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
Is there another Earth out there? 3 2
Is there life on it? 4 2
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
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, 1584 4
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
And then the discoveries started rolling in: New Planet Seen Outside Solar System New York Times April 19, 1996 10 More Planets Discovered Washington Post August 6, 2000 First new solar system discovered USA TODAY April 16, 1999
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
The Transit Method Credit: Amir Give'on and Daphna Wegner
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
The Kepler Mission http://kepler.nasa.gov/ 12
Exoplanet Detections, 1995-2013A Search for Earth-size Planets Radius Relative to Earth Orbital Period in days Batalha, 2014
Small HZ Planet Candidates (in progress) A Search for Earth-size Planets
Kepler exoplanet statistics: narrowing in on η Earth (Debiased) Planet occurrence with size (Debiased) Planet occurrence with period Fressin et. al. 2012 Dong & Zhu et. al. 2013 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%.
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 2008. 200 million years, 0.054-3 Jupiter masses, 115 a.u. 1500K VLT, Anne-Marie Lagrange et. al., Nov 2008. 12 million years, 8 Jupiter masses, 8 a.u. 1500K 16 28 Planetary systems directly imaged to date 32 Planets, 2 multiple-planet planet systems Some of these may not be planets (source: exoplanet.eu)
Solar system vs. Fomalhaut 17
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What does the Solar System look like from far away? 19 Credit: Cassini mission
What does the Solar System look like from far away? Feb 14, 1990 6 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
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
Photometry (can determine length of day, surface type, weather) E. B. Ford, S. Seager & E. L. Turner, Nature, 2001
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)
Red Edge 24 Seager et al. 2005; Data from Middleton & Sullivan 2000
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
Stars are a billion times brighter
than the planet hidden in the glare.
Like this firefly.
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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Light from telescope Coronagraph to remove starlight Deformable mirror Coronagraph imager planet Leftover starlight Starshade See http://exep.jpl.nasa.gov/coronagraphvideo/ for a video explaining the principle of operation See https://www.youtube.com/watch?v=gc7pjlckze4 for a video explaining the principle of operation 32
Direct Imaging
Many different solutions to diffraction (coronagraphs) Courtesy of James Lloyd 34
The Ames Coronagraph Experiment (ACE) 35
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
Principle of Pupil Apodization-type type coronagraphs Image plane starlight Telescope pupil Resulting image 37
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
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
Initial Images from the Lab 40
Challenge #2: optical aberrations Image plane starlight Telescope pupil Resulting image 41
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
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
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
CAD model Eduardo Bendek, NASA Ames Coronagraph Experiment
Results 1.8e-7, 1.2-2.0 λ/d 6.5e-8, 2.0-4.0 λ/d 655nm 1.9e-8, 2.0-3.4 λ/d 655nm 9.25e-009, 2.2-3.2 l/d -5-4 6e-6, 1.2-2.0 λ/d 10% BB @ 655nm -4-3 -2-5.5-3 -2-4.5-5 -1 0-6 -6.5-1 0 1-5.5-6 1 2 3-2 0 2-7 -7.5-8 2 3 4 5 Preliminary result Limited by auxiliary Reimaging optics -4-2 0 2 4-6.5-7 -7.5-8 10-6 PIAA (ACE, 2013) Contrast 10-8 10-10 Theoretical limits Stable point source limit VNC (GSFC, 2013) 0.001 λ/d Tip/tilt errors VVC4 (HCIT 2013) PIAA (HCIT, 2013) 0.01 λ/d Tip/tilt errors VVC4 (HCIT 2013) HBLC (HCIT, 2013) 0 1 2 3 4 IWA ( λ/d) Ruslan Belikov, NASA Ames Coronagraph Laboratory
Video lab tour http://gizmodo.com/5896588/the-lens-welllook-through-to-find-a-new-earth 47
Selected future space missions and concepts 2010 2020 2030 Kepler JWST Direct imaging of large planets Small sats (0.25-0.7m, ~$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
Highlighted effort: ACESat 45cm space telescope Capable of directly imaging Earthlike planets around Alpha Centauri Submitted to NASA s SMEX program in Dec 2014 49
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
Future 51
Personal Vision of Earth-like planet exploration path 2010 2020 2030 20?? 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
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