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Lecture 4 1:Lecture 4 1:Lecture 4.1:Lecture 4.1:
AstrobiologyAstrobiology::
Search forSearch for exoplanetsexoplanets: methods current status and future directions: methods current status and future directionsSearch for Search for exoplanetsexoplanets: methods, current status, and future directions : methods, current status, and future directions
В. Г. Турышев В. Г. Турышев Jet Propulsion Laboratory, California Institute of Technology
4800 Oak Grove Drive, Pasadena, CA 91009 USAГосударственный Астрономический Институт им. П.К. Штернберга
Университетский проспект, дом 13, Москва, 119991 Россия
Курс Лекций: «Современные Проблемы Астрономии»для студентов Государственного Астрономического Института им. П.К. Штернберга
7 февраля – 23 мая 2011
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Overview
Astrobiology:The study of life in space, combining aspects of astronomy, biology and geology.
• Planet detection methods:– Indirect:
• Doppler shift; astrometric wobble• Doppler shift; astrometric wobble– Semi-direct:
• Transits; microlensing– Direct:
• Imaging, interferometry• AstrobiologyAstrobiology
– Life in Universe… what is it? and what to look for?• Ground-based and space projects• Drake equation
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Martian Meteorite
D. S. McKay et al., Science (1996)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Martian Nannobacteria?
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Mars Pathfinder: Twin peaks view
NASA Planetary Photojournal (http://photojournal.jpl.nasa.gov/)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Water on Mars?
River channel
Nanedi Vallis(from Mars Global Surveyor)( y )
• Grand Canyon required several millions of years to form
• The same should be true for Nanedi Vallis
~3 km
The same should be true for Nanedi Vallis
3 km
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
MER Rovers
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Endurance Crater (from MER Rover Opportunity)
http://marsrovers jpl nasa gov/home/index htmlhttp://marsrovers.jpl.nasa.gov/home/index.html
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Spherules (Blueberries) on Mars
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Life on Earth could be Martian
Mars may have been ready for life first, and seeded the Earth. We know rocks travel safely between them. We should go & see!
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Solar System: Europa
EUROPA(from Galileo)(from Galileo)
Courtesy: JPL/NASAPlanetary Photojournal
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Titan’s organic haze layer
Haze is thought toHaze is thought toform from photolysis(and charged particleirradiation) of CH4
(Picture from Voyager 2)(Picture from Voyager 2)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Lakes on Titan?
• Image taken by the Huygens Probe, launched from theCassini spacecraft (January, 2005)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Titan shoreline?
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Many other conditions may be “habitable”may be habitable
Life here could have started at the bottom of the ocean at volcanic ventsbottom of the ocean at volcanic vents.
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGYFrom Greek Philosophers ...
“There are infinite worlds both like and unlike this world of ours...We must believe that in all worlds there are living creatures and plants and other things we see in this world.”‐‐‐ Epicurus (c. 300 B.C)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY…to Medieval Scholars...Scholars...
“I [regard]… as false and fdamnable the view of
those who would put inhabitants on Jupiterinhabitants on Jupiter, Venus, and Saturn, and the moon, meaning by ‘inhabitants’ animals like ours and men in particular ”particular.
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY…and Medieval Martyrs...y"There are countless suns and countless earths all rotating around their suns in exactly the same way as the seven planets of our system. We see only the suns because they are the largest bodies and are luminous, but their planets remain invisible to us because they are smaller and non-luminous. The countless worlds in the universe are no worse and no less inhabited than our Earth”
Giordano Bruno (1584)Giordano Bruno (1584)
in De L'infinito Universo E Mondi
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Extrasolar Planets
• 1st extrasolar planet discovered in 1995– 51 Peg b (Mayor & Queloz 1995)
– Discovered by radial velocity method
• As of February 26, 2011, 529 extrasolar planets have b di d (htt // l t )been discovered (http://exoplanet.eu)
• Most of those planets are gas giants that orbit close to their star but that’s because they are easier to detecttheir star, but that s because they are easier to detect
• As our technology improves, future missions will find Earth-like planetsa e p a e s
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
NASA’s Origins Theme HasTwo Defining QuestionsTwo Defining Questions
Are We Alone?Where Did We Come From?
