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Occulting Ozone Observatory (O3 ) a Briefing to the NAS EOS-1 Panel

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Jet Propulsion Laboratory California Institute of Technology Occulting Ozone Observatory (O3) a briefing to the NAS EOS-1 Panel Doug Lisman, Jet Propulsion Laboratory, California Institute of Technology Stuart Shaklan, Jet Propulsion Laboratory, California Institute of Technology Edward Schwieterman, University of California Riverside November 20, 2019 This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. © 2019 1 Introduction ExoPlanet Exploration Program • O3 is a small starshade mission with focused science objectives that: – Images previously undetectable planets, including rocky HZ planets and, after multiple observations, constrains their orbit and size to inform planetary system diversity and exozodi levels – Detects the likely presence (not abundance) of O3 at rocky planets, as a robust proxy for O2, although Venus has other NUV absorbers and to confirm a biologic origin requires a follow-on mission – Detects the likely presence (not slope) of Rayleigh scattering at larger gas planets • Prominent low-wavelength spectral features yield smaller telescopes and starshades – The mission detailed here operates a 16-m starshade at 16-Mm from a shared and co-launched 1-m telescope (notionally CASTOR, a CSA study mission) with excellent retarget agility and low ∆V – The exact telescope remains flexible, with separate funding for diverse science desired, and the APC paper presents dedicated 60-cm and shared 1.5-m cases and the exact telescope – • A 3-yr. mission with dedicated search phase informs a target down-select to boost yield – Yield is reported here for confirmed planets with constrained size and orbit and separately for the the select planets that are searched for ozone; additional unconfirmed candidates are not counted • Original 2009-10 O3 study was rooted in a search for an elegant low-cost solution – Led by David Spergel and Jeremy Kasdin (see Savransky et al 2010 and Thomson et al 2011) – Produced the new starshade architecture presented by multiple speakers at this meeting 2 Agenda ExoPlanet Exploration Program • Starshade design • Instrument design • Biosignature assessment • Star list, observational strategy, expected yield • Launch mass margin • Likely mission cost range • A small starshade SRM variant mission • Conclusions 3 O3 Starshade Design ExoPlanet Exploration Program Bus system with Propellant tanks install fixed solar array inside payload cylinder Deploy control system interfaces to launch vehicle and jettisons as a module after unfurling petals O3 8-m disk compares to current 10-m disk prototype shown O3 petal matches 4-m long pathfinder petal shown 4 O3 Instrument Design ExoPlanet Exploration Program Secondary Mirror with alignment actuators mirror Primary steering mirror - Fast Integrated Beam- splitters Ozone Ch. 200-300 nm Continuum 300-400 nm Insertable bandpass filters Formation Ch. Reimaging mirrors 400-500 nm 4K x 4K CCD Ozone can be detected with a simple 2-channel photometer. The 3rd channel shown here is for lateral formation sensing in out of band starlight. 5 Biosignature Comparison ExoPlanet Exploration Program Today’s Earth Spectrum O 3 O2 O2 H2O H2O H2O CO2 H O O3 Hartley Band O2 2 A-Band 0.05 O2 A-Band detection requires SNR of 20. O3 Hartley Band O3 Hartley Band detection requires SNR of 5. 0.04 (200-300 nm) O3 Hartley Band receives more of the integrated stellar 0.03 flux vs. O2 A-Band, except for the coldest target star Epsilon Indi 0.02 O2 A-Band Planck Function Planck (759-771 nm) Band fraction of starflux) - 0.01 In A given Fresnel number is achieved with a smaller ( N -N starshade at shorter wavelengths 2 2 H2O 0.00 Starshade radius =√(F l Z), where Z is telescope separation distance N O Tau Ceti 2 Zeta Tuc CO 2Pav Delta Eridani p. 82 Eridani 82 Eridani 40 Epsilon Er i H O Beta Hydri 2 Epsilon Indi Gamma Lep Gamma Gamma Pav Gamma N2O 6 O3 H2O H2O CH4 CO2 Hartley Ozone Band – High Sensitivity O2 Proxy ExoPlanet Exploration Program O3 is a sensitive marker of Earth’s photosynthetic biosphere & detectable over ~50% of Earth’s history. O2 has been a biosignature for only ~10-20% of Earth’s history 7 Potential False Positives with Venus type planets ExoPlanet Exploration Program Ultraviolet Image of Venus, JAXA HabEx Interim Report Venus has other NUV absorber gases that cannot be disentangled by O3 8 Star List ExoPlanet Exploration Program q. 59 Virginis 62 G. Eri Stars with known 55 Mu Arae Giants Scorpii Cancri 47 Ursae Majoris Gamma Gamma 10 p. Pav Leporis Zeta Eri Mu Herculis Tuc Gliese 570 Delta Beta Groonbridge 82 Pav Eri Hydri 1618 40 36 Oph Eri A Altair 100 mas IWA Tau Epsilon Ceti Procyon Indi Epsilon A Distance (parsecs) Distance Eri Sirius A 1 0.1 1 10 Luminosity relative to Sun 24 search phase target stars include 6 with 10 known Giant planets. 