Planet Searching from Ground and Space
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Planet Searching from Ground and Space Olivier Guyon Japanese Astrobiology Center, National Institutes for Natural Sciences (NINS) Subaru Telescope, National Astronomical Observatory of Japan (NINS) University of Arizona Breakthrough Watch committee chair June 8, 2017 Perspectives on O/IR Astronomy in the Mid-2020s Outline 1. Current status of exoplanet research 2. Finding the nearest habitable planets 3. Characterizing exoplanets 4. Breakthrough Watch and Starshot initiatives 5. Subaru Telescope instrumentation, Japan/US collaboration toward TMT 6. Recommendations 1. Current Status of Exoplanet Research 1. Current Status of Exoplanet Research 3,500 confirmed planets (as of June 2017) Most identified by Jupiter two techniques: Radial Velocity with Earth ground-based telescopes Transit (most with NASA Kepler mission) Strong observational bias towards short period and high mass (lower right corner) 1. Current Status of Exoplanet Research Key statistical findings Hot Jupiters, P < 10 day, M > 0.1 Jupiter Planetary systems are common occurrence rate ~1% 23 systems with > 5 planets Most frequent around F, G stars (no analog in our solar system) credits: NASA/CXC/M. Weiss 7-planet Trappist-1 system, credit: NASA-JPL Earth-size rocky planets are ~10% of Sun-like stars and ~50% abundant of M-type stars have potentially habitable planets credits: NASA Ames/SETI Institute/JPL-Caltech Dressing & Charbonneau 2013 1. Current Status of Exoplanet Research Spectacular discoveries around M stars Trappist-1 system 7 planets ~3 in hab zone likely rocky 40 ly away Proxima Cen b planet Possibly habitable Closest star to our solar system Faint red M-type star 1. Current Status of Exoplanet Research Spectroscopic characterization limited to Giant young planets or close-in planets For most planets, only Mass, radius and orbit are constrained HR 8799 d planet (direct imaging) Currie, Burrows et al. 2011, ApJ, 729, 128 2. Finding the nearest habitable planets Nearest = Best opportunity for characterization (especially direct imaging) and possible flyby (BT Starshot) 2. Finding the nearest habitable Exoplanets Nearby stars Star Temperature [K] 40 Eri A/B/C A Luyten's star Teegarden's star Tau Ceti YZ Ceti Procyon A/B DX F EZ Aquarii ABC Eps Eri AX Mic Cancri 61 Cyg Ross 154 Kapteyn's Ross 128 A/B star Sirius Lacaille Gliese 15 A&B A/B Gliese 9352 CN G 1061 Leonis Ross 248 Eps Indi UV & BL Ceti Gliese 440 Lalande Barnard's 21185 SRC 1843-6537 Gliese star 725 A/B K M α Cen SOUTH system NORTH 2. Finding the nearest habitable Exoplanets Nearby stars >75% of main sequence stars are M type Within 5pc (15ly) : 60 hydrogen-burning stars, 50 are M type, 6 are K-type, 4 are A, F or G 4.36 Alpha Cen A 4.36 Alpha Cen B 8.58 Sirius A 10.52 Eps Eri 11.40 Procyon A 11.40 61 Cyg A 11.89 Tau Ceti 11.40 61 Cyg B A F G 11.82 Eps Ind A M K 15.82 Gliese 380 2. Finding the nearest habitable Exoplanets Main Exoplanet Detection techniques Transit photometry Microlensing Requires orbit gravitational lensing alignment distant background star Radial Velocity Astrometry starlight planet light optimal for finding nearest exoplanets Direct Imaging optimal for characterization 2. Finding the nearest habitable Exoplanets Radial Velocity extending to cool M-type stars Detection limit Star Temperature [K] Sirius for ground-based optical RV α Cen A Expected detection F, G, K stars limit for space astrometry (NEAT, α Cen B THEIA, STEP) F, G, K stars Procyon A Proxima Cen Eps Eri Barnard's star CN Leonis Circle diameter is proportional to 1/distance Circle color indicates stellar temperature (see scale right of figure) Astrometry and RV amplitudes are given for an Earth analog receiving the same stellar flux as Earth receives from Sun (reflected light) Expected detection limit for near-IR RV Habitable Zones within 5 pc (16 ly): surveys (SPIROU, IRD + others) Astrometry and RV Signal Amplitudes for Earth Analogs M-type stars 2. Finding the nearest habitable Exoplanets Direct imaging: Contrast challenge Habitable Zones within 5 pc (16 ly) Star Temperature [K] 1 Gliese 1245 A LP944-020 2 Gliese 1245 B SRC 1845-6357 A 3 Gliese 674 DEN1048-3956 4 Gliese 440 (white dwarf) Wolf 424 A 5 Gliese 876 (massive planets in/near HZ) A 6 Gliese 1002 Van Maanen's Star LHS 292 7 Gliese 3618 DX Cnc Ross 614 B 8 Gliese 412 A Teegarden's star 9 Gliese 412 B TZ Arietis 4 9 10 AD Leonis CN Leonis 11 Gliese 832 YZ Ceti Wolf 424 B 2 UV Ceti GJ 1061 7 EZ Aqu A,B & C LHS380 6 Proxima Cen BL Ceti Ross 248 1 Gl15 B Kruger 60 B Ross 154 Barnard's Star Ross 128 Ross 614 A Kapteyn's star 40 Eri C F 40 Eri B Procyon B Wolf 1061 Gl725 B 3 5 Gl725 A Gliese 1 Lalande 21185 Gl15 A 8 Lacaille 9352 Kruger 60 A 10 Sirius B 11 Luyten's star Gliese 687 AX Mic 61 Cyg A G