search for extra-terrestrial planets: the darwin mission - target stars and array architectures

177 Pages·2005·9.03 MB·English

SEARCH FOR EXTRA-TERRESTRIAL PLANETS:
THE DARWIN MISSION
-
TARGET STARS AND ARRAY ARCHITECTURES
________________________________________________________________________

Dissertation

zur Erlangung des akademischen Grades
DOCTOR RERUM NATURALIUM

an der
NATURWISSENSCHAFTLICHEN UNIVERSITAET
der KARL-FRANZENS UNIVERSITAET GRAZ
INSTITUT FUER GEOPHYSIK, ASTROPHYSIK UND METEOROLOGIE

vorgelegt von
Mag. Dipl. Ing. Lisa Kaltenegger

begutachtet von
Univ-Prof. Dr. Arnold Hanslmeier
und
Univ.-Prof. Dr. Theo Neger

@2004

To my parents
who taught me curiosity about this world and to follow my dreams
most of the DARWIN team: Lisa, Roland, Lothar, Mikael, Malcolm, Luigi, Anders, Olivier
Special Thanks to
Anders and Malcolm for their enthusiasm, constructive comments, motivations, time to
discuss and iterate ideas and their support
The DARWIN team for the enthusiasm and spirit even if times got too busy to sleep much
Prof Hanslmeier for his interest in new fields of research, his support and for giving me
the possibility to undertake my research on this fascinating topic
Frank Selsis for providing comments and teaching me much about atmospheres
Oliver Absil, Wes Traub, Adam Burrows and Jim Kasting for interesting discussions
Mikael and the Dc0 corridor for filling work in the small office with fun & laughter
Christian and Luigi for always having 5min to discuss

my friends for locating me anywhere in the world to pass by for a cup of coffee & a talk
wherever I happen to be
Maria for getting this document printed 1000km away & for sharing her breakfast
Kotska and Rachel for always having a cup of tea for me, whatever the hour
Iris and Claudia for making me smile even when I did not get much sleep, a smile that
always came with cyber-caffeine

the Dekanat at the KF-University Graz for accepting unconventional forms of
transmission of documents and for their friendly information service
List of acronyms

