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by: Stephan Kuvalis


Stephan Kuvalis

GPA 3.89

Philip Armitage

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Philip Armitage
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This 47 page Class Notes was uploaded by Stephan Kuvalis on Thursday October 29, 2015. The Class Notes belongs to ASTR 3300 at University of Colorado at Boulder taught by Philip Armitage in Fall. Since its upload, it has received 28 views. For similar materials see /class/231955/astr-3300-university-of-colorado-at-boulder in Astronomy at University of Colorado at Boulder.




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Date Created: 10/29/15
Results of radial velocity searches Since the planet is not directly detected only information is that which can be derived from the radial velocity curve mass actually Mpsininclination orbital period orbita radius eccentricity of the orbit Can also measure some properties of the host star such as its mass and metalcity normally expressed as the abundance of elements heavier than helium relative to the abundance in the Sun Selection effects biases You see first what s easiest to see For a particular mass star the planets that produce the largest radial velocity signal are those that are a massive and b orbit at small distance from the star Also need to detect the whole orbit of the planet around the star so need to monitorthe starfor a long time Recall the orbital period of Jupiter about 10 years 39 lLiiieSpIinng09 w w lLi eSpIingZW9 Reported daLa March SUUG Reported date March UUd 1 A g 7 More than 3 Lkuplamvls 7 O 9 x wim ltimi A AA l 5 200 known l g 7 extrasolar 3 o u A 1 3 planets found g r i to date E 07 A A l w i line of constant is 0 6 1 l E V g 20 5 A A A A A a r of roughly equal g l detectability g A l i E 001 g 7 i Z 73 mm 0 3 A i H E 39 39 7 x A 02 A 153 8000i if A I 39 A fJA Al 7 2 A A Z 0 A A 5quot W 1 A A A A aAA 1 I I I 0 And c nA 0000177 iii H mi H l 39 01 l 10 0 01 01 1 1 semjrmalor axis AU semtrmaJor BXJS AU Exhaleneshial Liiie Spring 2009 iLiiELSpIingZWS Massive gas giant planets are reasonably common at least 5 10 of Solar mass stars have detectable planets and there are probably many more that currently elude detection But two maior surprises giant planets in ultrashort period orbits sometimes just a few days a lt O 1 AU These planets which orbit closer to their stars than Mercury does to the Sun are called hot Jupiters giant planets with often very eccentric orbits some known extrasolar planets have e gt O 9 which in the Solar System is an orbit more typical of a comet than a planet rLiiie Splingzm Why are hot Jupiters surprising Recall for the Solar System we argued that giant planets form in the outer Solar System beyond the snowline where icy materials can condense due to low temperature The disk at NO OSAU is too hot for even dust to survive so how did the cores of hot Jupiters form gas rocky materials gas rock ices present hot Jupiter location snowline rfew AU v39 H lLi e Springzws Why are eccentric planets surprising all the major planets in the Solar System have close to circular orbits planets form from protoplanetary disks in which the gas is likely to have near circular orbits Note it terrestrialrocky planets also often have very eccentric orbits implications for habitability 39 Life Spring 2008 Planetary migration Most popular theory for origin of the hot Jupiters planets formed at normal location in disk beyond the radius of the snowline planets lost energy and angular momentum to the gas in the disk planets spiraled in to the small radius where they re now seen dea was proposed betore extrasolar planets were found seems to match the main properties of the hot Jupiters 39 I 7 Spring2008 Origin of the eccentric orbits Also quite uncertain perhaps the typical outcome of the giant planet formation process is several massive planets that orbit too close together to be stable for long time periods planets interact gravitationally and scatter least massive planets are ejected survivors are left with eccentric orbits 39 Life Spring 2008 sthetheor ot iant lanettormation wron Some theoretical expectations are confirmed Frequency of planets a vs stellar metal content planet traction More heavy elements means more planetesimals expect cores of giant planets to form more quickly so it is more likelyto form a giant planet in time before the gas in the disk is lost 39 Life Spring 2008 Planet formation may be less efficient than we thought betore whole generations of planets may be swallowed by their stars as a result of migration Extraterrestrial Life Spring2008 eccentricity Violent and very chaotic process Close to the star scattering often results in physical collisions between planets Many planets are 7 ejected into interstellar space l thl5 39 Life Spring 2008 0 0 0 quot gt m m c P N Cumulative Fraction of Systems 0 o 02 04 06 08 Not proven to be the answer but the distribution of eccentricity resulting from such a model is a good match to the one that is observed Ex atelrestrial Life Spring 2008 Extraterrestrial Life Lecture 25 Course questionnaires at end of class today Final homework due Thursday Answer keys to all homeworks will be on the web by the end of the week Today practical or at least conceivable approaches to interstellar travel Extraterrestrial Life Spring2008 on thrusters will be used on future interplanetary missions Facility inertial confinement fusion Only interstellar probe design that could be built with relatively near term technology development 39 Life Spring 2008 Difficulty with accelerating to velocities significant 0 10 for interstellar travel is the mass of the fuel Quantified via the rocket equation see textbook p 442 M M eVme ship fuel ship launch mass final mass velocity of the exhaust gas High exhaust velocities are best but it is hopeless to reach 0 1 0 using either chemical rockets vexhaust 5 kms or ion drives 50 km s Extraterrestrial Life Spring 2008 Proiect Orion 1950s 60s era concept for a spacecraft powered by exploding a few thousand nuclear bombs behind a shock absorbing plate Debris velocity can be 1000 kms or more Abandoned after the test ban treaty in 1963 More modern versions might use laser fusion of smaller deuterium tritium pellets Extraterrestrial Life Spring2008 Alternate approach leave the power source fuel on Earth and beam light at a large sail radiation pressure of the reflected light accelerates the probe Laser sails Advantage rocket equation limitations do not apply the fuel can be as heavy and inefficient as you want Can also be used with sunlight in the Solar System but this doesn t work for interstellar travel as the Solar flux falls off too fast Engineering challenge is in the mass needed for the sail material and achieving enough laser power 39 Life Spring 2008 Suppose we want to accelerate to O 1 c in one year Need one tenth of a g acceleration Force exerted by a laser beam of luminosity L reflecting off a sail is 2L C Using Newton s 3rd law F ma This is the laser power needed to accelerate a probe of mass m at acceleration a Example for a 100kg probe including the mass of the sail and supporting structure need 1 L x100kggtlt3gtlt108 msxlms2 15GW Again not unreasonable power requirement Grand Coulee dam on the Columbia has 7 GW capacity However currenty efficiency of high powerlasers is very low highest power continuous lasers are only megawatt class No physics reason why higher efficiencies could not be achieved in the future E Another consideration is that it would be hard to focus the laser power onto the sail After 1 year of acceleration probe will be at a distance from 1 5a 5 x1014 m 3000 AU Remember that to focus a beam of light of wavelength A into an angle 6 we need a dish of size D N M0 fthe sail were 100km across we would need a mirror of 2km size to focus the laser power onto the sail A more powerful laser with a smaller mirror might be more feasible n M w lLifeSpring2008 M fantimatter could be created in kg quantities and if itcould be stored safely could be used as a fuel to accelerate to reasonable fraction of the speed of light Anti particles positrons antiprotons are routinely made and accelerated l i in particle accelerators A Harder to make neutral antimatter atoms perhaps a few million have been created in experiments 1 million antihydrogen atoms 1 7x 103921 kg Know of no lightweight way to store large quantities Emaierresm al Life Spring 2008 Antimatter as a fuel All elementary particles have antiparticles e g electron s antiparticle is the positron proton s is antiproton When particles meet their distinct antimatter counterpart annihilate into pure radiation E is the energy yield m is the mass of the particles that annihilate Antimatter fuel has the highest possible energy density e g one years output from the Grand Coulee dam could be matched by annihilating 1 2 kg of antimatter with same amount of normal matter cw M w Life Spring 2009 Difficulties in interstellar travel are formidable but not impossible given known laws of physics Engineering might be possible with today