Groombridge 1618 61 Cyg B Eps Indi Eps Eri α Cen B 40 Eri A Tau Ceti K α Cen A Procyon A Sirius M Circle diameter indicates angular size of habitable zone Circle color indicates stellar temperature (see scale right of figure) Contrast is given for an Earth analog receiving the same stellar flux as Earth receives from Sun (reflected light) 3. Characterizing exoplanets 3. Characterizing Exoplanets Transit Spectroscopy Starlight passing through planet atmosphere during transit reveals atmospheric composition Bean et al. 2010 NASA TESS mission finds best transits JWST transit spectroscopy 3. Characterizing Exoplanets Why directly imaging ? Woolf et al. Spectra of Earth (taken by looking at Earthshine) shows evidence for life and plants 3. Characterizing Exoplanets Taking images of exoplanets: Why is it hard ? 17 3. Characterizing Exoplanets 18 3. Characterizing Exoplanets Around about 50 stars (M type), rocky planets in Contrast and Angular separation habitable zone could be imaged and their spectra 1 λ/D 1 λ/D 1 λ/D acquired with ELTs λ=1600nm λ=1600nm λ=10000nm D = 30m D = 8m D = 30m K-type and nearest G-type stars are more challenging, but could be accessible if raw contrast can be pushed to ~1e-7 (models tell us it's possible) M-type stars Thermal emission from habitable planets around nearby A, F, G type stars is detectable with ELTs log10 contrast 4+ diameter space telescope can K-type stars image habitable planets around F-G-K stars in optical light G-type stars 1 Re rocky planets in HZ for stars within 30pc (6041 stars) F-type stars Angular separation (log10 arcsec) 3. Characterizing Exoplanets Around about 50 stars (M type), rocky planets in Contrast and Angular separation - updated habitable zone could be imaged and their spectra 1 λ/D 1 λ/D 1 λ/D acquired with ELTs λ=1600nm λ=1600nm λ=10000nm D = 30m D = 8m D = 30m K-type and nearest G-type stars are more challenging, but could be accessible if raw contrast can be pushed to ~1e-7 (models tell us it's possible) M-type stars Thermal emission from habitable planets around nearby A, F, G type stars is detectable with ELTs log10 contrast 4+ diameter space telescope can K-type stars image habitable planets around F-G-K stars in optical light G-type stars 1 Re rocky planets in HZ for stars within 30pc (6041 stars) F-type stars Angular separation (log10 arcsec) 3. Characterizing Exoplanets Approximate timeline Direct imaging + spectroscopy is the more promising technique for exoplanet characterization, but is also very challenging. Current systems can only detect thermal emission→ limited to young giant planets Near future (2020s): ● TESS + JWST transit spectroscopy ● WFIRST mission will measure reflected light of nearby giant planets at optical wavelengths ● Continuous progress from ground-based systems → will also reach reflected light (already some early results with high resolution spectroscopy) End 2020s/early 2030s: ● Habitable exoplanets spectroscopy with ELTs in near-IR, mostly around M-type stars ● Thermal imaging with ELTs for hotter stars 2030s+: ● Space mission (HabEx or LUVOIR): visible light spectroscopy (+ some near-IR). ● Further advances with ELTs, reaching deeper contrast, more targets, shorter wavelength Both tracks are complementary long term: ● Larger telescopes for better spectroscopy ● possible resolved imaging with interferometer ● fly-by (starshot) Breakthrough Initiatives Breakthrough Listen Radio and optical search for artificial signals from other civilizations. Uses multiple radio telescopes + optical spectroscopy. Breakthrough Starshot Send lightweight unmanned starchips to nearby exoplanets (flyby) using laser propulsion. Multi-GW ground-based laser coherent array focuses on meter- scale sail. Acceleration phase fow a few minutes, travel time ~20yr, flyby time ~1hr. Images/spectra sent back to Earth by laser comm Breakthrough Watch Identify and characterize nearby (<5pc) habitable planets using Earth-based (ground and space) observations. Breakthrough Watch will find targets for Breakthrough Starshot BTW Report Top Recommendations Phase 1 focused on Alpha Cen A & B Space-based astrometry (30cm telescope) 10 um ground-based imaging (ESO/VLT, Gemini, Magellan) Phase 2 efforts expands effort to dozens of nearby stars, includes spectroscopic characterization ELT instrumentation: • 10 um imaging of Earth-like planets around Sun-like and hotter stars • Near-IR/Visible imaging of Earth-like planets around nearby M stars (including Prox Cen b) RV & Astrometry: Possible participation to RV / Astrometry mission(s) TOLIMAN Space Astrometry Mission 30cm telescope accurately measures the angular separation between Alpha Cen A and B (~4” apart). Planet would orbiting one of the two stars will induce a periodic modulation of the angular separation. Now starting 6-month study, led by Peter Tuthill (Univ.