Welcome to
Starry Monday at Otterbein
Astronomy Lecture Series
-every first Monday of the monthMarch 5, 2007
Dr. Uwe Trittmann
Today’s Topics
• Life in the Universe
• The Night Sky in March
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.)
Life in the Universe – Some
Questions
• What is life?
• What are the prerequisites for life?
• Where can it exit?
• How can we find it?
What is Life?
• Common features:
– reacts to environment
– metabolism (draws energy from environment)
– reproduction
• Life on Earth
– Based on complex chemistry of carbon
– Fundamental building blocks are amino acids
• Small compounds containing C, O, H, N, S
– It seems unlikely that life can be based on
significantly different chemistry
The “evolution” towards life
• Evolution is not just
biological evolution!
Cosmic Evolution:
the universe gets organized
Quasars
Cosmic Evolution
The prerequisites for life
•
•
•
•
Need the right “stuff”
Liquid water
Atmosphere is a plus!
Stable energy source (star)
– Hot stars die fast!
• Right temperature range
• …
Habitable Zones
• 1 A.U. = average Earth-Sun distance
Major Epochs of Life Development
1)
2)
3)
4)
Cosmic evolution of biogenic compounds
prebiotic evolution
early evolution of life
development of advanced life
“The stuff”: Biogenic Elements
•
•
•
•
•
•
Carbon
Hydrogen
Oxygen
Nitrogen
Phosphorus
Sulfur
 all but hydrogen come from exploded stars!
Cosmic evolution of biogenic
compounds
1) nucleo-synthesis and ejection into the interstellar
medium
2) chemical evolution in the interstellar medium
3) protostellar collapse
4) chemical evolution in the solar nebula
5) growth of planetesimals from dust
6) accumulation and thermal processing of
planetoids
From “dead stuff” to life
Organic material
Protocell
Last common ancestor
Eukarya
Procarya
Archea
“Creating life”: Miller-Urey Experiment
• Idea: build complex
biochemical
molecules from
simple chemicals plus
electric discharges
• Simulates early Earth
conditions:
– lightning
– primordial oceans
 Successful
experiment!
Life in hostile environments
• “One current theory is that life originated
deep beneath the surface of the ocean at
deep sea hydrothermal vents. These
hydrothermal vents were first discovered in
1979. Soon after, scientists made an
exciting discovery. These vents release hot
gaseous substances from the center of the
earth at temperatures in excess of 572 °F.”
Life from Meteors: Panspermia
• “In the early twentieth century, a Swedish chemist
named Svente Arrhenius developed a theory called
panspermia. Arrhenius' theory accounted for life's
origins by simply stating that life did not originate
on the Earth, but originated elsewhere in the
universe. He believed that cellular life reached the
Earth hiding inside a meteor which hit the Earth
long ago. Newly uncovered evidence suggests that
this might be possible.”
Life in frozen oceans?
• “Three billion years ago, the Sun which lights our
solar system was thirty percent less luminous than it
is today. Mant people believe that if the Earth's
atmosphere was the same then as it is today, the
oceans would be frozen. But recently, Jeffrey Bada
of the Scripps Institution of Oceanography has
proposed that the oceans would not completely
freeze. Instead, he calculates that only the top 300
meters of the ocean would freeze over.“
Evidence for Panspermia: Meteor
ALH84001
• “In 1996, a meteor was found in Allan Hills,
Antarctica. Upon examination, it was
discovered that this meteor, which is 4.5
billion years old, fell to the earth 13,000
years ago, and possibly contained evidence
of life on Mars. Inside the meteor, along
tiny cracks, scientists found evidence of
what many believe to be ancient bacteria.“
Reverse Panspermia
• There is life on Earth, maybe it was
“exported” to other parts of the solar system
(Mars, Europa, Titan)
• See Sky & Telescope January 2007: Is Earth
Contagious?
Is Life on Earth…
a) A miracle?
b) An accident?
c) More-or-less inevitable given the laws of
physics and chemistry, and suitable conditions?
• Principle of Mediocrity: There’s nothing special
about the astronomical, geological, physical and
chemical circumstances on Earth; most likely
nothing special about biology either
Life in the Solar System?
