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Detailed Spectroscopy of Exoplanets with
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The New Worlds Observer
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Webster Cash
University of Colorado
November 21, 2008
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
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NWO Science Telescope
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
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Organizations, Roles and Leads:
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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
25 Aug 2008
NWO Science Telescope
Stars are very bright and their glare
makes it difficult to see fainter objects
near them
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25 Aug 2008
NWO Science Telescope
New Worlds Observer
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25 Aug 2008
NWO Science Telescope
New Worlds Observer
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25 Aug 2008
NWO Science Telescope
Fly the Telescope into the Shadow
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25 Aug 2008
NWO Science Telescope
Dropping It In
Note: No Outer Working Angle
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25 Aug 2008
NWO Science Telescope
Extinguishing The Spot of Arago
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I Stand on the Spot of Arago and Explain How to Remove the Spot of Arago
•
Occulters Have Very Poor Diffraction Performance
•
Must satisfy Fresnel Equation, Not Just the Fraunhoffer Equation
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Must Create a Zone That Is:
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Must Be Practical
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The 1818 Prediction of Fresnel led to the famous episode of:
Spot of Arago (variously Poission’s Spot)
Occulters Often Concentrate Light!
Deep
Wide
Broad
Binary
Size
Tolerance
25 Aug 2008
Below 10-10 diffraction
A couple meters minimum
Suppress across at least one octave of spectrum
Non-transmitting to avoid scatter
Below 150m Diameter
Insensitive to microscopic errors
NWO Science Telescope
NWO has an Opaque Starshade
• Apodizing Function
Apodization Function
Transmission
Offset Hypergaussian function
  r  a n 

T  exp   
  b  
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
• Opaque Starshade
Radius
Parameter
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Occulter inner radius
a
Petal 1/e length
b
Hypergaussian order
n
Distance to telescope
z
Number of petals
P
NWO Science Telescope
Performance
A 50m diameter occulter at 80,000km can reveal Earths at over 20pc
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NWO Science Telescope
Shadow of 16 Petal Mask
Log
Linear
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25 Aug 2008
NWO Science Telescope
Target Stars: Exo-zodiacal Light
4m Case
1.5m
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25 Aug 2008
4m
2.4m
NWO Science Telescope
From
10mP. Oakley
Map Planetary Systems
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Prime Goal is Exploration
of the Solar
Neighborhood
Uranus
NWO will allow us to
make maps of over 100
nearby planetary systems
from the habitable zone
outward
Galaxies
Zodiacal Light
Jupiter
Saturn
Detect and classify all
major planets
Neptune
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25 Aug 2008
NWO Science Telescope
10 arcseconds
Study Exoplanets
• NWO will perform spectroscopy of discovered planets
• This will reveal their true natures
H2O
O2
CH4
NH3
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25 Aug 2008
NWO Science Telescope
Four Color Photometry – Molecules!!
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25 Aug 2008
NWO Science Telescope
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
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NWO Science Telescope
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
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NWO Science Telescope
NWO Allows Ample time for General Astrophysics
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While starshade retargets, telescope is free for general
astrophysics
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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
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Scheduling & ops by STScI or equiv.
Hubble
NWO
Instantaneous sky
~50%
~80%
Continuous sky
~20%
~35%
25 Aug 2008
NWO Science Telescope
Starshade Critical Technology
Enabling Technologies
Precision Shape Control
•Maintain edge position
•Maintain structure shape
Thin Edge Treatment
•Maintain edge stability
•Minimize stray light
Precision Deployment
•Minimize jitter
•Maintain petal location
Opaque Membrane
•Maintain opacity
•Lightweight
2 Axes Formation Flying
•Maintain 1m alignment
•Minimize jitter
Enhancing Technologies
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25 Aug 2008
Solar Electric Propulsion
•NEXT engine
•Increase observable targets
•Reduce propellant mass
NWO Science Telescope
Lightweight S/C Structures
•Increase observable targets
•Reduce overall mass
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
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25 Aug 2008
NWO Science Telescope
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
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NWO Science Telescope
Other Exozodi Issues
• Confusion from dust structure
Epsilon Eridani
− “Is that a planet or a dust clump?”
− Can we tell by its color before
wasting time on a spectrum?
Greaves et al. (2005)
• Maybe …
Beta Pic
Red
− Solar System zodi has
red scattered light color
− Known debris disks show
red, grey, & blue colors
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25 Aug 2008
NWO Science Telescope
HD 92945
Neutral
AU Mic
Blue
Target Stars: Exposure Times
i = 60˚
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From A. Roberge
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NWO Science Telescope
Target Stars: Habitable Zones
50 mas IWA
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NWO Science Telescope
From M. C. Turnbull
Target Stars: Habitable Zones
NWO Detection
Space
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25 Aug 2008
NWO Science Telescope
From M. C. Turnbull
Characterizing the Planet
• “Habitability” = liquid
water on surface
• Spectrum mostly
shows atmosphere
• How to know it’s “habitable”?
– Very strong H2O signature, like Earth
– H2O + (surface temp or planet size or orbit)
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NWO Science Telescope
Turnbull et al. (2006)
Characterizing Planets: Spectroscopy
NWO
Karkoschka et al. 1998
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NWO Science Telescope
Characterizing Planets: Photometric Variability
From P. Oakley
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NWO Science Telescope
The Starshade is Adaptable
Starshade
Telescope
Primary Science
15 m
1m
25 m
1.5 m
50 m
4m
TPF + Characterization
100 m
10 m
Lifefinder
N x 70 m
Nx4m
Exo-zodi mapper
Outer Planet imager
Planet Imager
Increasing
Resolution
NWO Can also work with existing telescopes such as JWST
The starshade offers a scalable technology
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NWO Science Telescope