s technology given enough investment certainly seems feasible in the far future At one tenth the speed of light probes could cross the Galaxy in one million years Fermi paradox if there are civilizations 100s of millions of years olderthan ours in the Galaxy why have they not spread out through the Galaxy already Fermi paradox Ematerreskial Life Spring 2008 Phylogenetic Tree 0 Life When did critical events in the evolution of life I on Earth occur Bachml Amwa Enmrvula I 3 Most dates more than about 1 billion years 1 ago are based on i indirect evidence can be disputed A phylogenam tree based on rRNA dam sli owing the separation oi battenL amiaaa and eukarvmes prokaryotes eukaryotes multicellular organisms intelligent life Extraterrestrial Life Spring2008 Prokaryotes have much more diverse metabolic pathways than more complex organisms anaerobic do not require oxygen necessary since the early atmosphere was oxygen poor can derive energytrom reactions involving heat inorganic materials such as hydrogen sulphur etc photosynthesis probably developed early but did not initially use water and did not yield oxygen as a byproduct P ro karyotes Single celled organisms bacteria and archaea that lack cell nucleus and other organization within the cell sotopic evidence rock beds called stromatolites suggest that the simplest life may have started 3 5 3 8 billion years ago About the time the Late Heavy Bombardment on the Moon ended Extraterrestrial Life Spring 2008 quotring 2008 Genetic complexity Mycoplasma genitalium 0 58 million base pairs 100 coding E coli 4 8 million base pairs 100 Some simple eukarya 10 100 million base pairs Homo sapiens 3 4 billion base pairs Wheat 17 billion Amoeba 670 billion 39 Life Spring 2008 Eukaryotes Single or multicellular organisms that have cell nuclei and complex internal structures e g mitochondria May have arisen from symbiosis beneticial relation between initially separate prokaryotic organisms that eventually tused Cell nuclei date to at least 2 1 billion years ago but possibly older Multicelled organisms date to 1 2 billion years ago Extraterrestrial Life Spring2008 Atmospheric composition on Earth Current atmosphere of Earth nitrogen N2 78 oxygen 02 21 argon water vapor trace amounts of other species Oxygen is a reactive gas and its abundance can be deduced from geological evidence Source photosynthesis of modern plants CO2 H20 gt CHZO 02 Sinks respiration decay inorganic reactions 39 Life Spring 2008 Timescale tor the sinks to remove 02 from the atmosphere is extremely short about 2 million years Substantial oxygen atmosphere exists because some carbon avoids reacting with oxygen by becoming buried in sediments Ex aterrestrial Life Spring 2008 ncrease in the 02 content of atmosphere 2 4 billion years ago may reflect tirst organisms that released 02 as byproduct of photosynthesis epoch when 02 production became large enough to overwhelm oxygen sinks mplications for detecting lite on extrasolar planets presence of 02 or 03 is an indicator of life absence of oxygen does not prove that life does not exist for more than half Earth s history our atmosphere was oxygen free quotring 2008 How 39 are 39 events Asteroid impacts Major climate change Development of an oxygen atmosphere Mass extinctions driven by sudden changes to the Earth may have promoted subsequent diversity 0 1 Stephen Jay Gould s book Wonderful Life 39 Life Spring 2008 Oxygen level log wt pOgi VIDCtll Kl tlluul Hl tll l ozone layer A plokaiyotes 94 cwmt term 4 miv yn l 1 animals Ex aterrestrial Life Spring 2008 Mm van5 Wm M 3mm Rmn IDJEII l t i swwa smug E1 spectral signature of ozone in the mid intrared Ex aterrestyial Life Spling2008 quot 39 to otherquot quotquot quot39 planets t we accept the ordering prokaryotic organisms 3 5 billion years ago eukarya 2 1 billion years ago multicellular life 1 2 billion years ago nterence Simplest forms of life arose almost as quickly as possible on Earth recall that heavy bombardment of the Earth continued till 4 billion years ago BUT several billion years were needed before any complex life forms arose 39 Life Spring 2008 One interpretation of this data Probability ease of life developing on a habitable world liquid water energy is high Probability of complex life arising from evolution of simple life is unclear but might be small Limitation only one example fthe probability of life getting started is high it probably happened independently more that once but no evidence of that survives A more pessimistic view is also logicallytenable suppose the probability of life developing say per billion years is very small 1 in a million suppose the probability of complex life developing is similarly small n this case on a planet mamas intelligent e it is likely that simple life arose unusually early The early appearance of life on Earth may not imply that lie starts easily impossible to sayfor sure without additional evidence Extraterrestrial Life Lecture 22 Habitable extrasolar planets may be common define habitable as meaning Earth mass planets at around 1 AU from Solar type stars Some other requirements for habitability geological activity magnetic field are hard to determine from afar Can we detect the signs of atmospheric modification that on Earth are due to life 39 Life Spring 2008 Depending upon the wavelength of the observations changes can be large factor of two Rnl lrcFv Flux Permits atleast determination of the rotation rate of the planet length of the day crude idea of what fraction of the surface is covered by land and ocean 39 I 39r emingzoorz Atoms energies of spectral lines reflect the differences between energy of electrons in different energy levels Molecules changes in the vibration and or rotation state of the molecules lead to emission of absorption of radiation in spectral lines Easiest molecules to observe in optical and infrared are O2 03 CO2 and H20 CH4 also possible potential biosignatures Characterizing extrasolar planets n the near future extrasolar planets will be unresolved a single pixel only no maps direct detection of continents Brightness of the planet will change as the planet rotates depending upon the rotation rate variety of surface terrain oceans continents ice covered areas extent of cloud cover 39 Life Spring 2009 Spectroscopy Break up light into constituent colors form a spectrum plot of the flux as a function of the wavelength Spectra contain lines narrow regions where the flux is either larger or smaller than nearby in the spectrum whose wavelengths energies correspond to characteristic energies in atoms or molecules Wavelengths of spectral lines are diagnostic of composition of the atmosphere 39 Life Spring 2008 N 4000 5000 EM 7000 Ex aterrestrial Life SpringZ008 Molecules have already been detected in giant planet atmospheres in transmitted starlight during transits 1 ODE 1 000 ennui gqiuisu 6309 o 995 r 3 0 990 quotn9l39 39 uuun Niln E g 0 985 7 6 5 0930 3 m lt 095 ner O 970 0 955 quotumquot n m 7150 7100 J70 0 50 mo 1 30 200 250 39 Life Spring2008 Absorption Molecules have already been detected in giant planet atmospheres in transmitted starlight during transits JU l l I x B d d I i th 1 32211 22d gmonia Methane In d d I t ih Ad iwfuini W9 me a a gIant planet atmosphere Swane et al 2008 7 Modell Model water water methane l I l l a 20 Wavelength pm Extraterrestrial Life Spring 2008 For terrestrial planets hope to detect molecular signatures either in reflected light in the optical or in thermal emission in the infrared Radiance WmVsrMm a ntrared spectrum quotring 2008 PadRaw The red edge More detinitive signatures of lite exist but are less certain nut um H O ll c llquot Wuvelarigih lm e g chloroplasts in cells involved in photosynthesis lead to a signature of vegetation reflect in green and absorb in the blue and the red Unfortunately this signature seems to be hard to see on a realistic planet that has clouds Life Spring 2008 For terrestrial planets hope to detect molecular signatures either in reflected light in the optical or in thermal emission in the infrared FwdWmquot Optical spectrum Extraterrestrial Life Spring 2008 msmm yr Gsiar mnnxnw Whiler Wyn lw V v T qt quotWquot WKer a sin mm jxiu TFFOp4cal Earth spectrum i x 70 t 5 m jxin L 39 lIM hardw am a mm With teasible instruments the spectrum will be of quite low resolution but ought to be able to see O2 O3 and water quite easily Extraterrestrial Life Spring2008 The Terrestrial Planet Finder Possible future NASA mission to image habitable planets and measure the spectrum of their atmospheres TFP coronograph single telescope with a device to block out the starlight allowing planet imaging TPF interterometer 4 or more telescopes flying in formation whose light would be combined to cancel out the starlight New Worlds Observer Colorado concept to block the starlight with an external occulting disk 39 Life Spring 2008 Exn39awrresn39ial Lile Spring 2009 Simulated NWO image Exn39abrresm al Life Spring 2008 Emamrreslrial Life Suing 2008 Outlook Technically appears feasible to search for signs of atmospheric modification by life on extrasolar