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Lecture 23: Extraterrestrial Life
SCI238 W08 Lecture 23: Extraterrestrial Life atmospheres have been detected around two extrasolar planets; but no water yet… L23 – Apr 03/08 ET Life
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Today’s Lecture Final Exam: Sat. 12 April, 7:30-10pm in PAC 1,2
see old exam on web for format more emphasis on second half of Term (60/40?) a little cosmology astrobiology a new scientific discipline the chemistry of life the search for life in our Solar System where might life exist in other planetary systems? the “Rare Earth” hypothesis the Drake Equation: intelligent life in the Universe communicating with intelligent life in the rest of the Universe L23 – Apr 03/08 ET Life
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we observe that central black hole mass correlates with galaxy luminosity (mass)
so initial gravitational potential well must also play a part L23 – Apr 03/08 ET Life
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Models of Galaxy Formation
hierarchical lots of small galaxies form, then merge to make bigger ones problem: simulations leave far too many small ones around monolithic large clouds of inter-galactic gas collapse to form large galaxies problem: difficult to make such large clouds of gas in such a short time and combinations how long ago were merger events? how massive were merging galaxies? L23 – Apr 03/08 ET Life
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Are We Alone? Humans have speculated throughout history about life on other worlds. it was assumed by many scientists & thinkers of the 17th & 18th Centuries that life was present on other worlds and widely accepted by the public at the turn of the 20th Century scientists became more sceptical once we began to explore the planets L23 – Apr 03/08 ET Life
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Are We Alone? Recent advances in astronomy and biology have renewed interest. discovery of extrasolar planets indicate that planetary systems are common indications that liquid water can exist on other worlds organic molecules are found throughout the Solar System and Galaxy geological evidence suggests life on Earth arose as soon as it was possible discovery that living organisms can survive in the most extreme conditions This interest has spawned a new science called astrobiology. the study of life in the Universe L23 – Apr 03/08 ET Life
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Astrobiology This new discipline includes: cosmoschemistry
chemical evolution the origin and evolution of life planetary biology and chemistry the formation of stars and planets space science expansion of terrestrial life into space L23 – Apr 03/08 ET Life
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Questions in extraterrestrial life
Is there intelligent life in our Galaxy? … in the Universe? …in the solar system? Can we communicate with other forms of life? When will we communicate with these other forms? How? Is there any other form of life in our Solar System? … in out Galaxy? Was there life in any form in the past in our Solar System? How did life originate on our planet? spontaneously? carried to Earth by (?) a meteorite? Could we recognize other forms of life? L23 – Apr 03/08 ET Life
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it is “easy” to produce the building blocks of life
this simple experiment produces amino acids – the basic building blocks of life as we know it… but not so easy to turn them into life L23 – Apr 03/08 ET Life
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Clues to growth of amino acids?
fossils ~2Gyr old (left) compared with modern blue-green algae clustering of millions of amino acids into droplets, which “grow, divide” L23 – Apr 03/08 ET Life
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oily droplets made by exposing freezing mixture to strong UV light produce cell-like membranes
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life exists under very harsh conditions
boiling water at right and rich sulphur clouds in ocean depths but water is a common factor L23 – Apr 03/08 ET Life
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The Murchison Meteorite: arrow points to organic matter
=> chemical evolution has occurred elsewhere L23 – Apr 03/08 ET Life
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From organic compounds to life: not an easy step
exploration of the Solar System has revealed no sign of large life forms/civilizations we must search for microbial life L23 – Apr 03/08 ET Life
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Mars: the best candidate for extraterrestrial life?
some reasons why Mars is the best candidate to host such life: Mars was apparently warm & wet for some periods in its distant past conditions, similar to early Earth, made it possible for life to evolve had the chemical ingredients for life has significant amounts of water ice pockets of underground liquid water might exist if there is still volcanic heat Mars at 2001 opposition Hubble Space Telescope image L23 – Apr 03/08 ET Life
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Viking Lander (1976) We have searched for life on Mars.
Viking scooped up soil and ran tests looked for products of respiration or metabolism of living organisms results were positive, but could have been caused by chemical reactions no organic molecules were found results inconsistent with life L23 – Apr 03/08 ET Life
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Viking Lander (1976) this is not the final word.
Viking sampled only surface soil took readings at only two locations life could be elsewhere or underground L23 – Apr 03/08 ET Life
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Martian Meteorite ALH84001 L23 – Apr 03/08 ET Life
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Martian Meteorites rocks ejected by impact from Mars have been found in Antarctica. analysis of one revealed… age of4.5 billion years old landed on Earth 13,000 yrs ago contained complex organic molecules & chains of crystals similar to those created by Earth bacteria L23 – Apr 03/08 ET Life
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Martian Meteorites also found fossils of nanobacteria.
recently discovered on Earth they have DNA, but are they life? big news, but since then… structures seen could also be formed by chemical & geological porcesses Earth bacteria have been found living in the meteorite CONTAMINATED! L23 – Apr 03/08 ET Life
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Possibly Life on Jovian Moons?
beneath its icy surface, Europa may have an ocean of liquid water. tidal heating keeps it warm possibly with volcanic vents on the ocean floor conditions may be similar to how Earth life arose life need not only be microbial Ganymede & Callisto may also have subsurface oceans, but tidal heating is weaker. L23 – Apr 03/08 ET Life
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Possible Life on Jovian Moons
Titan has a thick atmosphere and oceans of methane & ethane. water is frozen perhaps life can exist in liquids other than water pockets of liquid water might exist deep underground. and in 5Gy – it will be warmer… L23 – Apr 03/08 ET Life
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Life in other planetary systems…
what are the requirements on a planet for it to produce life as we know it? liquid water the planetary system must be old enough for life to have evolved the star must survive long enough for life to evolve development of planetary crust – planet has to cool magnetic field? composition of planet? stability of life-sustaining conditions – e.g. no very large variations in surface temperature over ? 500 million years large single Moon provides climate stability L23 – Apr 03/08 ET Life
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Which Stars make Good Suns?
which stars are most likely to have planets harboring life? must be long lived and old enough that life could arise in a few x 108 y this rules out massive O & B main sequence stars they must allow for stable planetary orbits this rules out binary and multiple star systems they must have relatively large habitable zones habitable zone is the region where large terrestrial planets could have surface temperature that allow water to exist as a liquid L23 – Apr 03/08 ET Life
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Width and location of habitable zone depend on the type of star
in the solar system the habitable zone is from inside Earth’s orbit to just beyond Mars’ this will change as the sun evolves L23 – Apr 03/08 ET Life
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need both habitable zone and time…
if life takes ≥ 109 yr to evolve => best bet is stars ≤ 3MSun but below 1MSun size of habitable zone shrinks rapidly L23 – Apr 03/08 ET Life
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Planets and binary systems?
a planet in a binary star system must have a stable, uniform orbit to maintain the right conditions for life L23 – Apr 03/08 ET Life
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Have we detected habitable planets around other stars?
NO…current technology is insufficient, because an earth-like planet is too small to be resolved or for us to notice its gravitational pull on its parent star would be lost in the glare of its parent star launch of the Kepler mission (October 2008?) which will… measure the light curves of stars to look for transits of Earth-sized planets measure planets’ orbits to determine if they are in the star’s habitable zone L23 – Apr 03/08 ET Life
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Detecting habitable planets around other stars
In the next decade, NASA plans to launch Terrestrial Planet Finder. an interferometer in space will take spectra and make crude images of Earth-sized extrasolar planets spectrum of a planet can tell us if it is habitable. look for absorption lines of ozone and water L23 – Apr 03/08 ET Life
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Earth-like Planets: Rare or Common?
expectation (models, some observations) is that Earth-like planets are common. billions of stars in our Galaxy have at least medium-size habitable zones theory of planet formation indicates terrestrial planets form easily in habitable zones some scientists have proposed a “rare Earth” hypothesis. L23 – Apr 03/08 ET Life
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Earth-like Planets: Rare or Common?
Rare Earth Hypothesis: Life on Earth resulted from a series of lucky coincidences… terrestrial planets may form only around stars with high abundances of heavy elements the presence of Jupiter deflects comets and asteroids from impacting Earth yet Jupiter did not migrate in towards the Sun Earth has plate tectonics which allows the CO2 cycle to stabilize climate our Moon, result of a chance impact, keeps tilt of Earth’s axis stable are these “coincidences” unique or fairly ordinary? we will not know the answer until were have more data on other planets in the Galaxy L23 – Apr 03/08 ET Life
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location in the galaxy matters too
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# civilizations in the galaxy: the Original Drake Equation
The Drake Equation estimates the number of civilizations detectable at radio wavelengths (first expressed in 1961 by Cornell University astronomer Frank Drake.): Rs = the rate of forming stars fp = fraction of stars with planets np = number of planets in habitable zone fb = fraction where life developed fi = fraction where intelligent life developed fc = fraction that communicate Lc = lifetime of communicating civilization L23 – Apr 03/08 ET Life
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a “picture” form of the Drake equation
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How Many Civilizations Exist in the Galaxy with whom we could make contact? A simpler version of the Drake Equation NHP = number of habitable planets in the Galaxy flife = fraction of habitable planets which actually contain life fciv = faction of life-bearing planets where a civilization has at some time arisen fnow = fraction of civilizations which exist now Number of civilizations = NHP x flife x fciv x fnow L23 – Apr 03/08 ET Life
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if we are a good example: it takes a long time for intelligent life to evolve on a planet
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on Earth life took a long time to evolve
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How Many Civilizations Exist in the Galaxy with Whom We could make Contact?
