Are We Alone?Are We Alone?

Chris De PreeRARE CATS

June 2002

The QuestionsThe QuestionsAre 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 Are there other Planetary Systems?Systems?An old questionWe are hereScience FictionHow do stars form?

– Gravitational collapse– Protostar– Protostellar disks

Protostellar Disks: Beta PictorisProtostellar Disks: Beta Pictoris

How do we detect other planetary How do we detect other planetary systems?systems?Direct imaging

– Benefits– Drawbacks– Transits

Astrometry– Benefits– Drawbacks

Doppler Shift Technique– Method of choice

Direct ImagingDirect ImagingRelative Brightness

– Searchlight and FireflyAngular 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: HSTDirect Imaging: HST(Gliese 229A and 229B)(Gliese 229A and 229B)

Spectra of Planetary AtmospheresSpectra of Planetary Atmospheres

Planetary TransitsPlanetary Transits

Direct Imaging--The FutureDirect Imaging--The FutureBest Hope: InterferometryTerrestrial Planet Finder (NASA)Darwin (ESA)Simulated Interferometric Image

– Venus, Earth, Mars

DARWINDARWIN2015 Launch6 1.5m Tel.Formation flying

AstrometryAstrometryThe wobble of the Sun due to Jupiter

as seen from 10 pc (2 million Astronomical Units)

Doppler Shift TechniqueDoppler Shift Technique

The Planets So Far (>50!) No. NAME Msini P SMA Ecc. Vel (Mjup) (d) (m/s) 1 HD83443 0.35 2.986 0.038 0.08 56.0 2 HD46375 0.25 3.024 0.041 0.02 35.2 3 HD187123 0.54 3.097 0.042 0.01 72.0 . . . 8 51Peg 0.46 4.231 0.052 0.01 55.2 . . . 54 GJ876c 0.56 30.12 0.13 0.27 81 55 HD168443b 7.73 58.10 0.29 0.53 473 56 HD179949 0.86 3.092 0.043 0.0 112 57 HD160691 1.87 743 1.6 0.62 54 58 HD27442 1.13 426 1.15 0.02 34

Sample of Systems DiscoveredSample of Systems DiscoveredThe First: 51 Pegasi

– Mayor & Queloz (1995)– Why did it take so long?

Upsilon Andromeda47 Ursa MajorisThe most recent: Eta EridaniMany with small, elliptical orbits

51 Pegasus (look for the 51 Pegasus (look for the wobble!)wobble!)

Upsilon AndromedaUpsilon Andromeda

47 Ursa Majoris (~3 year period)47 Ursa Majoris (~3 year period)

Epsilon Eridani (~7 year period)Epsilon Eridani (~7 year period)

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

Astrobiology (SETI Online)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 MoleculesLooking for Organic Molecules On Earth (Miller-Urey Experiment) In the Interstellar Medium (molecular lines)

– Ethyl alcohol (CH3CH2OH)– Formaldehyde (H2CO)– Methyl Cyanoacetylene (CH3C3N)– Acetylaldehyde (CH3CHO)

Radio waves penetrate the ISM

Conditions Favorable to LifeConditions Favorable to LifeLifetime 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 Habitable Zones around known starsstars

Should we look for other Should we look for other civilizations?civilizations?

The Drake EquationN = R* × fp × ne × fl × fi × fc × 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?How might we detect civilizations?SETI (Search for ExtraTerrestrial

Intelligence)Radio TelescopesThe “Water Hole”

The “Water Hole”The “Water Hole”

Will Life Always Arise?Will Life Always Arise?

Can Life Survive Long Term?Can Life Survive Long Term?

What Kinds of Messages are we What Kinds of Messages are we Sending into the Universe?Sending into the Universe?

Recent ProposalRecent Proposale.g. Rare Earth, Peter D. Ward & Donald

Brownlee“the alien search is likely to fail…”

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

ConclusionsConclusionsPlanetary systems and life-supporting

conditions are abundantIn 10-15 years, we may have a list of

100s of planetary systemsWith new telescopes, we will be able to

explore atmospheres of other planetsDetecting communicative intelligent life

might be possible in the Galaxy