planets within the next decade Any TPF mission will be complex and thus expensive competes with other NASA priorities Q will detection of oxygen 39or ozone convince people that life is really present mameslrfal Life String 2000 Extraterrestrial Life Lecture 26 Expected number of civilizations in the Galaxy is proportional to their mean lifetime What hazards are there to civilizations Natural hazards impacts from asteroids and comets how frequent how dangerous 39 in Siberia 1908 m acts b asteroids and comets are observed Damage from the Tunguska impact I Witnessed by a handful of people but no one known to have been injured Exbate39lrestrial Life Springva Ex ateirestrial Life SpringZOOB Smaller events atmospheric explosions with yield of a few kT are quite commonly detected by satellites 1972 event visible during daylight over Utah and Wyoming appears to have been a 10m diameter rock that grazed the Earth s atmosphere Large events are much rarer but have enormously greater consequences 10km asteroid created a crater 180km in diameter off the Yucatan peninsula Parts of the crater can be traced out indirectly on the ground Ex aterreshial Life SpIiIIgZOOB mpactors have speeds of 12 30 kms kinetic energy A 1 km diameter asteroid with a velocity of 20 kms has an impact energy of 3 x 102 Joules 75 000 megatonnes TNT equivalent Thin rock layer was deposited world wide as a result of this impact event dentified as having an impact origin by Alvarez in the early 1980s timing 65 Myr ago coincides with the decline of the dinosaurs Distinguish between impactors potentially large enough to cause a global catastrophe d gt 1 km or so and smaller events that would cause regional devastation Exhaterrestrial Life SpiingZOOB Extraterrestrial Life Spring392008 Numbers of near Earth asteroids Near Earth asteroid population is continually replenished by new bodies that leak out of the asteroid belt Thought that all 3km size asteroids that could encounter the Earth are known along with most of the 1km bodies about 1000 No known large body will impact the Earth in the torseable tuture very small probability of a large comet arriving from the outer Solar System with little warning Life Spring2008 Smaller bodies are much more numerous Number dn with size between rand rdr increases steeply with decreasing r Have determined the rough numbers of but have not individually cataloged all the smaller bodies with sizes below 1km PAN Starrs project is underway first of tour telescopes operational and will complete census down to a size of about 300m Probably another decade or more before all 100m objects still quite dangerous have been found Extraterrest Life Spring 2008 Viaaw n 1 HM ru Lognmpact Energy Ham5 mm mm Brawn nrzl m Annual mm mun Distnvemdns olhn 2 am lt Tunguska x Rabmnwnz m l 20w 5W Vlhmmn out mm mum 5 7 LogNltHj u u a u m 4 m m I r a u m 0 a w u a Lognmpam interval yaarsj Diameter Km Estimated size distribution from Chapman 2004 39 Life Spring 2008 mpact danger is roughly the same it the impact is on land or at sea e g Apophis 350m across would cause a devastating tsunami it it hit the ocean near a populated area Unlike earthquakes precise location of an impact could be predicted accurately in advance would be possible to evacuate in advance Total Residual Hazard Annual Mortality 3 E b o N a 0 t l U Lug Diameter km h an insurance type estimate the risk from asteroids is dominated by rare but devastating events e g a 1km asteroid impact occurs perhaps once per million years but might cause 100 million deaths Per year the average number of deaths is much smaller than from traffic accidents earthquakes etc Life Spring 2008 t a near Earth asteroid was found to be on a collision course what options are there Trajectory ot asteroids is dominated by gravity predictable in most cases for at least 100 years Structure of asteroids is not as well known solid bodies or rubble piles Extraterrestrial Life Spring 2008 39 Life Spring 2008 Small 100m asteroid impad with a spacecraft would knock it off course if applied early enough Spacecraft mass m velocin v hitting an asteroid of mass M gives it a velocity kiok e g an asteroid of 100m diameter has a mass M 1 6 x 109 kg Collision at 10 kms with a 1000 kg spaoecraft gives a veloo1 y nudge of 6 x103 ms very small But enough to defied the trajectory 2000 km over 10 years Similar strategy to the NASA mission Dee ofwould work best for a small asteroid or comet Large body 1km across is much harder to deflect Explosions might work but there would be a danger of fragmenting the asteroid into many equally dangerous pieces Summary Large impacts have occurred on Earth in the past and may well influence the course of evolution in unpredictable ways Small impacts asteroids lt1 km in size can be locally devastating but do not threaten civilization Census of the most dangerous asteroids is almost complete none in dangerous orbits Window of time a technological civilization is vulnerable appears to be small not too hard to deflect asteroids Frequency of impacts in other planetary systems is completely unknown ASTR lGEOL 3300 Extraterrestrial Life nstructor Phil Armitage TA Emily Knowles HoW did lite originate Is there life elsewhere in the Universe Scientific study of the many issues related to these grand questions astrobiology 39 Life Spring 2008 s there lite in the Universe Habitability of Mars was discussed in late 19th century Martian canals proven not to exist in 1965 with first tlybys of Mars quotring 2008 Overview How can we define lite The quality Which people animals and plants have When they are not dead Collins English dictionary Dead39A person animal or plant that is dead is no longer living NASA Exobiology program detinition Lite is a self sustaining chemical system capable of undergoing Darwinian evolution 39 Life Spring 2008 How did lite originate Until surprisingly recently common theory was that of spontaneous generation lite arises from non living matter whenever conditions are favorable Disproved by experiments by Pasteur 1864 lite does not arise spontaneously in closed sterilized containers Lite arises from pre existing lite question of its ultimate origin is meaningful Life Spring 2009 Opportunity ro ver image First in situ Mars landers 1976 Viking First extrasolar planet around a Solar like star found 1995 Today 221 planets mostly massive known outside the Solar System Ex aterrestyial Life SplingZ008 What is extraterrestrial lite Lite extant or tossil beyond the Earth n the case of Mars Earth extraterrestrial lite could in principle have single point of origin Discovering lite that had an independentorigin would be most exciting Extraterrestrial lite may or may not resemble lite on Earth certainly need not be intelligent 39 Life Spring 2008 Properties of lite on Earth As sole example lite on Earth is template for understanding requires water energy and source of nutrients working definition of habitability probably arose very early in Earth s history 3 3 8 billion years ago vs Earth age of 4 6 billion yr has evolved via natural selection now appears and permeates almost all terrestrial environments very diverse plants microbes humans Exbateirestrial Liferspringzwe But all life on Earth is amazingly similar based on same set of chemicals DNA RNA proteins transmits genetic information occurs within structures cells viruses prions Ex atenesfrial Ufep n92008 Problem of the origin of lite Hypothesis origin of lite must have involved living organisms any present identified on Earth today What were they with a simpler biochemistry than Materskis Life Spring 2008 U ndersea vents Thermal pools Yellowstone Extraterrestrial Life spring 2008 Problem of the origin of lite Evolution 5 Wq M an v Extraterrestrial lite in the Solar System 2003 Mars Closest Approach Mars liquid water likely to have been present for an undetermined period in Martian history and possibly is present today Ex aierrestrial life rihg52008 Extraterrestrial life in the Solar System Jupiter s moon Europa may possess a subsurface ocean Ex atelrestrial Life Spring 2008 Lite on extrasolar planets Sun is one of 100 billion 10 stars in the Milky Way galaxy a Around 1011 galaxies in the Universe enormous number of stars that might host habitable worlds 39 I 39r emingzooa s intelligent 39 39 lite common Fermi paradox Sun is 4 6 billion years old much youngerthan many other stars in the Milky Way 10 billion years old Atter tew thousand years of modern civilization we can communicate with other stars and can conceive of sending a probe to nearby systems t intelligent life is common many civilizations must be millions billions of years more advanced than us so why aren t they here already 39 Life Spring 2008 39 39 life in the Solar Svstem l l 1 i Plumes of water ice from Enceladus possibly indicating liquid su bsurtace water Liquid water is unlikely to exist on any other bodies in the Solar System Life Spring 2009 Lite on extrasolar planets Surveys of nearby stars show 5 10 host detectable planets mostly massive planets due to observational limitations Abundance of Earth like potentially