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

National Aeronautics and Space Administration

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.

National Aeronautics and Space Administration

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.

National Aeronautics and Space Administration

4

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).

National Aeronautics and Space Administration

5

Earth is 10 billion/million times fainter than Sun

10-10

visible

10-6

infrared

National Aeronautics and Space Administration

6

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

National Aeronautics and Space Administration

7

Coronagraph Search Space

Example exoplanets.Over 250 are known.

National Aeronautics and Space Administration

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

National Aeronautics and Space Administration

9

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.

National Aeronautics and Space Administration

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

National Aeronautics and Space Administration

11

National Aeronautics and Space Administration

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

12

National Aeronautics and Space Administration

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

13

National Aeronautics and Space Administration

14

National Aeronautics and Space Administration

Telescope

15

National Aeronautics and Space Administration

Xinetics SiC 0.8-m Mirror

16

National Aeronautics and Space Administration

Coronagraph optics

17

National Aeronautics and Space Administration

Low-order Wavefront Sensor

18

National Aeronautics and Space Administration

19

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.

National Aeronautics and Space Administration

20

Thank you !

National Aeronautics and Space Administration

21

Backup Charts

National Aeronautics and Space Administration

22

National Aeronautics and Space Administration

23