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A105 Stars and Galaxies Today’s APOD Solar Lab after class today Final Exam – Tuesday, Dec. 12 12:30-2:30 PM Swain West 119 Final Exam… • Open Book – Bring Text –Part I – Multiple Choice –Part II – News Articles –Part III – Short Written Summary • Comprehensive/emphasis on galaxies, cosmology, life elsewhere Today’s Topics • Planets around other stars – how do we find them – what are they like? – what kinds of stars have planets? • How likely it is that life exists elsewhere than Earth? (Drake Equation) • How would we detect life on other planets? Our Solar System Gas Giants Terrestrial Planets Ice Giants Searching for Planets • Nearly 200 “extra-solar” planets have been discovered • How are planets discovered? Radial velocity Transits – Gravitational lensing – Wobbles in stars’ positions Discovering Planets from Spectra o Remember the Doppler Shift! o Absorption lines shift left or right if stars move toward or away from us o Planetary orbits cause stars’ radial velocities to change Periodic velocity changes due to orbiting planet Velocity vs. Time VERY high precision is needed to measure these very small velocity changes Velocity (meters per second) Velocity of 51 Peg 80 60 40 20 0 -20 -40 -60 -80 0 About 7 orbits in 30 days 10 20 P=4.2 days Time (days) 30 40 A Planet around e Eridani A planet orbits the star e Eridani at a radius of 3.2 A.U. e Eridani is similar to our Sun e Eridani is only 10.5 light years away The planet is similar to Jupiter The planet orbits e Eridani in 7 years e Eridani has at least one more planet u And has at least 3 planets terrestrial planets Planetary Transits If the Earth lies in the same plane as the orbit of a planet we see a transit •The planet passes across the face of the star •Some of the starlight is blocked by planet and the star appears dimmer Seeing planets near stars is hard Looking for an Earthlike planet around a nearby star is like standing on the East Coast of the United States and looking for a pinhead on the West Coast — with a VERY bright grapefruit nearby. • Very large telescopes will help This photo shows an image of the faint star GQ Lupi taken in the infrared. The faint object to the right of the star is a possible planetary companion. It is 250 times fainter than the star itself and it located 0.73 arcsecond west. At the distance of GQ Lupi, this corresponds to a distance of roughly 100 astronomical units. The planet probably has a mass of about 2 x Jupiter. Imaging Planets? • Orbiting the brown dwarf ~225 light years away • Young, about 1000K • Further from its “sun” than Pluto is from ours (brown dwarf is blocked out) Another possible planet Location of brown dwarf Possible planet Properties of KNOWN ExtraSolar Planets • • • • All are gas giants like Jupiter and Saturn Most are larger than Jupiter Many orbit close to their parent stars Some are in systems with multiple planets Known Planets Are Close to Stars Hot Jupiters These hot Jupiters form further out, and migrate inward as they eject smaller bodies from their planetary systems Selection Effects • Close-in, massive planets are easier to detect • Far-out planets and light-weight planets are MUCH HARDER to detect • So far, we’ve only been able to detect massive, close-in planets • Techniques, sensitivity are improving • Terrestrial planets soon! The Habitable Zone Too hot! Too cold! •The planet needs to be the right distance from the star. WHY? •The star needs to have the right mass. WHY? A planet needs the right star! Constraints on star systems: 1) Old enough to allow time for evolution (rules out high-mass stars - 1%) 2) Need to have stable orbits (might rule out binary/multiple star systems - 50%) 3) Size of “habitable zone”: region in which a planet of the right size could have liquid water on its surface. Even so… billions of stars in the Milky Way seem at least to offer the possibility of habitable worlds. You are here There are 400 Billion Stars in our Galaxy. How many harbor life? How common is life of any kind in the Milky Way? Very Rare Rare Common Very Common How common is intelligent, technological life? Very Rare Rare Common Very Common The Drake Equation • Start with 1011 stars in the Milky Way… • What fraction of the stars are similar to the Sun? • What fraction of solar type stars have planets? • What fraction of solar type stars with planets have planets in the habitable zone? • On what fraction of these planets will life emerge? • On what fraction of these will intelligence emerge? • What fraction of these will develop technology? • What fraction of a star’s life will a technological civilization survive (assume a solar-type star remains on the main sequence for 1010 years)? The Drake Equation What are the odds that there are intelligent, advanced, communicative civilizations out there? How many can we expect to exist in all of the Milky Way Galaxy? Make your own calculation of the number of intelligent, communicative, technologically advanced civilizations in the Milky Way. All stars in the Milky Way fraction with planets? fraction in the habitable zone? fraction with simple life? with technical society? with