Report by the ESA–ESO Working Group on Extra-Solar Planets 4 March 2005 Summary Various techniques are being used to search for extra-solar planetary signatures, including accurate measurement of radial velocity and positional (astrometric) dis- placements, gravitational microlensing, and photometric transits. Planned space experiments promise a considerable increase in the detections and statistical know- ledge arising especially from transit and astrometric measurements over the years 2005–15, with some hundreds of terrestrial-type planets expected from transit mea- surements, and many thousands of Jupiter-mass planets expected from astrometric measurements. Beyond 2015, very ambitious space (Darwin/TPF) and ground (OWL) experiments are targeting direct detection of nearby Earth-mass planets in the habitable zone and the measurement of their spectral characteristics. Beyond these, ‘Life Finder’ (aiming to produce confirmatory evidence of the presence of life) and ‘Earth Imager’ (some massive interferometric array providing resolved images of a distant Earth) arXiv:astro-ph/0506163v1 8 Jun 2005 appear as distant visions. This report, to ESA and ESO, summarises the direction of exo-planet research that can be expected over the next 10 years or so, identifies the roles of the major facilities of the two organisations in the field, and concludes with some recommendations which may assist development of the field. The report has been compiled by the Working Group members and experts (page iii) over the period June–December 2004. Introduction & Background Following an agreement to cooperate on science planning issues, the executives of the European Southern Observatory (ESO) and the European Space Agency (ESA) Science Programme and representatives of their science advisory structures have met to share information and to identify potential synergies within their future projects. The agreement arose from their joint founding membership of EIROforum (http://www.eiroforum.org) and a recognition that, as pan-European organisations, they served essentially the same scientific community. At a meeting at ESO in Garching during September 2003, it was agreed to estab- lish a number of working groups that would be tasked to explore these synergies in important areas of mutual interest and to make recommendations to both organisa- tions. The chair and co-chair of each group were to be chosen by the executives but thereafter, the groups would be free to select their membership and to act indepen- dently of the sponsoring organisations. The first working group to be established was on the topic of Extra-Solar Planet research, both detection and physical study, over a period extending from now until around 2015. The group worked on its report from June until December 2004 and reported its conclusions and recommendations to a second ESA-ESO meeting, held at ESA HQ in Paris in February 2005. Terms of Reference and Composition The goals set for the working group were to provide: A survey of the field: this will comprise: (a) a review of the methods used • or envisaged for extra-solar planet detection and study; (b) a survey of the associated instrumentation world-wide (operational, planned, or proposed, on- ground and in space); (c) for each, a summary of the potential targets, accuracy and sensitivity limits, and scientific capabilities and limitations. An examination of the role of ESO and ESA facilities: this will: (a) identify • areas in which current and planned ESA and ESO facilities will contribute; (b) analyse the expected scientific returns and risks of each; (c) identify areas of potential scientific overlap, and thus assess the extent to which the facilities complement or compete; (d) identify open areas which merit attention by one or both organisations (for example, follow-up observations by ESO to maximise the return from other major facilities); (e) conclude on the scientific case for the very large facilities planned or proposed. ii The working group membership was established by the chair and co-chair: the re- port is not a result of consultation with the community as a whole. The experts contributed considerable information for the report, but the conclusions and recom- mendations are the responsibility of the members. Chair: Michael Perryman ESA Co-Chair: Olivier Hainaut ESO Members: Dainis Dravins Lund Alain L´eger IAS Andreas Quirrenbach Leiden Heike Rauer DLR ECF support: Florian Kerber ESO–ECF Bob Fosbury ESA–ECF Experts: Fran¸cois Bouchy OHP Marseilles COROT Fabio Favata ESA Eddington Malcolm Fridlund ESA Darwin Roberto Gilmozzi ESO OWL Anne-Marie Lagrange LAOG Grenoble Planet Finder Tsevi Mazeh Tel Aviv Transits Daniel Rouan Obs de Paris-Meudon Genie Stephane Udry Gen`eve Radial velocity Joachim Wambsganss Heidelberg Microlensing Catherine Cesarsky (ESO) Alvaro´ Gim´enez Ca˜nete (ESA) March 2005 iii Contents 1 Survey of the Field 1 1.1 Introduction................................ 