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While confidence is developing in statistical distributions of planets above about 0.05 M J , the occurrence of lower-mass, and specifically Earth-mass planets remains a matter for speculation. In this spirit, the lower range of detection limits for lowmass planets for Kepler, Eddington and SIM is indicated in the table as 0. While these transit and astrometric discovery predictions must therefore be taken with certain caveats, they promise a major advance in the detection and knowledge of the statistical properties of a wide range of exo-planets: ranging from massive (Jupiter-mass) planets in long-period (Jupiter-type) orbits, and the occurrence and properties of multiple systems (via astrometry), through to Earth-mass planets in the habitable zone (via transits or microlensing). 39
3 The Period 2015–2025 3.1 Ground Observations: 2015–2025 3.1.1 OWL/ELT The 100-m diameter Overwhelmingly Large Telescope (OWL) is being studied by ESO. S/N = 10 will be reached at 35 mag (t = 1 hr) for imaging, and at 30 mag for R = 1000 spectroscopy (t = 3 hr). The resolution, λ/D ∼ 1 milli-arcsec in the V-band, is a factor 40 improvement over HST. Detection of Earth-mass exo-planets is part of the scientific case for the 100 m OWL/ELT project (see the on-line case for the European Large Telescope, ELT, at www-astro.physics.ox.ac.uk/∼imh/ELT, from which some of the following has been taken). This section focuses on the science case and technical issues for Earth-mass planet detection. For this, OWL must be equipped with advanced adaptive optics systems to compensate for atmospheric seeing and the production of a near-diffraction limited image or image core, expected to deliver Strehl ratios S (the peak image brightness relative to that in a near-perfect image) from several to many tens of percent. In the near-infrared (1–5 µm), values near 90% may be attainable, and are needed for planet detection. Ultimate detection capabilities depend sensitively on whether such high Strehl ratios can be delivered in practice (such advanced AO systems do not yet exist). In addition, the telescope design (e.g. number and shape of elements) has an impact on the final image quality, even with co-phasing techniques, so that the exo-planet objectives must be considered early in the project. Applied to a nearby solar-type star, adaptive optics produces an image with several components. A central ‘spike’ resembling a diffraction-limited image contains some S per cent of the total light, less a modest fraction diverted into the other, widerspread components of the telescope point-spread function. The spike is surrounded by a residual halo containing the remaining light distributed like an unmodified seeing disc, i.e. with a generally Lorentzian distribution. This halo overlies, and within the seeing disk generally dominates, the fainter wings of the telescope point-spread function. These wings combine the light diffused by the small-scale imperfections of the optics and the accumulated dust, as well as the light diffracted by the central obstruction and geometric edges (mirrors, and supporting structures in the beam). The diffraction pattern is strongly dominated by the secondary mirror supporting structure, and by the edges of the mirror segments, which also produce strong secondary peaks. The diffracted light can locally strongly dominate the uncorrected seeing light. The detailed structure of the halos in adaptive optics-corrected images is still being explored. At large radii they are composed of the rapidly varying diffraction-spot-sized ‘classical’ speckles. Less well-understood ‘super-speckles’ occur closer to the first 2– 3 diffraction rings; larger, brighter, less rapidly variable and therefore less likely to 40
Page 2 and 3: Report by the ESA-ESO Working Group
Page 4 and 5: The working group membership was es
Page 6: 3.2.2 The Darwin Ground-Based Precu
Page 9 and 10: Figure 1: Detection methods for ext
Page 11 and 12: those with masses between about 0.5
Page 13 and 14: Figure 2: Detection domains for met
Page 15 and 16: (c) Astrometric measurements do not
Page 17 and 18: Table 1: A summary of completed, op
Page 19 and 20: chemical composition of the primord
Page 21 and 22: Table 2: A summary of planned or op
Page 23 and 24: it passes behind the star. They arg
Page 25 and 26: shapes caused by extra-solar planet
Page 27 and 28: Table 3: A summary of completed, op
Page 29 and 30: ground requires simultaneous observ
Page 31 and 32: 0.35 arcsec of the centre, i.e. muc
Page 33 and 34: ferential phase observations with a
Page 35 and 36: 2.2 Space Observations: 2005-2015 I
Page 37 and 38: larger number of hot Jupiters would
Page 39 and 40: (Shao): this major SIM survey progr
Page 41 and 42: The planetary lensing events have a
Page 43 and 44: siting extra-solar planets are expe
Page 45: 2.3 Summary of Prospects 2005-2015
Page 49 and 50: Table 6: Magnitudes and separations
Page 51 and 52: per star in order to sample the (po
Page 53 and 54: een produced, diffraction effects c
Page 55 and 56: 3.2 Space Observations: 2015-2025 T
Page 57 and 58: Table 8: Detection capabilities: Ea
Page 59 and 60: 3.2.3 Terrestrial Planet Finder (TP
Page 61 and 62: ∼ 5 × 10 5 m, or 1.5 × 10 −4
Page 63 and 64: of Earth-like planets in general, a
Page 66 and 67: 4 The Role of ESO and ESA Facilitie
Page 68 and 69: Figure 7: Links between detection m
Page 70 and 71: 4.2.3 Summary of Follow-Up Faciliti
Page 72 and 73: 4.4 Astrophysical Characterisation
Page 74 and 75: Without any further mission dedicat
Page 76 and 77: and their suitability for supportin
Page 78 and 79: overlap of public and research inte
Page 80 and 81: 2.4. Evaluate observation time for
Page 82 and 83: A Space Precursors: Interferometers
Page 84 and 85: B Beyond 2025: Life Finder and Plan
Page 86 and 87: C ESO 1997 Working Group on Extra-S
Page 88 and 89: Table 10: ESO Working Group 1997: R
Page 90 and 91: Charbonneau, D., Brown, T. M., Noye
Page 92 and 93: Pedretti, E., Labeyrie, A., Arnold,

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