Beyond Kepler: Direct Imaging of Earth-like Planets

Transcription

1 Beyond Kepler: Direct Imaging of Earth-like Planets Rus Belikov History and science Technology Ames Coronagraph Experiment NASA Ames Research Center Tri-Valley Stargazers, May 15, 2015

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3 Is there another Earth out there? 3 2

4 Is there life on it? 4 2

5 Thousands of years ago, Greek philosophers speculated. There are infinite worlds both like and unlike this world of ours...we must believe that in all worlds there are living creatures and planets and other things we see in this world. Epicurius c. 300 B.C

6 Some gave their lives There are countless suns and countless earths all rotating around their suns in exactly the same way as the seven planets of our system. We see only the suns because they are the largest bodies and are luminous, but their planets remain invisible to us because they are smaller and non-luminous. The countless worlds in the universe are no worse and no less inhabited than our Earth Giordano Bruno in De L'infinito Universo E Mondi,

7 In 1995, a breakthrough: the first planet around another star. Didier Queloz and Michel Mayor A Swiss team discovers a planet 51 Pegasi 48 light years from Earth. Artist's concept of an extrasolar planet (Greg Bacon, STScI) 7

8 And then the discoveries started rolling in: New Planet Seen Outside Solar System New York Times April 19, More Planets Discovered Washington Post August 6, 2000 First new solar system discovered USA TODAY April 16, 1999

9 5,450 Exoplanets (candidates and confirmed) 1,838 confirmed planets (1,132 planetary systems) Wobble method #1: Radial Velocity (Wobble method #2: Astrometry) Direct detection

10 The Transit Method Credit: Amir Give'on and Daphna Wegner

11 You can see transits within our Solar System! Transit of Venus, June 5 th, 2012 atmosphere Overexposed and processed image Next Venus transit: 2117 December 10 11

12 The Kepler Mission 12

13 Exoplanet Detections, A Search for Earth-size Planets Radius Relative to Earth Orbital Period in days Batalha, 2014

14 Small HZ Planet Candidates (in progress) A Search for Earth-size Planets

15 Kepler exoplanet statistics: narrowing in on η Earth (Debiased) Planet occurrence with size (Debiased) Planet occurrence with period Fressin et. al Dong & Zhu et. al There are a lot of planets, at least as many as there are stars Consistent with independent result from microlensing (Villard et.. al. 2012) There are many more small planets than large planets Many potentially habitable candidates have been announced (but η Earth has not yet been officially determined) η Earth for Sun-like stars have ranged from 10-60%.

16 The Direct Imaging method HR8799 (2008) Fomalhaut (2008) Beta Pictoris (2008) Keck / Gemini, AO and ADI in infrared, Nov. 2008, Christian Marois et. al. 60 million years, 24, 38, 68 a.u.; 10, 10, 7 Jupiter masses Solar system size comparison Hubble, visible light, Paul Kalas et. al., Nov million years, Jupiter masses, 115 a.u. 1500K VLT, Anne-Marie Lagrange et. al., Nov million years, 8 Jupiter masses, 8 a.u. 1500K Planetary systems directly imaged to date 32 Planets, 2 multiple-planet planet systems Some of these may not be planets (source: exoplanet.eu)

17 Solar system vs. Fomalhaut 17

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19 What does the Solar System look like from far away? 19 Credit: Cassini mission

20 What does the Solar System look like from far away? Feb 14, light-hours hours (4 billion miles away) Nearest star (Alpha Cen) is 4.2 light YEARS away (2.5 trillion miles m away) Earth is ~10 10 times (25 magnitudes) dimmer than the Sun, and would appear ~ 0.8 away for Alpha Cen 20 Credit: Voyager mission

21 Earth twin simulations around acen (if we could block the second star) 1.4m telescope 0.3m telescope α Cen Earth twin image simulation 1.5m aperture, 1 hour exposure 21

22 Photometry (can determine length of day, surface type, weather) E. B. Ford, S. Seager & E. L. Turner, Nature, 2001

23 Spectroscopy: detecting biomarkers CO 2 CO 2 VENUS X 0.60 EARTH-CIRRUS O 2 H 2 O H 2 O O O 3 2 H 2 O H 2 O Iron oxides MARS EARTH-OCEAN H 2 O ice Detecting atmospheric oxygen and water likely indicates life (because very few non-biological processes can sustain an oxygen atmosphere)

24 Red Edge 24 Seager et al. 2005; Data from Middleton & Sullivan 2000

25 Direct Imaging Main Engineering Requirements Contrast ~10 10 for Earth-like planets ~10 7 for young hot planets and disks Inner Working Angle The smaller the better! Typically 1-31 λ/d required on missions 25

26 Stars are a billion times brighter

27 than the planet hidden in the glare.

