Transcript Document
Welcome to Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the monthMarch 5, 2007 Dr. Uwe Trittmann Today’s Topics • Life in the Universe • The Night Sky in March On the Web • To learn more about astronomy and physics at Otterbein, please visit – http://www.otterbein.edu/dept/PHYS/weitkamp.a sp (Observatory) – http://www.otterbein.edu/dept/PHYS/ (Physics Dept.) Life in the Universe – Some Questions • What is life? • What are the prerequisites for life? • Where can it exit? • How can we find it? What is Life? • Common features: – reacts to environment – metabolism (draws energy from environment) – reproduction • Life on Earth – Based on complex chemistry of carbon – Fundamental building blocks are amino acids • Small compounds containing C, O, H, N, S – It seems unlikely that life can be based on significantly different chemistry The “evolution” towards life • Evolution is not just biological evolution! Cosmic Evolution: the universe gets organized Quasars Cosmic Evolution The prerequisites for life • • • • Need the right “stuff” Liquid water Atmosphere is a plus! Stable energy source (star) – Hot stars die fast! • Right temperature range • … Habitable Zones • 1 A.U. = average Earth-Sun distance Major Epochs of Life Development 1) 2) 3) 4) Cosmic evolution of biogenic compounds prebiotic evolution early evolution of life development of advanced life “The stuff”: Biogenic Elements • • • • • • Carbon Hydrogen Oxygen Nitrogen Phosphorus Sulfur all but hydrogen come from exploded stars! Cosmic evolution of biogenic compounds 1) nucleo-synthesis and ejection into the interstellar medium 2) chemical evolution in the interstellar medium 3) protostellar collapse 4) chemical evolution in the solar nebula 5) growth of planetesimals from dust 6) accumulation and thermal processing of planetoids From “dead stuff” to life Organic material Protocell Last common ancestor Eukarya Procarya Archea “Creating life”: Miller-Urey Experiment • Idea: build complex biochemical molecules from simple chemicals plus electric discharges • Simulates early Earth conditions: – lightning – primordial oceans Successful experiment! Life in hostile environments • “One current theory is that life originated deep beneath the surface of the ocean at deep sea hydrothermal vents. These hydrothermal vents were first discovered in 1979. Soon after, scientists made an exciting discovery. These vents release hot gaseous substances from the center of the earth at temperatures in excess of 572 °F.” Life from Meteors: Panspermia • “In the early twentieth century, a Swedish chemist named Svente Arrhenius developed a theory called panspermia. Arrhenius' theory accounted for life's origins by simply stating that life did not originate on the Earth, but originated elsewhere in the universe. He believed that cellular life reached the Earth hiding inside a meteor which hit the Earth long ago. Newly uncovered evidence suggests that this might be possible.” Life in frozen oceans? • “Three billion years ago, the Sun which lights our solar system was thirty percent less luminous than it is today. Mant people believe that if the Earth's atmosphere was the same then as it is today, the oceans would be frozen. But recently, Jeffrey Bada of the Scripps Institution of Oceanography has proposed that the oceans would not completely freeze. Instead, he calculates that only the top 300 meters of the ocean would freeze over.“ Evidence for Panspermia: Meteor ALH84001 • “In 1996, a meteor was found in Allan Hills, Antarctica. Upon examination, it was discovered that this meteor, which is 4.5 billion years old, fell to the earth 13,000 years ago, and possibly contained evidence of life on Mars. Inside the meteor, along tiny cracks, scientists found evidence of what many believe to be ancient bacteria.“ Reverse Panspermia • There is life on Earth, maybe it was “exported” to other parts of the solar system (Mars, Europa, Titan) • See Sky & Telescope January 2007: Is Earth Contagious? Is Life on Earth… a) A miracle? b) An accident? c) More-or-less inevitable given the laws of physics and chemistry, and suitable conditions? • Principle of Mediocrity: There’s nothing special about the astronomical, geological, physical and chemical circumstances on Earth; most likely nothing special about biology either Life in the Solar System? • Planets • Moons • “The face on Mars” Life cares about (Atmospheric) History • Primary atmosphere: hydrogen, helium, methane, ammonia – Too light to “stick” to a planet unless it’s very big Jovian Planets • Secondary atmosphere: water, CO2, SO2, … – Outgassed from planet interiors, a result of volcanic activity Atmospheric Histories • Earth: Temperature allowed water to liquify; CO2 dissolved in oceans; early life contributes oxygen • Venus: run-away Greenhouse effect; CO2 could not be absorbed by water, rocks because of higher temperature closer to sun • Mars: CO2 dissolves in liquid water; temperature drops below freezing point (reverse greenhouse effect!); permafrost forms