Download F p = Fraction of good stars with planets

The Search for Life in the Universe
Dr. Dan Caton
Professor and Observatory Director
November 9, 2011
What we will look at…
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Overview of the search for extraterrestrial life
Brief review of exploration in our solar system
The chances for life elsewhere in our Galaxy
The problem of SETI—the search for
extraterrestrial intelligence
Historical, current and planned searches
Efforts to transmit
Why have we not found ET?
The search for respectability
International Astronomical
Union created a
Commission on ETL in
1982
Long of Interest
Poster from 1800-01
Intelligent Life Here?
Started by panspermia?
Venus too hot?
Our Moon
Life from Earth, in subsurface ice?
Mars—we looked at this already…
Jupiter or Saturn?
Maybe on one of the moons?
Beneath the ice on Europa?
Or…
Saturn’s Titan: Cassini / Huygens Mission
Cassini still orbiting Saturn,
Huygens probe landed on
its moon, Titan a few years
ago.
Beyond our Solar System: we turn to the stars…
SETI: Turn outward
for the Search for
Extraterrestrial
Intelligence: Searches
and Transmissions
Will confine ourselves to
Milky Way Galaxy
Questions to investigate
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What are the chances that intelligent life exists?
What evidence is there for life-supporting
extrasolar planets?
How does life form and evolve?
How do we communicate?
Can they exist?
Frank Drake first calculated
the chances of there being
civilizations in our Galaxy
with whom we could
communicate.
He developed his equation,
which became known as the
Drake Equation…
Frank Drake
The Drake Equation
N = R fS fP ne fl fi fc L
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R = Average rate of star formation (stars/year)
fS = fraction of stars that are “good” Suns
fP = Fraction of good stars with planets
ne = number of planets per star in ecoshell
fl = fraction of planets on which life develops
fi = fraction that develop intelligence
fc = fraction that reach electromagnetic
communicative phase
L = Lifetime in communicative phase (years)
R = rate of star fromation
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R ~ 4 stars/year
in our Galaxy
This probably
the best known
variable in the
Drake Equation
FS = fraction of stars that are “good” Suns
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O, B stars too
short-lived
K, M stars – flares
dangerous?
A –F stars just
right?
Fp = Fraction of good stars with planets
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Several hundred
exoplanets now
known (+ Kepler)
Something on the
order of 0.1 or 10%
of stars have
planets? Or, most?
Don’t really know
since just starting to
find small planets.
ne = number of planets per star in ecoshell
(the habitable zone)
ne ~ 1 - 2
fl = fraction of planets on which life develops
fl = fraction of planets on which life develops
How does life begin? The Miller-Urey Experiment
1952, University of
Chicago. Produced
amino acids.
Recent analysis (published 4/2011)
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After Miller’s death in 2007 the vials were re-examined,
including some from unpublished experiments.
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Vials associated with the original, published experiment
contained far more organic molecules than Stanley Miller
realized — 14 amino acids and five amines.
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The 11 vials scientists recovered from the unpublished
aspirator experiment, however, produced 22 amino acids
and the same five amines at yields comparable to the
original experiment.
Newest idea: life formed in ocean bottom
Timeline of Life on Earth
Our Ancestors began several million years ago
Primates
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Extinction of
dinosaurs
allowed
mammals (and
us) to develop
65 My ago
Are we the
pinnacle?
Is intelligence inevitable?
fi = fraction that
00
develop
intelligence
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Evolution and
natural selection
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not pointed to
intelligence
Dominant life form?
If replayed the tape
(Stephen J. Gould)
fi = 1?
fc = fraction that reach electromagnetic
communicative phase
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Fraction that
invent radio
Same physics
everywhere in
Universe
L = Lifetime in communicative phase (years)
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So far, ~ 100
years
Lots of ways to
end … bad ones
here end life
Or, we end the
“communicative”
part…
… by having signals disappear!
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Optical fiber
Satellite
TV/Radio
Low power
Wi-Fi
Small cell
phone
transmitters
Internet TV
Cell radio
L is important
because…
… “f’s” multiply out to ~ 1, so N ~ 1
N = R fS fP ne fl fi fc L
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So may be 100 + 10x or so civilizations in the
MWG to find
Let’s go look!
We will look in the radio—why?
Where in radio? Meet ET at the “Water Hole”
TV
First search was at Greenbank, WV …
… Project Ozma
• 1960
• 200 hours observing two
nearby solar stars in 21-cm
• nothing found but a
secret satellite
85-ft Harvard Dish has been used
Paul Horowitz
NASA thinks big: Cyclops
Details…
A thousand 100-meter dishes
• Could detect ET’s
broadcast, if within
100 ly (>6,000
stars)
• ~5 billion $ (half
what we spend in
US every day, or
<0.5% of US wars
cost since 2001)
NASA’s nemesis
William
Proxmire, the
late Senator
from
Wisconsin
Golden Fleece
Awards
Called off by
Carl Sagan
NASA’s initial hardware
Software: see a pattern?
This is a plot of signal (intensity of dots) in frequency vs. time
Here it is
A test: detection of Pioneer 10
But—Congress killed NASA’s SETI project…
First Intentional Transmission
The signal: digital
Let’s look at why digital …
Digital advantage sketch…
Graphical
The message consists of 1679 bits,
arranged into 73 lines of 23
characters per line (these are both
prime numbers, and may help the
aliens decode the message).
It consists, among other things, of
the Arecibo telescope, our solar
system, DNA, a stick figure of a
human, and some of the
biochemicals of earthly life.
For less than 3 minutes it was the
brightest source in the MWG at
that frequency.
Target: M13 (30,000 ly…)
Our unintentional signals
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Radio is line-of-sight
What is not received (most is not),
leaks out into space
Lets tune into …
…Channel
Earth
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As seen
from
Barnard’s
Star
NA East
NA East
Coast sets
Coast rises
Western
Europe
rises
Aust.
Japan
rise
Aust.
Japan
set
Western
Europe
sets
Cartoon…
Pioneer
10 & 11
Plaques
(1972-3)
Voyager Record: “Best of Earth”
Images and Sounds
• “Best of Earth”
• Narrated by Kurt Waldheim (19182007), then U.N. Secretary General
and now known (embarrassingly..) to
have been a Nazi war criminal.
Friend of fellow Austrian
Aaaaanold….
SETI@home
Uses data from …
“Parasitic” observations at Arecibo Telescope
Allen Array
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350 6.1-m dishes
1 – 10GHz (the
“water hole”)
Artist concept
Funded by Microsoft
co-founder Paul Allen
(and COB, Charter
Communications)
Newer, offset
Gregorian design
SETI Inspired Carl Sagan’s Contact
Ellie Arroway (Jodi Foster)
loosely based on (real) Jill
Tarter, former head of
NASA SETI, now at the
SETI Institute
Why no detection? …
…Enrico Fermi:
“Where is
everybody?”
Would not be complete without mentioning
Maybe in Historical Times? (Ezekiel 1)
4 I looked, and I saw a windstorm coming out of the north—an
immense cloud with flashing lightning and surrounded by
brilliant light. The center of the fire looked like glowing metal, 5
and in the fire was what looked like four living creatures. In
appearance their form was human, 6 but each of them had four
faces and four wings. 7 Their legs were straight; their feet were
like those of a calf and gleamed like burnished bronze. 8 Under
their wings on their four sides they had human hands. All four of
them had faces and wings, 9 and the wings of one touched the
wings of another. Each one went straight ahead; they did not
turn as they moved. ….
Interesting, but which myths do we choose to believe? (Brown
Mountain Lights and the Cherokee myths…
That’s our SETI discussion .. Questions?