We can not calculate the actual number since the values of the terms are unknown. The term we can best estimate is NHP including single stars whose mass < few M AND… assuming 1 habitable planet per star, NHP 100 billion unless the “rare Earth” ideas are true Life arose rapidly on Earth, but it is our only example. flife could be close to 1 or close to 0 Life flourished on Earth for 4 billion yrs before civilization arose. value of fciv depends on whether this was typical, fast, or slow We have been capable of interstellar communication for 50 years out of the 10 billion-year age of the Galaxy. fnow depends on whether civilizations survive longer than this or not L23 – Apr 03/08 ET Life
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Search for ExtraTerrestrial Intelligence
IF we are typical of intelligent species and… IF there are many intelligent species out there… then some of them might also be interested in making contact! THEN: let’s listen for them! That is the idea behind the SETI program. L23 – Apr 03/08 ET Life
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Search for ExtraTerrestrial Intelligence
Use radio telescopes to listen for encoded radio signals. search strategies are used to decide which stars to observe now they scan millions of frequencies at once We sent a powerful signal once in 1974 to the globular cluster M13. now we just listen due to low chance of success and large amount of time required, SETI is now privately funded. L23 – Apr 03/08 ET Life
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Project Phoenix in the 1990’s searched for extraterrestrial signals
(a) the 140 foot telescope at Green Bank Observatory (West Virginia) Project Phoenix in the 1990’s searched for extraterrestrial signals (b) a typical recording of an extraterrestrial signal – the Pioneer 10 spacecraft (from beyond Pluto) L23 – Apr 03/08 ET Life
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message broadcast toward direction of globular cluster M13
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The “Water Hole” at what wavelength should we look and listen?
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the number of civilizations/the distance to the nearest (ly)
Probability of Life Lifetime 1 10-2 10-4 10-6 10 years 102/104 1/- 10-2/- 10-4/- 103 years 104/2000 105 years 106/300 107 years 108/70 109 years 1010/15 L23 – Apr 03/08 ET Life
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Where are the Aliens? With our current technology it is plausible that… within a few centuries, we could colonize the nearby stars in 10,000 years, our descendants could spread out to 100s of light years in a few million years, we could have outposts throughout the Galaxy L23 – Apr 03/08 ET Life
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Where are the Aliens? Assuming, like us, most civilizations take 5 billion yrs to arise. the Galaxy is 10 billion yrs old, 5 billion yrs older than Earth IF there are other civilizations, the first could have arisen as early as 5 billion yrs ago there should be many civilizations which are millions or billions of years ahead of us they have had plenty of time to colonize the Galaxy So…where is everybody? Why haven’t they visited us? this is known as Fermi’s paradox named after physicist Enrico Fermi, who first asked the question in 1950 L23 – Apr 03/08 ET Life
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Possible Solutions to Fermi’s Paradox
We are alone. civilizations are extremely rare and we are the first one to arise then we are unique, the first part of the Universe to attain self-awareness Civilizations are common, but no one has colonized the Galaxy. perhaps interstellar travel is even harder or costlier than we imagine perhaps most civilizations have no desire to travel or colonize perhaps most civilizations have destroyed themselves before they could we will never explore the stars, because it is impossible or we will destroy ourselves L23 – Apr 03/08 ET Life
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Possible Solutions to Fermi’s Paradox
There is a Galactic civilization. it has deliberately concealed itself from us we are the Galaxy’s rookies, who may be on the verge of a great adventure We may know which solution is correct within the near future!! L23 – Apr 03/08 ET Life
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The Fine Structure Constant
α = 2πe2/hc = ± a “finely tuned universe”? the anthropic principle “weak”: the existence of life imposes a selection effect on where and when we observe the universe ”strong”: the presence of observers imposes constraints on the physical constants of the Universe see: L23 – Apr 03/08 ET Life
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And… some thoughts on interstelllar travel
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Why is Interstellar Travel Difficult?
The distance between the stars in HUGE! We will most likely be limited by the speed of light. Our current interstellar spacecraft, Pioneers 10 & 11 and Voyagers 1 & 2, will take 10,000 yrs to travel 1 light-year. our spacecraft need to go 10,000 times faster in order to travel to the stars within human lifetimes L23 – Apr 03/08 ET Life
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Why is Interstellar Travel Difficult?
This will require new types of engines and new energy sources. accelerating the USS Enterprise to half the speed of light would require 2,000 times the total annual energy output of the entire world Constructing a starship would be expensive. would require political will and international cooperation Theory of Relativity will complicate life for space travelers. a 50 l.y. round trip to Vega might seem like 2 years to the crew… while 50 years has passed on Earth! L23 – Apr 03/08 ET Life
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Starship Propulsion Chemical rockets are impractical for interstellar travel. going faster requires more fuel, which make the ship more massive and harder to accelerate Nuclear powered ships produce more energy per kg of fuel. two designs, employing fission & fusion, have been studied the best they could achieve is 10% of the speed of light travel to the nearby stars would take decades L23 – Apr 03/08 ET Life
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Starship Propulsion Matter-Antimatter engines would convert 100% of fuel to energy. problem is where to get the fuel! antimatter does not exist naturally producing large amounts of antimatter takes tremendous amounts of energy storing antimatter is a big problem as well Ships that do not carry their own fuel: solar sails would harness the photon pressure from sunlight interstellar ramjets would scoop up Hydrogen from the ISM to fuel its nuclear fusion engine L23 – Apr 03/08 ET Life
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Starship Propulsion nuclear (H-bomb) powered solar sail
interstellar ramjet L23 – Apr 03/08 ET Life
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