remote sensing of life and habitable worlds: habstars, earthshine, and tpf margaret c turnbull...

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?


Slightly Smaller Question: Are there habitable terrestrial planets orbiting

nearby stars?


Habitable Zones 101

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(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


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2014

2019

4m x 6m

3-4m x 3-46.5-17 um

10-6 starlight suppression

Darwin?

40 mas IWA

10-10 starlight suppression

Opticalwavelengths

0.5-1.05 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 albedoHabitable Zone, e = 0 to 0.35

0.7 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?



Need high resolution: The Earth-Sun system at 10pc has a 100 milliarcsecond separation

(by definition)

1. Imaging


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


2. Spectroscopy: Mid-IR

CH4

O3

CO2

H2O

N2O

H2O

TPF Book


TPF Book

2. Spectroscopy: Mid-IR


R~20, 15d

TPF Book

2. Spectroscopy: Mid-IR at realistic res


2. Spectroscopy: Optical

Earthshine contains the reflection spectrum of the Earth and is spatially unresolved, like an extrasolar planet would be for TPF


Woolf et al. 2002

2. Spectroscopy: Optical

Woolf et al. 2002

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Secret Hyperion Data: Desert

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Secret Hyperion Data: Forest

This is why astronomers are so revered.

2. Spectroscopy

Turnbull PhD thesis 2004

2. Spectroscopy: Near-IR(VATT CorMass data)

2. Spectroscopy: Optical and NIR at realistic resolution

R~50

Turnbull PhD thesis 2004

Targets for the TPF MissionSpectral Characterization:

Optical/NIR (Rayleigh, O2, H2O, O3, plants)Mid-IR (CO2, H2O, O3)

Types of Stars:Main Sequence

MS > 2 GyrF, 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$1 billion

$2 (6?) 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 TargetsApproach #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 Targetshabstar, '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 Targets1. Timescale for Global Biosignature

Production

TPF timescale for habitability: 2 Gyr

Rule out young starsCa II HK activity

RotationX-rays


Production


Production

TPF timescale for habitability: 2 Gyr

Rule out young starsCa II HK activity

RotationX-rays

Maximum Mass 1.7 Msun (F0)


Production


Production

Lean 1997, ARA&A, 35, 33Wilson & Hudson 1991, Nature, 351, 42Tkachuck 1983, Origins, 10, 51

Habstars as TPF Targets2. Dynamical Stability

Safe interior to hereSafe exterior to here


Good systems

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s

Varying flux from companion


17 systems: Earths in HZ=OK4 systems: habitable moons

Habstars as TPF Targets3. Metallicity

Metallicity cut-off at half-solar

P < 3 yrs, M > 1 MJUP

Does this trend persist for longer orbital periods?Does this trend persist for terrestrial planets?

Habstars as TPF Targets3.5 Kinematics

Kinematics as a proxy for metallicity

High velocity group tends to be lower metallicity

Habstars as TPF Targets3.5 Kinematics

Kinematics as a proxy for metallicity

High velocity group tends to be lower metallicity

X-ing?

Also tossed the highvelocity stars with highmetallicity: 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 TargetsApproach #2: Instrumental Approach

(i.e. observe the “easy” targets)

376 stars w/IHZ > 40 mas

814 stars w/OHZ > 40 mas


(i.e. observe the “easy” targets)NOTES:

2. planet brightness depends on...

3. planet fractional brightness depends on...

Engineers say: 10-10 is doable

1/(distance)2

10 pc -> 30th mag

33 pc -> 32.5th mag

1/L*

-> ~2.5 Lsun for inner HZ

-> ~ 0.5 Lsun for outer HZ



OHZ > 40 mas

Habstars as TPF TargetsResults: 479 Scientifically Interesting Targets,

10 of which are fully observable56 of which are partially observable...d < 20 pc

N=162

What’s Next? More Prep Sci for TPFWe 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 stillGiving light, dying.

Sara Teasdale (1884-1933)

remote sensing of life and habitable worlds: habstars, earthshine, and tpf margaret c turnbull...

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