Search for Life Outside the Solar system• Remote detection of the signposts
of biological activities on extra‐
Tracing Our Cosmic Roots• Formation of galaxies, stars, heavy elements planetary systems and of biological activities on extra
solar planetselements, planetary systems and ….. life on the Early Earth
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
The Search for Extrasolar Planets
Since it appears the conditions for planet formation are common, we’d like to know how many solar systems there are, and what they look like.• Indirect Methods:• Indirect Methods:
1) .Doppler shift (spectroscopy -> radial velocity): stellar wobble due to tug by a orbiting planet (the main method so far, nearly all detections)( , y )
2) .Astrometric wobble of the star’s orbit • Semi-direct Methods:
1) Transits (periodic dimming of the star caused1) .Transits (periodic dimming of the star caused by a planet passing in front of it) – Kepler mission (launched, Nov., 2008)
2) .Microlensing (planet’s gravity): OGLE2) .Microlensing (planet s gravity): OGLE• Direct Methods:
1) .Planet imaged directly (perhaps with coronograph) reflected or emitted (IR or radio) light – TPF(IR or radio) light TPF
2) .Planet imaged by interferometer – Dwarwin, TPF
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Precision Radial Velocity Searches
Shift isShift is1 part
in100
million
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Discovery of Extrasolar planets
We get the orbital period, semimajor axis, and a lower limit on theand a lower limit on the mass of the planet. This can only detect giant planets relativelygiant planets relatively close in (but could see Jupiter).
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planet Detection Methods: Radial Velocity
away
toward
http://en.wikipedia.org/wiki/Doppler_spectroscopy
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planet Detection Methods: Radial Velocity
away
obse
rver
toward
o
http://en.wikipedia.org/wiki/Doppler_spectroscopy
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Astrometry
This works best for large orbits (which take a long time) and stars that are nearby. Interferometry would allow very small motions to be measured.y
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planet Detection Methods: Astrometry
• SIM PlanetQuest:– Space-based, 9-meter
baseline, optical interferometer operating in the visible bandin the visible band
– Micro-arcsec accuracy– Detect Earth-like planets
( t ) h d l d l hhttp://planetquest jpl nasa gov/ – (not-)scheduled launch ~2015/16…
http://planetquest.jpl.nasa.gov/SIM/simImageGallery.cfm
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Transits
• We can watch for the dimming of the star if the planet crosses in front of it.
This is b the ratio of their areas 1%• This is by the ratio of their areas: 1% for Jupiter and 0.008% for the Earth.
• This has been seen for one case (confirming the radial velocity detections).
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
The Kepler Project
Transits provide the only way right now that we can reliably study the occurrence of extrasolar terrestrial planets (none known now).
• To detect Earth-size planets a wide-• To detect Earth-size planets a wide-view telescope monitors 100,000 stars in a single field of view for >4 years
Sunshade
• Finds hundreds of terrestrial planets within 2 AU of stars
CCD’s
Electronics
Sunshade• For Earth-size and larger
planets, determines:
– Frequency
– Size distribution
Orbital distributionSchmidt Corrector
– Orbital distribution
– Association with stellar characteristics
Primary Mirror
Thermal Radiator– Launch: Nov., 2008
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
“Microlensing” : Gravitational lenses
In principle, this method could even see Earth-mass planets. You have to have a huge and long-g gtime monitoring program with high time resolution and good photometric precision.
The downside is that you will only y ydetect the planet once, and can’t learn anything more about it. One tentative detection has been claimed (but how to confirm it?).
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planet Detection Methods:Gravitational MicrolensingGravitational Microlensing
• Gravitational field of the lensing star bends andlensing star bends and focuses light rays from the background starDi d t• Disadvantage:– Chance alignment that only
last days/weeks
• Advantage:– Could currently detect
Earth-like planets
http://planetquest.jpl.nasa.gov/science
p
• OGLE: 4 planets (one is only ~5.5 MEarth)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planet Detection Methods:Gravitational MicrolensingGravitational Microlensing
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planet Detection Methods: Direct Imaging
• Planets are ~109-1011 times fainter in the visible range and ~105-106 in infrared compared
Image taken at Cerro Paranal in Chile.
