neighborhood factors This is a VERY simplistic approximation with lots of exceptions atmospheres tidal heating of moons etc 4
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