1. The Search for (Habitable) Planets C. Beichman, JPL

2. From 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 )

3. …to Medieval Scholars... “I [regard]… as false and damnable the view of those who would put inhabitants on Jupiter, Venus, and Saturn, and the moon, meaning by ‘inhabitants’ animals like ours and men in particular.”

4. …and Medieval Martyrs... "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) in De L'infinito Universo E Mondi

5. …To Hollywood Producers… Klaatu Borada Nikto “Your choice is simple. Join us and live in peace or pursue your present course and face obliteration. We shall be waiting for your answer. The decision rests with you.”

6. NASA’s Origins Theme Has Two Defining Questions Are We Alone? Search for Life Outside the Solar system Remote detection of the signposts of biological activities on extra- solar planets Where Did We Come From? Tracing Our Cosmic Roots Formation of galaxies, stars, heavy elements, planetary systems and ….. life on the Early Earth

7. NASA Origins Science Goals Understand How Stars and Planetary Systems Form and Evolve 2 Determine Whether Habitable or Life-bearing Planets Exist Around Nearby Stars 3 1 Understand How Galaxies Formed in the Early Universe

8. Some Fundamental Scientific Facts 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

9. Organic Chemistry Ubiquitous: Comets

10. IR, submm, mm spectra reveal gas phase, ices, mineralogical signatures of many species, incl: H 2 O, CO 2, CH 3 OH, CO, CH 4, formic acid (HCOOH) and formaldehyde (H 2 CO), etc. …Star Forming Regions…

11. …and distant galaxies Polycyclic Armomatic Hydrocarbons (PAHs) –Complex 2-D carbon molecules (>25 carbon atoms) –Found in many active galaxies Pierre et al 2001 z=1.5 ?? Barthel 2001 PAH Perhaps in distant quasar at z~1.5 (wait for SIRTF) CO detected in a very distant quasar (z=4.1!) –Found with more complex species in more nearby objects

12. Life is Hardy Life needs water, a source of energy, and cosmically abundant elements Extremophiles can live in hot (~120 C!) acid lakes, near undersea volcanic vents, in underground aquifers, and within rocks in Antarctica

13. Life Affects The Earth’s Atmosphere

14. Earth’s Gases With And Without Life Tim Lenton, Centre for Ecology and Hydrology

15. Kant-Laplace Theory of Star Formation Favors Planet Formation

16. Star Formation & Protoplanetary Disks The formation of planets is an integral part of our theory of how stars form –Hundreds of planetary masses of gaseous and solid material in the protostellar disk Solar System-scale dust disks found around nearby stars

17. Fomalhaut Debris Disks From the Ground Sub-millimeter (SCUBA/JCMT) observations of disks reveal evacuated cavities the size of our solar system as well as clumps that may be structures associated with planets Many groups searching for planets using AO Beta Pic Eps Eri

18. SIRTF Observations of Disks NASA’s next Great Observatory will map disks, survey 100s stars – single, binary –with, w/o planets –ages from 1 million to 5 billion yr SIRTF launches April 18 after 25 years!

19. SIRTF Is 10 days From Launch

20. Finding Planets Indirectly Gravitational Effects on Parent Star –Radial Velocity Changes –Positional Wobble (Astrometry) Effect of Planet on Star’s Brightness –Transits of edge-on systems –Gravitational micro-Lensing

21. Radial Velocity Searches Mayor et al Marcy et al.

22. Gas Giant Planets Over 100 planets found using radial velocity wobble – ~10% of stars have planets – Most orbits < 2-3 AU – Half may be multiple systems ??? Marcy et al. Planets on longer periods starting to be identified – 55 Cancri is solar system analog Radial velocity technique not sensitive to terrestrial planets

23. Number of Planets Increasing as Mass -1

24. The Royal Society sent Captain Cook along with Joseph Banks to Tahiti to observe a transit of Venus on June 3, 1769 to set the scale of the Solar System Planetary Transits: Then and Now Fundraising: Cook, Joesph Banks, and Lord Sandwich.

