an exoplanet coronagraph on a stratospheric science platform
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National Aeronautics and Space Administration
An Exoplanet Coronagraph on a Stratospheric Science Platform
Wesley A. Traub and Pin ChenJet Propulsion Laboratory, California Institute of
Technology
Bridging the Gap to SpaceBoulder, CO 26-28 Oct. 2009
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Science MotivationWe 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 coloror 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.
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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.
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Pointing Platforms 2/3 axis frame, tip-tilt mirror, magnetically levitated bearings.
Planetscope concept Solar Bolometric ImagerBernasconi et al., Adv. Sp. Res. 2004
The Planetscope Precursor package will occupy the bottom 0.5x2x2 m3 volume of the Solar Bolometric Imagergondola (Pietro Bernasconi, PI), and will incorporate a Mars-prototype anemometer from Ball Aerospace (Rich Dissly, mgr.) and Cornell Univ. (Don Banfield, PI).
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Earth is 10 billion/million times fainter than Sun
10-10
visible
10-6
infrared
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Known exoplanets with separation and brightness accessible to Planetscope.
Planet Msini Period Sep. Delta
(MJ) (days) (arcsec) mag
Eps Eri b 0.86 2496 1.27 22.1
55 Cnc d 3.92 5551 0.43 22.6
HD 160691 c 3.10 2494 0.36 22.6
HD 190360 b 1.50 2891 0.34 22.6
HD 217107 c 2.10 3150 0.33 23.0
HD 39091 b 10.35 2151 0.28 22.4
47 UMa c 0.76 2594 0.27 21.8
14 Her b 4.74 1753 0.21 21.8
HD 33636 b 9.28 2447 0.19 22.3
Ups And d 3.75 1290 0.17 20.8
Gam Cep b 1.59 905 0.17 20.7
47 UMa b 2.54 1089 0.16 20.4
HD 10647 b 0.91 1003 0.13 20.7
HD 89307 b 2.73 3090 0.13 21.7
HD 117207 b 2.06 2727 0.12 21.3
HD 128311 c 3.21 919 0.12 20.6
HD 38529 c 12.70 2164 0.12 22.7
HD 70642 b 2.00 2231 0.11 21.4
HD 216437 b 2.10 1353 0.10 21.4
HD 169830 c 4.04 2102 0.10 21.7
HD 160691 b 1.67 630 0.10 19.5
HD 147513 b 1.00 528 0.10 19.5
HD 37124 d 0.66 2295 0.10 21.2
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Coronagraph Search Space
Example exoplanets.Over 250 are known.
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8Blue (0.4-0.6 m), Green (0.6-0.8 m), Red (0.8-1.0 m)
Color Gives a First Impression of a Planet
Solar system planetshave colors that label them by type.
Planet spectra
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Lab demo, with planets added
Trauger & Traub, Nature, April 2007
D
Jupiter
Earth
½ Jupiter
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.
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10Traub
IWA-OWA = 2-30 λ/Dfor 550 nm & 2.5 m
C = (2σ/Nλ)2
for σ = λ/1000& σ = λ/10000
& N = 60
C (1 sec)
C (1 hr)
“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.
Contrast & known RV exoplanets vs angle
Expected free-atmospherespeckle contrast
Expected PSF fromcoronagraph
Expected dome-seeingcontrast uncertainty
in 1 hour
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Expected disk sensitivities
name RA (h)Dec
(deg)V
(mag) d (pc) Ld/Lstaras
(1AU)Log C (1AU)
as (5AU)
Log C (5AU)
eps Eri 9.5 -9 3.7 3.2 1.00E-04 0.31 -5.91 1.56 -7.60
tau Cet 1.7 -15 3.5 3.6 1.00E-05 0.28 -6.99 1.39 -8.68
61 Vir 13.3 -18 4.7 8.5 2.00E-05 0.12 -6.21 0.59 -7.90
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Exoplanet targets
targetradius (as)
separation (as)
log(C) planet
signal(elec/min)
yr(max sep)
RA (hr)
Dec (deg)
V (mag)
d (pc)
#Z (pl=zo
di)
eps Eri b 0.79 0.65 - 0.79 -8.25 13.212012.7-
13.4 3.5 -10 3.7 3.2 51
55 Cnc d 0.50 0.23 - 0.50 -9.09 0.24 2013.7 8.9 28 6.0 13.4 54
HD 190360 b 0.17 0.12 - 0.17 -8.30 1.82 2013.7 20.0 30 5.7 15.9 8
47 UMa c 0.26 0.24 - 0.26 -8.56 1.76 2014.3 11.0 40 5.1 14.0 20
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Telescope
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Xinetics SiC 0.8-m Mirror
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Coronagraph optics
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Low-order Wavefront Sensor
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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.
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Thank you !
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Backup Charts
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