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
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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 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
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Stars are very bright and their glare makes it difficult to see fainter objects
near them
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New Worlds Observer
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New Worlds Observer
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Fly the Telescope into the Shadow
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Dropping It In
Note: No Outer Working Angle
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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
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NWO has an Opaque Starshade
• Opaque Starshade
Offset Hypergaussian function
Apodization Function
expn
r aT
b
• Apodizing Function
Radius
Tra
nsm
issi
on
Parameter
Occulter inner radius a
Petal 1/e length b
Hypergaussian order n
Distance to telescope z
Number of petals P
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Performance
A 50m diameter occulter at 80,000km can reveal Earths at over 20pc
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Shadow of 16 Petal Mask
Linear Log
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Target Stars: Exo-zodiacal Light
From P. Oakley1.5m 2.4m 4m 10m
4m Case
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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
JupiterSaturn
Uranus
Neptune
Zodiacal Light
Galaxies
10 arcseconds
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Study Exoplanets
• NWO will perform spectroscopy of discovered planets
• This will reveal their true natures
O2
H2O
CH4
NH3
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Four Color Photometry – Molecules!!
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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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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 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%
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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
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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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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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• 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 MicBlue
HD 92945Neutral
Beta PicRed
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Target Stars: Exposure Times
i = 60˚
From A. Roberge
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Target Stars: Habitable Zones
50 mas IWA
From M. C. Turnbull
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NWO Detection Space
Target Stars: Habitable Zones
From M. C. Turnbull
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Characterizing the Planet
Turnbull et al. (2006)
– Very strong H2O signature, like Earth
– H2O + (surface temp or planet size or orbit)
• How to know it’s “habitable”?
• “Habitability” = liquid
water on surface
• Spectrum mostly
shows atmosphere
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Characterizing Planets: Spectroscopy
NWO
Karkoschka et al. 1998
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Characterizing Planets: Photometric Variability
From P. Oakley
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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 ImagerIncreasing Resolution
The starshade offers a scalable technologyThe starshade offers a scalable technology
NWO Can also work with existing telescopes such as JWST