habitable planets is unknown probably these are very common too How can we detect these planets How to search for life on them Ex aterreshial Life SpringZ008 Extraterrestrial Life Lecture 6 Liquid water is important because What are the requirements for the Earth or another planet solvent for organic molecules 39 r to be hab39table39 allows transport of chemicals within cells involved in many biologically important liquid water on surface Chem39ca39 reacnons atmosphere plate tectonics Ivolcanism Other solvents ammonia methane etc exist in liquid magnetic field form on planets but are much less promising for lite Normal atmospheric pressure liquid water requires 0 C 273K ltTlt 100 C373K require planets with surface temperatures in this range Life Spring2008 Extraterrest Life Spring2008 What A 39 the Earth 3 surface W fraction of The flux of energy is the amount of energy that passes incident radiation through unit area 1 m2 in one second incident is reflected Measured in units of watts m2 Solar Solar flux declines with distance as 1 d2 radiation v uX remainder is 4nd2 where d is the Sun planet distance and L is the total luminosity of the Sun watts then re radiated tthe Earth is not heating up or cooling down the total of incoming and outgoing radiation must balance Are there other sources of energy for a planet 39 Life Spring 2008 Life Spring 2008 W The traction of the incident tlux that is reflected is called Solar luminosity is 3 9 X 1026 watts the albedo ot the planet 0 lt A lt 1 Earth Sun distance is d 1 5 x1011 m 1 AU m The quotaetion that is absorbed is 1 A m The albedo varies greatly depending 26 Solar ux M W on the surface terrain 4nx15 x1011 m2 w m W u For the Earth a global average value is about A 0 3 1380 watts n12 This is the Solar flux that would be measured above the 59 Earth s atmosphere How does A change as the Earth rotates Extraterrestrial Life Spring 2008 Life Spring2008 First consider the reflected component of sunlight d Rg Fraction of total Solar luminosity that is reflected is 7 ux gtlt 2 ch as seenfmm Sun x A f 7 solzrlurninosi 7 1380 watts m1 x me x A 7 39 x10 mm Earth radius is RE 6 4 x106 m f 14x10 Seen from another star Earth is 10 billion times dimmer than the Sun How much energy is absorbed cf total world electricity consumption 5 x10 2 watts Note total forcing due to greenhouse gases is about 2 wa i e a few tenths of a percent of the total Solar flux this is why climate change is a complex scientific problem it A mm The absorbed radiation is reradiated as thermal radiation mostly in the infra red part of the spectrum R m As T increases the peak of thermal radiation moves to shorter wave engths and the total emission increases rapidly as T Sun 6000K visible Earth 300K R Thermal radiation emitted by the Earth is thz 4m x 0T4 l area of the Earth s power watts m2 emitted surface in m2 by thermal radiation at a temperature T a is a constant called the Stefan Boltzmann constant it equals 5 67 x108 watts per m2 per Setting the emission equal to the energy absorbed from sunlight determines the equilibrium temperature of the Earth Find that predict T 260K a bit too cold But we have ignored the influence of the atmosphere in blocking some of the outgoing radiation What does the surface temperature depend on T K Ll Z A d distance to the star luminosity of the star properties of the atmosphere and surface Habitable Zone Earth orbit Define the habilabe zone as the range of distances from the Sun for which a planet can have liquid water on its surface Empirically Venus is inside the habitable zone and Mars outside for the Solar System But calculating the exact boundaries is hard depends upon the nature of the planet and its atmosphere Additional complication Solar luminosin changes with time slowly Sun was less luminous in the pastand is slowly getting more luminous Faint Sun problem initial Solar luminosity is predicted to be 70 of the current luminosity butno evidence that temperature on the early Earth was much colder Thought to be an atmospheric effect The continuouslynabitable zone is the range of radii for which liquid water is possible mrougnouta planet s lifetime Obviously narrower than the instantaneous habitable zone possibly much narrower Means that stars whose luminosity ohanges relatively quickly are unpromising hosts for life bearing planets Whatabout planets on elliptical orbits that dip in and out of the habitable zone surface temperature adjusts to the Solar forcing on a imescaleltlt1 year e g seasons temperature underground or in the oceans ad39usts much more slowl planets with non circular orbits can t be ruled out immediately Basic properties of Mars Distance from Sun 1 52 AU recall F 2 so Mars gets 45 of the sunlight compared to the earth Orbital eccentricity e 0 09 20 difference between nearest and furthest distance from the Sun Orbital period 1 9 years Martian day 24 hours 37 minutes Radius 3400km Mass 11 of the mass of the Earth Extraterrestrial LifesSp ngzoaB Terrain on Mars polar caps smooth terrain heavily cratered terrain Two very different hemispheres on Mars Extraterrstrial Life Spiingzaoa mmediate implications for habitability Less Solar radiation colder 39on average on the surface Lower surtace gravity GM 8 R2 on the Earth g 9 8 ms2 on Mars g 3 7 ms2 G 6 8 x1011 Nm2kg392 More difficult for Mars to retain an atmosphere than the Earth Ex ater rest al Life Spring Appearance of the surface correlates with the typical elevation Southern hemisphere heavily cratered old surface with a high mean elevation Northern hemisphere less craters young with a low mean elevation Map at www google commars Ex aterleskial L39ife 57 ngle Geological eras on Mars Noachian 4 6 3 8 billion years ago some of the heavily cratered surtace dates from this time Hesperian 3 8 1 0 billion years ago Amazonian 1 0 billion years ago to present Some but not all of the Martian surface has been resurtaced by volcanic activity in relatively recent times Extraterrestrial Life Spring Polar caps Martian polar caps vary with the seasons in winter extending to about 60 degrees latitude Contain water ice plus a layer of CO2 ice which thickens in winter and sublimes in summer Extraterrestrial Life Spring2008 I11 Elevation m m a o a 300 1000 1260 3444 N a c a o a 6007 Distance km Radar on Mars Express suggests a water ice thickness of several km equivalent to 1 1m of water spread over surtace mm paint 225 am 0 Pressure 1 data c mm c Temperature 374 c Drawing c no r stale Martian pressure is quite close to the triple point of water liquid water on the surface would be short lived typically water exists only in ice or vapor phases Mars Express orbiter has ground penetrating radar that can map the subsurface ot the poles Extraterrestrial Life Spring 2008 Martian atmosphere Pressure 6 millibar lt 1 of Earth s pressure Temperature at surface 130 300K Composition 95 C02 3 N2 2 Argon Ozone is present at 0 01 parts per million compared with 10 ppm for Earth Surface is not shielded from solar U V radiation Extraterrestrial Life Spring2008 Martian winds blow from the summer pole to the winter pole significant traction of the CO2 moves seasonally Mm lerember 17 2am dust storms on Mars Life Spring 2008 39 Life Spring 2008 Satellites Two small moons Phobos and Deimos About 10km across with density similar to that of some asteroids May be objects captured from the asteroid belt 39 Life Spring 2008 Old terrain in the south appears to be magnetized Younger terrain in the north is unmagnetized dea early in Mars historythe planet supported a magnetic dynamo like the Earth This early magnetic field became frozen into and preserved within rocks as they cooled still see that in the old southern region Region to the north has been melted more recently after the dynamo ceased no magnetic field is preserved there 39 I 39r emingzooa Magnetic field mm 4500 a ism I ARCADIA owwus l mum Umm a Wssx Lnngitude 2m 1w Map of Martian magnetic field from Mars Global Surveyor Acuna et al 1999 Life Spling 2009 39 39 39 context of stars and planets Architecture of the Solar System Sun mass 2 x 1030 kg 1 Solar mass 4 rocky terrestrial planets in the inner Solar System Earth 6 x 1024 kg 2 gas giants Jupiter Saturn mostly made of gas but not of Solar composition 2 ice giants Uranus Neptune about 10 Earth mass cores with few Earth mass atmospheres small bodies asteroids comets Kuiper belt Scale mean distance between Earth Sun is defined as 1 astronomical unit 149 598 000 km Size of the Solar System is 50 AU 39 Life Spring 2008 SALT first light image 47 Tuc Places in the Universe where stellar density is N106 times higher even here stars very rarely interact with each other Can consider stars to be the building blocks of the Universe Distances to stars are measured in light years distance that light travels in 1 year Speed of light c 300 000 kms n one year there are 365 25 x 24 x 3600 s 316 x 107s 1lightyear30x105kmlsx316x107s 95x10 2km about 60 000 AU Nearest star is 4 light years away 240 000 AU 39 Life Spring 2009 IAU a e D 30 light years What is the angular separation between a planet orbiting a nearby