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C ESO 1997 Working Group on Extra-Solar Planets The ESO 1997 Working Group on the Detection of Extra-Solar Planets consisted of 16 members, and met on four occasions during 1996 and 1997. The assignment was to ‘advise ESO [...] on how to help designing a competitive strategy in this field that is predicted to expand dramatically in the next years, and to become one of the leading fields of astronomy in the next century.’ The 1997 Working Group and its task were somewhat comparable to the current effort, with the notable difference that this time the Working Group was asked to provide recommendations to both ESA and ESO, thereby encompassing both space- and ground-based astronomy. This appendix looks briefly at the findings and recommendations of their final report, published on 10 September 1997. This may provide some understanding of why some recommendations were successfully implemented while others were not, and what lessons can be learned from the past. In the introduction of their report the 1997 Working Group states: ‘Only by allocating a major fraction of time on some of its telescopes and developing new technology — and doing it now – will ESO fully exploit its potential in this field and be truly competitive.’ They then laid out their plan to achieve this goal. They identified six areas in which ESO could play a critical role, namely: radial velocity searches, narrowangle astrometry, microlensing, direct detection, transits and timing of eclipses. The recommendations, planned timeframe, and status and achievements of each of these is summarised in Table 10. Radial Velocity Searches: The main recommendation was to devote a major fraction of the observing time at the CAT and the 3.6 m to monitor the radial velocities of about 1000 stars over the next 5–10 years. They called for the development of a dedicated spectrograph providing an accuray of about 1 m/s. Such a survey was considered indispensable to provide targets for VLTI which was assumed to become operational by 2002. They also advocated high-fidelity calibration of the iodine cell for UVES and the timely development of CRIRES to provide a survey using twilight observations in order to obtain complimentary information in the IR. Narrow-Angle Astrometry: The Working Group considered astrometry a very attractive method for the study of planets because it allows for determination of orbits and planet masses directly. It was considered complimentary to other search methods exploring different regions of parameter space. Achieving an accuracy of about 10 micro-arcsec was considered feasible. Realisation of the technique was regarded as technically very challenging, requiring knowledge of the length of the baseline to within 50 µm and the knowledge of the delay between the two stars with 5 nm precision over a 100 m baseline. 79
Microlensing: Microlensing was identified as a method which is in principle able to detect Earth-mass planets. Since searches for Jovian planets were already in the development phase in 1997 the Working Group suggested that ESO should focus on detecting Earth-mass planets. They suggested that a dedicated 2.5 m telescope should monitor the bulge with a large (1 ◦ ) field detector (16k by 16k CCD) during a 120 night season. It would observe a few million uncrowded stars achieving 1 % photometric accuracy reaching V = 20 in a 4-minute exposure. A high sampling rate is crucial to obtain the characteristic of the short (5 hr) planet event on the microlensing light curve. No specific time frame was given but the Working Group called for an aggressive ESO-based campaign. When VST/OmegaCam becomes operational in 2006, the technical capabilities for the above programme will be available. Microlensing searches for Earth-mass planets, though, are not part of the major science goals for VST/OmegaCam. Direct Detection: Direct detection was considered essential for deriving many physical properties of extra-solar plants such as size, temperature, chemical composition etc. The Working Group stressed that it would be extremely challening to achieve the required contrast levels in particular from the ground. They identified a very powerful adaptive optics system as a key ingredient in combination with coronographic instrumentation and sophisticated data processing. They pointed out that spectroscopic signatures of planetary atmospheres should be detectable with high-resolution spectroscopy in the NIR (CRIRES) via their time-dependent Doppler shift. Other spectral features will be unique to the planet and therefore appear as ‘alien’ features in the stellar spectrum. They called for further studies of instrumental requirements, and an early realization of an instrument like CRIRES. Transits and Timing Eclipses: The Working Group noted the potential of this method for detecting planets down to Uranus size, along with planets with rings and moons of giant planets. They mention the possibility of obtaining spectra of planets’ atmospheres during transits. They also noted that timing of eclipses in binary stars was a simple method for detecting giant planets in these systems. 80
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Report by the ESA-ESO Working Group
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The working group membership was es
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3.2.2 The Darwin Ground-Based Precu
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Figure 1: Detection methods for ext
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those with masses between about 0.5
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Figure 2: Detection domains for met
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(c) Astrometric measurements do not
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chemical composition of the primord
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Table 2: A summary of planned or op
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Table 3: A summary of completed, op
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