AO Adaptive optics
AU Astronomical unit
BB Black body
BC Beam combining
BCS Beam combining scheme
BD Brightness distribution
CHZ Contiuously habitable zone
DNA Desoxy-ribonucleine acid
EGP Extrasolar giant planet
ESA European space agency
FOV Field of View
FT Fourier transform
FWHM Full Width Half Minimum
GENIE Ground-based European Nulling Interferometer Experiment
Gpa Giga-pascal
Gyr Giga-year
Hd Habitable distance
HST Hubble space telescope
HZ Habitable zone
IAC Institute of Astrophysics of the Canary Islands
IO Integrated optics
IR Infrared
LZ Local zodiacal
L2 Second Lagrangian point
M Mass
MBI Multi beam injection
MM Modulation Map
MMZ Modified Mach Zehnder
Mpa Mega-Pascal
Myr Mega-year
NIR Near infrared
NM Nulled output map
OPD Optical path delay
PAL Present atmospheric level
Pc Parsec
PSF Point Spread Function
RNA Ribonucleine acid
SNR Signal to noise ratio
SWG Science working group
T Transmission factor
TM Transmission maps
TOA Time of arrival
TPF Terrestrial planet finder
VLTI Very large telescope Interferometer
VRE Vegetation red edge
WFE Wave front error
1 EXTRASOLAR PLANET SEARCH, FORMATION OF PLANETS AND
CHARACTERISTICS 4
1.1 INTRODUCTION 5
1.2 STELLAR AND SUB-STELLAR OBJECTS 5
1.2.1 BROWN DWARFS AND EXTRASOLAR PLANETS 6
1.3 EVOLUTION OF SUBSTELLAR MASS OBJECTS 7
1.3.1 ATMOSPHERE MODELS AND SPECTROSCOPIC CHARACTERISTICS 9
1.3.2 JUPITER AND GL229 B 10
1.3.3 EXTRASOLAR GIANT PLANETS 10
1.4 PLANETARY SYSTEM FORMATION 13
1.4.1 FORMATION THEORIES OF OUR SOLAR SYSTEM 15
1.5 EGP FORMATION 16
1.5.1 TERRESTRIAL PLANET FORMATION 18
1.5.2 DISK GAPS CLEARED BY PLANETS 20
1.5.3 ORBITAL MIGRATION 21
1.5.4 THEORY OF MIGRATION DUE TO TIDAL DISK FORCES 21
1.5.5 STABILITY CRITERIA FOR ORBITAL CONFIGURATIONS 22
1.5.6 ENVIRONMENT OF PROTOPLANETARY EVOLUTION 23
1.5.7 DIFFERENT OBSERVABLE FEATURES OF PLANET FORMATION SCENARIOS 23
1.5.8 STELLAR METALLICITY PLANET CONNECTION 24
1.6 DETECTED EGPS 24
1.6.1 MULTIPLE PLANETARY SYSTEMS 27
1.6.2 UPSILON ANDROMEDAE 27
1.6.3 55 CANCRI SYSTEM 28
1.6.4 PLANETS IN MULTIPLE STAR SYSTEMS 29
2 TARGET SELECTION FOR DARWIN 30
2.1 SELECTION CRITERIA 31
2.2 DIFFERENT ISSUES DISCUSSED FOR STAR TARGET SELECTION 33
2.3 HABITABLE DISTANCE 34
2.4 DETAILED INFORMATION ON THE STARS 34
3 DETAILS ON THE DARWIN TARGET STARS AND OVERALL STATISTICS 35
3.1 ADDITIONAL SELECTION CRITERIA 36
3.2 OVERALL STATISTICS 38
3.3 BINARIES AND HIGH PROPER MOTION STARS: 41
3.4 ANGULAR EXTEND OF THE CLOSEST 10 STARS IN EACH STELLAR CLASS AND THE
CORRESPONDING HABITABLE DISTANCE 41
3.5 ANGULAR EXTENT OF THE CLOSEST 40 STARS AND THE CORRESPONDING HABITABLE
DISTANCE 45
3.6 ANGULAR EXTEND OF THE CLOSEST 40 G STARS AND THE CORRESPONDING HABITABLE
DISTANCE 49
3.7 ANGULAR EXTEND OF THE COMPLETE SAMPLE OF TARGET STARS AND THE CORRESPONDING
HABITABLE DISTANCE 51
4 DETAILS OF TARGET STARS BY STELLAR SUBGROUP 51
4.1 F TARGET STARS 51
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4.2 G TARGET STARS: 53
4.3 K TARGET STARS 55
4.4 M TARGET STARS 57
4.5 CALCULATION OF BASIC STELLAR DATA: INTERPOLATION MODEL 60
5 DARWIN MISSION TARGETS 61
6 HABITABILITY 63
6.1 DEVELOPMENT OF LIFE ON EARTH 63
6.2 SEARCH FOR LIFE 63
6.3 ORIGIN OF LIFE 64
6.4 CIRCUMSTELLAR HABITABLE ZONES 66
6.4.1 HZ AROUND DIFFERENT STELLAR TYPES 68
6.4.2 GREENHOUSE GASSES 69
6.4.3 NEOPROTEROZOIC EARTH 69
7 FEATURES OF A HABITABLE PLANET 70
7.1 CHARACTERIZATION OF A PLANET 70
7.2 SPECTRA 71
7.2.1 INFLUENCE OF CLOUD COVERAGE 72
7.3 VISIBLE & IR 73
7.3.1 S/N RATIO OF A DIRECT DETECTION OF AN EARTHLIKE PLANET 74
7.3.2 THE EFFECTIVE AND SURFACE TEMPERATURES 74
7.4 DETERMINING PLANET CHARACTERISTICS 76
7.4.1 PLANET CHARACTERISTICS IN THE IR 76
7.4.2 PLANETS CHARACTERISTICS IN THE VISIBLE 77
7.5 BIOMARKERS 78
7.5.1 BIOMARKERS IN THE IR 78
7.5.1.1 Silicate in the IR 79
7.5.1.2 Simulated IR spectra around different host stars 80
7.5.2 BIOMARKERS IN THE VISIBLE AND NEAR-IR 80
7.5.3 SURFACE FEATURES AS BIOMARKERS IN THE VISIBLE 81
7.5.3.1 The red edge 81
7.5.4 OXYGEN AND OZONE AS SPECTRAL SIGNATURE OF LIFE 84
7.5.4.1 False positive detections 85
7.6 EFFECTS OF DUST RINGS AND MOONS 85
7.7 ECCENTRIC ORBITS AND HABITABLE MOONS 86
7.8 ROCKY MOONS IN THE HZ 86
7.9 EARTH 87
7.9.1 CARBONATE-SILICATE CYCLE 87
7.9.2 EARTH CHANGED PLACE WITH VENUS 88
7.9.3 MIGRATING NEPTUNE PLANETS 88
7.9.4 EVOLUTION OF THE XUV FLUX WITH TIME 89
7.10 SUMMARY: INDICATORS OF HABITABILITY AND BIOLOGICAL ACTIVITY 90
8 DETECTION METHODS 92
8.1 DIRECT IMAGING 93
8.2 DIRECT IMAGING 93
8.2.1 "PSF SUBTRACTION" 94
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8.3 INTERFEROMETER 95
8.3.1 NULLING INTERFEROMETRY 95
8.4 GROUND BASED VERSUS SPACE BASED 97
9 INTERFEROMETRY 98
9.1 PUPIL PLANE INTERFEROMETRY 98
9.2 BASIC EQUATIONS FOR AN INTERFEROMETER ARRAY 98
9.3 EVALUATION OF A TRANSMISSION MAP 100
9.4 MODULATE A PLANETARY SIGNAL. 103
9.4.1 SIGNAL MODULATION 103
9.4.2 INTERNAL MODULATION 103
9.4.3 INHERENT MODULATION 104
9.5 MODULATION OF A PLANETARY SIGNAL ξξξξ (PLANMOD) 105
9.5.1 MODULATION USING SUB-INTERFEROMETERS 106
9.6 DETECTED SIGNAL AND TRANSMISSION VALUE 107
9.7 BEAM-COMBINING SCHEME EFFICIENCY (BCS EFFICIENCY) 108
9.8 OPTICAL FILTERING OF THE BEAMS 109
9.8.1 SINGLE MODE COUPLING THEORY 110
9.9 INTEGRATED OPTICS BEAM COMBINER 111
9.10 STARLIGHT REJECTION ρρρρ 112
STAR
9.11 IMAGE-PLANE INTERFEROMETRY 112
9.12 MODULATION USING ROTATION OF THE ARRAY 114
9.13 NOTES ON MODULATION OF A PLANETARY SIGNAL 115
9.14 NORMALIZATION 115
10 CHARACTERIZATION OF DIFFERENT PROPOSED CONFIGURATIONS 117
10.1 BACKGROUND FLUX 117
10.2 TRANSMISSION AND MODULATION PROPERTIES 118
10.3 PLANET LOCATION 120
10.4 SIGNALS OF MULTIPLE PLANETS 121
10.5 WAVELENGTH DEPENDENCE 123
10.6 ANGULAR EXTENT OF THE HABITABLE ZONE FOR THE PRIME DARWIN TARGETS 126
10.7 OVERVIEW CONFIGURATIONS 128
10.7.1 CHARACTERISTICS BOWTIE 132
10.7.2 MODIFIED DUAL CHOPPED BRACEWELL (DETAILED EXAMPLE CALCULATIONS) 137
10.7.3 LINEAR DOUBLE CHOPPED BRACEWELL 141
10.7.4 TTN 145
10.7.5 TCB 148
11 CONCLUSIONS 152
12 REFERENCES 154