star and the star tame 1 D Simplity small angles tan 6 6 15x108 km D 30 x 95 x1012 km 5 gtlt10 7 radians Other units 3 x 10395degrees or 0 1 arcseconds 3600 arcseconds 1 degree ring 2008 Extraterrestrial Life Spring2008 0 1 arcsec is similar to the resolution of best current telescopes BUT currently not possible to image planets due to glare of nearby star 39 Life Spring 2008 Sun is a relatively common type of star surface temperature T N 6000 K radius 700 000 km 100 times radius of Earth 39 Life Spring 2008 Energy source of stars Sun other stars derives energy from nuclear fusion Specifically the reaction 4 x H gt He Mass of 4 hydrogen nuclei is very slightly larger than the mass of one helium nucleus excess Am is released as energy according to 2 E me where c is the speed of light Sun is 4 6 billion years old enough hydrogen in the core to sustain Sun for a total of about 10 billion years Extraterrestrial Life Spring 2008 Endpoint of such stars is a planetary nebula and a white dwarf Hring2008 Massive stars M gt 8 Solar masses short lived 100 million years or less rare atter tusing H gt He go on to form many heavier nuclei via subsequernt tusion all the way up to iron tinally explode as supernovae leaving behind a neutron star or black hole 39 LifeSpring2008 Classification of stars Mass of stars ranges from 0 1 Solar masses up to 100 Solar masses Low mass stars are much more common than high mass stars Low mass stars M lt 2 Solar masses Greatest interest for astrobiology as long lived main sequence litetime while tusing H gt He in the core is billions of years Luminosity slowly increases over time After all the hydrogen is consumed turther tusion reaction torm carbon nitrogen and oxygen Extraterrestrial Life Spring 2008 Nearby place where massive stars can be found is in the Orion Nebula region of current star formation 39I39hc Orion Kabuki mtl 39l39mpL llum Chislci Vi ANTL39 lt1 lS HC Extraterrestrial Life Spring2008 Explosion ejects products of stellar tusion back into the gas of the Galaxy forms the raw material for new generations of stars galactic recycling 39 Life Spring 2008 Strong evidence that the onlyelements formed in the Big 0 100 million 5 billion 9 billion 13 7 billion Bang were hydrogen and helium All the heavier elementscarbon oxygen nitrogen iron etc were formed in the cores of stars E s a w gt we are literally star dust or nuclear waste 53 g E E g 9 w E e 2 since heavy elements are needed to make to 3 E terrestrial planets very first stars to form 5 i i would not have had any planets suitable E E f for life on tIme cale of the Univer 5 a cosmos is becoming more hospitable 0 for life 1 B 2 g L S Mars astrobiology experiments Only astrobiology experiments so tar tlew on the NASA Viking landers in the 19703 Pair of identical orbiters and landers Survived on the surface for 4 6 years Carried cameras chemical and biological experiments Boom to scrape soil from the near surface for analysis 39 Life Spring 2008 Labeled release experiment Added 1 ml of nutrient water plus organic U Ub compounds to 0 5 cm3 of Martian soil hunt a mmw Organic compounds were labeled marked with radioactive carbon 40 isotope Sample was incubated for 10 days Gases were analyzed for 14C UEYFCYIM ml L I mm Liuuumst On Earth microbes would give off 002 CO and CH4 Which would contain the radioactive isotope and could be detected 39 I 39r Spring2008 Gas exchange experiment 1 cm3 of soil was incubated in a nutrient broth Any gases that were produced were analyzed by a gas chromatograph that was sensitive to CO2 oxygen methane hydrogen and nitrogen ll lLAtlL39l u mom On Earth oxygen or CO2 would be detected cm EXCNAHLE On Mars oxygen was detected not only in the standard experiment but also in the control run with sterilized soil 39 Life Spring 2008 Basic principle of all 3 biology experiments was similar expose soil to an environment favorable for lite water light nutrients wait search for byproducts of lite CO2 O2 CH4 Discriminate between lite and abiological chemical reactions using a control experiment repeat the experiments using soil that had been heated to 1600 to completely sterilize any living organisms On Earth these experiments were shown to yield positive results for lite in the standard case and negative results for the control Life Spring 2009 Radioactivity Counts Minute Viking Lander 1 Cycle 1 12000 worm madmanw m o o 0 Datum Yemevaure m o o o s c o a an ammadmal to o o 0 mm Ens mpevam o 2 4 8 10 Sets from VL1 sol 9 Result radioactive gas was rapidly released when the nutrient was added Second addition caused an initial drop then a slow rise Control sample gave no release of radioactive gas Extraterrestrial Life Spring2008 Pyrol ic release experiment fill Simulated Martian atmosphere conditions soil was exposed to a simulated Martian 5 atmosphere containing CO2 that was labeled with 14C xenon lamp provided sunlight after 5 days atmosphere was flushed sample was heated to 625C to break down organic compounds gas was analyzed for 14C that had been taken up by lite i Experiment yielded a positive result 140 seen both for the standard run and in the control run 39 Life Spring 2008 Sample injector Tregulated oven Also chemical analysrs he Viking ot the soil using a gas chromatograph Somewhat contradictory results were obtained Most mass spectrometer common interpretation instrument Mass spectrometer Column Solar UV tlux on the surface of Mars destroys fth H2 packed or organic molecules close to the surface 39 open tubular Capil39a W No life was present in the Martian soil apparently positive results from the biology experiments retlected Very sensitive to organic molecules but none were detected inorganic reactions probably an oxidant such as a in the Martian soil peroxide present in the soil that was not anticipated in advance Largely renders irrelevant the biological experiments even the basic ingredients for life very simple organic compounds that are found even in space were not present in the Martian soil llustrates the difficulty of trying to detect life in very untamiliar environments Ex atelrestrial Life Spring 2008 Ex aterrestrial Life Spring 2008 ExoMars mission NASA philosophy Follow the water surviving life seems teasible only in rare spots where there might be liquid water Counterarguments Was the Viking GC MS sensitive enough to detect organic molecules from a small number of microbes in the soil e g would it work in Antarctic permafrost The specific soil conditions needed to provide the set of results seen in the biology experiments have proved hard to duplicate in the laboratory Accumulated evidence suggests a wetter and warmer Mars in the past can we search for life Nonetheless consensus opinion is that Viking did that died out billions Ofyears ago not detect life 0 Marsm Ultimate goal sample return but from where quotring 2008 Ex aterrestyial Life SplingZ008 Signatures of ancient lite Where to look Locations where geological evidence points to standing microtossils but contusion possible with very bodies of water in the past small mineral precipitates Heat destroys biosignatures need to avoid volcanic isotopic carbon signatures ratio 130 to 12C areas or ancient lava ows survival of complex biomolecules amino acids chlorophyll lipids these may survive better on Mars than on Earth because of the lack of plate tectonics Amino acids can survive for billions of years at modest depths 1 2m Existing lite need to locate warm spots where ice water might exist at different times during the year life might exist in the subsurface at modest depth there detection of chiral signature of life but this is destroyed in wet environments 39 Life SpringZ008 39 Life Spring2008 ExoMars mission payload 2013 launch date Rover with a drill to extract samples from 2m depth Ground penetrating radar Gas chromatograph mass spedrometer much more sensitive than Viking s version 1000 times better Organic detedor sensitive to amino acids nucleobases Life marker chip detects organic molecules with very high speo1fio139ty Enceladus Small N500 km diameter moon of Saturn orbits between Mimas and Tethys Two distinct hemispheres northern is quite heavily cratered old southern shows almost no craters across wide area Albedo is almost 100 icy surface must be very treash Extraterrestrial Life Spring 2008 Enceladus orbits within and appears to be the source of Saturn s taint E ring Ejects icy particles into the ring some of which are later re accreted by the satellite note ring particles are fully exposed to sunlight so chemistry can happen driven by this exposure ring 2008 r i Surface of Enceladus that is devoid of craters resembles Europa appears to have tectonic activity Enceladus 9 Definitely a young surtace probably affected by liquid water in the same way as Europa 39 Life Spring 2008 Enceladus north pole as views by Cassiniduring last week s tlyby ot the satellite Extraterrestrial Life Spring 2008 Surface of Enceladus that is devoid of craters resembles Europa appears to have tectonic activity Figure 2134 Mosaic oi Cassini SS images displaying several different tectonic styles that