with CO2 locked away Hothouse Venus: 850 °F Water on Mars? Mars Louisiana Runoff channels Outflow Channels Life on Mars? • Giovanni Schiaparelli (1877) – observed “canali” (channels) on Martian surface • Interpreted by Percival Lowell (and others) as irrigation canals – a sign of intelligent life • Lowell built a large observatory near Flagstaff, AZ (Incidentally, this enabled C. Tombaugh to find Pluto in 1930) • Speculation became more and more fanciful – A desert world with a planet-wide irrigation system to carry water from the polar ice caps? – Lots of sci-fi, including H.G. Wells, Bradbury, … • All an illusion! There are no canals… Viking Lander Experiments (1976) • Search for bacterialike forms of life • Results inconclusive at best Jupiter’s Galilean Moons Europa Europa might have liquid water oceans under the surface Life? Titan • Titan is the only moon in the solar system known to have an atmosphere • Life on Titan would be methane-based Is There Life Elsewhere in the Solar System? • Moon and Mercury lack liquid water, atmosphere • Venus is too hot, lacks water • Titan has methane/ammonia/nitrogen atmosphere, but is probably too cold • Europa, Ganymede, and Callisto may have liquid water – Perhaps the most likely sites for other life in Solar System • Mars is too cold and lacks liquid water – But formerly had more atmosphere, higher temperatures, and running water – Viking lander tests were at best inconclusive – 1996 claim of evidence of fossils in Martian meteorite Is there life FAR out there? • Depends on a lot of unknown factors • Cannot probe it to find out (takes “forever” to get there) • Need to look for “signals” of life • Do we have a chance of finding life? Green Bank (or Drake) Equation • Estimated number of technological civilizations present in the Milky Way galaxy is given by the average rate of star formation fraction of stars having planetary systems average number of planets within the habitable zone for various types of star and star system fraction of habitable planets that develop life fraction of life-bearing planets on which intelligence appears fraction of intelligent life forms that develop technology average lifetime of a technological civilization • Could be 100 to 1 billion (?) Illustration of Drake Equation Time is of the Essence • A lot of things can go wrong in “cosmic instances” like a few thousand years • It is “guesstimated” that a technological civilization might last about 3000 years Extinction of the Dinosaurs • Possibly caused by impact of a large meteorite – Large amount of dust thrown into atmosphere, causing global cooling, disruption of the food chain – Evidence: • Iridium layer found in fossil record at about time of extinction of dinosaurs • Large numbers of species become extinct at about the same time • Crater in Yucatan may be “the one” • Are extinctions periodic? SETI • If average lifetime is 1 million years, then the average distance between civilizations in the galaxy is 150 ly – Thus 300 years for messages to go back and forth • Communications via radio signal – Earth has been broadcasting in RF range for most of this century – Earth is brighter than the Sun in radio – 18–21 cm wavelength range good for interstellar communication • SETI search is ongoing – SETI@Home: http://setiathome.ssl.berkeley.edu • If they exist, should we contact them? SETI with Radio Telescopes • Radio frequencies are used because – Civilizations are likely to use these frequencies – We can observe them from the ground • Biggest radio telescope is in Arecibo, Puerto Rico Our Message to the Aliens • Golden plate with essential info on humans • On board Pioneer 10 space probe • Started in the 70’s • past solar system The Night Sky in March • Long nights, early observing! • Winter constellations are up early: Orion, Taurus, Gemini, Auriga, Canis Major & Minor, the spring constellations come up: Cancer, Leo, Big Dipper • Saturn dominates the evening, Jupiter early morning. Moon Phases • Today (Waning gibbous, 96%) • 3 / 11 (Last Quarter Moon) • 3 / 18 (New Moon) • 3/ 25 (First Quarter Moon) Today at Noon Sun at meridian, i.e. exactly south 10 PM Typical observing hour, early March Moon Saturn SouthWest Plejades Hyades Zenith Big Dipper points to the north pole West High in the sky: Perseus and Auriga with Plejades and the Double Cluster SouthWest The Winter Constellations – – – – – Orion Taurus Canis Major Gemini Canis Minor The Winter Hexagon • • • • • • Sirius Procyon Pollux Capella Aldebaran Rigel South • M44, Praesepe, an open star cluster East • Saturn in Leo Mark your Calendars! • Next Starry Monday: April 2, 2007, 8 (!!!) pm (this is a Monday • Observing at Prairie Oaks Metro Park: – Friday, April 27, 8:30 pm • Web pages: – http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.) – http://www.otterbein.edu/dept/PHYS/ (Physics Dept.) ) Mark your Calendars II • • • • Physics Coffee is every Wednesday, 3:30 pm Open to the public, everyone welcome! Location: across the hall, Science 256 Free coffee, cookies, etc.