10 -10 in infrared compared to their host stars
• Extremely difficult to image due to glare! g
• First image of a planet (imaged in IR)– Orbits around a brown dwarf
at about twice the distance of Neptune
– Planet is about 5 MJupiter
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planet Detection Methods: Direct Imaging
• TPF mission:– Visible-band
coronagraph– Mid-IR formation-flying
i t f tinterferometer– Detect Earth-like planets– Target habitable zones
d thttp://planetquest.jpl.nasa.gov/TPF/tpf_what_is.cfm
around stars– Use spectroscopy to
study atmospheres of planetsplanets
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
The Problem with Direct Imaging
• The host star is MUCH brighter (106) than anybrighter (106) than any planet (except very young Jupiters in the infrared)infrared).
• The planet is VERYThe planet is VERY close in angle (micro-arcsecs) to the star, so any stray light from theany stray light from the star can overwhelm the light from the planet.
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Nulling Interferometry
You can try to keep the star at a destructive null fringe, while the planet will be slightly off the fringe and soslightly off the fringe and so still visible. Might be able to reduce the star’s brightness by a million times?by a million times?
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
A Big Surprise : Close-in Jupiters
• It is easiest to find a massive planet that is close to the star (it repeats quickly and has a large velocity amplitude).
• The first discovery 51 Peg had a 4 day orbit (0 05 AU!) and the mass ofThe first discovery, 51 Peg, had a 4 day orbit (0.05 AU!) and the mass of Jupiter. Many are now known, but that doesn’t mean they are most common, just easiest to find (and present in some numbers).
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Properties of the systems found
Another surprise was that many of the orbits are eccentric. In a few cases, there are several planets. Known ~ 200, most of them: giant planets. The
ll t l t f Gli 581 M 5 03 MEsmallest planet so far: Gliese 581c, M ~ 5.03 ME
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Known extrasolar planets529
• 529 extrasolar planets identified as of Feb. 26, 2011
529
– 490 by radial velocity• 122 planetary transit
– 12 microlensing12 microlensing– 17 direct imaging– 10 pulsar planets– 64 multiple planet systems
• None of these planets are very interesting, however, from an g, ,astrobiological standpoint
• Info from Extrasolar Planets Encyclopedia (Jean SchneiderEncyclopedia (Jean Schneider, CNRS): http://exoplanet.eu/
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
How did the close Jupiters get there?
• They could have been dragged there by the accretion disk. (Corollary: many planets fall into their star!)
• They could have gotten there by interacting with another planetThey could have gotten there by interacting with another planet.• They could have formed there (direct collapse mechanism?)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Planets Around Normal Stars
http://planetquest.jpl.nasa.gov/science/science_index.cfm
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
A solar-type star that is 44 light years away
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
55 Cancri
• Binary star system, 40 light years away
• A solar-type star and a faint red dwarf star separated byred dwarf star, separated by 1065 AU
• Four planets orbit around the Sun-like star: 3 are similar in mass to Jupiter, one (the inner planet) is comparable
htt // i i j l /lib / t l /i /061302 01 j to Neptunehttp://origins.jpl.nasa.gov/library/extrasolar/images/061302‐a‐01.jpg
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
47 Ursae Majoris
• Sun-like star, 46 light years away
• 47 UMa b:– ~3 MJupiter planet– Orbits ~2 AU from star
• 47 UMa c:– ~1 MJupiter planet– Orbits ~8 AU from star
• 47 UMa b may have disrupted terrestrial planet formation
• Any terrestrial planets may be small and dry
h // k d / k /http://en.wikipedia.org/wiki/47_Ursae_Majoris
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
HD 69830
• Has a slightly lower mass, radius and luminosity than the Sun… therefore, the habitable zone is closer to the star than in our system
• Three Neptune-mass planets orbit the star:– ~10 MEarth planet at 0.08 AU,
– ~12 MEarth planet at 0.2 AU,
– ~18 MEarth planet at 0.6 AU
• The outermost planet appears to lie in the habitable zone… if that planet has a moon… life could exist on it?!
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Gliese 581
• Faint, low-mass red dwarf located 20 light years away
• Three planets orbit the star:
– ~16 MEarth planet at 0.04 AU,
– ~5 MEarth planet at 0.07 AU,
– ~8 MEarth planet at 0.25 AU
• The 2 outer planets were discovered in April 2007 and studies are still ongoingstill ongoing
• It appears that the middle planet orbits within the habitable zone, but due to its proximity to the star, it may experience a runaway y y ygreenhouse effect (similar to Venus)
• The outer planet lies near the outer edge of the habitable zone…could life exist? Stay tunedcould life exist? Stay tuned…
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Interferometric Missions
P h d d f ill b bl t• Perhaps a decade from now we will be able to directly image older extrasolar giant planets.
