Are We Alone? Chris De Pree RARE CATS June 2002

The Questions Are there other planetary systems? How do we detect other planetary systems? What is Life? How common are the conditions favorable to life? How might we detect other life?

Are there other Planetary Systems? An old question We are here Science Fiction How do stars form? –Gravitational collapse –Protostar –Protostellar disks

Protostellar Disks: Beta Pictoris

How do we detect other planetary systems? Direct imaging –Benefits –Drawbacks –Transits Astrometry –Benefits –Drawbacks Doppler Shift Technique –Method of choice

Direct Imaging Relative Brightness –Searchlight and Firefly Angular Separation –From the surface of the Earth Keck (0.5”, 0.04” with adaptive optics) –From Space HST (0.04”) –1 AU is 1” at 1 pc Most stars are much further away

Direct Imaging: HST (Gliese 229A and 229B)

Spectra of Planetary Atmospheres

Planetary Transits

Direct Imaging--The Future Best Hope: Interferometry Terrestrial Planet Finder (NASA) Darwin (ESA) Simulated Interferometric Image –Venus, Earth, Mars

DARWIN 2015 Launch 6 1.5m Tel. Formation flying

Astrometry The wobble of the Sun due to Jupiter as seen from 10 pc (2 million Astronomical Units)

Doppler Shift Technique

The Planets So Far (>50!) No.NAMEMsiniPSMAEcc.Vel (Mjup)(d)(m/s) 1 HD HD HD Peg GJ876c HD168443b HD HD HD

Sample of Systems Discovered The First: 51 Pegasi –Mayor & Queloz (1995) –Why did it take so long? Upsilon Andromeda 47 Ursa Majoris The most recent: Eta Eridani Many with small, elliptical orbits

51 Pegasus (look for the wobble!)

Upsilon Andromeda

47 Ursa Majoris (~3 year period)

Epsilon Eridani (~7 year period)

What is life? Replication? Motion? Problems with definition? What is intelligence? How does intelligence arise?

Astrobiology (SETI Online) “The development of Exobiology and Astrobiology as interdisciplinary research fields has brought together astronomers, biologists and funding opportunities in a way that wasn't possible ten years ago.” “Much of the organic material found on the Earth in its earliest years probably had an interstellar heritage.”

Looking for Organic Molecules On Earth (Miller-Urey Experiment) In the Interstellar Medium (molecular lines) –Ethyl alcohol (CH 3 CH 2 OH) –Formaldehyde (H 2 CO) –Methyl Cyanoacetylene (CH 3 C 3 N) –Acetylaldehyde (CH 3 CHO) Radio waves penetrate the ISM

Conditions Favorable to Life Lifetime of parent star –High Mass Stars (millions of years) –Low Mass Stars (billions of years) –Most stars are low mass The “Habitable Zone” –Temperature Gradient –Tidal Forces might extend zone Liquid Water

Habitable Zones around known stars

Should we look for other civilizations? The Drake Equation N = R * × f p × n e × f l × f i × f c × L Solid: Star formation rate, fraction of stars with planets, number of Earth- like planets, Shaky: Chance that life arises, chance that intelligent life arises,...

How might we detect civilizations? SETI (Search for ExtraTerrestrial Intelligence) Radio Telescopes The “Water Hole”

Will Life Always Arise?

Can Life Survive Long Term?

What Kinds of Messages are we Sending into the Universe?

Recent Proposal e.g. Rare Earth, Peter D. Ward & Donald Brownlee “the alien search is likely to fail…”

(Paul) Allen Telescope Array (ATA) $12.5 Million Scanning Program “Frequency Space”

Conclusions Planetary systems and life- supporting conditions are abundant In years, we may have a list of 100s of planetary systems With new telescopes, we will be able to explore atmospheres of other planets Detecting communicative intelligent life might be possible in the Galaxy