Download - The Search For Extraterrestrial Life
Steven PrinsenDan Cipera
Mat RemillardMark Johnson
What Is Life? The Search Within Our Solar System Searching Beyond the Solar System Probability of Life
Broad definition• “The period between birth and death”• “The sum of all activities of a plant or an
animal” “Activities”
• Respiration• Reproduction• Nutrition• Excretion• Locomotion• Growth• Reaction to stimuli
Quartz Lifelike
Growth Nutrition Reproduce?
Not Lifelike Movement Excretions External Stimuli www.howstuffworks.com/quartz-watch.htm
• Fire– Lifelike
• Respiration• Growth• Movement• Reproduction• Eats• Excretes• Reacts to stimuli
– Not Lifelike• Evolving• Adaption to change
www.funsci.com/fun3_en/fire/fire.htm
Life Growth Reproduce Adapt Evolve
http://www.hickerphoto.com/rain-forest-streams-9157-pictures.htm
• 95% of Life– Hydrogen, Oxygen, Carbon, Nitrogen
• Last 5%– Calcium, Phosphorus, Chlorine, Sulfur,
Potassium, Sodium, Magnesium, Iodine, Iron, and trace elements
• Most abundant universal elements– Hydrogen, Oxygen, Carbon, Nitrogen– Helium, Neon
• Most abundant earth elements– Silicon, Iron, Magnesium, Oxygen
The Search For Life In The Universe, Goldsmith and Owen
• Carbon– Complex molecules– Nitrogen and Oxygen
• Monomers– Small molecules– Compose polymers– Amino Acids, sugars, fatty acids, nucleotides
• Polymers– More complex molecules– Proteins
Laevorotatory (L) vs Dextrorotatory (D) Non living material is 50/50 L configuration
Amino Acids D configuration
Sugars, DNA, RNA Increases efficiency
Amino Acids 20 used 100 per protein 20100 possible combinations
Astrobiology, November 10, 2008.
Meteorites L-amino acids 16% excess
Astrobiology, November 10, 2008.
Nucleotides Four types
A, T, G, C Specify Amino Acids 16 combinations
Sets of Three 64 combinations Redundancies Prevents mistakes
http://yihongs-research.blogspot.com/2008/09/new-generation-business-demands-new-dna.html
• Molecular level– DNA Mutation
• Gamma Rays• Cosmic Rays• Mutagens
– Changes reproductive efficiency• Energy
– From the Sun– Photosynthesis
Sunlight Steady energy
Key to survival 3.5 billion years
Photosynthesis Ensures a chance to survive
http://photo.net/photodb/photo?photo_id=3666216
Formed by accretion Hydrogen Reducing
Methane Ammonia Water Vapor
Resembles Jupiter and Saturn Left quickly Volatile elements joined earth last
H, C, N, O Life elements Comets
http://www.williamsclass.com/EighthScienceWork/Atmosphere/EarthsAtmosphere.htm
Hydrogen bound to Oxygen UV breaks up
Photodissociation Made new compounds
Chem Reactions with crust Mildly Reducing
CO CO2
N2
H2O H, H2
Mars, Venus
Astrobiology, Monica Grady
Water doesn’t imply life May be able to detect atmosphere data
Transiting planets Nonequilibrium reaction byproducts
Free Oxygen Photosynthesis
Terrestrial SimilaritiesM ≈ 1 Earth MassIron Core -> Magnetic FieldOrbit and Rotation
The 4 Most Vital Elements for LifeCarbon, Hydrogen, Oxygen, Nitrogen
Liquid Water!
Europa Galileo Missions Slightly smaller than our
moon Silicate Rock – Iron Core Atmosphere of Oxygen Smooth, icy surface Oceans Underneath?
Extremophiles?
Titan Cassini-Huygens
Mission 50% Larger than our moon Surface of water ice and
organic compounds Thick Atmosphere of Nitrogen Liquid Hydrocarbon Lakes
(Ethane and Methane)
But... -290 F (-179C)
Mariner ProbesNo Plate TectonicsNo Global Magnetic FieldAtmospheric Pressure roughly 1% of Earth'sNo liquid water on surface
… No multicellular organisms
Viking Landers Search for bacteria-like
organisms Soil showed C02
production when interacted with water
No organic molecules detected
Phoenix Lander (May 25 2008)
Water-ice in Martian subsurfaceSmall concentrations of salts
Mars Reconnaissance Orbiter (November 20,
2008) Vast glaciers of iceEvidence of a previously
“wet” Mars
Planned Missions Mars Science
Laboratory (2009) Maven (2013)
Other Proposals Mars Sample Return Astrobiology Field Lab Deep-Drill Lander
Idea is to Identify “Earth-like” planets- rocky worlds similar to our own
Very difficult- most exoplanets we’ve found thus far are gas giants the size of Jupiter
Planet’s gravity affects it’s parent star- causes slight variations in star’s radial velocity
These variations are detectable by measuring Doppler shifts (i.e. a spectrograph measuring Doppler shifts in spectral lines from a star)
Current instruments can detect ~1 m/sec shift; problem is, Earth-size planets induce ~0.1 m/sec shift
Also, can only tell mass- not diameter/ composition/ atmosphere/ etc.
