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Welcome to
Starry Monday at Otterbein
Astronomy Lecture Series
-every first Monday of the monthMay 5, 2008
Dr. Uwe Trittmann
Today’s Topics
• How to find Life in the Universe
• The Night Sky in May
On the Web
• To learn more about astronomy and physics at
Otterbein, please visit
– http://www.otterbein.edu/dept/PHYS/weitkamp.a
sp (Observatory)
– http://www.otterbein.edu/dept/PHYS/ (Physics
Dept.)
How to find Life in the Universe
• What is Life?
• How to detect Life?
• Where to look for Life?
• Life vs. Intelligent Life
What is Life?
•
•
•
•
•
Has a metabolism
Uses energy
Reacts to changes in the environment
Reproduces
…
Transforms its environment
Changes to environment hopefully observable
What kind of Life?
• Focusing on carbon – liquid water based life
– Carbon as a chemically unique element
– (Liquid) Water as a powerful solvent and
reactant
• Assuming lower life-forms, we cannot
expect life to actively produce signals
• Look for life on the surface of a rocky
planet
Water
• Phase diagram of water dictates temperature and
pressure range for liquid
Minimal
pressure:
610 Pa
-18º C: life on
Earth exists
+123º C: life on
Earth exists
Where to look for Life?
• Where you can find (detect) it ;-)
• If carbon-liquid water based life exists on
the surface of a planet
– Planet must have atmosphere for liquid water to
exist
– Planet must receive enough energy from host
star to liquify water
Planet must be in the habitable zone (HZ) of its
host star
Definition of “Habitable Zone”
• Region around a star where stellar radiation
maintains liquid water over a substantial part of
the surface of a rocky planet
• Note: planet must be big enough to hold on to its
atmosphere, and possibly replenish it through
outgassings from its interior.
Extend of HZ depends on time
•
•
•
•
Sun gets brighter as it ages
Planets orbits change over time
Planets rotational axis inclination changes
Early Solar system:
– Venus, Earth in HZ, Mars partially
• Now:
– Earth, Mars in HZ
Habitats beyond the HZ
• Temperature, pressure too low  go to interior
of planets/moons
– Earth: 5km under surface liquid water can exist
• Tidal heating: gravitational distortions will heat
interior of (soft) moons
– Io  Volcanism driven by Jupiter
– Europa  liquid water under ice?
• Saturn’s Titan
Not on surface of Planet
– Methane/Nitrogen based geology/climate at -180°C
 Hard to detect!
Greenhouse Effect affects Climate
• Earth absorbs energy from the
Sun and heats up
• Earth re-radiates the absorbed
energy in the form of infrared
radiation
• The infrared radiation is
absorbed by carbon dioxide
and water vapor in the
atmosphere
Typically happens
and stabilizes climate
on planet harboring
life
Good, because life
takes at least a billion
years to develop/
have effects on planet
The biggest effect life had on Earth
• Shakespeare?
• Building the Great Wall of China?
• Explosion of the Hiroshima bomb?
Transforming Carbondioxide into Oxygen!
(Zero oxygen 3 billion years ago, now 21%)
Chances of detecting Life
• How far away is the nearest Earth-like
planet?  19 ly (if 3% of stars have ELPs)
• Is it habitable?
–
–
–
–
Atmosphere
Rocky
Carbon/Water available
shielded from heavy bombardment
How to detect Life
• Life produces oxygen, methane
• Can detect ozone (made from O2), Methane
via its characteristic infrared radiation
• Plants use photosynthesis: chlorophyll
rejects colors not utilized (utilizes visible
frequencies) IR red-edge
• TV & Radio signals
 1992: Galileo spacecraft detects life on
Earth (and not on the Moon)!
(Very) Intelligent Life
• Looking for extraterrestrial
intelligence, we can
relax our
assumptions (neither
carbon nor waterbase necessary)
• We are looking for
signals of
civilizations rather
than signs of life
Classification of Civilizations
• Type I: uses energy sources of their planet
including solar radiation arriving at their planet
(us!)
• Type II: uses a large part of the total radiation of
their sun (shows up as reddening of the star’s
spectrum)
• Type III: uses a large part of the energy production
of their galaxy (might rearrange galaxy)
Galactic Exploration
• John von Neumann: build self-replicating
space probe that builds many replicas of
itself once it finds suitable conditions, send
them on their way
– Can colonize galaxy in only 100 million years
(less than 1% of lifespan)
• O’Neill colonies
Fermi Paradox
• If ETI exists it must be widespread
• If it’s widespread, why aren’t they among
us?