indicate a complex tectonic history South is towards the right he radius oi Enceladus is 25i krn Courtesy NA A JPLicalteoh image PlAUGiSt Extraterrestrial Life Spring2008 Plumes trom Enceladus Cassini discovered plumes of icy material jetting from the South Pole region Mass flow is about 100 200 kgs Mass of Enceladus is about 1020 kg this much mass loss would lead to a significant reduction in the moon s mass over the lifetime of the Solar Figure 2133 Cassini high phase angle ialsevcolor image oi the Enceladus plume showing lorwardv SYStem scattering by micronsized plume particles From Puma etal 2006 39 Life Spring 2008 Plume comes from relatively warm region 145K still only about 130C Flpure 213 7 Fatsereplur image at 12716 micron co at temperatures on Enceladus item the Cassml Composite irritated Spectrometer ClHS spewing the heat radiation lmm the warm tiger stripes in the Smith least ME K Ihan tit inwresolultpn averages shown hgewihe dashed line is the termtnatpr Spencer et a 2 U Extraterrestrial Life Spring 2008 One hypothesis internal heat of the moon is escaping unevenly heating the southern part enough for liquid water to be stable near the surface crack allow high pressure water to escape which instantly treezes Might also be a deeper ocean similar to Europa WWW mop Plume contains water In r NzntTJv form of ice CO2 nitrogen czuzn i ln W 39l39 llllli quotumaegis and methane twun g 1000 E t E Wu 539 om39rr IWit Jr l i it is 20 40 60 ED l Maslea Figure 2132 Cassini INMS mass spectrum at the Enceladus plume taken in July 2004 showing mass peaks due in H20 00 NZK CH4 and possibly 0sz and CEHF Waite etal 2006 Extraterrestrial Life Spring 2008 Possible structure note no direct evidence for such an ocean lee Shell ice Shell Ocean l70 km 10 MP6 W m r a n a g m 53 pure ice shell and an u rt ted a 2003 An internal liquid layer may exist at the base of the ice shell quotring 2008 Extraterrestrial Life Spring2008 Mystery What is the source of Enceladus heat small would not be heated enough by radioactive decayto sustain liquid water tidal heating mithbe enough depends upon the moon s structure and thus on whether water is present might not be in a steady state Further puzzle plumes contain gases that do not dissolve very easily in water but there is no evidence for sodium which would be expected to be present in an ocean Life Spring 2008 Alternative model gas is trapped in icy material which is unstable when pressure is released it degasses violently causing the plumes No liquid water is needed it this model is correct a vnuar c 1 Nat 39 Zm quot wg39ku39 azure ux gtfnaallng C i D Life Spring 2008 Astrobiology potential fthere is liquid water conditions may be more favorable for life than Europa because the system is open to space potentially larger energy source for chemical reactions M Orbital velocity v R close to surface of Enceladus v 100 ms mple elces tolearn if chemls w biology is underway in thewater Possible to fly gently through the plume in orbit and t or Jovian system Massive gas giant planet 0 001 Solar masses Orbital radius 5 2 AU distance beyond snowline where rock and water ice dominates 4 large Galilean moons I O periOd 3 55 days 1 2 4 resonance between Eaumpa d the orbital periods of the anyme e inner 3 satellites Callisto Extraterrestrial Life Spring 2008 Surface of Europa is made of water ice Mean density would be consistent with a 6 traction of water by mass e g 1450km rocky interior with a 110km thick layer of water liquid or ice at the surface 39 I 39r Spring2008 2 Local surface features Galileo images of the surface show blocks of ice km 10s km in size separated by rid es Crust has been fractured and then retrozen in place Appearance resembles pack ice floating on the ocean at the North Pole and off the coast of Antarctica Europa radius 1560km Gradient of mean density density of rock o 3530 kgm3 quotquot silicates Europa 3018 kgm3 Ganymede 1936 kgm3 mixture of rock plus Callisto 1851 kgm3 lower density ice 920 kgm3 Life Spring 2009 Evidence for an ocean on Euro a 1 Global surtace appearance Europa surface has very few impact craters only 3 with diameter gt 3km Young surface Cratering rate in the outer Solar System is not well determined models suggest an age between 10 million and 1 billion years Resurfacing must involve melting at least some of the ice Extraterrestrial Life Spring2008 3 Magnetic field measurements Jupiter has a strong magnetic field which Europa is orbiting through Magnetic fields are generated by currents flows of charged particles t Europa s interior does not conduct electricity the moon cannot generate its own magnetic field and the field measured near the surface should be that of Jupiter alone t Europa s interior conducts electricity then the motion of the moon through Jupiter s tield induces a current which distorts the Jovian field near the moon 39 Life Spring 2008 39 Life Spring 2008 llllllrrxllllx nulurxnlnvulunur llil 4m m u H03 Hiquot Hli lllll Uh Uh IHI Galileo measurements during a close tlyby Prediction based on Jupiters magnetic field it Europa has no field of its own Conclude that Europa does possess its own magnetic field and hence that some part of the interior of the moon must be an electrical conductor Extraterrestrial Life Spring2008 Heat source for Europa nternal heat of small bodies Moon Mars Mercury is not enough to sustain geological activity for the life of the Solar System Tidal heating Tides are raised on Europa by the different gravitational force from Jupiter on the near tar side of the moon Stress and try to crack the surface Dissipation ot the tidal energy results in heat in the moon s interior o moon closest to Jupiter Very strong tides lead to volcanic activity on the surface What could the conductor be Rock and ice are both poor conductors A salty ocean beneath the ice would be a good conductor explains the Galileo magnetic field measurements quite well An iron core would also be a good conductor cant exclude this possibility and it one exists analysis is much more complicated Extraterrestrial Life Spring 2008 tidal Moon is distorted very slightly by tidal gravitational force As it rotates tidal bulges don t quite align with the axis between the Moon and Jupiter Dissipation ot the tides leads to heating Extraterrestrial Life Spring2008 Possible oceans Current data provides little constraint on the thickness of the ice layer overlying the ocean Two models 1 Thin ice layer 1km tractured by tidal forces as Europa orbits Jupiter or local heating from volcanic events at the silicate water boundary 2 Thick ice layer at least 20km tractured by convection in the ice heated by tides 39 Life Spring 2008 39 Life Spring 2008 f Europa indeed has an ocean are the basic conditions for life met Water es carbon yes surface of the other Galilean moons showabundant impad craters meteorites on Earth deliver organic material and the same must be true for Europa Energy possibly unknown whether hydrothermal vents or volcanic activity occurs at the bottom of he ooean f energy is available conditions in Europa s ocean T 00 probably quite salty water fall within the range for which extremophiles survive on Earth Europa exploration No current spacecraft in the Jovi n system and no funded mission to return by NASA or ESA High priority for outer planetsquot science but expensive and difficult to fly to Europa distance low Solarflux radiation environment near Jupiter Europa orbiter could definitively establish the presence or absence of an ocean and measure the depth of the ice Lander could sample the ice near the surface and oonceivably drill through to the ocean How many civilizations are there in the Galaxy Number of stars in the Milky Way galaxy 1 011 100 billion Distance from the Sun to the galactic Center is about 25 000 light years Number of civilizations alive now depends upon traction of stars with habitable planets traction of habitable planets that develop lite traction of time that life becomes intelligent traction of civilizations that still exist 39 Life Spring 2008 Not so much atraditional equation more a framework for thinking about SET tHP astronomical question tlife tciV biological evolutionary questions talive sociological question The age of the Galaxy and the oldest planets in it is 10 billion years t on average a civilization survives for 100 000 years before destroying itself 105 years 7 10 5 1010 years fnlive N 39 I 39r Spring2008 Coditied as the Drake Equation Nciv N XfHP szie X civ X alive NciV is the number of civilizations alive today N is the number of stars in the Galaxy 10 tHP is the traction of stars with habitable planets tlife is the traction of habitable planets that develop lite tciV is the traction of planets on which life becomes intelligent talive is the traction of once intelligent civilizations that are still alive Frank Drake Life Spring 2009 An example Assume 39 pr 0 1 39f39i ez1 NEW 1011 gtlt01gtlt1gtlt101 x105 10 V I falive 105 Easyto come up with optimistic estimates that suggest the nearest civilization is close by can also pick numbers that make us alone in the Galaxy or