The search for habitable planets
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The Search for (Habitable) Planets. C. Beichman, JPL. 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 ).

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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)

…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.”

And medieval martyrs
…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

…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.”

Nasa s origins theme has two defining questions

Where Did We Come From?

Are We Alone?

Search for Life Outside the Solar system

  • Remote detection of the signposts of biological activities on extra- solar planets

  • Tracing Our Cosmic Roots

  • Formation of galaxies, stars, heavy elements, planetary systems and ….. life on the Early Earth

NASA’s Origins Theme Has Two Defining Questions

Understand How Stars

and Planetary Systems

Form and Evolve

Understand How Galaxies Formed in the Early Universe




Determine Whether Habitable

or Life-bearing Planets Exist Around Nearby Stars

NASA Origins Science Goals

Some fundamental scientific facts to remember
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

Star forming regions
…Star Forming Regions…

IR, submm, mm spectra reveal gas phase, ices, mineralogical signatures of many species, incl:

H2O, CO2, CH3OH, CO, CH4, formic acid (HCOOH) and formaldehyde (H2CO), etc.

And distant galaxies

Barthel 2001




Pierre et al 2001

…and distant galaxies

  • Polycyclic Armomatic Hydrocarbons (PAHs)

    • Complex 2-D carbon molecules (>25 carbon atoms)

    • Found in many active galaxies

  • 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

Life is hardy

Life is Hardy

  • Life needs water, a source of energy, and cosmically abundant elements

Life affects the earth s atmosphere
Life Affects The Earth’s Atmosphere undersea volcanic vents, in underground aquifers, and within rocks in Antarctica

Earth s gases with and without life
Earth’s Gases With And Without Life undersea volcanic vents, in underground aquifers, and within rocks in Antarctica

Tim Lenton, Centre for

Ecology and Hydrology

Star formation protoplanetary disks
Star Formation & Protoplanetary Disks Formation

  • 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

Debris disks from the ground

Fomalhaut Formation

Beta Pic

Eps Eri

Debris DisksFrom 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

Sirtf observations of disks
SIRTF Observations of Disks Formation

  • 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!

Finding planets indirectly
Finding Planets Indirectly Formation

  • 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

Radial velocity searches
Radial Velocity Searches Formation

Mayor et al

Marcy et al.

Gas Giant Planets Formation


Marcy et al.

  • Over 100 planets found using radial velocity wobble

    • ~10% of stars have planets

    • Most orbits < 2-3 AU

    • Half may be multiple systems

  • Planets on longer periods starting to be identified

    • 55 Cancri is solar system analog

  • Radial velocity technique not sensitive to terrestrial planets

Number of Planets Formation

Increasing as Mass-1

Planetary transits then and now

Fundraising: Cook, Joesph Banks, and Lord Sandwich. Formation

Planetary Transits: Then and Now

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

Transit determines planet s properties
Transit Determines Planet’s Properties Formation

  • Transits of HD 209458 determine properties of another Solar System

    • Confirmation of planet interpretation

    • Inclination= 85.9

    • Mass= 0.69 ± 0.07 Mjup

    • Radius =1.35 ± 0.06 Rjup

    • 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

Astrometric search for planets
Astrometric Search for Planets Formation

  • 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 Mearth over the next 10-20 years

Interferometery is one key to planet detection
Interferometery Is One Key to Planet Detection Formation

  • Break link between diameter, baseline

  • 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

Space interferometer mission sim will make definitive planet census
Space Interferometer Mission (SIM) Will Make Definitive Planet Census

  • 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’ ?

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 Me 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?

But what is a habitable planet
But What is a Habitable Planet? Planet Census

  • 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

Finding terrestrial planets

>10 Planet Census9


Finding Terrestrial Planets

  • Detecting light from planets beyond solar system is hard:

    • Planet signal is weak but detectable (few photons/sec/m2)

    • 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

Four hard things about tpf
Four Hard Things About TPF Planet Census

  • Sensitivity (relatively easy)

    • Detection in hours  spectroscopy in days.

    • Integration time  (distance/diameter)4

    • Need 12 m2 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

Signatures of life
Signatures of Life Planet Census

  • 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

Mars odyssey looks back at earth
Mars Odyssey Looks Back at Earth Planet Census

Christensen and Pearl 1997

Earthshine reveals visible spectrum
Earthshine Reveals Visible Spectrum Planet Census

Woolf, Traub and Jucks 2001

Goals for terrestrial planet finder
Goals for Terrestrial Planet Finder Planet Census

  • 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.

Tpf candidate architectures

Visible Coronagraphs Planet Census

IR Interferometers

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 (l/300)

      • Hold (l/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

The challenge of angular resolution

10 mm, 28 m


The Challenge of Angular Resolution

Cost ($$), Launch Date


How many planets are enough
How Many Planets Are Enough ? Planet Census

  • How many stars to avoid mission failure (Np = 0)

  • How many stars to ensure enough planets (Np >5)

 

 # Stars Dist(Aperture, Baseline)CostSchedule

Visible light planet detection
Visible Light Planet Detection Planet Census

  • 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 mm

Control of star light
Control of Planet CensusStar 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 deformable mirror

    • 10,000 actuators for final l/3000 wavefront (<1 Å)

Coronagraph status

10 Planet Census-5

5 Airy rings

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

Ir interferometer

Goal Earth at 10 pc Time Planet Census

Planet? R=3/SNR=5 2.0 hour

Atmosphere? R=20/SNR=10 2.3 day

CO2, H2O

Habitable? R=20/SNR=25 15.1 day

O3, CH4

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

Nulling interferometry

l Planet Census/B

Nulling Interferometry



Interferometer detects and characterizes planetary systems
Interferometer Detects and Characterizes Planetary Systems Planet Census

  • 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

Ir nulling

~1min Planet Census

  • JPL Modified Mach-Zender (Serabyn et al)

    • 1.4 10-6 nulllaser null @ 10.6 um

    • Aim for 10-6 null target broadband

      • Add spatial filter

      • Active pathlength stabilization

IR Nulling

  • UofA group (Hinz et al) demonstrated nulling with BLINC instrument on MMT

Pre tpf study will span wavelengths techniques years ground and space theory and observation

Hale Bopp Planet Census

Pre-TPF Study Will Span Wavelengths, Techniques, Years, Ground and Space, Theory and Observation

Planet finding is a decades long undertaking
Planet Finding Is A Decades-Long Undertaking Planet Census

  • 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

Collaboration on tpf darwin
Collaboration on TPF/Darwin Planet Census

  • 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

  • The NASA Vision Planet Census

  • 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