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The Search for Other Earths

Ray VillardSTScI

August 17, 2009

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“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

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Galileo, 1609

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1584"There are countless suns and countless earths all rotating around their suns in exactly the same way as the seven planets of our system . . . The countless worlds in the universe are no worse and no less inhabited than our Earth”

Giordano Brunoin De L'infinito

Universo E Mondi

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Exoplanet Discovery TimelinePast• 1992 Pulsar planets • 1994 Protoplanetary disks resolved in visible light• 1995 Radial velocity extrasolar planet discovery• 1999 Extrasolar planet transits observed• 2001 Extrasolar planet atmospheres measured• 2003 New planets discovered with transit method• 2004 Planet discovered with microlensing method• 2006 Transit planet day side temperature measured

Present• Transiting hot Jupiter atmospheres measured in detail• First transiting super- Earths• Direct imaging of young hot Jupiters

Future• 2011 Statistical frequency of earthlike planets determined (Kepler)• 2011 Planets found around Alpha Centauri??• 2013 JWST: transits and eclipses of planet around nearby red

dwarfs • 2015 Search for nearby Earths and super Earths• 2030 Definitive sampling of biospheres on exoplanet survey• 2040? Direct imaging of all sizes of exoplanets• 2101? First interstellar AI mission to directly sample exobiology

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THE OBSERVABLE DRAKE EQUATION

ETL = NP X FTP X FPw X FPL

ETL = Planets with extraterrestrial life in the GalaxyNp = Number of exoplanetsFpt = Fraction of terrestrial planetsFPw = Fraction of terrestrial planets with liquid waterFPl = Fraction of terrestrial planets with carbon-based life

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Planet Detection

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Detectability of the Solar SystemPrecision: 3 m/s

Saturnsaturn

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Mayor & Queloz 1995, Nature, 378, 355.Marcy & Butler 1996, Ap.J.Lett., 464, L147.

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Sagittarius Window Eclipsing Extrasolar Planet Search

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An optical/near-infrared space telescope with a filled aperture of at least 8-meters will probably be required to definitively answer the question “Are we alone?”

HST 2.4-mJWST 6.5-m ATLAST 8-m ATLAST 16-m

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2-m 4-m 8-m 16-m

Solar Type Stars

All Stars

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Life in the Universe

All Life

Liquid water

Carbon-based

Chemical Energy

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• A thermodynamic disequilibrium

• An environment capable of maintaining links between carbon, hydrogen, and other atoms

• A liquid environment

• A molecular system that can support Darwinian evolution.

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Total number of stars >100 billionTotal number of stars >100 billion

Total number of planets ~ several trillion ?Total number of planets ~ several trillion ?

Total number of moons ~ 10s of trillions ?Total number of moons ~ 10s of trillions ?

Earthlike Planets? .01% = 1 billion??Earthlike Planets? .01% = 1 billion??

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