Coronagraph for NRO-WFIRST: A Way Forward Wesley Traub Chief Scientist, NASA’s Exoplanet Exploration Program Jet Propulsion Laboratory, California Institute of Technology NRO Meeting Princeton University 4-6 September 2012 Ref.: Traub & Oppenheimer, Chapter on “Direct Imaging”, in “Exoplanets” book, S. Seager, editor, 2011. Copyright 2012 California Institute of Technology. Government sponsorship acknowledged.

NWNH “ ~ … carry out technology development for a direct imaging mission to detect and characterize exoplanets in the 2020s … “ “ ~ … ultimate goal is to be able to detect Earth-like planets in their habitable zones, and search for signs of life … “ Direct imaging instruments include: coronagraphs, starshades, & interferometers. NB: Direct imaging requires nearby targets (N ~ 100-200 stars), so transit method is not applicable (p ~ 0.5 % for HZ planet). Next: 3 charts on exoplanets 2 charts on coronagraphs 1 chart on a plan forward

Already known planetary systems 1-4 planets per star (o) 136 Prime target stars (x) 2321 Kepler planets (cone) 17 Corot (pencils) 471 RV, transit & imaging, +36 HAT +13 WASP (cloud) prime hunting grounds for direct imaging & astrometry missions

183,000 Kepler target stars K G F A B M I & III V VII 122,000 sample

Kepler planets: period distribution Area under red curve gives ratio (planet population)/(star population) = 0.47 ± 0.01 for periods P < 135 days. Extrapolation to HZ gives pl.pop./star.pop. = 0.10 2011 data release 2012 data release Ref., left box: Traub, ApJ 745 (2012)

Nominal coronagraph capability Based on current lab experience, I expect that an NRO-WFIRST coronagraph should have: contrast (planet/star) per snapshot ~ 10-9 ~ Jupiter at 5 AU ~ Neptune at 2 AU but can go deeper (~10-10) in sub-FOV area ~ Super-Earth at 2 AU bandwidth per snapshot ~ 20 % ( 2 bands needed for color, 3 bands desirable) ( IFU with ~ 2 % resolution desirable) FOV ~ (3 – 32) λ/D ~ 0.25 – 2.5 arcsec radius ~ 2.5 – 25 AU at 10 pc targets: planets, exozodi, & debris disks

What type of (internal) coronagraph? Simple instrument  acceptable cost But disjoint pupil (secondary & spider arms)  limited number of internal coronagraph designs Current throughput capability (personal ballpark guesses): shaped pupil: A = 0.2 x 6/6, Ω = small, BW = 20 % band-limited: A = (2 to 3)/6, Ω = large, BW = 20 % vector vortex: A = tbd, Ω = large, BW = 10 % PIAA: A = tbd, Ω = large, BW = 1 % visible nuller: A = 4/6, Ω = small, BW = 1 % IFU spectroscopy module: can be added to any of above needed to characterize planet A: Ω:

Strawman plan for a 6-month coronagraph study By April 2013, generate a community white paper addressing 3 major issues (below), for each candidate type of coronagraph for NRO-WFIRST (e.g., shaped pupil, band-limited, vector vortex, PIAA, visible nuller): 1. Provide a strawman instrument layout. Assuming that each nearby star system has such a target (e.g., a Jupiter at 5 AU, a Neptune at 3 AU, and a zodi like ours), state how many could be discovered and characterized in a given fraction (e.g., 20%) of the mission lifetime. 3. Estimate effort needed to get to TRL 6 by end of 2016. This plan is similar to the already ongoing discussions of filters, gratings, cameras, etc., for the wide-field survey elements (e.g., dark energy, microlensing, GO) of NRO-WFIRST, however for the coronagraph we have much more new ground to cover.

End This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.