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 20082

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


25 Aug 20083

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


25 Aug 20084

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

near them


25 Aug 20085

New Worlds Observer


25 Aug 20086

New Worlds Observer


25 Aug 20087

Fly the Telescope into the Shadow


25 Aug 20088

Dropping It In

Note: No Outer Working Angle


25 Aug 20089

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


25 Aug 200810

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


25 Aug 200811

Performance

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


25 Aug 200812

Shadow of 16 Petal Mask

Linear Log


25 Aug 200813

Target Stars: Exo-zodiacal Light

From P. Oakley1.5m 2.4m 4m 10m

4m Case


25 Aug 200814

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


25 Aug 200815

Study Exoplanets

• NWO will perform spectroscopy of discovered planets

• This will reveal their true natures

O2

H2O

CH4

NH3


25 Aug 200816

Four Color Photometry – Molecules!!


25 Aug 200817

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


25 Aug 200818

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


25 Aug 200819

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%


25 Aug 200820

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


25 Aug 200821

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


25 Aug 200822

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


25 Aug 200823

• 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


25 Aug 200824

Target Stars: Exposure Times

i = 60˚

From A. Roberge


25 Aug 200825

Target Stars: Habitable Zones

50 mas IWA

From M. C. Turnbull


25 Aug 200826

NWO Detection Space

Target Stars: Habitable Zones

From M. C. Turnbull


25 Aug 200827

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


25 Aug 200828

Characterizing Planets: Spectroscopy

NWO

Karkoschka et al. 1998


25 Aug 200829

Characterizing Planets: Photometric Variability

From P. Oakley


25 Aug 200830

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

Detailed Spectroscopy of Exoplanets with The New Worlds Observer

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