Darwin
Terrestrial Planet Finder
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
TPF-C: Visible-light coronagraph
http://planetquest.jpl.nasa.gov/TPF/tpf_what_is.cfm
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
TPF-I: Free-flying IR interferometer
http://planetquest.jpl.nasa.gov/TPF/tpf_what_is.cfm
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Comparison of Search Methods
Search Methods: what they can find
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Some Fundamental Scientific Facts To RememberFacts To Remember
• The necessary ingredients of life are widespread – Observation reveals uniformity of physical and chemical laws
– Origin of the elements and their dispersal is well understood
• Life on Earth can inhabit harsh environments– Micro- and environmental biology reveal life in extremes of
temperature, chemistry, humidity
• Life affects a planetary environment in a detectable way– Our own atmosphere reflects the presence of primitive through
advanced life
• Planets are a common outcome of star formation– Modern theory of star formation makes planet formation likely
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Eventually, imaging terrestrial planets?
Even if we can just get a spectrum we might bespectrum, we might be able to detect life.
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
The Elements of Life
• Organic Chemistry– By definition, involves H,C,N,O
• Most common elements (produced by most stars)• Well dispersed and available
– Occurs even in interstellar space• Many organic compounds found in ISM, comets, meteors (despite
t l h h diti )extremely harsh conditions)– Easily delivered to early Earth, or produced locally
• BiochemistryR i li id t ?– Requires liquid water?
– Arises naturally when basic conditions met?• What is “life”?
S t t f h i l ilib i hi h t t f it– System out of chemical equilibrium which extracts energy from its environment to maintain itself
– Energy source could be heat, light, chemical, other? Reliably reproduces with opportunity for evolution– Reliably reproduces, with opportunity for evolution
– Able to store and decode information for this
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Extrasolar planets within the HZ
June, 2004
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Basic Chemistry of Life (here on Earth…)
From H,C,N,O (plus some trace amounts of heavier elements like P and Fe) are built nucleic
id t i b h d tacids, proteins, carbohydrates, and lipids, which can do the chemistry needed for both metabolism and evolutionmetabolism and evolution.
Photosynthesis6CO2 + 6H2O + E C6H12O6 + 6O2
Carbon Dioxide + Water + Energy YIELDS Glucose + Oxygen
DigestionC6H12O6 + 6O2 6CO2 + 6H2O + E
Glucose + Oxygen YIELDS Carbon Dioxide + Water + Energy
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Emergence of Life on the Earth
• 0.0-0.5 Gyr: Formation & intense bombardment– surface is uninhabitable
• 0.5-1.0 Gyr: Surface stabilizes, simple life starts– RNA, DNA; thermophilic progenitor (chemical energy)
• 1.0-2.0 Gyr: Anerobic prokaryotes, stromatolite bedssingle celled no nuclei; oldest fossils formed– single-celled, no nuclei; oldest fossils formed
• 2.0-2.5 Gyr: Photosynthesis invented, free oxygen– surface life; use of sunlight; oxygen crisis
• 2.5-3.0 Gyr: Aerobic bacteria, eukaryotes– exploit available oxygen (more energy), cell nucleus
• 3.0-3.5 Gyr: bacteria diversify– Keep changing the mix, experiment
• 3.5-4.0 Gyr: Sexual reproduction invented– Evolve baby!– Evolve, baby!
• 4.0-4.5 Gyr: complex organisms appear– Let’s get together! Let’s get it together!
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
The “Tree of Life”Genetic analysis gives us a window into the distantGenetic analysis gives us a window into the distant past, and clues on how life developed. Most of the biomass on the Earth is still bacterial, and they are best at filling ecological niches Extreme life is foundbest at filling ecological niches. Extreme life is found in amazing places.
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Climate on the EarthThe Sun is getting brighter and was 30% fainterThe Sun is getting brighter, and was 30% fainter in the beginning. We’d be frozen now without greenhouse gases (and really frozen then). Somehow the greenhouse effect has beenSomehow the greenhouse effect has been regulated to keep liquid water on the surface. In less than a billion years, it will be hard to stop a runaway greenhouse on Earth (like Venus).
