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Unit 9: Search for Extraterrestrial Intelligence
• What is Life?
• Conditions for Life
• How Big is the Universe? How many
opportunities for life are out there?
• What types of life do we expect?
• What is SETI?
• Is SETI worthwhile science?
Unit 9: What is Life
All life (as we know it) has the following
characteristics:
• Capable of reproduction
• Has genetic material (excludes prions)
• Adaptation
• Made of one or more cells (excludes viruses)
• Respond to environmental stimuli
• Maintain homeostasis
Unit 9: Conditions for Life
• Raw materials (include hydrogen, oxygen, carbon,
nitrogen, sulfur, and phosphorus).
• Energy source, either chemical or solar.
• Liquid water (H2O).
• Moderate temperatures, pH, salinity, radiation
These conditions apply to life (mostly microbial) on
Earth. May not apply in other, extraterrestrial
locations.
From NASA Ask an Astrobiologist (May 2003): http://astrobiology.nasa.gov/ask-anastrobiologist/question/?id=589
Unit 9: Conditions for Life (Raw Materials)
• Why hydrogen, oxygen, nitrogen, sulfur, and
phosphorus? Small, moderately reactive.
• Why carbon? Forms four stable bonds
Unit 9: Conditions for Life (Water 1)
• Water is the molecule H2O
• Made of two O-H bonds
• Each O-H bond is a sharing of electrons
• Electrons (negatively charged) are more
attracted to the oxygen nucleus (8 protons) than
to the hydrogen nucleus (1 proton).
• The oxygen side of the bond tends to have a
surplus of electrons (partial negative charge)
and the hydrogen side tends to have a deficit of
electrons (partial positive charge).
O
H
H
Unit 9: Conditions for Life (Water 2)
• Opposite charges attract  water molecules stick
together and water molecules stick to anything else
with charge.
O
Hydrogen bond
(weak)
H
H
O
O
H
H
H
H
Unit 9: Conditions for Life (Water 3)
Some consequences of cohesiveness of water
• High surface tension (things float)
• Ice is less dense than liquid water (ice floats)
• Water has high boiling point (takes a lot of energy to
make water boil)
• Water has a low freezing point
Some consequences of adhesiveness of water
• Water is a good solvent (many things dissolve in water)
• Water makes sticks to things (makes things wet)
Other important properties of water
• Pure water has neutral pH (neither acidic nor basic)
Unit 9: Conditions for Life (“Moderate” Temperatures)
• Low Temperature:
Psychromonas ingrahamii
was isolated from the arctic
sea floor. It grows at -12ºC
(water freezes at 0ºC).
Image copyright Standards in Genomics Science,
Creative Commons-BY
• High Temperature:
Methanopyrus kandleri was
isolated fro a “black smoker”
2000-meters below sea level
in the Gulf of California. Has
been grown at temperatures
up to 122ºC (water boils at
100ºC).
Image copyright PM Poon, Creative Commons-BY,
SA
For comparison,the surface of Mercury is -170ºC at night and 450ºC during the day.
Unit 9: Conditions for Life (pH, Salinity, Radiation)
• Extreme Acidity (pH:
Ferroplasma acidarmanus
was isolated from mine
drainage in California. It
grows at about pH 0. pH 0 is
more acidic than battery acid.
• High Salinity: Salinibacter lives in environments that have 20-30%
salinity (seawater is 3.1 t0 3.8% salt).
• High Radiation: Deinococcus
radiodurans can withstand
exposure to radiation at
dosages 3000x higher than
naturally occur on the Earth’s
surface.
Unit 9: Conditions for Life (JPL-SAF)
At the Jet Propulsion Laboratory in Pasadena, California,
there is a building called the Spacecraft Assembly
Facility (SAF). This is a super-clean facility where
spacecraft, like the Mars Rovers, are built. No
microorganisms should exist in this facility because we
don’t want to send microbes into space and we don’t
want to accidentally “discover” space microbes!
Here are some of the 22 organisms adapted to
life in the SAF (some found nowhere else on
Earth!):
• Bacillus safensis (named after the SAF)
• Bacillus nealsonii (has two protective
outer coats rather than one)
• Bacillus odysseyi (also has two
protective outer coats rather than one)
Unit 9: Conditions for Life (Bacteria on the Moon)
The unmanned spacecraft, Surveyor 3, landed on the
moon on April 20, 1967.