28 Like this firefly.

29 3 Main Technological Challenges 1. Funamental physics: Diffraction 2. Manufacturing limitations: Optical aberrations 3. Environmental limitations: Mechanical Stability Diagram of a direct imaging instrument feedback from telescope DM system Coronagraph Science camera feedback LOWFS Starlight rejected by coronagraph

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32 Light from telescope Coronagraph to remove starlight Deformable mirror Coronagraph imager planet Leftover starlight Starshade See for a video explaining the principle of operation See for a video explaining the principle of operation 32

33 Direct Imaging

34 Many different solutions to diffraction (coronagraphs) Courtesy of James Lloyd 34

35 The Ames Coronagraph Experiment (ACE) 35

36 Testbeds and PIAA hardware ACE testbed PIAA lenses Lockheed Martin JPL PIAA mirrors Deformable mirror State of the art performance in the lab Ruslan Belikov, NASA Ames Coronagraph Laboratory

37 Principle of Pupil Apodization-type type coronagraphs Image plane starlight Telescope pupil Resulting image 37

38 Blocking the star: the PIAA Coronagraph (phase-induced amplitude apodization) Original uniformly illuminated pupil plane Focal plane Alpha Centauri A Tau Ceti Another Earth? Courtesy of K. Cahoy ExoEarth direct image simulations, 1.5m telescope with PIAA New, apodized pupil plane Focal plane PIAA is a powerful technology to block the star in order to reveal planets Successful track of technology development at Ames over the past 6 years (as well as at partner institutions) One of the potential architectures selected by NASA for the Exo-C C and AFTA missions Ruslan Belikov, NASA Ames Coronagraph Laboratory

39 ACE Optical Layout LOWFS CCD LOWFS Focal plane occulter and broadband Boston Micromachines Deformable mirror (32x32) Wavefront control uses a combination of EFC (Give on et al. 2007) and Speckle Nulling Broadband-capable PIAA mirrors made by L-3 Tinsley Ruslan Belikov, NASA Ames Coronagraph Laboratory

40 Initial Images from the Lab 40

41 Challenge #2: optical aberrations Image plane starlight Telescope pupil Resulting image 41

42 Solution: use a deformable mirror Made by Boston Micromachines, 32x32 actuators, 10mm active area LOWFS CCD LOWFS Focal plane occulter and broadband Ruslan Belikov, NASA Ames Coronagraph Laboratory

43 Challenge #3: Stability LOWFS CCD LOWFS Focal plane occulter and broadband Fast camera 1100 Hz maximum 14 bits/pixel Low noise Light rejected by the coronagraphic mask is collected for the LOWFS A A lens reimages the PSF on a fast camera A A controller grabs images, calculates modes (tip/tilt upstream and downstream the PIAA, focus, ) Commands are send to actuators (tip/tilt mirrors, piezo stages, ) Correction of 2 modes: tip/tilt upstream the PIAA 2 2 actuators: X and Y translation of the source with piezos Real-time controller 450 Hz maximum frequency in closed-loop loop 1100 Hz in open-loop (vibration analysis) 43 Ruslan Belikov, NASA Ames Coronagraph Laboratory

44 Performance of the LOWFS The vibration analysis, coupled with accelerometers, helped us to identify contributors The controller removes mostly residual turbulence below 1 Hz We will try to reduce vibrations, especially on the y axis, between 10 and 150 Hz Residue: Open-loop: 6x10-3 λ/d Closed-loop: loop: 2.5x10-3 λ/d/d Since we installed the LOWFS, the contrast improved by a decade 44

45 CAD model Eduardo Bendek, NASA Ames Coronagraph Experiment

46 Results 1.8e-7, λ/d 6.5e-8, λ/d 655nm 1.9e-8, λ/d 655nm 9.25e-009, l/d e-6, λ/d 10% 655nm Preliminary result Limited by auxiliary Reimaging optics PIAA (ACE, 2013) Contrast Theoretical limits Stable point source limit VNC (GSFC, 2013) λ/d Tip/tilt errors VVC4 (HCIT 2013) PIAA (HCIT, 2013) 0.01 λ/d Tip/tilt errors VVC4 (HCIT 2013) HBLC (HCIT, 2013) IWA ( λ/d) Ruslan Belikov, NASA Ames Coronagraph Laboratory

47 Video lab tour 47

48 Selected future space missions and concepts Kepler JWST Direct imaging of large planets Small sats ( m, ~$10 200M) Exo-C/S or AFTA (~1.4m / 2.4m, $1B / $2B+) NWT / LUVOIR /ATLST (4+m, $4B+) Earth-size Habitable zone No spectroscopy Not nearby systems Transit spectroscopy (Habitable planets unlikely) Earth-size Habitable zone Spectroscopy Two stars: αcen Earth-size Habitable zone Spectroscopy ~6-20 stars Earth-size Habitable zone Spectroscopy >100 stars 48

49 Highlighted effort: ACESat 45cm space telescope Capable of directly imaging Earthlike planets around Alpha Centauri Submitted to NASA s SMEX program in Dec

50 ACESat data simulation After filtering: Simulation parameters (ACESat mission) D = 45cm PIAA coronagraph 1e-8 8 starting contrast (assumed after MSWC) 0.5mas (1σ rms) random tip/tilt jitter 5 color filters 2-year mission Photon noise included (dominates over read) After shift-and-add Venus Earth pmars Note: pmars is larger but farther away than Solar Mars 50 Simulations by Jared Males

51 Future 51

52 Personal Vision of Earth-like planet exploration path ?? 2??? Kepler Small coronagraph (and/or other <2.4m telescopes) Life-finder (Large imager flagship) Planet resolver Interstellar probes Potentially Habitable Planets (Earth size, Earth T) Statistics Disk Science Science precursor Technology precursor Retiring key risks of ExoEarth imaging acen exo-earth imaging ExoEarth imaging Spectral Characterization Biomarker detection Geoff Marcy: Probe to Alpha Centauri, before this century is out 52

53 Conclusions Exo-earth imaging is within reach. (Around Alpha Centauri within a decade or around other stars within ~2 decades.) Remote detection of life is possible through biomarkers High contrast labs are developing coronagraphic technology to help us reach the goal of exo-earth earth imaging. 53