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Darwin and the Origins of Extrasolar Species
Rene Liseau Stockholm Observatory Delegate to
the Scientific Advisory Teams of

ESA
TE-SAT

NASA TPFI-SWG
http//www.astro.su.se/groups/infrared/index.html
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Outline Astronomical Jargon, Definitions
Acronyms Extrasolar Planets (known)
Extrasolar Planets (expected) Detection
Techniques (known possibilities) Detection
Techniques (selected ESA Darwin, NASA TPFI)
Optical Architecture (destructive interference,
formation flying) Mission Characteristics
(payload, launcher, orbit selection) The Future
(future missions)
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Astronomical Jargon
shall attempt to avoid
Sorry, if too trivial...
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Definitions
Acronyms
1 pc
1 AU
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Definitions
Acronyms
Seeing limited 1 8m diffraction limited
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Definitions
Acronyms
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Goals of Darwin

Find other Earths
Find X-solar Life
and
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What is Known
Discovery of Extra-solar Planets since 1995
update 26 November 2005        Global
statistics    146 planetary systems   170
planets   18 multiple planet systems
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Earth
Uranus Neptune
Jupiter Saturn
Sun
Exo-Planet Type
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mass 0.003 radius 0.1 density 5
mass 1000 radius 10 density
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mass 1 radius 1 density 1
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Distribution of KNOWN Exoplanets BIASED by
METHOD of OBSERVATION
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Observation of STELLAR REFLEX MOTION (Doppler)
orbit ltlt 0.001 RSun
P 1 yr Earth 30 km s-1
Sun lt 10 cm s-1
O ( 100 RSun )
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Observation of STELLAR REFLEX MOTION
P 1 yr Earth 30 km s-1
Sun 9 10-5 km s-1 12 yr
Jupiter O ( m s-1 )
5.2 AU Distance

Not Yet Sensitivity DV 10 m s-1
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Besides Vrad , other known observational methods
planetary transits radius and density
of
occulting planet
micro-lensing statistics of remote systems
distance of O (10 kpc)
direct imaging of structure in young disks
presence of planet(s)
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Besides Vrad , other known observational methods
pulsar timing planets mass
first detection of Earth-mass planets...
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known observational methods useful for exo-Earths
?
radial velocities N
stellar activity of O (m s-1)
stellar astrometry Y
from space O (marcsec)
planetary transits Y
from space ( DI/I lt 10- 4 )
micro-lensing Y
O (hour) , not repetitive
imaging of disk structure N O
(MJup) , not unique
pulsar timing Y
few systems, no Life
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known observational methods useful for exo-Earths
?
radial velocities N
stellar activity of O (m s-1)
stellar astrometry Y
from space O (marcsec)
planetary transits Y
from space ( DI/I 10-4 )
micro-lensing Y
O ( hour) , not repetitive
imaging of disk structure N O
(MJup) , not unique
pulsar timing Y
few systems, no Life
Life
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What is ? How originated ?
Life
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Definition of Life... ?
(1). Organisms tend to be complex and highly
organized. Chemicals found within their bodies
are synthesized through metabolic processes into
structures that have defined purposes. Cells and
their various organelles are examples of such
structures. Cells are also the basic functioning
unit of life. Cells are often organized into
organs to create higher levels of complexity and
function. (2). Living things have the ability to
take energy from their environment and change it
from one form to another. This energy is usually
used to facilitate their growth and reproduction.
We call the process that allows for this
facilitation metabolism. (3). Organisms tend to
be homeostatic. In other words, they regulate
their bodies and other internal structures to
certain normal parameters. (4). Living creatures
respond to stimuli. Cues in their environment
cause them to react through behavior, metabolism,
and physiological change. (5). Living things
reproduce themselves by making copies of
themselves. Reproduction can either be sexual or
asexual. Sexual reproduction involves the fusing
of haploid genetic material from two individuals.
This process creates populations with much
greater genetic diversity. (6). Organisms tend to
grow and develop. Growth involves the conversion
of consumed materials into biomass, new
individuals, and waste. (7). Life adapts and
evolves in step with external changes in the
environment through mutation and natural
selection. This process acts over relatively long
periods of time.
... etc ...
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Origin of Life ?
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What does Life DO ?
! Generates WASTE !
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Life transforms a planet - e.g. its Atmosphere
oxygen
methane
Time (Ga)
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Cyano Bacteria bluegreen algae
produce sugar and OXYGEN
oxygenic photosynthesis
2H2O CO2 hn ? CH2O O2 H2O
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Chemical Disequilibrium Atmosphere
simultaneously reducing .and. oxydizing
WATER .and.
CARBON DIOXIDE .and.
OXYGEN
2H2O CO2 hn ? CH2O O2 H2O
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IMPLIES BIOACTIVITY
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IMPLIES BIOACTIVITY

• Spectrum
• in
• Thermal Infrared
• Earth is Hot
• Atmospheric Lines Opaque
• Needs Space

