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65 Cards in this Set
- Front
- Back
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Stage of star most likely to support life
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Main Sequence where it is fusing hydrogen to form helium.
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Information from Spectrum of Star
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Composition
Temperature Luminosity Velocity in space Rotation speed |
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Specteral Sequence
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\OBAFGKM
O has shortest lifetime, hottest temperature, largest mass. |
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Ruling out OBAF
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O and B have to short of lives to even form planetary systems.
A and F have hotter UV rays and short life would limit complexity of life. Only 3% ruled out. Still a lot of choices. |
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Problems and solutions for m class stars
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Problems
Close orbits lead to synchronous rotation. Frequent energetic flares Solutions Moderate greenhouse effect could keep whole planet warm. UV light could form ozone for future life. Could be home to oldest biology |
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Multiple star systems
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Planet orbits around 2 stars=possible
Planet orbit around one star, not the other=possible Planet alternates from one star to the other=not possible |
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Brown Dwarfs and Life
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Moons could still work.
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astrometric technique
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Look at wobbles in position of star caused by gravitational tug of a planet.
Works best for massive planets near a star |
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Doppler Technique
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Look for changes in the spectra of the star due to motion.
Works best for massive planets near a star |
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Gravitational Lensing and finding small planets
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Hard to see planets from earth because of distance
When one star passes in front of another, the light from the star in back is bent around the other. If front star has a planet, it adds to this effect. Helps us see much smaller planets. |
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Planets discovered so far
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Larger
Closer to star Highly elliptical orbits. |
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Selection effect and planet discoveries
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Selection effect –we find what we are looking for.
Since Doppler effect finds one type of planet, that is what we have found the most of. |
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What we can learn from few pixles of a planets spectra
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Fraction of land and sea
Changes from day to day from clouds Changes from season to season |
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What we can learn from a full planet spectra
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Surface temp.
Types of ice and minerals Gasses in the atmosphere. |
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Oxygen, Methane and Life
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Oxygen produced in photosynthesis
Methane produced by life. |
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Rare earth hypothesis
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Circumstances that made life possible may be so rare that ours is the only inhabited planet.
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Heavy Element composition and Life
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Enables earth sized planets. May have earth like conditions.
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Jupiter and Earth's Impact Rate
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Reduced the number of possible impacts on Earth.
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Stable Earth Climate
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Plate tectonics allow the carbon dioxide cycle.
Large moon stabilizes axial tilt. |
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Unique Characteristics of Earth and our search for life
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Characteristics make life easier.
Makes us wonder how much variation is possible in conditions. |
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What is SETI looking for
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Technologically advanced life.
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Why only search in galaxy
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Signal weak over large distance.
Time to send and receive is too long outside galaxy. |
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NHP
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Number of habitable planets in our galaxy.
100 billion or more. |
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F-LIFE
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Fraction of habitable planets that actually have life
Could be close to 1 since life began so early on earth. If earth was somehow lucky, value would be close to zero. |
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F-CIV
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Fraction of life bearing planets on which a civilization capable of interstellar communication has at some time existed.
Could be 0 since it took us four billion years to reach this point. Could be around ½ since half the stars in our galaxy are older than us. |
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F NOW
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Fraction civilized planets that exist and are transmitting right now.
Impossible to estimate since we don’t know how long our civilization will last. Have been transmitting for fifty years, so low end gives 1/200 If civilization lasts for billions of years then1/10 works. |
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Flaws of the Drake equation
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Don’t know the value of any of the terms
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Difficulty calculating the lifetime of civilization
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Fnow is determined by sociology which doesn’t give concrete answers.
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Why intelligence might be rare
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It took a long time to reach this stage.
Cambrian explosions are results of chance environmental change. K-t event allowed mammals to flourish. |
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Evolution and why intelligence might be common
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Natural selection encourages increased intelligence in wide range of species.
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EQ
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Encephalization quotient- Comparison of brain mass to body mass.
EQ= 1 average intelligence for mass EQ<1 less mentally agile EQ> 1 more mentally agile. |
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Science and technology and intelligence
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Intelligence makes science and technology possible.
