Remote Sensing of Life and Habitable Worlds: Habstars, Earthshine, and TPF Margaret C Turnbull Carnegie Institution of Washington NRC/NAI Postdoctoral Fellow ee cummings

The Big Question: To what extent is the Universe alive? What is “life?” Where is life found? How does life originate? Is all life carbon/water based? What are the environmental limits of Earth-like life? What is the range of complexity for life? Are there other technological civilizations? Are there other inhabited planets in the Solar System? Is life “originating” on Earth now? Can life spread between planets/stars? Do we have cosmic ancestors/cousins? Is there a habitable “belt” within the Galaxy? What is a “habitable” planet? Why aren’t clouds green?

The Big Question: To what extent is the Universe alive? What is “life?” Where is life found? How does life originate? Is all life carbon/water based? What are the environmental limits of Earth-like life? What is the range of complexity for life? Are there other technological civilizations? Are there other inhabited planets in the Solar System? Is life “originating” on Earth now? Can life spread between planets/stars? Do we have cosmic ancestors/cousins? Is there a habitable “belt” within the Galaxy? What is a “habitable” planet?

Slightly Smaller Question: Are there habitable terrestrial planets orbiting nearby stars? What is a “habitable” planet?

Slightly Smaller Question: Are there habitable terrestrial planets orbiting nearby stars?

Habitable Zones 101 (In reality, HZ depends on planet characteristics, too.) 0.7 to 1.5 AU,  L * 1/2

The Terrestrial Planet Finder Mission Objectives: 1.Directly image terrestrial planets in the habitable zones of nearby stars 2.Characterize atmospheres and look for indicators of life 3.Do comparative planetology

The Terrestrial Planet Finder m x 6m 3-4m x um starlight suppression Darwin? 40 mas IWA starlight suppression Optical wavelengths um TPF-C TPF-I The technology driver is the need to suppress starlight...

What is required to achieve the TPF goals? Habitable Zone: the range of semimajor axes consistent with surface water on an Earth-like planet Types of Planets: at least 1/2 Earth surface area Earth albedo Habitable Zone, e = 0 to to 1.5 AU,  L * 1/2

Two Questions: 1. What do we need in terms of imaging capabilities? 2. Which wavelength range should we observe? What is required to achieve the TPF goals?

Need high resolution: The Earth-Sun system at 10pc has a 100 milliarcsecond separation (by definition) 1. Imaging

What is required to achieve the TPF goals? Need high sensitivity: The Earth is one ten billionth as bright as the Sun at optical wavelengths (reflected light), one millionth as bright in the mid-IR (emitted light) 1. Imaging Beichman 1999, TPF Book

What is required to achieve the TPF goals? 2. Spectroscopy: Mid-IR CH 4 O3O3 CO 2 H2OH2O N2ON2O H2OH2O TPF Book

What is required to achieve the TPF goals? TPF Book 2. Spectroscopy: Mid-IR

What is required to achieve the TPF goals? R~20, 15d TPF Book 2. Spectroscopy: Mid-IR at realistic res

What is required to achieve the TPF goals? 2. Spectroscopy: Optical Earthshine contains the reflection spectrum of the Earth and is spatially unresolved, like an extrasolar planet would be for TPF

What is required to achieve the TPF goals? Woolf et al Spectroscopy: Optical

Woolf et al Spectroscopy: Optical

Secret Hyperion Data: Desert

2. Spectroscopy: Optical Secret Hyperion Data: Forest

This is why astronomers are so revered. 2. Spectroscopy Turnbull PhD thesis Spectroscopy: Near-IR (VATT CorMass data)

2. Spectroscopy: Optical and NIR at realistic resolution R~50 Turnbull PhD thesis 2004

Targets for the TPF Mission Spectral Characterization: Optical/NIR (Rayleigh, O 2, H 2 O, O 3, plants) Mid-IR (CO 2, H 2 O, O 3 ) Types of Stars: Main Sequence  MS > 2 Gyr F, G and K stars “Minimum” Mission: Search 35 “core” stars to 90% completeness “Full” Mission: 130 more stars, 90% for the whole ensemble

The Cost $1 billion $2 (6?) billion “Minimum” Mission: Search 35 “core” stars to 90% completeness “Full” Mission: 130 more stars, 90% for the whole ensemble

Choosing TPF Targets Approach #1: Scientific Approach (i.e. observe the “best” targets) NOTES: 1.TPF targets will likely be a subset of or strongly intersecting set with SIM and RV search targets. 2.Want to have a conclusion in the case of a null result. 3.How picky can we be before we have no stars left?

