what will it take to find exolife - hot molhotmol.eu/pdf/5_ab3_findingexolife_jkuhn.pdf ·...
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What will it take to find ExolifeJeff Kuhn, Institute for Astronomy, Univ. Hawaii, Maui
Darya Rios
1. “Technology:” electromagnetic leakage or beamed messages
Signal’s depend on exo-sociology, so…absence of signal not easily interpretable
Conventional SETI, spectral (monochromatic) temporal patterned energy
2. Thermodynamics
“life requires power, generates heat” (Dyson and derivatives)
3. Atmospheric or chemical tags
Spectroscopic
Earth-like assumptions?
4. A “How to” guide: Technical Solution for (2) and (3)
HotMol Feb. 2017
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1. The search for extraterrestrial intelligence *SETI* “ is a search for extra-terrestrial civilization (ETC) …or
technology
• Defining SETI concepts go back to 1950’s and ’60s
– Fermi 1950: Fermi paradox
– Cocconi and Morrison 1959: SETI radio concept, 21cm
– Dyson 1960: Dyson sphere
– Drake 1961: Ozma, NRAO, 21cm search
– Kardashev: 1964, Type I-III civilization’s power utilization
– Shklovskii and Sagan 1966: “Intelligent life in the Universe”
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The Coherent Signal Detection Problem. Power Spectra
Pnoise = σ2/N
Psig/Pnoi N
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Cocconi and Morrison: Nature, 1959
• “It is reasonable to expect that sensitive receivers for this frequency will be made at an early stage of the development of radio astronomy. That would be the expectation of operators of the assumed source, and the present state of terrestrial instruments indeed justifies the expectation. “
• Astronomy and atomic physics guide the search strategy: HI 1420MHz, 21cm wavelength
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Drake, 1960: Beginning of
observational SETI (and NRAO)
2 stars for 2 months
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Searching for beamed alien signals
• Phoenix Project (1998-2004)– Arecibo, SETI institute – 800 stars searched– Most sensitive broad-band radio
search for beamed signals
• Allen telescope array (2007)– SETI Institute project with
Berkeley interferometer array– 30M$ private funding– DOD funding in 2011
• Optical SETI, intercepted beamed laser-like transmissions– COSETI (10” telescopes)– Berkeley (72” telescope)
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Finding a needle in a haystack…in a haystack somewhere in Europe
“No Earth-like SETIexperiment on eventhe nearest star coulddetect Earth radio ‘leakage’”
“A high-power radar beamedoutward could be detected byEarth-like SETI at 30pc”
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2. Dyson 1960Civilization, heat and thermodynamics
• Dyson sphere – Power-hungry civilizations use their stars radiated power
• Advanced civilization uses power, P, and must produce heat. Most of an ETC’s power is eventually converted into thermal radiation
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Kardashev, 1964
• Transmission of Information by Extraterrestrial Civilizations
– Type I (Earth is “early Type I”) uses intercepted stellar power for civilization’s purposes
– Type II Uses substantially all of a host-stars power for civilization
– Type III Uses substantially all of a host-galaxies power for civilization
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Shklovskii and Sagan, 1966
• Intelligent life uses more power as it advances…
– K = log10(P)/10 – 0.6 P-measured in Watts
– Earth (now consuming about 15TW) has K = 0.7
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Carrigan 2009 ApJ:No Dyson spheres in IRASIR survey
Wright et al. 2014No Dyson Sphere’s in WISEsurvey
Darya Rios
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Type-I thermodynamic signals (Earth-likes?)
• A useful normalizing factor is the power the planet intercepts from its host star, Pstar: Let Ω=P/Pstar
• (Even just manipulating the information content of a civilization could eventually require more power than any other function. On the earth our global information doubling time is 2 years…)
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Life and planetary scale heat life uses energy and generates heat
power consumption correlates w. information, doubles over 3yr
power consumption increasing faster than population,
“Advancement parameter”
Ω(t)=P(t)/Pstar,
10.10.010.00110-410-510-610-7
Roman periodglobal powerproduction
Present global powerproduction
Present human biological heatproduction
Photosyntheticglobal powerconsumption
Presentglobal opticalpower production
Global solarpowerabsorption
Global Warming
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Advanced life biosignaturesFinding advanced exolife
with ΩE < Ω < 1
Planet is “too warm”
compared to its stellar heat
budget
Thermal excess is
geographically clustered
Heat islands are not “too hot”
(not geothermal)
Reduced albedo due to
photonic power usage
Technology advancement
implies photonic power and
Ω → 1 Darya Rios
not this one
ETC Type I: planet with highIR/Vis brightness ratio
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Simulating Earth-like Visual
Brightness SignalsVisible brightness variation is dominated by scattered sunlight
Visual Reflectance/day
Man-made lights/night
1010
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Type I Civilization Heat Islands
Biological and technological activities produce unavoidable heat
Detroit
Chicago
Columbus
St.Louis
+10C
10μm observations from space
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An Earthlike civilization, thermal
detection: Ω ~ 0.01x50 of the current human civilization scaled from man-
made light signal
ETC F(10µm) signal with F(5µm) as reflectance
reference Total F
Simulated Thermal Civilization
Measured Thermal Civilization
Kuhn and Berdyugina, Int. Jour. As.Bio. 14, 401, 2015.