Intelligence may be common but science and technology may not be. |
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Error of early radio searches
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Frequency waves were used but they reflected against our ionosphere and did not leave earth.
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Frequency of Radio Searches
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Frequency chosen that is emitted by neutral hydrogen gas which is found abundantly throughout the universe.
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3 types of signals
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Signals used for communication on the planet where beings live.
Signals used by beings to communicate with colonies or spacecraft Intentional signal beacons (likely to be detected by SETI) |
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Other signals from intelligent life
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Infrared
Ultra violet, x-ray, gamma Neutrinos Gravity waves Something undetectable to us. Tract fuel they leave behind (fusion or fission) |
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Lagrange Point
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Points where gravity cancels
May be useful if intelligent life left artifacts there. |
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3 types of civilization
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Planetary (type 1) - Civilizations which use the resources of their home planet.
Stellar (type 2) - civilizations which corral the resources from their home star. Use Dyson spheres. Galactic (type 3) - civilizations which employ the resources of their entire galaxy. |
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radio searches today
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Targeted searches-aimed at individual stars.
Sky survey-sweep across the heavens. |
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Optical Searches
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Look for very short pulses of light capable of outshining star.
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Implications of SETI success
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Means we are not alone.
Could mean technical advances. Joining galactic civilization? |
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Evidence of aliens on earth and explanations
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10% of alien sightings remain unsolved
Roswell- Crash materiel identified as weather balloon. Crop circles-Easily made with ropes and boards. Alien abduction- Sleep paralysis Ancient artwork- people could have done it. |
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Main problem with interstellar travel
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Distance
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Maximum speed to travel and why
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Speed of light because theory of relativity prohibits faster travel.
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How energy limits travel
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We would need 100 times the energy used on earth annually.
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mass ratio and how it limits space travel
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Mass ratio- mass of fueled rocket to the mass of an empty rocket
To get higher ratio, must have multiple stages. 100 stage rocket only gets us .1% the speed of light. |
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Difference between fission and fusion
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Fission breaks large nuclei into smaller nuclei
Fusion forms larger nuclei from smaller nuclei |
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Problems with nuclear rockets
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May release radiation with fission rockets.
Fusion rockets would let off bombs in space which is against nuclear treaties. |
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Problems with interstellar arks
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Suspended animation sleep has not yet been accomplished.
No discovered way to stop aging process. Mutiny. |
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Time dialation is space travel
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Time appears to be shorter for those traveling near the speed of light.
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Matter/anti- matter annihilation propulsion
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Annihilation gives off energy.
Could get us up to 90% speed of light. No way to store anti-matter. |
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Interstellar ramjets
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Scoop up hydrogen and fuse it on board.
Need a huge collector At high speed, every atom is a deadly projectile. |
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Hyperspace
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outside normal 3D space and time.
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Black hole
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heavily curved space time
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Wormhole
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black hole that comes out at different place (u shaped)
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Fermi paradox question
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If our planet and we as humans are not special, where is everyone
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Von Neumann machine
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Self-replicating machines that colonize
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Rate of new civilization
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New civilization should come every 3 minutes to 2 days.
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time and size of planet as arguement for radio signals
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The least advanced civilization ahead of us should be 100,000 years ahead of us so we should receive radio signals.
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Coral model
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groups make colonies, send out more groups etc. whole galaxy should be colonized in 10 million years
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Acceptable reasons to colonize galaxy
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Persecution
Protect from natural hazards Avoid star death |
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Unacceptable reasons to colonize the galaxy
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Stop population expansion.
Conquest Aggressive nature |
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Solution1 fermi paradox
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We are alone
There are no galactic civilizations because we are the only civilization Some law of nature may have recently made life possible. We are not alone. We are just the first civilization |
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Solution 2 fermi paradox
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There are civilizations but no colonization
Technological difficulties No interest in colonization |
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Solution 3 fermi paradox
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There is a galactic civilization
Zoo hypothesis-we are deliberately kept in the dark. Waiting for us to signal them. |