1 1.2 The Search for Earth-Mass Planets and Habitability . 2 1.3 PresentLimits:GroundandSpace . 5 2 The Period 2005–2015 9 2.1 GroundObservations: 2005–2015 . 9 2.1.1 Radial Velocity Searches . 9 2.1.2 TransitSearches.......................... 12 2.1.3 ReflectedLight .......................... 17 2.1.4 Microlensing Searches . 17 2.1.5 Astrometry ............................ 20 2.1.6 DirectDetection ......................... 22 2.1.7 OtherSearches .......................... 27 2.2 SpaceObservations: 2005–2015 . 28 2.2.1 Space Transit Measurements: COROT, Kepler and Eddington 28 2.2.2 SpaceAstrometryMissions: GaiaandSIM . 30 2.2.3 Space-BasedMicrolensing: MPF. 32 2.2.4 Other Space Missions: JWST, Spitzer, SOFIA . 34 2.3 SummaryofProspects2005–2015 . 38 3 The Period 2015–2025 40 3.1 GroundObservations: 2015–2025 . 40 3.1.1 OWL/ELT ............................ 40 3.1.2 ObservationsatanAntarcticSite . 44 3.2 SpaceObservations: 2015–2025 . 48 3.2.1 Darwin............................... 48 iv 3.2.2 The Darwin Ground-Based Precursor: GENIE . 51 3.2.3 TerrestrialPlanetFinder(TPF) . 52 3.3 ESAThemes:2015–2025. .. .. 53 3.4 OtherConceptsandFuturePlans . 56 3.5 SummaryofProspects: 2015–2025. 57 4 The Role of ESO and ESA Facilities 59 4.1 TheExpectedDirectionofResearch. 59 4.2 Follow-UpObservations . .. .. 60 4.2.1 High-MassPlanets ........................ 60 4.2.2 Low-MassPlanets......................... 62 4.2.3 Summary of Follow-Up Facilities Required . 63 4.3 Statistics of Exo-Planets: Implications for Darwin/OWL . 64 4.4 Astrophysical Characterisation of Host Stars . .. 65 4.4.1 ADedicatedSpectralSurvey. 65 4.5 PotentialOverlapandCompetition . 66 4.6 Open Areas: Survey Mission Beyond Kepler/Eddington . 68 4.7 OtherConsiderations........................... 68 4.7.1 FundamentalPhysicalData . 68 4.7.2 FundamentalPlanetaryData . 69 4.7.3 AmateurNetworks ........................ 69 5 Recommendations 72 Appendices 75 A Space Precursors: Interferometers, Coronographs and Apodizers 75 B Beyond 2025: Life Finder and Planet Imager 77 C ESO 1997 Working Group on Extra-Solar Planets 79 v vi 1 Survey of the Field 1.1 Introduction The field of exo-planet research has exploded dramatically since the discovery of the first such systems in 1995. Underlying this huge interest three main themes of exo-planet research can be identified: (a) characterising and understanding the planetary populations in our Galaxy; (b) understanding the formation and evolution of planetary systems (e.g., accretion, migration, interaction, mass-radius relation, albedo, distribution, host star properties, etc.); (c) the search for and study of biological markers in exo-planets, with resolved imaging and the search for intelligent life as ‘ultimate’ and much more distant goals. Detection methods for extra-solar planets can be broadly classified into those based on: (i) dynamical effects (radial velocity, astrometry, or timing in the case of the pul- sar planets); (ii) microlensing (astrometric or photometric); (iii) photometric signals (transits and reflected light); (iv) direct imaging from ground or space in the optical or infrared; and (v) miscellaneous effects (such as magnetic superflares, or radio emission). Each have their strengths, and advances in each field will bring specific and often complementary discovery and diagnostic capabilities. Detections are a pre-requisite for the subsequent steps of detailed physical-chemical characterisation demanded by the emerging discipline of exo-planetology. As of December 2004, 135 extra-solar planets have been discovered from their ra- dial velocity signature, comprising 119 systems of which 12 are double and 2 are triple. One of these planets has also been observed to transit the parent star. Four additional confirmed planets have been discovered through transit detections using data from OGLE (and confirmed through radial velocity measurements), and one, TrES-1, using a small 10-cm ground-based telescope. One further, seemingly reli- able, planet candidate has been detected through its microlensing signature. The planets detected to date (apart from those surrounding radio pulsars, which are not considered further in this report) are primarily ‘massive’ planets, of order 1 MJ, but extending down to perhaps 0.05 MJ (around 15 M⊕) for three short-period systems, although the inclination (and hence true mass) of two of these is unknown1. Detection methods considered to date are summarised in Figure 1, which also gives an indication of the lower mass limits which are likely to be reached in the foreseeable future for each method. More information and ongoing projects