ariel The Atmospheric Remote-Sensing Infrared Exoplanet Large-survey Towards an H-R Diagram for Planets A Candidate for the ESA M4 Mission TABLE OF CONTENTS 1 Executive Summary ....................................................................................................... 1 2 Science Case ................................................................................................................ 3 2.1 The ARIEL Mission as Part of Cosmic Vision .................................................................... 3 2.1.1 Background: highlights & limits of current knowledge of planets ....................................... 3 2.1.2 The way forward: the chemical composition of a large sample of planets .............................. 4 2.1.3 Current observations of exo-atmospheres: strengths & pitfalls .......................................... 4 2.1.4 The way forward: ARIEL ....................................................................................... 5 2.2 Key Science Questions Addressed by Ariel ....................................................................... 6 2.3 Key Q&A about Ariel ................................................................................................. 6 2.4 Assumptions Needed to Achieve the Science Objectives ..................................................... 10 2.4.1 How do we observe exo-atmospheres? ..................................................................... 10 2.4.2 Targets available for ARIEL ................................................................................... 11 2.5 Expected Scientific Results ........................................................................................ 12 2.5.1 Tens of molecules, hundreds of planets, thousands of spectra… ...................................... 12 2.5.2 Chemical composition & evolution of gaseous planets ................................................... 12 2.5.3 Formation of gaseous planets ................................................................................. 15 2.5.4 Formation & evolution of terrestrial-type planets ........................................................ 15 3 Scientific Requirements ................................................................................................ 16 3.1 Wavelength coverage & Spectral resolving power ............................................................. 16 3.2 Optimised retrieval of molecular species & thermal profiles ................................................ 18 3.2.1 Transit spectra ................................................................................................... 18 3.2.2 Eclipse spectra ................................................................................................... 19 3.2.3 Observing strategy ............................................................................................. 20 3.3 The ARIEL Target Sample ......................................................................................... 20 3.4 Dealing with systematic & astrophysical noise .................................................................. 21 3.4.1 ARIEL performances requirements ......................................................................... 21 3.4.2 Correcting for stellar activity ................................................................................. 21 4 Proposed Science Payload ............................................................................................. 24 4.1 Payload Module Architecture ..................................................................................... 24 4.1.1 Deliverable Units Definition .................................................................................. 24 4.1.2 Payload Module Layout ........................................................................................ 25 4.1.3 Payload Optical Bench Design ................................................................................ 25 4.1.4 Payload Module Thermal Architecture ..................................................................... 25 4.2 Telescope Design .................................................................................................... 27 4.2.1 Optical Design .................................................................................................. 27 4.2.2 Manufacturing Plan ............................................................................................. 27 4.2.3 Alignment and Verification ................................................................................... 27 4.2.4 Structure & Baffles.............................................................................................. 29 4.2.5 Telescope Thermal Management ............................................................................ 29 4.3 Spectrometer Design ................................................................................................ 29 4.3.1 Optical Design .................................................................................................. 29 4.3.2 MIR-Spec Detector Selection ................................................................................ 31 4.4 Fine Guidance System / NIR Photometer Design ............................................................. 32 4.4.1 Design Concept ................................................................................................. 32 4.4.2 Use of FGS as WFE Sensor.................................................................................... 33 4.4.3 FGS Control Electronics & Software ........................................................................ 33 4.5 Instrument Electronics .............................................................................................. 34 4.5.1 Electrical Architecture ......................................................................................... 34 4.5.2 Detector Readout Schemes ................................................................................... 34 4.5.3 Payload Power Budget ......................................................................................... 35 4.5.4 Payload Data Rate .............................................................................................. 35 The ARIEL Mission Proposal Page ii 4.5.5 Telescope Control Electronics ............................................................................... 35 4.6 Calibration Scheme .................................................................................................. 36 4.6.1 Ground Verification, Calibration and Performance testing ............................................. 36 4.6.2 In-flight Calibration ............................................................................................ 36 4.7 Payload Constraints on System .................................................................................... 37 4.7.1 Pointing Stability ................................................................................................ 37 4.7.2 Cleanliness and Contamination Control .................................................................... 37 4.8 Predicting Payload Performance .................................................................................. 37 4.9 Payload Technology Readiness Assessment and Development Plans ....................................... 38 4.9.1 Baseline Payload Design TRL Levels ........................................................................ 38 4.9.2 Model philosophy ............................................................................................... 38 5 Proposed Mission and Spacecraft Configuration ................................................................... 40 5.1 Orbit ................................................................................................................... 40 5.2 Launcher .............................................................................................................. 40 5.3 Mission Concept ..................................................................................................... 41 5.3.1 Observing Modes ............................................................................................... 41 5.3.2 Pointing Constraints & Sky Coverage ....................................................................... 41 5.4 Spacecraft Design Concept ......................................................................................... 41 5.5 Critical Resource Budgets .......................................................................................... 42 5.6 Spacecraft Technology Readiness Levels (TRL) Assessment ................................................. 43 6 Management Scheme ................................................................................................... 45 6.1 Consortium Provided Elements ................................................................................... 45 6.2 ESA Provided Elements ............................................................................................ 46 6.3 Development Schedule ............................................................................................. 47 6.4 Ground Segment Provision ........................................................................................ 47 6.4.1 Ground Segment Architecture ............................................................................... 47 6.5 Data Release and Exploitation Policy ............................................................................ 48 6.6 Public Relations and Outreach ...................................................................................