Life in the Universe: Origins and Search for Extraterrestrial Life - Prof. Donald G. Lutte, Study notes of Astronomy

Download Life in the Universe: Origins and Search for Extraterrestrial Life - Prof. Donald G. Lutte and more Study notes Astronomy in PDF only on Docsity! ASTR-1020: Astronomy II Course Lecture Notes Section XII Dr. Donald G. Luttermoser East Tennessee State University Edition 4.0 Abstract These class notes are designed for use of the instructor and students of the course ASTR-1020: Astronomy II at East Tennessee State University. Donald G. Luttermoser, ETSU XII–3 2. Not only are organic compounds easy to make, we see them throughout the Galaxy! a) Nonterrestrial amino acids have been found in mete- orites. b) The spectral lines from amino acids and other organic molecules also have been detected in the interstellar medium. c) The spectral lines from organic molecules have been de- tected in the atmosphere of Saturn’s largest moon Titan. d) The Universe has no trouble creating organic com- pounds in a very simple and natural manner! 3. It’s a big step however to go from organic molecules to self- replicating organic molecules (i.e., life). Many experiments have been carried out since the Miller-Urey Experiment to try and understand how life got started from this building block mate- rial. a) Biologists have been able to grow structures from amino acids that resemble proteins. b) Long carbon-chained molecules are very fragile and are easily broken apart when left by themselves. However, experimentalists have found that long carbon-based molecule chains can form, grow, and survive in mud and clay. c) This may suggest that we may owe our very existence to our large natural satellite — the Moon! The Moon raises tides on the shores of the continents. This moistens the dirt making mud and the organically rich oceans deposit amino acids and other organic molecules in this mud. XII–4 ASTR-1020: Astronomy II d) As the tides continuously raise and lower, long carbon- based molecules chains began to flourish. As time went on, electrochemical reactions between the chains started to take place forming more complicated molecule chains until one chain was made that was able to make copies of itself — micro-organisms arose and flourished in the oceans as the tides swept this material back out. e) There is no magic going on here, just chemistry being powered by an energy source (i.e., the Sun). Mutations from cosmic rays and the UV radiation from the Sun cause further alterations to these long molecule chains =⇒ variation in lifeforms begin on Earth. Natural se- lection begins in earnest causing organisms that are suc- cessful in their environment to survive, be fruitful and multiply. And the rest is history! 4. The is also some thought in the scientific community that the building blocks of life may have been deposited on Earth from space since amino acids are fairly common in meteorites and the interstellar medium. This hypothesis is referred to as pansper- mia. C. The Search for Extraterrestrial Life 1. The study of possible life off the Earth (i.e., extraterrestrials ) is called exobiology. 2. The first question to ask is “are there simple lifeforms elsewhere in the Solar System?” a) The best planets (besides Earth) suited for life in the Solar System are Mars, Jupiter’s atmosphere, Europa’s submerged ocean, and Titan (although Titan may be too Donald G. Luttermoser, ETSU XII–5 cold to support the formation of long molecule chains). b) Saturn’s largest moon Titan: i) The Voyager spacecrafts observed organic com- pounds in Titan’s atmosphere. ii) The spacecraft Cassini, which is currently in or- bit around Saturn, confirmed these observations. Cassini launch a probe called Huygens which landed on Titan’s surface in January 2005. iii) During the primary mission Cassini investigated the structure and complex organic chemistry of Titan’s thick, smog-filled atmosphere. On the frigid, alien surface, the spacecraft and its Huygens probe revealed vast methane lakes and widespread stretches of wind-driven hydrocarbon sand dunes. Cassini researchers also deduced the presence of an inter- nal, liquid water-ammonia ocean. c) Vikings 1 and 2 looked for life on the surface of Mars with negative results. i) Images from the Viking orbiters and the recent Mars mapping missions have shown that liquid water did exist on the planet’s surface early in its history. ii) Indeed, recent evidence gathered by the Mars Global Surveyor suggest that Mars may still have a substantial amount of water ice in some areas less than 500 meters (1640 feet) below the surface. XII–8 ASTR-1020: Astronomy II iii) fp = fraction of stars with planets: — new planetary systems are being discovered every year in the solar neighborhood. — space observations over the past 20 years have discovered numerous of planetary sys- tems forming around stars in stellar nurs- eries. — stellar formation modeling give this fraction a value anywhere from 1/2 to 1! — to be conservative, let’s choose 1/2 for this fraction. — Np = N? fp = 1 × 1011 planetary systems. iv) n`z = number of planets per star that lie in the habitable zone for at least 4 billion years: — a habitable zone is a region around a star where a planet can have temperatures that permit the existence of liquid water =⇒ F5 V – K5 V stars. — models predict this number to range between 0.01 and 1 per star. — 4 billion years chosen here due to length of time it took intelligent life to evolve on Earth. — N`z = N? fp n`z = 10 9 − 1011 habitable zone planets. Donald G. Luttermoser, ETSU XII–9 v) f` = fraction of suitable planets on which life begins: — we can only guess at this number. — organic chemistry and the Miller Experiment suggests the answer is 1. — we perhaps need to include the fraction of those planets that possess a large natural satellite at this point in order for stable long molecule chains to form. — we will assume that this fraction ranges from 0.01 to 1. — N` = N? fp n`z f` = 10 7 − 1011 planets with life. vi) fI = fraction of lifeforms that evolve to intelli- gence and develops radio astronomy: — we can only guess at this number too. — 0.01? – 1? — NI = N? fp n`z f` fI = 10 5−1011 planets with intelligent life. vii) Fs = fraction of star’s life during which a tech- nological society survives: — completely unknown, destruction by nuclear war, overpopulation, pollution, mass extinc- tions from asteroid impacts. — if 100 years: Fs = 10 −8. — if 1,000,000 years: Fs = 10 −4. — Nc = 10 −3 − 107 technological civilizations in the Milky Way. XII–10 ASTR-1020: Astronomy II c) If Nc ≤ 1, we are the only technological civilization in the Galaxy. d) If Nc  1, technological civilizations are everywhere in the Galaxy. i) If Nc = 10 7 civilizations, the average separation of each system is 120 ly. ii) If this many exist, there should be many civiliza- tions more advanced than us =⇒ where are they? — UFO’s not the answer! No scientific evidence that these events are extraterrestrial in ori- gin. — Also, travel time is too long (can’t go faster than light) and it would be very expensive from a raw materials point of view. iii) Von Neumann Machines (machines that travel to the next nearest star and reproduce themselves, sending their offspring to the next nearest stars, etc.) should be seeding the Galaxy by now =⇒ where are they? iv) Maybe we are the first to achieve technology! (Somebody has to be first.) e) We the listeners: radio astronomy. i) Technological civilizations = ones that have radio telescopes. ii) The laws of chemistry and physics are universal =⇒ water (H2O) should be an important to all lifeforms. As such, ET might broadcast between