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Detecting faint astronomical sources with fixed
background brightness
D – Telescope diameterP – Point source brightness (phot/s)T – Integration time (s)Ω -- Angular resolution (λ/D)2
Bλ – Background brightness (phot/s/ster)S – Signal: P*D2*TN2 – Noise power: B*D2*Ω*T
S/N = P*D2Bλ*√𝑇/λ2
T =(S/N)*λ2/P2/Bλ / D4
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This is a scattered light problem…
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Stellar contrast of HZ Earthlikes
Habitable-zone optical/IR
contrast improves:
1. at longer wavelength
2. for cooler stars
3. for larger planets5REarthVis
10μm
5μm
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Detectable number of HZ advanced
Earth-like civilizations
2REarth
N scales as:D3
1/CΩR2
20
All stars within 60 light-years of Sun
N – number of detections
D – optical resolution diameter
C – limiting contrast sensitivity
Ω – advancement parameter
R – planet radius
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Finding exolife with the next
generation telescope...what does it
take? high level of scattered light suppression in order to see the faint terrestrial
planet against the optical “glare” of the nearby star adaptive optics at small λ/d and good coronagraph
sufficient sensitivity for detecting enough photons from the planet to allow statistical analysis of its variability
large aperture and low scattered light
low-enough thermal emissivity so that the planetary IR flux is not lost in the terrestrial thermal background
low IR emissivity (and low scattered light)
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WLT: Keck =
mirror +
moving mass
support
structure
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WLT’s: The Keck wavefront and
its PSF
A star looks like this withadaptive optics…
(Circular avg. removed)
Mirror Phase Errors
And like this when weremove the star…
(0.2 arcsec)3 order of magnitude
intensity range
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Off-axis telescopes
tohokuoffaxisshrt.ZMX
Configuration 1 of 1
3D Layout
Tohoku 1.85m off-axis telescope gregorian design concept11/14/2010
X
Y
Z
It is possible to fully baffle an OATfor scattered light suppression
Filled (unobstructed) pupil
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A 1.5m unobstructed better than a 5m (Palomar) telescope?
“Worlds largest night-time OAT”
An image of an exoplanet separated by two diffraction beamwidths from a star E. Serabyn1, D. Mawet1 & R. Burruss 1NATURE, 2010
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The telescope “landscape”
PLANETS
DKIST
Hale (OAT)
SOLARC, NST
Low-scatteringTelescopes
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1.9m PLANETS Telescope on Haleakala
Figure 19: The first telescope mode excited b
y wind will have a frequency higher than 50Hz
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World’s largesthigh dynamic rangetelescope
Daniel K InouyeSolar Telescopeon Haleakala
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Worlds Largest Telescopes (WLT)
GMT
TMT
EELT
Keck OWL
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How can an optical system
(like “Colossus”) break D2 scaling?
Colossus can relax rigid optical requirements compared to other
WLTs
Make it a narrow-field -- only a few arcsec -- telescope (F number
can be smaller and overall telescope smaller)
Make imaging system from scalable independent M1-M2 subunits
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col3.ZMX
Configuration 1 of 6
3D Layout
Colosus 0.1, 74m diameter5/21/2014
X
Y
Z
A Colossus Optical Configuration
60 x 8m phased-array telescopes
M1
M2
M1: 60 x 8m OAPM1 - R=40m parabolaImage F/ 5f = 380mM2: 60 x 45cm
74m
3.6m
This is where tip/tiltand adaptive wavefrontcorrections are made foreach subaperture
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Colossus Telescope
FOV: 8 arcsecStrehl ratio: S > 0.5 at wavelength, λ of 1000nm
Stre
hl
Surface: IMA
100.00
OBJ: 0.0000, 0.0000 (deg)
IMA: 0.000, 0.000 M
OBJ: 0.0006, 0.0000 (deg)
IMA: -0.005, 0.000 M
OBJ: 0.0000, 0.0006 (deg)
IMA: 0.000, -0.005 M
OBJ: -0.0006, 0.0000 (deg)
IMA: 0.005, 0.000 M
OBJ: 0.0000, -0.0006 (deg)
IMA: 0.000, 0.005 M
1.0000
col2.ZMXConfiguration 1 of 6
Spot Diagram
Colosus 0.1, 74m diameter8/27/2012 Units are µm.Airy Radius : 7.717 µmField : 1 2 3 4 5RMS radius : 0.406 7.860 7.860 7.860 7.860GEO radius : 0.590 20.138 18.229 20.138 18.229Scale bar : 100 Reference : Chief Ray
...If only the relative phase of each 8m telescope can be corrected
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How can an optical system
(like “Colossus”) break D2 scaling?
