what will it take to find exolife - hot molhotmol.eu/pdf/5_ab3_findingexolife_jkuhn.pdf ·...

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

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”

The Coherent Signal Detection Problem. Power Spectra

Pnoise = σ2/N

Psig/Pnoi N

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

Drake, 1960: Beginning of

observational SETI (and NRAO)

2 stars for 2 months

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)

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”

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

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

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

Carrigan 2009 ApJ:No Dyson spheres in IRASIR survey

Wright et al. 2014No Dyson Sphere’s in WISEsurvey

Darya Rios

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…)

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

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

Simulating Earth-like Visual

Brightness SignalsVisible brightness variation is dominated by scattered sunlight

Visual Reflectance/day

Man-made lights/night

1010

Type I Civilization Heat Islands

Biological and technological activities produce unavoidable heat

Detroit

Chicago

Columbus

St.Louis

+10C

10μm observations from space

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.

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

This is a scattered light problem…

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

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

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)

WLT: Keck =

mirror +

moving mass

support

structure

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

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

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

The telescope “landscape”

PLANETS

DKIST

Hale (OAT)

SOLARC, NST

Low-scatteringTelescopes

1.9m PLANETS Telescope on Haleakala

Figure 19: The first telescope mode excited b

y wind will have a frequency higher than 50Hz

World’s largesthigh dynamic rangetelescope

Daniel K InouyeSolar Telescopeon Haleakala

Worlds Largest Telescopes (WLT)

GMT

TMT

EELT

Keck OWL

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

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

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

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

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

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

Mirror phases encoded in the psf

One mirror phasechange p/2

0.01 arcsec

Image domain mirror phase recovery

88m Airy diffractionring

PSF from 59 randommirror phases

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

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

Slumped 6mm plate glass, measured

parabolicity, no polishing

Provisional patent submitted

Large active mirrors can have

stiffness created from a 3D printed

hybrid sandwich structure

Provisional patent submitted

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

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

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

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

An ExoLife Finder Telescope for Prox - B

Adjusting segment phases creates movable 10-8 “dark hole”

Coronagraphic Interferometric Telescope

SPIE 9145, 91451, 2014

A Prox-b Telescope/Coronagraph from an ExoLifeFinder telescope