HARPS 3.6 m telescope
(www.eso.org)
As planet transits in front of sun, dip in luminosity is recorded
Technique can be used to determine diameter and mass, thus giving a density
Orbit must lie in correct plane
Period must be sufficiently short, or telescope must observe star continuously for a longer time
www.space.com
Best way to determine a planet’s chemical make-up (analyzing spectral lines)
Fomalhault b was first exoplanet to be directly imaged visually - HST
Problem: for most stars, luminosity from star far outshines reflection from planet
Also, Earth’s atmosphere both narrows observable frequency ranges and causes blurring/seeing of visible light
Fomalhault b
www.spacetelescope.org
Space-based telescopes (Hubble, Kepler, TPF) negate the atmosphere problem
The light problem is much trickier (for example, at 10 pc, angular separation for 1 A.U. is 100 marcseconds)
To block out the light from the star, a coronagraph is needed
Kepler Space Telescopewww.seti-inst.edu
Possible designs for the Terrestrial Planet Finder
satellites
planetquest.jpl.nasa.gov
Ratio of Sun’s Luminosity to light reflected from Earth
-Lsun= 4e33 erg/sec-1 AU= 1.5e13 cm-Earth’s radius= 6.4e8 cm-Earth’s Albedo= 0.367
Flux from the sun to Earth:
26213
33
2sun erg/sec/cm101.4)104ππ(1.
104
4ππ
LF
“Luminosity” of Earth
sec/106.6)104.1()104.6)(14.3(367.0
))((23628
2
erg
FrL sunEEarth
Ratio
1033
23
107.1
1
104
106.6
Sun
Earth
L
L (About 1 in 20 Billion)
Occulter: part of a coronagraph that physically blocks light from a star
Problems: lower resolution, diffraction effects still obscure planet
New Worlds Mission- use a distant occulter to block star’s light
Geometry of occulter can be modified to “smooth out” diffraction rings
Occulter can also be “apodized”- modified to help offset diffraction effects
New Worlds Mission Concept
www.planetquest.jpl.nasa.gov
Chemical Composition- Water, Oxygen, Ozone, CO2
Can determine through spectral analysis
“Red Edge”- Chlorophyll in plants reflects in infrared
Changes in reflectivity
If a star passes in front of a background star, the gravity of the foreground star causes microlensing
The presence of a planet orbiting the foreground star affects the observable microlensing
This effect can be observed even with planets at Earth’s scale
Correct alignment is very rare, and only observable for a few days/weeks
An equation postulated by Dr. Frank D. Drake in 1961.
The Drake equation in it’s original form:
N*= Total stars in galaxy fs = sun-like stars (fraction)
fp = stars with planets (fraction) fi = planets with life (fraction)
ne = life supportable planets
fc = planets with intelligence (fraction)
fl = life time of communicative civilization (fraction)
Dr. Frank Drake
Galaxy Factors
Solar System Factors
“Earth” Factors
Wild Cards
Galaxy Factors
Type of galaxy Enough heavy elements Not small, irregular or elliptical
Position in galaxy Not positioned in the halo, edge, or center
Solar System Factors Stable planetary mass
Giant planets allow for orbital stability
Jupiter-like neighbor Absorbs comets and asteroids
A Mars Possible life source
Large Moon Stabilizes tilt
Right Mass of star Right amount of ultraviolet released Long enough lifetime
“Earth” Factors
Distance from star Habitat for complex
life Liquid water near
surface No tidal lock
Planetary mass Solid/molten core Enough heat for plate
tectonics Able to support
atmosphere and ocean Tilt
Mild seasons
Oceans’ size Sufficient amount
Atmospheric properties Adequate temperature Right composition and
pressure Carbon amount
Enough for life but not enough for runaway greenhouse effect
Oxygen Evolution Development of
photosynthesis Biological evolution
Complex plants and animals
“Earth” Factors Giant impacts
Few giant impacts No major sterilizing
impacts
Wild Cards Inertial interchange
event Snowball Earth Cambrian explosion
Plate tectonics Land mass creation Biotic diversity Silicate thermostat Magnetic field
An equation suggested by Professor Peter Ward and Professor Donald Brownlee from their book “Rare Earth”:
N*= Total stars in galaxy fc = planets with complex life (fraction)
fp = stars with planets (fraction) fi = planets with life (fraction)fpm = metal-rich planets (fraction) fm= planets with large moon
(fraction)ne = life supportable planets fj = Jupiter-sized planets
(fraction)ng = stars in habitable zone fme = low number of mass destruction events (fraction)fl = life time of complex life (fraction)
Drake Equation with Dr. Drake’s current estimation of intelligent life in our galaxy:
Rare Earth Equation with our estimation of intelligent life in our galaxy:
The Point:
If any of these many variables approach zero, the total will be near zero!
“I'll tell you one thing about the universe, though. The universe is a pretty big place. It's bigger than anything anyone has ever dreamed of before. So if it's just us... seems like an awful waste of space”.
-Ellie Arroway, Contact
“…And pray that there's intelligent life somewhere up in space, -'Cause there's bugger-all down here on Earth”.
-Monty Python and the Meaning of Life
What Is Life? The Search Within Our Solar System Searching Beyond the Solar System Probability of Life
Astrobiology, Monica Grady, The Natural History Museum, London, 2001
The Search For Life In The Universe, 2nd Edition, Goldsmith and Owen, Addison-Wesley Publishing Company, 1992
A Race To Find Alien Planets, Carlisle, Sky & Telescope, January 2009, p28.
Circular Polarization and the Origin of Biomolecular Homochirality, Bailey, Bioastronomy, 1999
On the Origins of Biological Homochirality, Sandra Pizzarello, Astrobiology, November 10, 2008.
www.nasa.gov Rare Earth, Ward, Brownlee, Springer Science, 2000 Titan: Earth in Deep Freeze, Barnes, Sky & Telescope,
December 2008 Are We Alone, Imaging Extrasolar Earthlike Planets from
Space, Presentation by Prof. N. Jeremy Kasdin David J. Des Marais et al. “The NASA Astrobiology Roadmap.”
9 Oct 2008. 19 Oct 2008