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PROBLEM OF CONTRAST
Scattered Solar Radiation
1O10
versus
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Planetary Thermal Emission
log10
Visible
InfraRed
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PROBLEM OF CONTRAST
1
10-11 to 10-7 of central peak intensity in the
wings of the PSF
... and in real life not inifinite signal-to-noise
PSF Point Spread Function
Fourier Transform of Modular Transfer Function
(MTF)
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Solution Darwin the Mission Nulling
Interferometer
Destructive Interference provides Needed Contrast
Long Baselines provide Needed Resolution
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Nulling Interferometer Point Sources
simplest case 2 element Bracewell interferometer
to null stellar radiation e.g. at 10
pc distance and l 10 mm Sun 1.6 Jy
(N 3.6 mag ) Earth 0.23 mJy
(N 20.7 mag)

star on optical axis

1 Jy 10-26 W m-2 Hz-1
q 0
Rejection Rate qn gt 105 n 2 for
Bracewell

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This is wonderful !
So - does everything come for free ?
We gain resolution but loose information and field
But for POINT SOURCES OK!
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D
Filled aperture D contains all spatial
frequencies up to 1/D gt Image of
the source
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D
B
d/2
Interferometer B picks out 1 spatial frequency
1/B in coherent field of view 1/d
Example l 10 mm, B 200 m, d 2
m Resolution 10 milliarcsec Field of view
1 arcsec
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Equilateral triangle - Darwin architecture 3.5 m

• BCS in the centre of triangle
• 120 deg between telescopes
• Variable distance TS to BCS

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Modulation properties
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Spectroscopy
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Beam Combination by Single Mode Waveguide
Single mode waveguide (SMW) used for modal
filtering to improve nulling ratio.Phase
relations in SMW of injected on-axis light such
that resulting amplitude is zero.Internal
modulation by alternating phase shifts between
(-120º, 0º, 120º) and (120º, 0º, -120º)
A
B
C
fB(t)
fA(t)
fC(t)
Focusing Optics
Stellar light can not propagate in fibre core and
is rejected into the cladding
Single Mode Waveguide
Detector
Ref. O. Wallner et. al Multi-axial single mode
beam combiner
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Beam Combination
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Signal-to-Noise (S/N)
Local zodi
Thermal BG
Exo zodi (10)
Detector
Total noise
Leakage
Transmitted planet signal
Equivalent signal of absorption lines
SNR integrated over line width
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Science Requirements
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Science Requirements, cntd.
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Assumptions
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Main Observational Requirements

• Nulling of on axis star by 105
• Baseline accuracy 1 cm
• Optical Path Difference (OPD) 20 nm
• Telescope pointing 24 mas
• Amplitude matching 10- 2

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Control Modes
Flyers randomly distributed in a sphere (15 km)
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Baseline Control Mode

• mN-FEEP
• Inertial attitude using star-trackers 1
• RF range measurement 1 cm
• RF goniometry
• omni-directional 10 deg
• narrow angle scanning antennae 0.06 deg

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Propulsion

• Fine control mN - thrust
• Coarse control mN - thrust
• FEEP - Field Emission Electric Propulsion
• Cold gas

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Micro propulsion
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Preliminary Mission Analysis
Mission analysis initiated with ESOC.
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IRSI - Darwin Nuller at L2
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• Completed system studies
• Alcatel (1997 ? mid 00)
• Seven spacecraft in formation
• Launched to L2 by Ariane5
• Mission feasible !
• ESA internal studies
• Theta-2 stellar rejection suffices
• Reducing number of collectors
• Dual launch feasible
• Two Soyuz could be used
• Multi Axial Beam Combination
• New conceptual payload design
• Wavefront filtering and
• Beam combination by Single Mode Fibre
• Minimum number of collectors (3)
• 3 collectors
• 1 beam combiner

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• Current System Assessment Study
• Parallel study Alcatel and Astrium
• Phase 1 (Sep. 05 ? Spring 06)
• Review
• Requirements
• Payload
• Mission
• Trade-off
• Phase 2 (Spring 06 ? Oct. 06)
• Preliminary design
• Payload
• Spacecraft
• Redundancy philosophy
• Mission analysis
• Phase 3 (Oct. 06 ? Spring 07)
• Design consolidation
• Payload
• Spacecraft

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Launch Vehicle

• Dual Soyuz
• Cost of a Soyuz / Fregat launch vehicle assumed
  to be 40 Meuro
• Cost of A5 launch vehicle assumed to be 150
  Meuro
• The cost of Soyuz from Kourou is expected to
  increase
• Extra cost ( fuel and complexity) for
  rendez-formation not accounted for.

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• The challenges
• Technological (but no show
  stoppers!)
• Nanometer and milli-arcsecond beam control
• Optical path length control lt 1 nm
• Beam intensity matching lt 1
• Formation flying
• 4 (or more) spacecraft in close formation
• Correction of relative displacement and attitude
• Cryogenic payload
• Passive cooling to 40K of optical elements
• Detector operating at 6-8K
• Funding (major
  obstacle!)

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Testing Formation Flying
Swedish precursor mission PRISMA
Possible Future Big Darwin
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The Future Planet Imager
20 x 20 pxl image of Earth at 10 pc 0.02 marcsec
pxls 6250 km baselines
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Possible Architecture Planet Imager
Densified pupil supertelescope
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and fly it in space
or pack down the VLA
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Thanks !
cold gas micro propulsion Courtesy Lasse
Stenmark, Ångström Lab, Uppsala