colors of a second earth - 東京大学 · 2016-11-07 · a terrestrial planet candidate in a...
TRANSCRIPT
![Page 1: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/1.jpg)
Colors of a Second Earth: a Future Path Towards Astrobiology From Space
2016 Inter-Academy Seoul Science Forum 17:00-17:30 November 3 @ The Plaza Hotel, Seoul
Yasushi Suto
Department of Physics and Research Center for the Early Universe, the University of Tokyo
![Page 2: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/2.jpg)
Issac Asimov (1941): Nightfall
Illustration by Alisa Haba n Planet “Lagash” has no “night” except the total
eclipse due to an inner planet every 2049 years n People understood the true world for the first time
(illustration: Alisa H
aba)
![Page 3: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/3.jpg)
Nightfall: We didn’t know anything
n “Light !” he screamed. Aton, somewhere, was crying, whimpering horribly like a terribly frightened child. “Stars -- all the Stars -- we didn't know at all. We didn't know anything.”
![Page 4: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/4.jpg)
Adieu, dit le renard. Voici mon secret. Il est très simple : on ne voit bien qu'avec le coeur. L'essentiel est invisible pour les yeux.
The essential is invisible for the eyes
Le Petit Prince: Antoine de Saint Exupéry
![Page 5: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/5.jpg)
Don’t assume that everything in the world is bright
http://earthobservatory.nasa.gov/Features/NightLights/page3.php
![Page 6: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/6.jpg)
L'essentiel est invisible pour les yeux
Even more important and surprising things may be hidden somewhere in dark regions of the universe
![Page 7: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/7.jpg)
Yes, our universe is full of planets
In 1995, Mayor and Queloz made us realize that
“we didn’t know anything”
51 Peg b →
http://exoplanet.eu/
3476 planets 2600 planetary systems 590 multiple planet systems (as of July 2016)
Year of discovery Num
ber
of p
lane
ts d
isco
vere
d pe
r ye
ar
![Page 8: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/8.jpg)
How to find planets ? n Radial velocity
n Periodic modulation of the velocity of star due to the presence of planets
n Transit n Periodic dimming of the
stellar light due to the occultation of planets in front of the star
n Direct imaging n Separate the light from the
star and planets Ground-based observation (2000)
![Page 9: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/9.jpg)
Kepler mission (March 6, 2009 launch) Photometric survey of transiting planets
Searching for terrestrial/habitable planets
http://kepler.nasa.gov/
![Page 10: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/10.jpg)
Are we alone ?
a Pale Blue Dot ? or pale blue dots ?
![Page 11: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/11.jpg)
Science with exoplanets
n the final question: Are we alone ? n origin of the earth n origin of the Solar System n habitable planets ⇒ origin of life n signature of extra-terrestrial life ? ⇒ extra-terrestrial intelligence ?
“Where are they ?” E.Fermi (1950)
![Page 12: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/12.jpg)
Earth imaged by Voyager 1 (February 4, 1990)
n Image from 40
AU away n A Pale Blue Dot
(Carl Segan)
![Page 13: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/13.jpg)
Earth and Moon from Saturn (2013)
n Viewed from Cassini on July 20, 2013 n about 20,000 happy Americans are waving their
hand towards Cassini, but how can we know that ?
![Page 14: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/14.jpg)
Can we detect signatures of life on our Earth ?
![Page 15: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/15.jpg)
Search for signatures of life on “Earth” with Galileo mission! (1990)
n Launched in May, 1986 n Earth observed on
December 8, 1990 n Conclusion: it is likely
that life exists on Earth ! n Abundant O2
n Red-edge of vegetation n CH4 abundance out of
thermal equilibrium n Artificial pulsed radio signal
Sagan, Thompson, Carlson, Gurnett & Hord: Nature 365(1993)715
![Page 16: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/16.jpg)
Sagan et al. (1993): spectrum of atmosphere
Strong O2 absorption @A-band(0.76µm)
![Page 17: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/17.jpg)
Red edge of (exo)plants: a possible biosignature in exoplanets
n Red-edge n Significant increase
of reflectivity of leaves on Earth (terrestrial planets) for λ>7000Å
n Widely used in the remote-sensing of our Earth Seager, Ford & Turner
astro-ph/0210277
Reflection spectrum of leaves
Chlorophyll Chlorophyll
![Page 18: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/18.jpg)
Sagan et al. (1993): colors of the earth
Chile
Argentina
Peru/Colombia
Red-edge of the vegetation on the earth detected by the Galileo mission
Wavelength [µm]
Refle
ctiv
ity
![Page 19: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/19.jpg)
Simulated Earth observed at 10pc away
![Page 20: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/20.jpg)
Habitable zone around host stars
Kasting, Kopparapu, Raminez & Harman: arXiv:1312.1328
![Page 21: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/21.jpg)
Occurrence of earth-size habitable planets around Sun-like stars
n Planets with (1-2) Earth radius around GKstars n Kepler Transit planets corrected for selection effect n 11±4 % (1-4 times the Solar flux on the earth) n 5.7+2.2-1.7 % (orbital period of 200-400days)
Petigura, Howard & Marcy: arXiv:1311.6806
![Page 22: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/22.jpg)
Starshade project: direct imaging of a second earth
Space telescope + occulting satellite at 50,000km away! (Princeton Univ. + JPL/Caltech)
![Page 23: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/23.jpg)
Colors of a Second Earth: estimating the fractional areas of ocean, land and vegetation
of Earth-like exoplanets ApJ. 715(2010)866, arXiv:0911.5621
Colors of a Second Earth. II: Effects of Clouds on Photometric Characterization of Earth-like
Exoplanets ApJ. 738(2011)184, arXiv:1102.3625
n Yuka Fujii, H.Kawahara, A.Taruya, Y.Suto (Dept. of Phys., Univ. of Tokyo), S.Fukuda, T.Nakajima (Univ. of Tokyo, Center of climate system research), Edwin Turner (Princeton Univ.)
