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An Exoplanet Coronagraph on a Stratospheric Science Platform. Wesley A. Traub and Pin Chen Jet Propulsion Laboratory, California Institute of Technology Bridging the Gap to Space Boulder, CO 26-28 Oct. 2009. Science Motivation.
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An Exoplanet Coronagraph on a Stratospheric Science Platform Wesley A. Traub and Pin Chen Jet Propulsion Laboratory, California Institute of Technology Bridging the Gap to Space Boulder, CO 26-28 Oct. 2009
Science Motivation We now know that several hundred exoplanets exist around nearby stars. (And we expect Kepler to find several thousand around distant stars.) For all of these, we will know their mass and period (---> semi-major axis). For the transiting ones, we know their radius (--> mean density). However for nearly all of them, we will have no information on their color or spectrum, which are our first clues to their atmospheric properties. Eventually, we need SIM Lite to find all the nearby planets, and Terrestrial Planet Finder to fully characterize their spectra. Spectra, at R ~ 70, will tell us about H2O, CO2, CH4, O3, O2, plants, atmosphere, continents, oceans, rotation rate, and weather. These clues will also give us signs of life.
We will not have SIM or a coronagraph in the coming 5 years, perhaps longer. So today we should practice the technique of observing an exoplanet’s colors, using a balloon platform. We believe that a 1-2 m class telescope plus coronagraph on a balloon platform will have the sensitivity to do this. Targets are the well-known Jupiters that are bright and well-separated from their stars. Benefits will be the first colors of these exoplanets, higher TRLs, A tech demo for space, and scientist/engineer training.
Pointing Platforms 2/3 axis frame, tip-tilt mirror, magnetically levitated bearings. Solar Bolometric Imager Bernasconi et al., Adv. Sp. Res. 2004 Planetscope concept The Planetscope Precursor package will occupy the bottom 0.5x2x2 m3 volume of the Solar Bolometric Imager gondola (Pietro Bernasconi, PI), and will incorporate a Mars-prototype anemometer from Ball Aerospace (Rich Dissly, mgr.) and Cornell Univ. (Don Banfield, PI).
Earth is 10 billion/million times fainter than Sun 10-10 visible 10-6 infrared
Known exoplanets with separation and brightness accessible to Planetscope.
Coronagraph Search Space Example exoplanets. Over 250 are known.
Color Gives a First Impression of a Planet Solar system planets have colors that label them by type. Planet spectra Blue (0.4-0.6 m), Green (0.6-0.8 m), Red (0.8-1.0 m)
Lab demo, with planets added Jupiter ½ Jupiter D Earth 500 D-shaped images of dark hole, Rotated to sample annulus on sky, Planets added, Common speckles removed, Planets pop out of noise. Shows that Earth could have been detected. Trauger & Traub, Nature, April 2007
Contrast & known RV exoplanets vs angle “Dome Seeing” Contribution: C(1 sec) assumes night best (rms = 1 nm) but only 0.1 nm of this going to speckles in the range IWA-OWA, with 0.9 nm going to piston and tilt. C(1 hr) assumes above reduced by (1 sec / 1 hr)1/2 , i.e., this is the uncertainty in the average background speckle level. C (1 sec) C = (2σ/Nλ)2 for σ = λ/1000 & σ = λ/10000 & N = 60 C (1 hr) Expected free-atmosphere speckle contrast IWA-OWA = 2-30 λ/D for 550 nm & 2.5 m Expected dome-seeing contrast uncertainty in 1 hour Expected PSF from coronagraph Traub
Summary A balloon coronagraph could b e built using available technology. A few one-night flights would demonstrate feasibility. A long-duration, multi-night flight would permit new science.
