Extra-solar Planet Imaging with a Space Telescope and a Nulling Interferometric Coronagraph

摘要: This paper describes a space mission for the direct detection and spectroscopy of Jupiter-like Earthlike extrasolar planets in visible light using modest aperture (1-4m) telescope with nulling interferometer based coronagraphic instrument. concept is capable satisfying scientific objectives Terrestrial Planet Finder at fraction complexity less cost than previous concepts. We discuss key features our design, we present latest results technology developments needed achieving ten billion to one star suppression ratio required. INTRODUCTION With flux optical ~10-10 between planet its star, hardest problem imaging extra solar that contrast suppression, very low background against which detect requires control both scattered diffracted light. The Hubble Space Telescope (D=2.4m) can V = 30 object, so 27 magnitude object takes much 1 hr integration. In terms resolution orbit Jupiterlike 10 parsec subtends an angle approximately 0.5 arc seconds, diffraction limited only 30cm or greater (at 0.75μm wavelength), earth-like 0.1as be resolved 1.5m diameter aperture. A interferometer, however, used suppress scattering, instrument located behind sized single resolve (Shao, 1990). principle, effectively cancels starlight has 100% transmission when path from λ/2 different star. For aperture, about D=1m, could by synthesizing cm baseline, D=4m, baseline. call coronagraph. schematic system shown Figure 1. It synthesizes four element pupil central After nulling, array coherent mode fibers negate effects residual stellar leakage (scattering) due imperfections optics train. simple after this forms final image, spectrometer measure spectra signs life. combines all advantages simplicity size, telescope. Advances enable approach (Wallace, Shao, Levine Lane, 2003). further use fiber spatial filter conjunction (Liu, Levine, 2003) . progress toward demonstration these subsystems presented below. combination makes deep possible without requirement achieve maintain extreme (λ/4000) wavefront quality over (large) full IMAGING PROPERTIES OF THE VISIBLE NULLING CORONAGRAPH interferes two apertures, destructively. figure below as (Shao 2002). Light “on axis” destructively interfered, but “off passes through nuller detected. Behind place camera image field view. coronagraph IR where pixel detector used. It’s important understand what does image. projects grating on sky. images sky camera/nuller depends angular position object. way similar Lyot Coronagraph blocked stop. Single Aperture Pointing/Tracking control: Diffraction Control: Achromatic Nulling Scattered Fiber-optic Spatial Filter Array Imaging System / Low Resolution Spectrometer 1: Schematic shearing 2003 23 25 September 2003, Long Beach, California AIAA 2003-6303 Copyright © American Institute Aeronautics Astronautics, Inc. All rights reserved.