• Planets
• Moons
• “The face on
Mars”
Life cares about (Atmospheric)
History
• Primary atmosphere: hydrogen, helium,
methane, ammonia
– Too light to “stick” to a planet unless it’s very
big  Jovian Planets
• Secondary atmosphere: water, CO2, SO2, …
– Outgassed from planet interiors, a result of
volcanic activity
Atmospheric Histories
• Earth: Temperature allowed water to
liquify; CO2 dissolved in oceans; early life
contributes oxygen
• Venus: run-away Greenhouse effect; CO2
could not be absorbed by water, rocks
because of higher temperature closer to sun
• Mars: CO2 dissolves in liquid water;
temperature drops below freezing point
(reverse greenhouse effect!); permafrost
forms with CO2 locked away
Hothouse Venus: 850 °F
Water on Mars?
Mars
Louisiana
Runoff channels
Outflow Channels
Life on Mars?
• Giovanni Schiaparelli (1877) – observed “canali”
(channels) on Martian surface
• Interpreted by Percival Lowell (and others) as
irrigation canals – a sign of intelligent life
• Lowell built a large observatory near Flagstaff, AZ
(Incidentally, this enabled C. Tombaugh to find Pluto in 1930)
• Speculation became more and more fanciful
– A desert world with a planet-wide irrigation system to carry
water from the polar ice caps?
– Lots of sci-fi, including H.G. Wells, Bradbury, …
• All an illusion! There are no canals…
Viking Lander Experiments
(1976)
• Search for bacterialike forms of life
• Results inconclusive
at best
Jupiter’s Galilean Moons
Europa
Europa might have
liquid water oceans
under the surface
 Life?
Titan
• Titan is the only moon in the solar system
known to have an atmosphere
• Life on Titan would be
methane-based
Is There Life Elsewhere in the
Solar System?
• Moon and Mercury lack liquid water, atmosphere
• Venus is too hot, lacks water
• Titan has methane/ammonia/nitrogen atmosphere, but
is probably too cold
• Europa, Ganymede, and Callisto may have liquid
water
– Perhaps the most likely sites for other life in Solar System
• Mars is too cold and lacks liquid water
– But formerly had more atmosphere, higher temperatures,
and running water
– Viking lander tests were at best inconclusive
– 1996 claim of evidence of fossils in Martian meteorite
Is there life FAR out there?
• Depends on a lot of unknown factors
• Cannot probe it to find out (takes “forever”
to get there)
• Need to look for “signals” of life
• Do we have a chance of finding life?
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
Our Message to the Aliens
• Golden plate
with essential
info on
humans
• On board
Pioneer 10
space probe
• Started in the
70’s
• past solar
system
The Night Sky in March
• Long nights, early observing!
• Winter constellations are up early: Orion, Taurus,
Gemini, Auriga, Canis Major & Minor, the spring
constellations come up: Cancer, Leo, Big Dipper
• Saturn dominates the evening, Jupiter early
morning.
Moon Phases
• Today (Waning gibbous, 96%)
• 3 / 11 (Last Quarter Moon)
• 3 / 18 (New Moon)
• 3/ 25 (First Quarter Moon)
Today
at
Noon
Sun at
meridian,
i.e.
exactly
south
10 PM
Typical
observing
hour,
early
March
Moon
Saturn
SouthWest
Plejades
Hyades
Zenith
Big Dipper
points to the
north pole
West
High in the
sky:
Perseus and
Auriga
with Plejades and
the Double
Cluster
SouthWest
The Winter
Constellations
–
–
–
–
–
Orion
Taurus
Canis Major
Gemini
Canis Minor
The
Winter
Hexagon
•
•
•
•
•
•
Sirius
Procyon
Pollux
Capella
Aldebaran
Rigel
South
• M44,
Praesepe,
an open
star
cluster
East
• Saturn
in Leo
Mark your Calendars!
• Next Starry Monday: April 2, 2007, 8 (!!!) pm
(this is a Monday
• Observing at Prairie Oaks Metro Park:
– Friday, April 27, 8:30 pm
• Web pages:
– http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)
– http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)
)
Mark your Calendars II
•
•
•
•
Physics Coffee is every Wednesday, 3:30 pm
Open to the public, everyone welcome!
Location: across the hall, Science 256
Free coffee, cookies, etc.