25. Transit Determines Planet’s Properties Transits of HD 209458 determine properties of another Solar System –Confirmation of planet interpretation –Inclination= 85.9  –Mass= 0.69 ± 0.07 M jup –Radius =1.35 ± 0.06 R jup –Density= 0.35 g/cc <Saturn Active ground based efforts using 10 cm to 10 m telescopes COROT, Kepler and Eddington will find few  hundreds of Earths, thousands of Jupiters Spectroscopy probes atmosphere –Cloud heights, heavy-element abundances, temperature and vertical temperature stratification, and wind velocities

26. Astrometric Search for Planets Astrometry measures positional wobble due to planets Interferometry enables measurements at the micro- arcsecond level Result of new observing systems will be a census of planets down to a few M earth over the next 10-20 years

27. Interferometery Is One Key to Planet Detection Enables precision astrometry, high resolution imaging, starlight nulling Make astrometric census of planets Detect “Hot Jupiter’s” Detect exo-zodiacal dust clouds Image protostellar disks Break link between diameter, baseline

28. Space Interferometer Mission (SIM) Will Make Definitive Planet Census A Deep Search for Earths Are there Earth-like (rocky) planets orbiting the nearest stars? Focus on ~250 stars like the Sun (F, G, K) within 10 pc Sensitivity limit of ~3 M e at 10 pc requires 1 µas accuracy A Broad Survey for Planets Is our solar system unusual? What is the range of planetary system architectures? Sample 2000 stars within ~25 pc at 4 µas accuracy Evolution of Planets How do systems evolve? Is the evolution conducive to the formation of Earth-like planets in stable orbits? Do multiple Jupiters form and only a few (or none) survive? What We Don’t Know Are planetary systems like our own common? What is the distribution of planetary masses? – Only astrometry measures planet masses unambiguously Are there low-mass planets in ‘habitable zone’ ?

29. But What is a Habitable Planet? Not too big –Avoid accreting material to become gas giant Not too small –Lose atmosphere Not too hot or too cold –No liquid water Not too close to star –Avoid tidal lock

30. Finding Terrestrial Planets Detecting light from planets beyond solar system is hard: –Planet signal is weak but detectable (few photons/sec/m 2) –Star emits million to billion more than planet –Planet within 1 AU of star –Dust in target solar system  300 brighter than planet Finding a firefly next to a searchlight on a foggy night >10 9 >10 6

31. Four Hard Things About TPF Sensitivity (relatively easy) –Detection in hours  spectroscopy in days. –Integration time  (distance/diameter) 4 –Need 12 m 2 of collecting area (>4 m) for star at ~10 pc Angular resolution (hard) –100 mas is enough to see ~25 stars, but requires >4 m coronagraph or >20 m interferometer –Baseline/aperture  distance Starlight suppression (hard to very hard) –10 -4 to 10 -6 in the mid-IR –10 -8 to 10 -10 in the visible/near-IR Solar neighborhood is sparsely populated –Fraction of stars with Earths (in habitable zone) unknown –Unknown how far we need to look to ensure success –Surveying substantial number of stars means looking to ~15 pc

32. Signatures of Life Oxygen or its proxy ozone is most reliable biomarker –Ozone easier to detect at low Oxygen concentrations but is a poor indicator of quantity of Oxygen Liquid water on a planet’s surface is considered essential to life. Carbon dioxide indicates an atmosphere and oxidation state typical of terrestrial planet. Abundant Methane can have a biological source –Non-biological sources might be confusing Find an atmosphere out of equilibrium Expect the unexpected

33. Mars Odyssey Looks Back at Earth Christensen and Pearl 1997

34. Earthshine Reveals Visible Spectrum Woolf, Traub and Jucks 2001

35. Goals for Terrestrial Planet Finder Primary Goal: Direct detection of emitted or reflected radiation from Earth-like planets located in the habitable zones of nearby solar type stars. –Determine orbital and physical properties –Characterize atmospheres and search for bio-markers –Search a statistically meaningful sample of stars (30-150) The Broader Scientific Context: Comparative Planetology –Understand properties of all planetary system constituents, e.g. gas giant planets, terrestrial planets and debris disks. Astrophysics: An observatory with the power to detect an Earth orbiting a nearby star will be able to collect important new data on many targets of general astrophysical interest.

