Lecture 4 1:Lecture 4.1: AstrobiologyAstrobiology:

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


Martian Meteorite

D. S. McKay et al., Science (1996)


Martian Nannobacteria?


Mars Pathfinder: Twin peaks view

NASA Planetary Photojournal (http://photojournal.jpl.nasa.gov/)


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


MER Rovers


Endurance Crater (from MER Rover Opportunity)

http://marsrovers jpl nasa gov/home/index htmlhttp://marsrovers.jpl.nasa.gov/home/index.html


Spherules (Blueberries) on Mars


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!


Solar System: Europa

EUROPA(from Galileo)(from Galileo)

Courtesy: JPL/NASAPlanetary Photojournal


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)


Lakes on Titan?

• Image taken by the Huygens Probe, launched from theCassini spacecraft (January, 2005)


Titan shoreline?


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


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


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


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


Precision Radial Velocity Searches

Shift isShift is1 part

in100

million


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).


Planet Detection Methods: Radial Velocity

away

toward

http://en.wikipedia.org/wiki/Doppler_spectroscopy


Planet Detection Methods: Radial Velocity

away

obse

rver

toward

o

http://en.wikipedia.org/wiki/Doppler_spectroscopy


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


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


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).


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


“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?).


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)


Planet Detection Methods:Gravitational MicrolensingGravitational Microlensing


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


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


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.


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?


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).


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


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/


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?)


Planets Around Normal Stars

http://planetquest.jpl.nasa.gov/science/science_index.cfm


A solar-type star that is 44 light years away


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


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


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?!


Gliese 581

• Faint, low-mass red dwarf located 20 light years away

• Three planets orbit the star:



– ~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…


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


TPF-C: Visible-light coronagraph

http://planetquest.jpl.nasa.gov/TPF/tpf_what_is.cfm


TPF-I: Free-flying IR interferometer

http://planetquest.jpl.nasa.gov/TPF/tpf_what_is.cfm


Comparison of Search Methods

Search Methods: what they can find


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


Eventually, imaging terrestrial planets?

Even if we can just get a spectrum we might bespectrum, we might be able to detect life.


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


Extrasolar planets within the HZ

June, 2004


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


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!


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.


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).


Habitable Zones (liquid surface water)


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


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


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!


…we are listening!Allen Array

You can help too! Downloadseti@home

2007

Rapid Prototype Array Arecibo (Puerto Rico)


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!


Thank you very much!


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


Jupiter versus Earth

• MJupiter ~ 318 times MEarth

• RJupiter ~ 11 times REarth

• Jupiter ~ 0.24 times EarthJupiter Earth

http://en.wikipedia.org/wiki/Jupiter

Documents

Lecture 4 1:Lecture 4.1: AstrobiologyAstrobiology: