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Characterizing and Detecting Extrasolar Planets

Characterizing and Detecting Extrasolar Planets. David Spergel February 2004. PREDICTION. Some time in the next decade, SIM, Kepler, Eclipse, JPF, or some other telescope will be detect an Earth-like planet. This will revolutionize astronomy. Will We Find Life?.

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Characterizing and Detecting Extrasolar Planets

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  1. Characterizing and Detecting Extrasolar Planets David Spergel February 2004

  2. PREDICTION Some time in the next decade, SIM, Kepler, Eclipse, JPF, or some other telescope will be detect an Earth-like planet. This will revolutionize astronomy

  3. Will We Find Life? • The necessary ingredients of life are widespread • Observation reveals uniformity of physical and chemical laws • Origin of the elements and their dispersal is well understood • Life on Earth can inhabit harsh environments • Micro- and environmental biology reveal life in extremes of temperature, chemistry, humidity • Life affects a planetary environment in a detectable way • Our own atmosphere reflects the presence of primitive through advanced life • Planets are a common outcome of star formation • Modern theory of star formation makes planet formation likely

  4. 10 -30 m Optical Telescope as Life Finder • TPF will likely be a 4-8 meter class optical telescope or a “small” mid-IR interferometer • It will be capable of detecting Earths out to 10-15 pc • 10-30 m telescope would be the next step: Characterize planets and detect a large sample

  5. Direct Planet Imaging: Good News • Much faster detections • Immediate detection of entire system • Enormous additional science • Size and Albedo • Spectroscopy • Biomarkers

  6. Ford/Seager/Turner Model • See FST, Nature, 412, 885 (2001). • 180x360 deg resolution map of surface • Pixel auto-classification by satellite imagery • BDRFs - in 4 bands for 6 pixel types • Single scattering, no elevation variations • Gray cummulus clouds only • Monte Carlo to 1% accuracy: B, G, R, NIR • Water with waves (specular & isotropic components) • Permanent ice (strong backscattering) • Seasonal/sea ice (80% dirty ice, 20% dirt) • Bare ground (90% sand, 10% clay) • Grass/brush land (67% dirt, 33% clover) • Forested land (75% leaves, 25% peat)

  7. Scattered Light The scattered light comes from a small part of the planet surface

  8. Viewing Geometry No Clouds: high contrast between land and ocean Ford, Seager,Turner, Nature, 2001

  9. Clouds Clouds: bright, variable, correlated in space and time. Ford, Seager,Turner, Nature, 2001

  10. Extrasolar Planets TIME (Days) Ford, Seager,Turner, Nature, 2001

  11. Plants in visible versus near infrared light

  12. Optical Plant Signature as a Biomarker • Chlorophyll causes strong absorption blueward of 0.7 m. • The high reflectance red-ward of 0.7 m is from light scattering in the gaps between plant cells. • This “red edge” is an evolutionary adaptation which helps plants stay cool enough to allow efficient photosynthesis.

  13. Reflection by plants water absorption baseline chlorophyll absorption Benjamin pothos hibiscus Red Edge rose chinquapin wavelength（nm）

  14. APO 3.5m Earthshine Spectra (Feb 2002) RED EDGE? water vapor water vapor water vapor oxygen (A) oxygen () oxygen (B)

  15. >109 >106 Bad News • Detecting light from planets beyond solar system is hard: • Planet signal is weak but detectable (few photons/sec/m2) • Star emits million to billion more than planet • Planet within 1 AU of star • Dust in target solar system 300 brighter than planet • Finding a firefly next to a searchlight on a foggy night

  16. The Diffraction Problem (Visible) Wavelength (l) Focal plane The image in the focal plane is the spatial Fourier transform of the entrance field 1 Diameter (D) Entrance Pupil 1e-10

  17. Airy Rings Linear Scale Log Scale (1e-10 is black)

  18. Coronagraphs at >3l/D • Interferometers at > 1 l/B 10 mm, 28 m Coronagraph The Angular Resolution Challenge Cost ($$), Launch Date +

  19. Control of Star Light • Control diffracted light with various apodizing pupil and/or coronagraph masks • Square masks • Graded aperture • Multiple Gaussian masks • Band limited masks • Control scattered light • Deformable mirror with 10,000 actuators for final l/3000 wavefront (<1 Å)

  20. Wavefront Sensing and Control

  21. What is the biggest problem? Wavefront Error! Phase Aberrations Amplitude Aberrations

  22. Coronagraph Status • Rapid progress in past year • HCIT (Trauger at JPL) is now achieving contasts of ~ few 10-9 with band-limited masks and active optics • Significant progress in understanding control and imaging

  23. Can a VLST be Life Finder? • Life Finder will have special requirements • Stability (or sensing) • Uniform amplitude or control • Need to evaluate 10-30 m in space versus 100m on ground • Requirements: • Ability to do 5-10% photometry within an hour (size depends on distance to Earth-like planet) • Small field, spectral resolution improves ability to remove speckle • Wave front sensing and control

  24. Planet Finding Is A Decades-Long Undertaking • Like cosmology, the search for planets and life will motivate broad research areas and utilize many telescopes for decades to come

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