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Echo Exoplanet Characterisation Observatory Exp Astron (2012) 34:311–353 DOI 10.1007/s10686-012-9303-4 ORIGINAL ARTICLE EChO Exoplanet characterisation observatory G. Tinetti · J. P. Beaulieu · T. Henning · M. Meyer · G. Micela · I. Ribas · D. Stam · M. Swain · O. Krause · M. Ollivier · E. Pace · B. Swinyard · A. Aylward · R. van Boekel · A. Coradini · T. Encrenaz · I. Snellen · M. R. Zapatero-Osorio · J. Bouwman · J. Y-K. Cho · V. Coudé du Foresto · T. Guillot · M. Lopez-Morales · I. Mueller-Wodarg · E. Palle · F. Selsis · A. Sozzetti · P. A. R. Ade · N. Achilleos · A. Adriani · C. B. Agnor · C. Afonso · C. Allende Prieto · G. Bakos · R. J. Barber · M. Barlow · V. Batista · P. Bernath · B. Bézard · P. Bordé · L. R. Brown · A. Cassan · C. Cavarroc · A. Ciaravella · C. Cockell · A. Coustenis · C. Danielski · L. Decin · R. De Kok · O. Demangeon · P. Deroo · P. Doel · P. Drossart · L. N. Fletcher · M. Focardi · F. Forget · S. Fossey · P. Fouqué · J. Frith · M. Galand · P. Gaulme · J. I. González Hernández · O. Grasset · D. Grassi · J. L. Grenfell · M. J. Griffin · C. A. Griffith · U. Grözinger · M. Guedel · P. Guio · O. Hainaut · R. Hargreaves · P. H. Hauschildt · K. Heng · D. Heyrovsky · R. Hueso · P. Irwin · L. Kaltenegger · P. Kervella · D. Kipping · T. T. Koskinen · G. Kovács · A. La Barbera · H. Lammer · E. Lellouch · G. Leto · M. A. Lopez Valverde · M. Lopez-Puertas · C. Lovis · A. Maggio · J. P. Maillard · J. Maldonado Prado · J. B. Marquette · F. J. Martin-Torres · P. Maxted · S. Miller · S. Molinari · D. Montes · A. Moro-Martin · J. I. Moses · O. Mousis · N. Nguyen Tuong · R. Nelson · G. S. Orton · E. Pantin · E. Pascale · S. Pezzuto · D. Pinfield · E. Poretti · R. Prinja · L. Prisinzano · J. M. Rees · A. Reiners · B. Samuel · A. Sánchez-Lavega · J. Sanz Forcada · D. Sasselov · G. Savini · B. Sicardy · A. Smith · L. Stixrude · G. Strazzulla · J. Tennyson · M. Tessenyi · G. Vasisht · S. Vinatier · S. Viti · I. Waldmann · G. J. White · T. Widemann · R. Wordsworth · R. Yelle · Y. Yung · S. N. Yurchenko Received: 30 April 2011 / Accepted: 9 May 2012 / Published online: 2 August 2012 © Springer Science+Business Media B.V. 2012 G. Tinetti (B) · A. Aylward · N. Achilleos · R. J. Barber · M. Barlow · C. Danielski · P. Doel · S. Fossey · P. Guio · S. Miller · R. Prinja · G. Savini · L. Stixrude · J. Tennyson · M. Tessenyi · S. Viti · I. Waldmann · S. N. Yurchenko University College London, London, UK e-mail: [email protected] J. P. Beaulieu · V. Batista · A. Cassan · J. P. Maillard · J. B. Marquette Institut d’Astrophysique de Paris, Paris, France J. P. Beaulieu e-mail: [email protected] 312 Exp Astron (2012) 34:311–353 Abstract A dedicated mission to investigate exoplanetary atmospheres repre- sents a major milestone in our quest to understand our place in the universe by placing our Solar System in context and by addressing the suitability of planets for the presence of life. EChO—the Exoplanet Characterisation Observatory—is a mission concept specifically geared for this purpose. EChO will provide simultaneous, multi-wavelength spectroscopic observations on a stable platform that will allow very long exposures. The use of passive cooling, few moving parts and well established technology gives a low-risk and potentially long-lived mission. EChO will build on observations by Hubble, Spitzer and ground-based telescopes, which discovered the first molecules and atoms in exoplanetary atmospheres. However, EChO’s configuration and specifications are designed to study a number of systems in a consistent manner that will eliminate the ambiguities affecting prior observations. EChO will simultaneously observe a broad enough spectral region—from the visible to the mid-infrared—to constrain from one single spectrum the temperature structure of the atmosphere, the abundances of the major carbon and oxygen T. Henning · O. Krause · R. van Boekel · J. Bouwman · C. Afonso · U. Grözinger · L. Kaltenegger · Max Planck Institut fur Astronomie, Heidelberg, Germany T. Henning e-mail: [email protected] M. Meyer · K. Heng Eidgenossische Technische Hochschule, Zurich, Switzerland M. Meyer e-mail: [email protected] G. Micela · A. Coradini · A. Sozzetti · A. Adriani · A. Ciaravella · D. Grassi · A. La Barbera INAF, Palermo, Roma, Torino, Italy G. Micela e-mail: [email protected] I. Ribas IEEC-CSIC, Institut de Ciencies de l’Espai, Barcelona, Spain e-mail: [email protected] D. Stam · R. De Kok SRON Netherlands Institute for Space Research, Utrecht, Netherlands D. Stam e-mail: [email protected] M. Swain · L. R. Brown · P. Deroo · G. S. Orton · G. Vasisht Jet Propulsion Laboratory, Pasadena, CA, US M. Swain e-mail: [email protected] M. Ollivier · P. Bordé · C. Cavarroc · O. Demangeon · P. Gaulme · B. Samuel Institut d’Astrophysique Spatiale, Orsay, France Exp Astron (2012) 34:311–353 313 bearing species, the expected photochemically-produced species and magne- tospheric signatures. The spectral range and resolution are tailored to separate bands belonging to up to 30 molecules and retrieve