even the Universe First two factors can be addressed via astronomy and biology in a normal scientitic way last two can only realistically be determined by nding other civilizations Extraterrestrial Life Spring2008 Detecting extrasolar planets o d ORE Fraction of total Solar luminosity that is reflected is ux x area of Earth as seen from Sun x A solar luminosity 1380 watts m2 XJTR x A 39 x102 5 watts Earth radius is RE 2 6 4 x106 m f 1 4x 10quotquot Seen from another star Earth is 10 billion times dimmer than the Sun f l I r A w Hubble Deep Field PRC95 Dla SY 5 CPU January 15 1996 R Williams 157 Sal NASA No direct detections ot extrasolar planets HsT IWF39Pcz Contrast between star and planet is the main problem e g brightest stars in this image are around 18 h magnitude 35 arcseconds 39 Life Spring 2008 39 Life Spring 2008 ndirect detection methods Most successful method so far is based on the fad that a planet does not stridly orbit the slar but rather the enter of mass of the star planet system center of mass e g in an equal mass binary star system each star orbits at the same distance from the common center of mass Radial velocity searches for planets Sun wobbles slightly in response to the gravity from orbiting planets in the Solar System mostly from Jupiter Small effed center of mass of the Solar System Sun planets is within the Sun itself But detectable either by looking for the motion of the star on the sky or by looking for changes in the radial velocity of a star How large is the radial velocity signal caused by a planet a p a center of mass Suppose the star planet separation is a t e star has mass M and the planet MD the distances of the star and planet from the center of mass are The orbital velocity of the planet is given by the formula where G 6 67 x10 m3 kg s392 Newton s gravitational constant eg for the Earth a15x10 m M 2x1030kg Orbital velocity 29 800 msquot about 30 km per second During one planetary orbit the staralso does one orbit around the center of mass Distance the star travels is smallerthan the distance the planet travels by the ratio of their distances from the center of mass a lapltlt1 Stellar velocity caused by the orbiting planet is How large is the effed Jupiter a 7 8 x10 m M 2 x1030 kg Very small but measurable For the Earth v 0 1msquot not detectable Doppler Shift due to Stellar Wobble unseen my Radial velocity is measured via the Doppler shift light is slightly blueshifted when the star moves toward us edshifted when it moves away Origin of life on Earth Two approaches bottom up which of the chemical structural parts of modern lite could have formed from abiotic processes on the early Earth top down which of the constituents of current cells could have been part of earlier simpler lite torms Basic reguirements genetic information DNA catalytic molecules proteins cell membranes lipids Extraterrestrial Life Spring2008 Result large number of complex organic molecules formed in the experiment including a number of amino acids A Production of Amino Acids Under Possible Primitive Earth Conditions Stanley L Millerquot a a H mm chm hum Unlvtrliky 5 Chicago cbiugo 1mquot within weeks of the discovery of the structure of DNA Oceanic synthesis Amino acids can also be formed under conditions similar to hydrothermal vents Protected against impacts common thermophiles seem like simple organisms However complex organic chemicals are also destroyed by the high temperatures today water cycles through such systems on a timescale of only 10 million years 39 Life Spring 2008 MillerUrey experiment 1953 experiment mixture of several simple gases water hydrogen methane and ammonia was exposed to sparks lightning and cycled through a model of the ocean atmosphere Extraterrestrial Life Spring 2008 Experimenthas been repeated many times results stand under these conditions amino acids are synthesized easily Are the conditions a realistic depiction of the early Earth H20 H2 CH4 and NH3 are major constituents of the atmosphere of the giant planets Chemically this is a reducing atmosphere very different from the oxidizing conditions on the Earth today Early Earth was likely devoid of oxygen atmospheric composition would have been controlled by volcanic outgassing Large CO2 concentration needed for strong greenhouse effect to offset the taint young Sun leads to less efficient synthesis of organic molecules Extraterrestrial Life Spring2008 Meteoritic delivery Comets or meteorites can also be a source Murchison meteorite may contain as many as 70 amino acids Synthesis of small molecules site is very uncertain but there are several plausible candidates possibly the atmosphere ocean vents extraterrestrial delivery 39 Life Spring 2008 What about chirality T e got The two elmnliomers of brumuthlorclllmroiuellrane Both meteoritic amino acids and those synthesized in Miller Urey type experiments tend to be almost racemic mixtures equal amounts of left handed and right handed versions Additionally the set of 20 amino acids used in biology today is not particularly tavored 39 Life Spring 2008 The RNA world hypothesis Currently DNA encodes information for building proteins Proteins catalyze the cellular mechanisms that lead to their formation RNA ribonucleic acid can fulfill both functions carry information that can be copied can catalyze reactions including the formation of proteins though less etticientlythan current mechanisms Hypothesis tirst lite may have been based around RNA with the DNA protein symbiosis evolving later Formation of more complex molecules Getting to the RNA world or similar schemes based on other molecules from simple precursors is the hardest step Proteins alanine glycine lt gt dipeptide HZO Presence of water as a product means that in water dissociation rather than polymerization is favored Moreover more or less random order of the monomers is obtained even under conditions where proteins torm 39 Life Spring 2008 Sugars pre biotic synthesis of sugars has been demonstrated experimentally trom tormaldehyde CHZO in the presence of mineral catalysts BUT these reactions yield a mix of many sugars as many as 40 with no chiral preterence Chirality ot ribose affects the 3D structure of RNA upon which the hereditary system rests how did one form of ribose come to dominate Speculation perhaps ribose was not part of the first RNA like molecules 39 Life Spring 2008 39 LifeSpring2008 O R has Forming RNA 0 he39c 9mm 0 Constituents of RNA N NH 13 OH 4 NH2 sugarrbose ozpluo 5 N N base adenine guanine 0 1 39 39 53 l cytosrne uracIl Weak 3 mos phosphate 0 OH phospna39c op70 I O 3 Synthesis of the bases especially adenine appears to be relatively easy HCN can yield adenine in water when exposed to ultraviolet light Extraterrestrial Life Spring2008 Polymerization of nucleotides Neither of the critical steps reactions of the bases with ribose reaction to join in the phosphate have been demonstrated to occur under plausible early Earth conditions though there are many possible pathways n particular water and high temperatures are untavorable tor the survival of RNA Where might early lite have started 39 Life Spring 2008 Role of mineral catalysts Often suggested that mineral catalysts such as clays may have played a critical role Early chemistry took place on surfaces Chiralin may have been inherited from surface defects Enclosure within cell membranes came later 1 Organic molecules formed either in the atmosphere at undersea vents or via delivery from space Short strands of RNA formed with the help of catalytic materials perhaps clays R A became capable of self replication Membranes formed to enclose RNA Natural selection led to an increase in complexity until eventually something recognizany living ormed 3 was Prospects for progress Clearlythis topic involves too much extrapolation from known conditions to allow for robust conclusions Life started somehow can we ever know how better understanding of the the atmospheres of lanets from observing ot deeper knowledge of the function of all the molecules involved in life lab experim s discovery of life elsewhere Extraterrestrial Life Lecture 8 New homework due next Thursday can post queries of general interest at www et life blogspot com Last time long term climate regulation Today dating of rocks and surfaces when was the first life on Earth how has the atmosphere evolved over billions of years which planets have been volcanically active and when did that activity cease Extraterrest Life Spring 2000 Heavily cratered terrain 4 6 billion years old Younger terrain 3 billion years old 39 Life Spring2008 Venus has relatively few impact craters small bodies will not penetrate the atmosphere lack of large craters suggests that the surface is resurfaced relatively often Extraterrestrial Life Spring 2008 Relative ages of terrain on Moon Mars Mercury etc can often be determined visually by looking at the cratering on the surface Saturation so many craters that each new one destroys older ones Young terrain few impact craters are visible Newer impact craters overlap older ones or cut across otherfeatu res eg channels