36. TPF Candidate Architectures Visible Coronagraph –System concept is relatively simple, 4-10 m mirror on a single spacecraft –Components are complex Build adequately large mirror of appropriate quality ( /300) Hold ( /3000) stability during observation with deformable mirror IR Interferometer − Components are simple: 3-4 m mirrors of average quality −System is complex: 30 m boom or separated spacecraft

37. The Challenge of Angular Resolution + Coronagraphs at >3 /D Interferometers at > 1 /B 10  m, 28 m Coronagraph Cost ($$), Launch Date

38. How many stars to avoid mission failure (N p = 0) How many stars to ensure enough planets (N p >5)    # Stars  Dist  (Aperture, Baseline)  Cost  Schedule    How Many Planets Are Enough ?

39. Visible Light Planet Detection A simple coronagraph on NGST could detect Jupiters around the closest stars as well as newly formed Jupiters around young stars Advanced coronagraph/apodized aperture telescope –2~4 m telescope (Jupiters and nearest Earths) –8~10 m telescope (full TPF goals) Presence and Properties of Planets –Planet(s) location and size  reflectivity –Atmospheric or surface composition –Rotation  surface variability –Radial and azimuthal structure of disks Simulated NGST coronagraphic image of a planet around Lalande 21185 (M2Vat 2.5pc) at 4.6  m

40. Control of Star Light Control diffracted light with various apodizing pupil and/or image plane (coronagraph) masks –Square masks –Graded aperture –Multiple Gaussian masks –Band limited masks Control scattered light with d eformable mirror −10,000 actuators for final l/3000 wavefront (<1 Å)

41. Coronagraph Status Current contrast limited to 10 -5 due to DM imperfections and lab seeing −New DM due from Xinetics in March Kodak selected to provide large (1.8m), high precision (<5 nm) Mirror − Very similar to SNAP mirror! Innovative ideas to improve angular resolution by combining interferometer and coronagraph ideas 5 Airy rings 10 -5

42. IR Interferometer Interferometer with cooled two to four 3~4 m mirrors –30 m boom –75-1000 m baseline using formation flying Operate at 1 AU for 5 years to survey 150 stars Goal Earth at 10 pc Time Planet? R=3/SNR=5 2.0 hour Atmosphere? R=20/SNR=10 2.3 day CO 2, H 2 O Habitable? R=20/SNR=25 15.1 day O 3, CH 4

43. Nulling Interferometry  B /B

44. Interferometer Detects and Characterizes Planetary Systems TPF produces image of planetary system – Orbital location – Temperature and radius TPF produces spectrum to search for biomarkers 1-2 m telescopes to find Jupiters, nearest Earths 3-4 m telescopes for full TPF goals

45. IR Nulling JPL Modified Mach-Zender (Serabyn et al) –1.4  10 -6 null laser null @ 10.6 um –Aim for 10 -6 null target broadband Add spatial filter Active pathlength stabilization ~1min UofA group (Hinz et al) demonstrated nulling with BLINC instrument on MMT

46. Pre-TPF Study Will Span Wavelengths, Techniques, Years, Ground and Space, Theory and Observation Hale Bopp

47. Planet Finding Is A Decades-Long Undertaking Like cosmology, the search for planets and life will motivate broad research areas and utilize many telescopes for decades to come NASA’s program for planet finding will be broad and rich, with results emerging on many time scales, from the immediate to the long-term There are exciting, mid-term ways to detect giant planets and the nearest Earths

48. Collaboration on TPF/Darwin Strong ESA/NASA interest in joint planet-finding mission –Collaborative architecture studies –Discussions on technology planning and development Joint project leading to launch ~2015 –Scientific and/or technological precursors as required and feasible

49. The NASA Vision – To improve life here – To extend life to there – To find life beyond The Science Vision “Search for Life outside of earth and, if it is found, determine its nature and its distribution in the galaxy…[This] is so challenging and of such importance that it could occupy astronomers for the foreseeable future” --- NAS/NRC Report