Colossus can relax rigid optical requirements compared to other
WLTs
Make it a narrow-field -- only a few arcsec -- telescope (F number
can be smaller and overall telescope smaller)
Make imaging system from scalable independent M1-M2 subunits
Relax the stiffness of the M1 backbone structure to match
intrinsic atmospheric phase errors, extra stiffness and mass is
wasted
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Sub-aperture piston phase errors come
from the atmosphere and a low-mass
truss structure
Atmosphere path errorPlot range -15 15 μm
Strehl of 0.5 needs 66nm (rms) mean phaseaccuracy between mirrors, or relative phaseerror < 0.8%
R0 = 20cm
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How can an optical system
(like “Colossus”) break D2 scaling?
Colossus can relax rigid optical requirements compared to other
WLTs
Make it a narrow-field -- only a few arcsec -- telescope (F number
can be smaller and overall telescope smaller)
Make imaging system from scalable independent M1-M2 subunits
Relax the stiffness of the M1 backbone structure to match
intrinsic atmospheric phase errors, extra stiffness and mass is
wasted
Measure and correct mirror phase using the bright source in the
FOV
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Mirror phases encoded in the psf
One mirror phasechange p/2
0.01 arcsec
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Image domain mirror phase recovery
88m Airy diffractionring
PSF from 59 randommirror phases
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How can an optical system
(like “Colossus”) break D2 scaling?
Colossus can relax rigid optical requirements compared to other
WLTs
Make it a narrow-field -- only a few arcsec -- telescope (F number
can be smaller and overall telescope smaller)
Make imaging system from scalable independent M1-M2 subunits
Relax the stiffness of the M1 backbone structure to match
intrinsic atmospheric phase errors, extra stiffness and mass is
completely wasted
Measure and correct mirror phase using the bright source in the
FOV
Decrease the areal mass density of M1 by replacing mass with
actuated force distribution
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Thin mirrors and gravity deformation:
Optimal actuator mass and spacing
D
a
zpp = 10ρa4/Et2
a, t in cm, E in Pa, rho cgsBorosilicate…Z = 25nm, a=20cm, t=5cm
M=100g t=1cm with a=10cmD=8m 5000 actuators
Area mass density 500kg/m^2 60kg/m^2
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Slumped 6mm plate glass, measured
parabolicity, no polishing
Provisional patent submitted
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Large active mirrors can have
stiffness created from a 3D printed
hybrid sandwich structure
Provisional patent submitted
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WLT scaling laws and Colossus
Keck
GMTTMT
EELT
OWL
*Col
Colossus mass and cost estimates from Dynamic Structures, Ltd....for same aperture as “conventional” telescope, one order of magnitude $ savings
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ELF Basics
Give up on “stiff (edge matched)” primary mirror Partially filled subaperature phased array
Give up on large field-of-view 2 arcsec, allows optically fast, small telescope volume
Carefully control the wavefront with the telescope, before reaching the instrument independent, phased, unobstructed high Strehlsubapertures
Replace structural mass with active mass, depend on tensile rather than compressive material properties decrease optical support system moving mass
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Telescope as coronagraph
What happens if we take the collecting area of a TMT but optimize for
dynamic range and spatial resolution?
This is a coronagraphy problem with segmented mirror optics
Its possible to achieve comparable resolution and sensitivity to Colossus
with a much smaller collecting area
A Partially Filled Aperture Interferometric Telescope
ParFAIT
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PSF of arrays of mirrors
PSF = PSF X PSF
),(2
)exp(
Function"Airy "
)()()(
yx
jj
k
akiS
O
kSkOkP
O S P
(“Structure Function”)
Aper = Aper * Aper
Aper = mirror window function (0,1)
PSF = 2D FFT Poweraj = mirror centers
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An ExoLife Finder Telescope for Prox - B
Adjusting segment phases creates movable 10-8 “dark hole”
Coronagraphic Interferometric Telescope
SPIE 9145, 91451, 2014
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A Prox-b Telescope/Coronagraph from an ExoLifeFinder telescope
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