•
•
•
•
ETI must have had plenty time to occur
Maybe they do not exist
Maybe we didn’t look hard/long enough?
Maybe they are among us?
Signals
• Probably electromagnetic waves
– Easy to generate
– not exceedingly absorbed by interstellar
medium, planetary atmospheres
– Information can be imprinted on them with
minimal energy cost
• Travels fast (but not fast enough?!)
• We are detectable since 12. December 1901
Green Bank (or Drake) Equation
• Estimated number of technological civilizations present
in the Milky Way galaxy is given by
the average rate of star formation
 fraction of stars having planetary systems
 average number of planets within the habitable zone for
various types of star and star system
 fraction of habitable planets that develop life
 fraction of life-bearing planets on which intelligence
appears
 fraction of intelligent life forms that develop technology
 average lifetime of a technological civilization
• Could be 100 to 1 billion (?)
Illustration of Drake Equation
Time is of the Essence
• A lot of things can go
wrong in “cosmic
instances” like a few
thousand years
• It is “guesstimated”
that a technological
civilization might last
about 3000 years
Extinction of the
Dinosaurs
• Possibly caused by impact of
a large meteorite
– Large amount of dust thrown into atmosphere,
causing global cooling, disruption of the food chain
– Evidence:
• Iridium layer found in fossil record at about time of
extinction of dinosaurs
• Large numbers of species become extinct at about the same
time
• Crater in Yucatan may be “the one”
• Are extinctions periodic?
SETI
• If average lifetime is 1 million years, then the average
distance between civilizations in the galaxy is 150 ly
– Thus 300 years for messages to go back and forth
• Communications via radio signal
– Earth has been broadcasting in RF range for most of this
century
– Earth is brighter than the Sun in radio
– 18–21 cm wavelength range good for interstellar
communication
• SETI search is ongoing
– SETI@Home:
http://setiathome.ssl.berkeley.edu
• If they exist, should we contact them?
SETI with Radio
Telescopes
• Radio frequencies are
used because
– Civilizations are likely
to use these
frequencies
– We can observe them
from the ground
• Biggest radio
telescope is in
Arecibo, Puerto Rico
CETI – Talking to Aliens
• How can we communicate?
– Put up a big sign (?!)
– Send a (radio) signal
– Send a space probe with a message
• Should we try to communicate?
Our Messages to the Aliens
• Golden plate
with essential
info on
humans
• On board
Pioneer 10
space probe
• Started in the
70’s
• past solar
system
In 1974 sent radio
signal from Arecibo
to globular cluster
M13 (300,000 stars,
21,000ly away)
Brighter than the Sun
“The signal,
transmitted at 2380
megahertz with a
duration of 169
seconds, delivered an
effective power of 3
trillion watts, the
strongest man-made
signal ever sent.”
Our EM Message to the
Aliens
The Night Sky in May
• Nights shorter and EDT => later observing!
• Spring constellations are up: Cancer, Leo, Big
Dipper
• Mars, Saturn dominate early evening, Jupiter early
morning.
Moon Phases
• Today: New Moon
• 5 / 11 (First quarter Moon)
• 5 / 19 (Full Moon)
• 5 / 27 (Last Quarter Moon)
• 6 / 3 (New Moon)
Today
at
Noon
Sun at
meridian,
i.e.
exactly
south
10 PM
Typical
observing
hour,
early May
Saturn
Mars
Zenith
Big Dipper
points to the
north pole
South
• Saturn near
Praesepe
(M44), an
open star
cluster
• Oops, that
was last
year! Now
Saturn is
here!
South
• Spring
constellations:
– Leo
– Hydra
– Crater
– Sextans
East
• Canes
Venatici:
– M51
• ComaVirgo
Cluster
• Globular
Star
Clusters
– M3, M5
East
Virgo and
Coma
with the VirgoComa
galaxy
cluster
VirgoComa
Cluster
• Lots of
galaxies
within a
few
degrees
M87, M88
and M91
East
– Hercules
– Corona
Borealis
– Bootes
Globular Star
Clusters:
•M3
• M 13
• M 92
M13: Globular Cluster
These guys will know of our existance in 21,000 years!
Mark your Calendars!
• Next Starry Monday: June 2, 2008, 8 pm
(this is a Monday
• Observing at Prairie Oaks Metro Park:
– Friday, May 9, 2008, 9:00 pm
• Web pages:
– http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)
– http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)
)