Habstars as TPF Targets habstar, 'hab stär, noun, -s A star which has: (1) A habitable zone that is dynamically stable* on a timescale that is comparable to the timescale of global biosignature production, (2) A habitable zone that is spatially static on that same timescale, and (3) A metallicity that is consistent with the existence of terrestrial planets. * and does not overlap any major resonances w/companions

Habstars as TPF Targets 1. Timescale for Global Biosignature Production TPF timescale for habitability: 2 Gyr Rule out young stars Ca II HK activity Rotation X-rays

Habstars as TPF Targets 1. Timescale for Global Biosignature Production

Habstars as TPF Targets 1. Timescale for Global Biosignature Production TPF timescale for habitability: 2 Gyr Rule out young stars Ca II HK activity Rotation X-rays Maximum Mass 1.7 M sun (F0)

Habstars as TPF Targets 1. Timescale for Global Biosignature Production

Habstars as TPF Targets 1. Timescale for Global Biosignature Production Lean 1997, ARA&A, 35, 33 Wilson & Hudson 1991, Nature, 351, 42 Tkachuck 1983, Origins, 10, 51

Habstars as TPF Targets 2. Dynamical Stability Safe interior to here Safe exterior to here

Habstars as TPF Targets 2. Dynamical Stability Safe interior to here Safe exterior to here

Habstars as TPF Targets 2. Dynamical Stability Good systems Evil systems Varying flux from companion  

Habstars as TPF Targets 2. Dynamical Stability 17 systems: Earths in HZ=OK 4 systems: habitable moons

Habstars as TPF Targets 3. Metallicity Metallicity cut-off at half-solar P 1 M JUP Does this trend persist for longer orbital periods? Does this trend persist for terrestrial planets?

Habstars as TPF Targets 3.5 Kinematics Kinematics as a proxy for metallicity High velocity group tends to be lower metallicity

Habstars as TPF Targets 3.5 Kinematics Kinematics as a proxy for metallicity High velocity group tends to be lower metallicity X-ing ? Also tossed the high velocity stars with high metallicity: spiral arm- crossing orbits

Habstars as TPF Targets Result: 479 Scientifically Interesting Targets within 30 pc

Approach #2: Instrumental Approach (i.e. observe the “easy” targets) Choosing TPF Targets NOTES: 1.angular HZ size depends on...

Approach #2: Instrumental Approach (i.e. observe the “easy” targets) NOTES: 1.angular HZ size depends on... Choosing TPF Targets Engineers say: 40 mas is doable stellar apparent magnitude 5th mag -> 100 mas 6th mag -> 50 mas 7th mag -> 30 mas -> 6.5th mag or brighter stars

Choosing TPF Targets Approach #2: Instrumental Approach (i.e. observe the “easy” targets) 376 stars w/IHZ > 40 mas 814 stars w/OHZ > 40 mas

Choosing TPF Targets Approach #2: Instrumental Approach (i.e. observe the “easy” targets) NOTES: 2. planet brightness depends on planet fractional brightness depends on... Engineers say: is doable 1/(distance) 2 10 pc -> 30th mag 33 pc -> 32.5th mag 1/L * -> ~2.5 L sun for inner HZ -> ~ 0.5 L sun for outer HZ

Choosing TPF Targets Approach #2: Instrumental Approach (i.e. observe the “easy” targets)

Choosing TPF Targets Approach #2: Instrumental Approach (i.e. observe the “easy” targets) OHZ > 40 mas

Habstars as TPF Targets Results: 479 Scientifically Interesting Targets, 10 of which are fully observable 56 of which are partially observable...d < 20 pc N=162

What’s Next? More Prep Sci for TPF We now have: -30 PC TPF Stellar Database -Some idea of what Earth looks like from outer space But we still need: -to fill in lots of missing stellar data -to make a user-friendly database -to learn about the variability of Earth’s spectral features/biosignatures -to figure out, as a community, what TPF can and should reasonably do

Moon, work thin to the width of a quill, in the dawn clouds flying, How good to go, light into light, and still Giving light, dying. Sara Teasdale ( )