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Habitable Zones (liquid surface water)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
SETI: search for extraterrestrial intelligence• Our only real hope of detecting ET (unless they come to us) is
Orbital Chaos70 Vir system
• Our only real hope of detecting ET (unless they come to us) is by listening to the radio– Radio travels at the speed of light, over the whole Galaxy
R di i l t d– Radio is a low energy way to send a message– We already have the ability to send and receive
across the Galaxy• Where should we listen?
– Not the currently known extrasolar systems! – Solar-type stars? Milky Way?
• How should we listen?– Frequencies that are relatively quiet. – How narrow-band?The “water hole”?How narrow band?The water hole ?
• What should we listen for?– A regular carrier pattern. Complexity.
P b bilit t h thi ?• Probability to hear something?– The Drake equation
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
The Drake Equation
How Likely is Radio Contact With Extraterrestrial Intelligences?NIC = RIC x LIC = Rstar x Pplanets x Phabitability x Psimple life x Pcomplex life x Pradio signals x Lradio era
RIC x LIC : rate at which civilizations appear x their lifetimeAstronomy
Rstar : rate at which stars are formed in the GalaxyPplanets : probability a star will have planetsP : probability a planet will be suitable for lifePhabitability : probability a planet will be suitable for life
Biology
Psimple life : probability bacteria will arise on a suitable planetPcomplex life : probability bacteria will evolve into complex life
SociologyP di i l : probability complex life will send out radio signalsPradio signals: probability complex life will send out radio signalsLradio era : total duration during which radio is sent
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Evaluating the Odds Optimistically
NIC = RIC x LIC = Rstar x Pplanets x Phabitability x Psimple life x Pcomplex life x Pradio signals x Lradio era
Optimistic Estimates• Rstar : observed rate: 10 per year• Pplanets : observed discoveries: 0.5 • Phabitability : extreme life: 0.5• Psimple life : rapidity of life on Earth 1.0• P : long time on Earth 0 2• Pcomplex life : long time on Earth 0.2• Pradio signals : who knows? 0.02• NIC = Lradio era/100 : pick your favorite duration…IC radio era p y
So if Lre is greater than a few hundred years, there’s probably somebody out there. Lre needs to be a million years for them to be neighbors (meaning within 1000 ly). The Galaxy’s a big place, and its been around a long time!
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
…we are listening!Allen Array
You can help too! Downloadseti@home
2007
Rapid Prototype Array Arecibo (Puerto Rico)
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Evaluating the Odds Pessimistically
NIC = RIC x LIC = Rstar x Pplanets x Phabitability x Psimple life x Pcomplex life x Pradio signals x Lradio era
Pessimistic Estimates
• Rstar : observed rate: 10 per year• Pplanets : observed discoveries: 0.1 (no terrestrials known) • Phabitability : extreme life: 0.01 (surface liquid water)• Psimple life : rapidity of life on Earth 0.1 (we got lucky)• P : long time on Earth 0 01 (looks tough)• Pcomplex life : long time on Earth 0.01 (looks tough)• Pradio signals : who knows? 0.001 (what good are radios?)• NIC = Lradio era/100x106 : duration doesn’t much matter…IC radio era
Pessimistic Conclusion: There’s nobody home (except for us!). y ( p )Let’s be careful, live long, and prosper!
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Thank you very much!
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Jupiter versus Earth
• Jupiter Gas Giant– Upper atm 75% H, 24% He, 1% other elementsUpper atm 75% H, 24% He, 1% other elements– Transitions from gaseous to liquid H as density
increases inward, possibly a rocky core up to 12 MEp y y p E
• Earth Terrestrial Planet– Atmosphere is 78% N 21% O 1% other molecules– Atmosphere is 78% N, 21% O, 1% other molecules
(H2O, CO2, etc.)– Solid crust, highly viscous mantle, liquid outer core,Solid crust, highly viscous mantle, liquid outer core,
solid inner core
EXOPLANETS and ASTROBIOLOGYEXOPLANETS and ASTROBIOLOGY
Jupiter versus Earth
• MJupiter ~ 318 times MEarth
• RJupiter ~ 11 times REarth
• Jupiter ~ 0.24 times EarthJupiter Earth
http://en.wikipedia.org/wiki/Jupiter
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