http://www.space.com/scienceastronomy/color-changing-planets-alien-life-100513.html
![Page 24: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/24.jpg)
n Beyond a pale blue dot n Impossible to spatially resolve the surface of
a second earth n Color should change due to the rotation n A second earth = a dot
Colors of a second earth
![Page 25: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/25.jpg)
n Adopted Earth data in March n Spin inclination = 0 (vernal equinox) n cloudless
A pale blue dot ? Not really 0.08
0.00
time[hour]0.0 24.0
Eurasia
America
0.4-0.5[μm]
0.5-0.6[μm]
0.6-0.7[μm]0.7-0.8[μm]
Fujii et al. (2010)
Simulated photometric light-curves
of Earth
Ref
lect
ivit
y
Africa
![Page 26: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/26.jpg)
Estimating fractional areas of surface components from colors of a second earth
n 2 week observation of a cloudless Earth at 10 pc away
n Reasonably well reproduced
n possible to identify vegetation ! Fujii et al. (2010)
![Page 27: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/27.jpg)
Surface latitude map estimated from real satellite data with cloud model
ocean
soil
vegetation
cloud snow
Fujii et al. (2011)
![Page 28: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/28.jpg)
Proxima Centauri b
![Page 29: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/29.jpg)
A terrestrial planet candidate in a temperate orbit around Proxima Centauri
n G.Anglada-Escude et al. Nature 25 August 2016 issue, 536(2016)437 n Proxima Centauri b
n Orbital period 11days n Mp sin i =1.3 Mearth
n Eccentricity < 0.35 n Semi-major axis = 0.05 AU n Equilibrium temperature = 230 K
http://www.eso.org/public/usa/news/eso1629/
![Page 30: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/30.jpg)
Breakthrough Initiatives
n A program founded on July 20, 2015 by a Russian internet investor Yuri Milner to search for extraterrestrial intelligence n Breakthrough Listen to discover signs of
extraterrestrial civilizations through radio and laser transmissions
n Breakthrough Message to study the ethics of sending messages into deep space
n Breakthrough Starshot to develop a proof-of-concept light sail spacecraft fleet capable of making the journey to Alpha Centauri
http://breakthroughinitiatives.org/Initiative
![Page 31: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/31.jpg)
Breakthrough Starshot
n StarChip n A cm-sized nano-spacecraft of several grams n With camera, computer, communication laser,
plutonium power source, and light sail n A 4m×4m light sail for each spacecraft is
accelerated by the focused ground-based lasers n 0.2c in 10 minutes
n A fleet of 1000 StarChips to Proxima Centauri in 20 years
n Technology not available yet, but in 20 years
http://breakthroughinitiatives.org/Initiative/3
![Page 32: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/32.jpg)
StarChip
![Page 33: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/33.jpg)
Light sail accelerated by ground lasers
![Page 34: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/34.jpg)
Summary a second earth ≠ a pale blue dot ! n Future direct imaging of daily change of colors
of another earth is challenging, but may reveal the presence of ocean, land, cloud, and/or even vegetation on their surface
n Detection of a second Earth may not be a mere fairly tale nor a science fiction any more
n Detection of oxygen, water vapor, and even the red-edge should be a promising path towards astrobiology from space
![Page 35: Colors of a Second Earth - 東京大学 · 2016-11-07 · A terrestrial planet candidate in a temperate orbit around Proxima Centauri ! G.Anglada-Escude et al. Nature 25 August 2016](https://reader034.vdocuments.site/reader034/viewer/2022042222/5ec94d2ddd3b02355545f78d/html5/thumbnails/35.jpg)
Take-home message Exoplanets are very faint,
but the future of exoplanetary science
is amazingly bright.
“We didn’t know anything” (Issac Asimov 1941) “Where are they ?” (Enrico Fermi 1950)