12 select stars for revisit phase are shown in bold type. Exozodiacal light limits HZ observations to the closest stars. 9 Observation Strategy ExoPlanet Exploration Program • Search all 24 stars in Year-1 with broadband imaging • Down-select and observe each of 12 stars 4 times each over Years 2/3 • Search for Ozone/Rayleigh scatter with one 30-day observation at 8 select stars 10 Year 1 Search Phase Observation Sequence ExoPlanet Exploration Program 90 60 Mu Herculis Groombridge 1618 47 Ursae START Majoris 30 Altair 55 59 Virginis 0 Cancri 36 Oph A Tau Epsilon Gliese 570 Ceti Eridani Procyon A 62 G. -30 Gamma 40 Scorpii Mu Ecliptic Latitude (deg) Pav Epsilon Arae Eri Sirius Indi q. Gamma A END Delta Eri -60 Leporis Year 1 Pav p. 82 search phase Zeta Beta Eri Erii Hydri Tuc -90 0 30 60 90 120 150 180 210 240 270 300 330 360 Ecliptic Longitude (deg) All 24 well distributed target stars can be searched in Year-1 with modest ∆V of ~300 m/s. Star-Sun angle constraint of 40° to 83° is preserved. 11 Yield Calculations ExoPlanet Exploration Program • Set exozodiacal light at median density level of 4 zodis, with 1 zodi at 22 mags/arc-sec2 • Set planet sensitivity for SNR of 4 w.r.t. residual exozodi after calibration to 5% accuracy • Compute search completeness for given planet size/albedo by numerically integrating the intercept of IWA, contrast curve (Lambertian phase function) over a given orbit size range • Compute planet yield following the HabEx report, from which figure is lifted Planet occurrence rates per SAG-13 Planet categories per Kopparapu et al 2018 Compiled by Chris Stark Here we approximate 3 fixed orbit ranges 12 Expected Planet Yield with constrained orbits and size ExoPlanet Exploration Program Yield estimate after 5 visits to 1-dozen stars 9 8 Hot: 0.075-0.95 AU 7 Warm: 0.95-1.67 AU 6 Cold: 1.67-20 AU 5 4 3 2 1 0 Small R ocky Rocky Super- Sub- Neptunes Giants Planets Earths Neptunes (3.5-6 Re) (6-14.3 Re) (0.5-1 Re) (1-1.75 Re) (1.75-3.5 Re) O3 is expected to yield about 23 exoplanets with constrained orbits & size. An additional ~15 unconfirmed or constrained detections are expected in Year-1. 13 Yield from 8 Characterized Planets ExoPlanet Exploration Program Yield estimate for 8 Characterized Stars 7 (1 30-day integration time) 6 5 4 3 2 1 0 Small R ocky Rocky Super- Sub- Neptunes Giants Planets Earths Neptunes (3.5-6 Re) (6-14.3 Re) (0.5-1 Re) (1-1.75 Re) (1.75-3.5 Re) 14 Launch Mass Margin ExoPlanet Exploration Program Mass Element Comments (kg) 16-m Starshade Payload CBE 410 8-m dia. Inner disk & 4-m long petals (Qty 24) Deck mounted WISE bus with prop tanks inside Starshade Bus System CBE 500 starshade central cylinder 43% mass growth 390 Same as 30% margin against launch capacity Max expected EOM starshade dry mass 1300 Max propellant for 3 yr mission 1000 1600 m/s ∆V at 308s Isp with 6% residual prop Max Telescope launch wet mass 800 Max Starshade Deployment Control System 200 Module is jettisoned after deployment Total Launch Mass 3300 Launch Mass Capacity 3900 Falcon-9 direct to E-S L2 Extra launch mass margin 600 O3 has excess launch mass capacity that could be used for extended mission ∆V, and/or to carry a secondary payload 15 Expected Mission Cost Range ExoPlanet Exploration Program Cost Element Comments ($M) 16-m Starshade Payload 110 Includes TRL-6 campaign Fixed solar array, no science data, Starshade Bus System 60 includes propulsion module Telescope System 0 Contributed via mission partnership Includes 30% Reserves, Project Mgt., Project Wrapper Cost 170 SE, MA, MOS/GDS, ATLO, Science Total Flight System Cost 340 Launch Service Cost 160 Falcon-9 Likely Nominal Cost 500 50% uncty due to brief JPL Foundry Additional Cost Uncertainty 250 study & use of mass based cost models Likely Maximum Cost 750 O3 mission cost is likely to be in the range of $500M to $750M The cost information contained in this document is of a budgetary and planning nature and is intended for informational purposes only. It does not constitute a commitment on the part of JPL and/or Caltech. 16 A SRM Variant Mission ExoPlanet Exploration Program • The CGI switch to prism-based spectroscopy enables a small low-cost SRM variant mission, in similar fashion to O3 • A slit and prism dedicated to the existing 425-552 nm imaging band supports Rayleigh scatter detection with a 22-m starshade at 22-Mm from WFIRST for 103-mas IWA • A separate slit and prism (e.g., CGIs Band 3 covering 675-785 nm) can subsequently be used to search for O2 & H2O at detected atmospheres with separation increased to 31-Mm – IWA grows to 146-mas vs.
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