Detailed Spectroscopy of Exoplanets with The New Worlds Observer

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Detailed Spectroscopy of Exoplanets with

The New Worlds Observer


Webster Cash

University of Colorado

November 21, 2008

NWO Science Telescope

25 Aug 2008

2

Where Next with Space Missions for Exoplanets?



There Has Been Stunning Progress in Study of Exoplanets


It takes 10 to 20 years to launch a space observatory


14 years ago this field didn’t exist


where will it be in 20 years with or without space????


A Space Exoplanet Mission Must Have A


Dramatic Leap In Sensitivity and Inner Working Angle


High Quality Spectroscopy


Capability WAAAAAY Beyond What We have Seen So Far


Otherwise the Mission Will Rendered Mundane


In Short We Need High Quality Spectroscopy of Earth
-
twins


And broad capability to study planetary systems in detail


Anything less would be a gamble

NWO Science Telescope

25 Aug 2008

3

NWO Team Membership:

Organizations, Roles and Leads



Team consist of 43 active members


9 organizations are participating


Additional involvement is provided from each organization and includes technical area experts
and graduate/undergraduate students



Organizations, Roles and Leads:


Colorado University
: PI, Science, Optical Design, and Systems Analysis:
Webster Cash


Northrop Grumman:

Deputy PI and Starshade Development:
Amy Lo


Ball Aerospace Technology Corporation
: Telescope Development:
Charley Noecker


USNO:

Astrometry:
Ralph Gaume


NASA GRC
: Occulter (Starshade) Propulsion:
Scott Benson


KinetX:

Mission Design and Navigation:
Bobby Williams


GSI:

Lead Scientist:
Maggie Turnbull


University College of London
: Exoplanet Spectra Modeling:
Giovanna Tinetti


NASA GSFC
: Study Management:
Kate Hartman

NWO Science Telescope

25 Aug 2008

4

Stars are very bright and their glare
makes it difficult to see fainter objects
near them

NWO Science Telescope

25 Aug 2008

5

New Worlds Observer

NWO Science Telescope

25 Aug 2008

6

New Worlds Observer

NWO Science Telescope

25 Aug 2008

7

Fly the Telescope into the Shadow

NWO Science Telescope

25 Aug 2008

8

Dropping It In

Note: No Outer Working Angle

NWO Science Telescope

25 Aug 2008

9

Extinguishing The Spot of Arago


I Stand on the Spot of Arago and Explain How to Remove the Spot of Arago


Occulters Have Very Poor Diffraction Performance


The 1818 Prediction of Fresnel led to the famous episode of:


Spot of Arago (variously Poission’s Spot)


Occulters Often Concentrate Light!



Must satisfy Fresnel Equation, Not Just the Fraunhoffer Equation



Must Create a Zone That Is:


Deep

Below 10
-
10

diffraction


Wide

A couple meters minimum


Broad

Suppress across at least one octave of spectrum



Must Be Practical


Binary

Non
-
transmitting to avoid scatter


Size

Below 150m Diameter


Tolerance

Insensitive to microscopic errors

NWO Science Telescope

25 Aug 2008

10

NWO has an Opaque Starshade


Opaque Starshade

Offset Hypergaussian function

Apodization Function

exp
n
r a
T
b
 

 
 
 
 
 
 
 

Apodizing Function

Radius

Transmission

Parameter

Occulter inner radius

a

Petal 1/e length

b

Hypergaussian order

n

Distance to telescope

z

Number of petals

P

NWO Science Telescope

25 Aug 2008

11

Performance

A 50m diameter occulter at 80,000km can reveal Earths at over 20pc

NWO Science Telescope

25 Aug 2008

12

Shadow of 16 Petal Mask

Linear

Log

NWO Science Telescope

25 Aug 2008

13

Target Stars: Exo
-
zodiacal Light

From P. Oakley

1.5m

2.4m

4m

10m

4m Case

NWO Science Telescope

25 Aug 2008

14

Map Planetary Systems


Prime Goal is Exploration
of the Solar
Neighborhood


NWO will allow us to
make maps of over 100
nearby planetary systems
from the habitable zone
outward


Detect and classify all
major planets

Jupiter

Saturn

Uranus

Neptune

Zodiacal Light

Galaxies

10 arcseconds

NWO Science Telescope

25 Aug 2008

15

Study Exoplanets


NWO will perform spectroscopy of discovered planets


This will reveal their true natures

O
2

H
2
O

CH
4

NH
3

NWO Science Telescope

25 Aug 2008

16

Four Color Photometry


Molecules!!