On November 12, 1969, Apollo 12 landed on the moon
and astronaut, Pete Conrad, collected the camera
casings from Surveyor 3.
In 1970, NASA scientists isolated 50 to 100 cells of the
bacterium, Streptococcus mitis, from the Surveyor 3
camer casings. These bacterial cells had survived
unprotected space flight, radiation exposure, two years
on the surface of the moon, and roughly three years
without food or water.
http://science.nasa.gov/science-news/science-at-nasa/1998/ast01sep98_1/
Unit 9: How Big is the Universe?
Detecting Intelligent Life
The Drake Equation (1961) is a back-of-the-envelope
equation that attempts to give a ballpark number to the
question, how many detectable, intelligent civilizations do
we expect in the universe? Here is the equation:
N = R* x fp x ne x fl x fi x fc x L where
N = number of civilizations that might possibly communicate with us
R* = the average rate of star formation per year in our galaxy
fp = fraction of those stars that have planets
ne = average number of those planets that are potentially habitable
fl = fraction of habitable planets that go on to develop life
fi = fraction of “living” planets that develop intelligent life
fc = fraction of intelligent civilizations that develop detectable
communication
L= length of time civilizations release detectable signals
Estimates of N range from around 2 to around 20,000. In
other words, we don’t know.
Unit 9: How Big is the Universe?
Detecting Intelligent Life
Assuming that all intelligent civilations are made of things
that we would consider living, we can re-work the Drake
Equation to estimate the number of opportunities for life
(intelligent or not):
Nlife = R* x fp x ne x fl x L where
N = number of civilizations that might possibly communicate with us
R* = the average rate of star formation per year in our galaxy
fp = fraction of those stars that have planets
ne = average number of those planets that are potentially habitable
fl = fraction of habitable planets that go on to develop life
L= length of time civilizations release detectable signals
Both of the omitted terms, fi and fc are fractions. Thus, Nlife
must be higher than Nintelligence. Drake estimated both fi and
fc to be around 0.01 (based on pure guess). Thus Drakes
estimate of the number of planets with life will be about
100,000. Again, this number is a pure guess.
Unit 9: Nearby Bodies Appropriate for Life
Within our solar system (http://astrobiology.nasa.gov/tags/life-in-our-solar-system/)
Mars: Evidence of flowing water on the surface of Mars
within the past few years.
Europa (moon of Jupiter): Has a salty ocean under a thick
ice shell.
Hyperion (moon of Saturn): Has craters containing
hydrocarbons.
Outside of our solar system
Goldilocks Planet (Gliese 581g): 20 light years away from
Earth (87th closest star). Vogt et al (2010) announced that
it could support life (Vogt was quoted in the press as saying
he thought thinks there is a 100% probability of life). Swiss
researchers find no evidence of existence of this planet
(ScienceNow 2010).
ScienceNow. (2010). Recently discovered habitable world may not exist. Retrieved online from
http://news.sciencemag.org/sciencenow/2010/10/recently-discovered-habitable-world.html
Vogt, S.S., Butler, R.P., Rivera, E.J., Haghighpour, N., Henry, G.W., and Williamson, M.H. (2010).
The Lick-Carnegie exoplanet survey: A 3.1M planet in the habitable zone of the nearby M3V star
Gliese 581. Astrophys. J. 723: 954-965.
Unit 9: What is SETI?
SETI stands for Search for Extraterrestrial
Intelligence. It is a program (briefly run by
NASA, with federal funding and now
privately funded) that attempts to detect
nonrandom radio signals as evidence of
technologically-advanced civilizations.
Unit 9: Is SETI Worthwhile Science?
1. What do you think scientists expect to find
through SETI and SETI@home?
2. Why do you think NASA chose to eliminate
funding for SETI in the 1990s? (Refer here for
more information:
http://history.nasa.gov/garber.pdf
3. Do you believe SETI and SETI@home are
worthwhile projects? Why?
4. What outcome(s) do you think will result from
SETI and SETI@home?