Lisa Kaltenegger PhD thesis 2004 2
ABSTRACT

The DARWIN mission is an Infrared free flying interferometer mission based on the new
technique of nulling interferometry. Its main objective is to detect and characterize other Earth-like
planets, analyze the composition of their atmospheres and their capability to sustain life, as we know it.
DARWIN is currently in definition phase.

This PhD work that has been undertaken within the DARWIN team at the European Space
Agency (ESA) addresses two crucial aspects of the mission. Firstly, a DARWIN target star list has been
established that includes characteristics of the target star sample that will be critical for final mission
design, such as, luminosity, distance, spectral classification, stellar variability, multiplicity, location and
radius of the star. Constrains were applied as set by planet evolution theory and mission architecture.
The catalogue contains nearby stars that might harbor planets that are potentially habitable to complex
life. On the basis of theoretical studies, the angular separations of potential habitable planets from their
parent stars for the target systems have been established. The resulting target list allows to model
realistic observation scenarios for nulling interferometry and translates into architectural constraints for
the mission.

Secondly, a number of alternative mission architectures have been evaluated on the basis of
interferometer response as a function of wavelength, achievable modulation efficiency, number of
telescopes and starlight rejection capabilities. The study has shown that the core mission goals should
be achievable with a lower level of complexity as compared to the current baseline configuration.

Lisa Kaltenegger PhD thesis 2004 3