NWO Science Telescope

25 Aug 2008

17

Find Earth
-
like Planets


NWO can look close enough to the central star to see Earth twins


NWO can find more Earths than any other approach


NWO can separate barren rocks from water worlds

Need best completeness diagram here

NWO Science Telescope

25 Aug 2008

18

Search for Life


NWO can do detailed spectroscopy of Earth
-
like planets


Resolution in the 100 to 1000 range


Can easily detect water in the atmosphere


Can see surface features as the planet rotates


Can detect the key biomarkers

NWO Science Telescope

25 Aug 2008

19

NWO Allows Ample time for General Astrophysics


While starshade retargets, telescope is free for general
astrophysics


At least
50%

of telescope time is devoted to general astrophysics


Telescope can see within
50

degrees of sun


Capable of

weeks

of continuous integration


Telescope operation similar to JWST


Scheduling & ops by STScI or equiv.

Hubble

NWO

Instantaneous sky

~50%

~80%

Continuous sky

~20%

~35%

NWO Science Telescope

25 Aug 2008

20

Starshade Critical Technology

Enabling Technologies

Precision Shape Control



Maintain edge position


Maintain structure shape

Precision Deployment



Minimize jitter


Maintain petal location

Opaque Membrane


Maintain opacity


Lightweight

2 Axes Formation Flying


Maintain 1m alignment


Minimize jitter

Enhancing Technologies

Solar Electric Propulsion


NEXT engine


Increase observable targets


Reduce propellant mass

Lightweight S/C Structures


Increase observable targets


Reduce overall mass

Thin Edge Treatment


Maintain edge stability


Minimize stray light

NWO Science Telescope

25 Aug 2008

21

Science Goals


Completely Map the Nearby Stellar Systems


Catalogue All Major Planets and Belts


Classify Each


(Develop Classification Schemes!)


Measure Approximate Orbit of Each


Spectroscopically Study the Most Interesting Planets


Find Water Planets


Search for Life


Watch Planetary Systems Forming


General Astrophysics with a True Hubble Follow
-
on

NWO Science Telescope

25 Aug 2008

22

Detect and Study ExoZodis


Orbiting dust scatters starlight an cause “exozodiacal light”


The exozodi can be strong enough to obscure the planets


We currently know NOTHING of the nature of exozodis

Knowledge of Exozodi is key to
the direct detection of exoplanets


NWO can measure hundreds of
such systems


NWO can detect planets despite
high levels of exozodi

NWO Science Telescope

25 Aug 2008

23


Confusion from dust structure


“Is that a planet or a dust clump?”


Can we tell by its color before
wasting time on a spectrum?





Greaves et al. (2005)

Epsilon Eridani

Other Exozodi Issues


Maybe …


Solar System zodi has
red scattered light color


Known debris disks show
red, grey, & blue colors




AU Mic

Blue

HD 92945

Neutral

Beta Pic

Red

NWO Science Telescope

25 Aug 2008

24

Target Stars: Exposure Times

i

= 60˚

From A. Roberge

NWO Science Telescope

25 Aug 2008

25

Target Stars: Habitable Zones

50 mas IWA

From M. C. Turnbull

NWO Science Telescope

25 Aug 2008

26

NWO Detection
Space

Target Stars: Habitable Zones

From M. C. Turnbull

NWO Science Telescope

25 Aug 2008

27

Characterizing the Planet

Turnbull et al. (2006)


Very strong H
2
O signature, like Earth


H
2
O + (
surface temp
or
planet size
or
orbit
)


How to know it’s “habitable”?


“Habitability” = liquid
water on surface


Spectrum mostly
shows atmosphere

NWO Science Telescope

25 Aug 2008

28

Characterizing Planets: Spectroscopy

NWO

Karkoschka et al. 1998

NWO Science Telescope

25 Aug 2008

29

Characterizing Planets: Photometric Variability

From P. Oakley

NWO Science Telescope

25 Aug 2008

30

The Starshade is Adaptable

Starshade

Telescope

Primary Science

15 m

1 m

Exo
-
zodi mapper

25 m

1.5 m

Outer Planet imager

50 m

4 m

TPF + Characterization

100 m

10 m

Lifefinder

N x 70 m

N x 4 m

Planet Imager

Increasing
Resolution

The starshade offers a scalable technology

NWO Can also work with existing telescopes such as
JWST