intelligence? with long-lasting technology? = NHP flife fciv fnow We do not know the values for the Drake Equation NHP : probably billions. flife : ??? Hard to say (near 0 or near 1) fciv : ??? It took 4 billion years on Earth fnow : ??? Can civilizations survive long-term? Search for Extra-Terrestrial Intelligence SETI experiments look for deliberate signals from E.T. Can We Find Extra-Terrestrial Intelligence? • Looking for SIGNALS is the easiest way • We can also transmit a signal (but it’s a long wait for the answer...) • Different kinds of signals to listen for: – local communication signals: on Earth, this includes TV, radio, etc. – communication between the planet and another site, such as satellites and spacecraft – A BEACON signal used to try to communicate with other civilizations. Can Earth Be Heard from Space? • YES! Earth has been broadcasting TV and radio communications for the last 50 years. ET civilizations up to 50 light years away could be picking us up. • We can “listen” but radio wavelengths may be best – Biggest collecting area - Arecibo telescope. – The background sky is the quietest at wavelengths of about 0.1 mm. At shorter wavelengths, emission from the galaxy is loud, and at longer wavelengths, interstellar clouds absorb the signals Message to M13 Nov 1974 • Message was beamed from the Arecibo radio telescope – toward the M13 star cluster – 24,000 light-years away – a 1679 (23 x 73) pulses and spaces • The message was transmitted only once and was intended to serve as a exercise in how we might go about trying to contact extraterrestrials. Message to M13 • Formed a picture showing when arranged in a rectangle – numbers 1-10 – elements, chemicals of life – a DNA molecule – a stick figure of a human – solar system – diagram of radio telescope Searching for ET • NASA funded SETI until 1993 • Present efforts all privately funded – SETI Institute (Frank Drake) • seti@home -- help analyze SETI data – Planetary Society • META (million channel extraterrestrial assay) -scans one million channels in the band • BETA (billion channel version of META) • 84 ft. dish antenna at Harvard Univ. • connected to supercomputers that look for nonrandom patterns in the signals (most of the signals come from natural sources such as stars) • 250 megabytes of data each second Your computer can help! SETI @ Home: a screensaver with a purpose. Visiting ET? • With foreseeable technology, we can achieve speeds of 10% of the speed of light • We can travel 10 light years in 100 years • We can reach the nearest star in 43 years • Allow each new colony 5000 years to duplicate the technology • Colonies could spread out about 50 light years every 25,000 years How long to colonize? Assume 100,000 years per 20 parsec hop Total time to cover the Galaxy: 1500 hops x 100,000 years = 150,000,000 years The Fermi Paradox • • • • Emil Konopinski LANL Fuller Lodge Cafeteria Enrico Fermi Edward Teller Herbert York Emil Konopinski LANL Tech Area Enrico Fermi The Fermi Paradox The Drake Equation – A few hundred technical civilizations 150,000,000 million years to colonize the Galaxy WHERE IS EVERYBODY????? Where is Everyone? • Some factors in Drake equation may be much smaller than we believe – is life, or intelligent life, very rare? • Do civilizations hide to avoid a “galactic scourge?” • Do technological civilizations selfdestruct? • Is no one more advanced than we are? • The Zoo hypothesis… Possible solutions to the paradox Civilizations are common but interstellar travel is not. Perhaps… Interstellar travel more difficult than we think Desire to explore is rare Civilizations destroy themselves before achieving interstellar travel These are all possibilities, but not very appealing… Possible solutions to the paradox We are alone: life/civilizations much rarer than we might have guessed. • Our own planet/civilization looks all the more precious… OR - There IS a galactic civilization… … and some day we’ll meet them… Difficulties of Interstellar Travel • • • • Far more efficient engines are needed Energy requirements are enormous Ordinary interstellar particles become like cosmic rays Social complications of time dilation Traveling to Another Star? • Distances between stars are much greater than we can imagine • Sci-fi books and movies have dramatized space travel to make it seem possible – Interstellar travel may never happen – Even the Voyager spacecraft (some of the fastest ever flown) traveled at only 20 km/s through space not even 1% of the speed of light. They would take 60,000 years to reach even the nearest star 100.000000% Maximum Speed Achieved 10.000000% 0.100000% 0.010000% Space Shuttle 0.001000% Automobile 0.000100% Plane 0.000010% Train Horse 1000 100 10 1000 100 10 Years Before Present YEARS BEFORE 1 Now 0.000001% 0.1 0.01 0.001 10 100 1000 Years From Now YEARS AFTER % Speed of Light 1.000000% Can we travel to new worlds? • • • Within the lifetime of today’s children we will be able to send robotic spacecraft to visit our nearest neighbors At 10% of the speed of light (30,000 km/sec) travel time will be about 100 years Then wait another 10-20 years for the data to return SOLAR LAB! Kirkwood Obs. NOW!