Extraterrestrial Life Springm Overall the rate of cratering has declined since the early history of the Solar System Late heavy bombardment of the Moon 1 billion years impact after Solar System rate on formation the Moon time 39 hp SplilrgZUQB Galilean satellite of Jupiter same environment but very different patterns of cratering on the surface Extraterrst Life Spring 2008 Absolute age dating Absolute dating of rocks is possible in the lab by measuring the abundance of radioadive elements and their decay produds An isotope is an atomic nucleus with a given number of protons and neutrons e g Carbon 12 has 6 protons and 6 neutrons carbon 13 has 6 protons and 7 neutrons Radioactive isotopes are unstable and decay into other isotopes daughter isotopes via a variety of processes Example decay of uranium 238 238U gt23 Thquot He Thetimescale for this reaction is 4 5 billion years The thorium is itself unstable and eventually decays to a stable isotope of lead Radioactive decay is probabilistic cannot be predicted Given one atom of 238U there is a fixed probabi t it will decay in the next second i it survives there is the same chance of decay in the next second The halflife is thetimescale on which 50 of the original nuclei will have decayed varies enormouslyam different radioactive isotopes Result is exponential decay of the abundance of the parent nucleus Nz Noe LI nuclei originally decay present time Example 40K gt40Ar Suppose that when a rock solidifies a small sample of it contains 1000 atoms of radioadive potassium After one half life 1 25 billion years 500 parent nuclei 40K remain 500 daughter nuclei 40Ar have been formed and remain trapped in the rock we measure a 5050 ratio between potassium and argon can conclude that the rock i If life or 1 25 billion years old that s when it last solilifiel so as to trap the daughter products This works because rodlts have very specific chemical composition uranium is notuniformly spread throughout the Earth but rather is concentrated in particularminerals n the previous example beforethe rock formed the potassium would still deca butt e arg n would escape and would not be incorporated into the same material Long lived isotopes Rely on long lived isotopes to date the formation of the Solar System and the age of the Sun no rocks on Earth survive from the first 500 million years oldest rocks are parts of meteorites that contain calcium and aluminium dated at 4 567 billion years old using uranium lead c r hronomete This age is conventionally the age of the Solar System Short lived isotopes Short lived much less than a billion years isotopes are useless for dating the Solar System they ve all decayed long ago Rather constrain the birth environment of the Sun isotopes form in supernova explosions so if we see the daughter products trapped in rocks we know the rocks must have formed not so long after a supernova explosion can be used to date relative events early in the Solar System history e g the formation of the Moon 39139ch Orion Vcbula rml 39impwmm Elmer m Axru iSMC 25Al decays with a half life of only 700 thousand years Presence of this isotope at above average abundance in the early Solar Nebula suggests formation in a dense cluster of stars Reliability of radioactive dates depends upon knowing that the rock is unaltered Since formation lunar samples re evaluation of the formation of the Moon last year 40 million years after the formation of the Solar Systemcosmic ray contamination terrestrial samples igneous rock has solidified from a iquid metamorphic rock has been transformed by high pressure sedimentary rock is compressed sediments Often errors are not dominated by difficulties of the measurement but by possible systematic effects Limits of life on Earth Some archaea and bacteria extremophiles can live in environments that we would consider inhospitable to life heat cold acidity high pressure etc Distinguish between growth and survival many organisms can survive intervals of harsh conditions but could not live permanently in such conditions e g seeds spores nterest analogs tor extraterrestrial environments extreme conditions may have been more common on the early Earth origin of life some unusual environments e g subterranean are very widespread Extraterrestrial Life Spring 2008 Grand Prismatic Spring Yellowstone National Park Colors on the edge of the spring are caused by different colonies of thermophilic cyanobacteria and algae 50 species of such thermophiles mostly archae with some cyanobacteria and anaerobic photosynthetic bacteria Sulfaobus optimum T N 800 minimum 600 maximum 900 also prefer a moderately acidic pH Live by oxidizing sultur which is abundant near hot springs 39 I 39r Spring2008 Adaptations ot thermophiles Generally thermophiles are very similar to ordinary archaea and bacteria DNA same amino acids etc Series of quite subtle differences e g cell membranes are made up of lipids that are more stable to high temperature additional enzyme reverse DNA gyrase causes the DNA to fold up in a way that is more stable against heat Thought that the absolute maximum temperature is around 1500 above this DNA breaks up very readily 39 Life Spring 2008 Thermophiles Temperatures up to 55C are common but T gt 550 is associated usually with geothermal teatures hot springs volcanic activity etc Thermophiles are organisms that can successfully live at high temperatures Best studied extremophiles may be relevant to the origin of life Very hot environments tolerable for life do not seem to exist elsewhere in the Solar System 39 Life Spring 2009 Hydrothermal vents high pressure in the deep ocean allows liquid water at T gtgt 1000 Vents emit superheated water 3000 or more that is rich in minerals Hottest water is liteless but cooler margins support array of thermophiles oxidize sulphur manganese grow on methane carbon monoxide etc Known examples can grow i e multiply at temperatures as high as 110 1200 but can also survive at much lower temperatures Extraterrestrial Life Spring2008 Low temperatures growth below the freezing point is very difficult but some liquid water exists below 00 in thin films or in water under high pressure Slow multiplication of bacteria living in permatrost has been seen at temperatures as low as 200 39 Life Spring 2008 Lake vostok Atacama desert in Chile IS one of the drIest locations Large sub glacial lake on Earth 14 000 km2 at a depth of 3750m under Antarctica Average annual rainfall in parts of the Atacama is lt 1mm yr Water is not trozen probably very oxygen rich May have been isolated for around a million years from N0 Plants have lived tor more than one million years any other environment DIttIcult locatIon to find life the NASA Viking experiments Terrestrial analog for an ocean on Europa would fail Microbes can be grown from shallow subsurtace layers successfully Exbatelrestrial Life Splingy2008 Exbatenestrial Life Spring 2008 Other extremes Radiation High pressures 10m of water adds 1 atmosphere of pressure Viable organisms have been recovered from the Mariana trench 10 900m 1100 atm Main adaptations are in the cell membranes Radiation exposure is measured in Gray Gy 5 10 Gray is fatal for humans some microbes can survive 30 000 Gray Saline environments haloarchaea thrive in waters with Adaptation ettiCiehtrePair meChahismS tor DNA that is near saturation levels of salt e g Dead Sea and damaged by the rad39at39Oh ux are found in rock salt deposits Adapted to make use of very little water Puzzle such high levels of radiation are nottound naturally on Earth may be that radiation tolerance is Subterranean environments microbes appear to exist a byprOdUCt 0t adaptat39on to Very dry enV39rOnmentS in dry hot subterranean environments several km depth Properties and origin unclear 2008 Ex aterreshial Life SplingZ008 Travel time from Mars to Earth is typically1 10 Myr all the known specimens probably came from a handful of impact events Ejection events likely produced large 30km craters but pressures and temperatures in some of the ejecta would have been low enough to allow survival Microbes within the rock would be shielded from ultraviolet nterest some meteorites from Mars have been recovered rad39anon and 008mm rays many from Antarctica 39 Life Spring 2008 Extraterrestrial Life Spring2008 Sterilization of space missions to Mars Europa Galileo orbiter was crashed into Jupiter to avoid any chance that it might collide with and contaminate Europa Astrobiology missions to Mars Europa need to be sterilized to very high standards assembly in clean room oonditions irradiation with gamma ys heated to 105 124C for several hours hydrogen peroxide plasma sterlilization mplications for extraterrestrial life Life can flourish in environments well beyond those that are obviously habitable Need liquid water but 200 lt Tlt 1200 OK modest expansion of traditional habitable zone requirement Subterranean organisms seem of greatest interest for Mars Lake Vostok may be similar to Europa Can only speculate as to whether life on Earth started in an extreme environment


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