Transcript Are We Alone?

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. NAME
P
(d)
2.986
3.024
3.097
SMA
Ecc.
HD83443
HD46375
HD187123
Msini
(Mjup)
0.35
0.25
0.54
0.038
0.041
0.042
0.08
0.02
0.01
Vel
(m/s)
56.0
35.2
72.0
51Peg
0.46
4.231
0.052
0.01
55.2
GJ876c
HD168443b
HD179949
HD160691
HD27442
0.56
7.73
0.86
1.87
1.13
30.12
58.10
3.092
743
426
0.13
0.29
0.043
1.6
1.15
0.27
0.53
0.0
0.62
0.02
81
473
112
54
34
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1
2
3
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8
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54
55
56
57
58
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 (CH3CH2OH)
– Formaldehyde (H2CO)
– Methyl Cyanoacetylene (CH3C3N)
– Acetylaldehyde (CH3CHO)
 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* × fp × ne × fl × fi × fc × L

Solid: Star formation rate, fraction of
stars with planets, number of Earthlike planets,
 Shaky: Chance that life arises,
chance that intelligent life arises, . . .
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How might we detect civilizations?
SETI (Search for ExtraTerrestrial
Intelligence)
 Radio Telescopes
 The “Water Hole”

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”
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Conclusions
Planetary systems and lifesupporting conditions are abundant
 In 10-15 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
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