The science of EChO
Authors: Tinetti Giovanna , Cho James Y-K. , Griffith Caitlin A. , Grasset Olivier , Grenfell Lee , Guillot Tristan , Koskinen Tommi T. , Moses Julianne I. , Pinfield David , Tennyson Jonathan , Tessenyi Marcell , Wordsworth Robin , Aylward Alan , van Boekel Roy , Coradini Angioletta , Encrenaz Therese , Snellen Ignas , Zapatero-Osorio Maria R. , Bouwman Jeroen , du Foresto Vincent Coudé , Lopez-Morales Mercedes , Mueller-Wodarg Ingo , Pallé Enric , Selsis Franck , Sozzetti Alessandro , Beaulieu Jean-Philippe , Henning Thomas , Meyer Michael , Micela Giuseppina , Ribas Ignasi , Stam Daphne , Swain Mark , Krause Oliver , Ollivier Marc , Pace Emanuele , Swinyard Bruce , Ade Peter A.R. , Achilleos Nick , Adriani Alberto , Agnor Craig B. , Afonso Cristina , Prieto Carlos Allende , Bakos Gaspar , Barber Robert J. , Barlow Michael , Bernath Peter , Bézard Bruno , Bordé Pascal , Brown Linda R. , Cassan Arnaud , Cavarroc Céline , Ciaravella Angela , Cockell Charles , Coustenis Athéna , Danielski Camilla , Decin Leen , De Kok Remco , Demangeon Olivier , Deroo Pieter , Doel Peter , Drossart Pierre , Fletcher Leigh N. , Focardi Matteo , Forget Francois , Fossey Steve , Fouqué Pascal , Frith James , Galand Marina , Gaulme Patrick , Hernández Jonay I. González , Grassi Davide , Griffin Matt J. , Grözinger Ulrich , Guedel Manuel , Guio Pactrick , Hainaut Olivier , Hargreaves Robert , Hauschildt Peter H. , Heng Kevin , Heyrovsky David , Hueso Ricardo , Irwin Pat , Kaltenegger Lisa , Kervella Patrick , Kipping David , Kovacs Geza , Barbera Antonino La , Lammer Helmut , Lellouch Emmanuel , Leto Giuseppe , Morales Mercedes Lopez , Valverde Miguel A. Lopez , Lopez-Puertas Manuel , Lovi Christophe , Maggio Antonio , Maillard Jean-Pierre , Prado Jesus Maldonado , Marquette Jean-Baptiste , Martin-Torres Francisco J. , Maxted Pierre , Miller Steve , Molinari Sergio , Montes David , Moro-Martin Amaya , Mousis Olivier , Tuong Napoléon Nguyen , Nelson Richard , Orton Glenn S. , Pantin Eric , Pascale Enzo , Pezzuto Stefano , Poretti Ennio , Prinja Raman , Prisinzano Loredana , Réess Jean-Michel , Reiners Ansgar , Samuel Benjamin , Forcada Jorge Sanz , Sasselov Dimitar , Savini Giorgio , Sicardy Bruno , Smith Alan , Stixrude Lars , Strazzulla Giovanni , Vasisht Gautam , Vinatier Sandrine , Viti Serena , Waldmann Ingo , White Glenn J. , Widemann Thomas , Yelle Roger , Yung Yuk , Yurchenko Sergey 
Published: November 2011

The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?

In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.

The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.

EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates.