Astrobiology: Life on other planets

Astrobiology
Searching for life on other planets

Friday, February 13, 2009

The Drake equation can be
used to organize our thoughts


Fermi paradox


Fermi paradox

• Time for an intelligent species to colonize
galaxy: 106 years


Fermi paradox

galaxy: 106 years

• Age of the Galaxy: 1010 years


Fermi paradox

galaxy: 106 years

• Age of the Galaxy: 1010 years
• where are they?


How many planets are there?


We now have
discovered many
planets around
other stars, but no
Earth analogs (yet)


We now have
discovered many
planets around
other stars, but no
Earth analogs (yet)

nsing
microle
habitable? pulsar


Future missions
approved by
NASA will probe
‘habitable zone’


Kepler Transit search
(scheduled launch 2/2009)


In a transit search, we see when a
planet passes in front of its star


Transit searches are a cheap
way to hunt for planets


USING PHOTOMETRY TO DETECT
EARTH-SIZE PLANETS
The relative change in brightness (ΔL/L) is equal to the relative areas
•
(Aplanet/Astar)

Jupiter: Earth or Venus
1% area of the Sun (1/100) 0.01% area of the Sun (1/10,000)

Small planets need ultra-precise photometry. Must be done with wide-
ﬁeld CCD imager in space.


What have we learned from
planet searches so far?


Only high metallicity
stars have planets
FISCHER & VALENTI Vol. 622

lity

/Star

tirety
sical
ance
0.3 × Solar 3 × Solar
03). In addition, a Fig. 5.—Same results as Fig. 4, but divided into 0.1 dex metallicity bins. The
s been underway increasing trend in the fraction of stars with planets as a function of metallicity is
004). No planets well ﬁtted with a power law, yielding the probability that an FGK-type star has a
gas giant planet: P( planet) ¼ 0:03½(NFe =NH )=(NFe =NH ) Š2:0 .
veys, suggesting
nets with orbital
ikely lower than)

Stars with planets are young.

The Sun may be one of the oldest stars with planets
– 37 –

s
net
pla

rs
ith

sta
rs w

cal
l lo
Sta

Al


What planets support life?


What is life?


Life as we know it


What planets support life?

What kinds of planets can support life?
What fraction of planets that can support life do support life?


The Habitable Zone is the range of distances
from a star which allow a planet to support life


What are the minimal
conditions for life?
• How hot? • How radioactive?
• How cold? • How poisonous?
• How dry? • How much
pressure?
• How acid?
• How barren?
• How salty?
Organisms that push these limits are called
extremophiles


Thermophiles thrive at 90ºC (190ºF)

Endolithic life eat and breath
rock two miles undeground


Dry valleys of antarctica
3 inches
annual
precipitation
-68ºC
Dry 200
mph winds
evaporate
all moisture


Cryptoendolithic
ecosystem inside rocks
Algae

White lichen

Black Lichen


Bacteria living at bottoms of
perpetually frozen lakes.


Extreme life in Permafrost


Atacama Desert
dryest place on earth
2 mm
decadal
precipitation
recent
discoveries
of life below
4 inches


Lifeless desert in Oceans
• Centers of oceans
have very little life.
• Plenty of liquid
water
• Plenty of sunlight
energy
• Missing some key
chemicals
– Phosphorus


Lessons from terrestrial life
• Life can exist with only a bare minimum of
ingredients:
– Liquid Water
– Some energy source
• Sunlight, Rocks, Geothermal energy
– Basic chemical ingredients
• Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus


Old Habitable Zone Theory
• If planet is too close to star, fries through
runaway greenhouse effect
• If planet is too far from star, freezes, can’t
support life.


New Habitable Zone Theory
• Many other factors besides distance from the Sun
help determine planetary climate
– Greenhouse effect
– Plate Tectonics
– Impacts (Early Earth atmosphere stripped)
– Tidal Heating (Io, Europa)
• Liquid water can be found in a variety of unlikely
environments
– Europa, Callisto, Ganymede
– Early Mars very wet, present Mars dry?


How many habitable planets will
actually be alive?
• Basic ingredients to make life are common
throughout the cosmos

• Look at History of Life on Earth
• Life began shortly after Earth cooled
• Suggests that Life is easy to make.


Basic ingredients of life


• Organic molecules detected in interstellar
space.


space.
• Water (Ice) detected throughout galaxy,
solar system.


space.
• Water (Ice) detected throughout galaxy,
solar system.
• The basic chemical ingredients of life are
common throughout the galaxy.


Organic Molecules in interstellar
space
• Amino Acids
• Nucleic Acids
• Soot


Given the right ingredients, how
easy is it to make life?

34


Earliest Life
• Bands of Carbon in
ancient rock


Conclusion from oldest life


• Earth was not habitable until
3.8 billion years ago.
– Too many impacts melted
surface.


surface.
• 3.8 billion years ago, many
fewer impacts.
– Earth became inhabitable.


surface.
fewer impacts.
• Oldest life on Earth 3.8 billion
years old.


surface.
fewer impacts.
years old.
• Life formed on Earth as soon
as Earth could support life.


surface.
fewer impacts.
years old.
• Life formed on Earth as soon
as Earth could support life.
• Life is easy to form?


Searching for life in the
Solar System

38


led
ce
n
Ca


Detection of life around other stars

ned
tpo
pos
ly
nite
efi
Ind


Biomarkers in atmosphere


• Earth’s atmosphere shows
strong signals of two biogenic
molecules
– Oxygen
• Produced by plants
– Methane
• Produced by Cows


molecules
– Oxygen
– Methane
• Normally, methane burns in
Oxygen
– Natural Gas


molecules
– Oxygen
– Methane
• Normally, methane burns in
Oxygen
– Natural Gas
• Two can only exist in
combination because both
being produced by life.


What planets support
intelligent life?


Simple life


Complex Life


Lessons from Extremophiles
• Complex life on Earth restricted to narrow
range of habitats.
– Not in Antarctica, too cold, dry
– Not inside rocks, nothing to eat, breath
– Not inside geothermal vents, too hot
– Not in clouds, too heavy
– Not in driest deserts, too dry


Formation of Oxygen Atmosphere
• Life begins to saturate
atmosphere with
Oxygen
• Oxygen kills off life
• Oxygen combines with
rock
• Life comes back,
makes more oxygen
• Oxygen kills off life
• Process continued for
800 million years.


Lessons from formation of life
• Complex multicellular life did not evolve until
recently.
– Cambrian Explosion 600 Mya.
• Complex life could not have evolved without
Oxygen atmosphere.
• Complex life more fragile than simple life.
• Complex life difficult to evolve.


Lessons from Mars
• Planetary climates
can change
• Complex life (if it
ever existed) likely
wiped out today.
• Simple life could
have survived.


Answer to Fermi
Paradox?
• Sun may be among the ﬁrst stars to have
planets
• Life may be common
• Complex life may be rare
• Complex life may take a long time to form
• We may be alone?


Intelligent life
• No information how • Search for Extraterrestrial
common intelligent life is. Intelligence: SETI
– Cannot be federally funded
– Took most of history of
by congressional mandate
earth to evolve an
earthworm. – Now part of NASA’s
Astrobiology Institute
• Definition of Intelligent life:
– Just another means to
Ability to operate radio
search for life
transmitters
– Privately Funded SETI
• Search for intelligent life institute
by searching for radio
transmission


The End


Astrobiology: Life on other planets

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