the composition and temperature structure of planetary atmospheres. The target list for EChO includes planets ranging from Jupiter-sized with equilibrium temperatures Teq up to 2,000 K, to those of a few Earth masses, with Teq ∼ 300 K. The list will include planets with no Solar System analog, such as the recently discovered planets GJ1214b, whose density lies between that of terrestrial and gaseous planets, or the rocky-iron planet 55 Cnc e, with day-side temperature close to 3,000 K. As the number of detected exoplanets is growing rapidly each year, and the mass and radius of those detected steadily decreases, the target list will be constantly adjusted to include the most interesting systems. We have baselined a dispersive spectrograph design covering continuously the 0.4–16 μm spectral range in 6 channels (1 in the visible, 5 in the InfraRed), which allows the spectral resolution to be adapted from several tens to several hundreds, depending on the target brightness. The instrument will be mounted behind a 1.5 m class telescope, passively cooled to 50 K, with the instrument structure and optics passively cooled to ∼45 K. EChO will be placed in a grand E. Pace · M. Focardi · S. Molinari Un. Firenze, Florence, Italy B. Swinyard UCL-RAL, Didcot, UK T. Encrenaz · V. Coudé du Foresto · B. Bézard · A. Coustenis · P. Drossart · P. Kervella · E. Lellouch · N. Nguyen Tuong · J. M. Rees · B. Sicardy · S. Vinatier · T. Widemann LESIA, Obs. de Paris, Meudon, France I. Snellen University of Leiden, Leiden, The Netherlands M. R. Zapatero-Osorio · F. J. Martin-Torres · A. Moro-Martin · J. Sanz Forcada CAB, Madrid, Spain J. Y-K. Cho · C. B. Agnor · R. Nelson QMUL, London, Uk T. Guillot Obs. Nice, Nice, France M. Lopez-Morales IEEC, Bellaterra, Spain I. Mueller-Wodarg · M. Galand Imperial College, London, UK E. Palle · C. Allende Prieto · J. I. González Hernández IAC, Tenerife, Spain F. Selsis Un. Bordeaux, Bordeaux, France 314 Exp Astron (2012) 34:311–353 halo orbit around L2. This orbit, in combination with an optimised thermal shield design, provides a highly stable thermal environment and a high degree of visibility of the sky to observe repeatedly several tens of targets over the year. Both the baseline and alternative designs have been evaluated and no critical items with Technology Readiness Level (TRL) less than 4–5 have been identified. We have also undertaken a first-order cost and development plan analysis and find that EChO is easily compatible with the ESA M-class mission framework. Keywords Exoplanets · Planetary atmospheres · Space mission 1 Introduction The Exoplanet Characterisation Observatory, or EChO, is a proposed M class mission currently under assessment by the European Space Agency P. A. R. Ade · M. J. Griffin · E. Pascale Cardiff University, Cardiff, UK G. Bakos Princeton, NJ, USA P. Bernath · R. Hargreaves University of York, York, UK C. Cockell ROE, Edinburgh, UK L. Decin IvS, Leuven, Belgium L. N. Fletcher · P. Irwin University of Oxford, Oxford, UK F. Forget · R. Wordsworth LMD, Paris, France P. Fouqué Obs-MIP, Toulouse, France J. Frith · D. Pinfield UH, Hatfield, UK O. Grasset Un. Nantes, Nantes, France J. L. Grenfell TUB, Berlin, Germany C. A. Griffith · T. T. Koskinen · R. Yelle UoA, Tucson, AZ, USA Exp Astron (2012) 34:311–353 315 (ESA) (http://sci.esa.int/echo). In this article we present scientific and technical information about the proposed satellite. 1.1 Scientific objectives The scientific objectives of EChO are to: 1. Measure the atmospheric composition, temperature and albedo of a highly representative sample of known extrasolar planets, orbiting different stellar types (A, F, G, K and M). The sample will include hot, warm, and habitable-zone exoplanets, down to the super-Earth size (∼1.5 Earth radii). The climate of a planet depends on the amount of stellar irradiation reflected out to space and absorbed. The combination of visible albedo and infrared temperature will be key to understanding how the energy is redistributed (Figs. 1 and 2). M. Guedel Un. Vienna, Vienna, Austria O. Hainaut ESO, La Silla, Chile P. H. Hauschildt HS, Hamburg, Germany D. Heyrovsky CU Prague, Prague, Czech Republic R. Hueso · A. Sánchez-Lavega EHU Bilbao, Bilbao, Spain D. Kipping · D. Sasselov CfA-UCL, CfA, Cambridge, MA, US G. Kovács Konkoly Obs., Budapest, Hungary H. Lammer Un. Graz, Graz, Austria G. Leto · G. Strazzulla INAF/OACt, Catania, Italy M. A. Lopez Valverde IAA/CSIC, Granada, Spain M. Lopez-Puertas IAA-CSIC, Granada, Spain C. Lovis Obs. Geneve, Geneva, Switzerland 316 Exp Astron (2012) 34:311–353 2. Measure the spatial (vertical and horizontal) and temporal variability of the thermal/chemical atmospheric structure of hot giants, Neptunes and super-Earths orbiting bright stars. The photometric accuracy of EChO at multiple wavelengths will be sufficient to observe the planet not merely as day/night hemispheres or terminator but to divide the planet into longitu- dinal slices, hence producing coarse maps of exoplanets (see Sections 5.1 and 5.2).
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