1. Today’s APODAPOD  Homework & Quiz 10 on Friday  Reading on Oncourse – “Essay 3” The Sun Today A100 Life in the Universe

2.  This week’s reading is available from the Resource Tool on Oncourse – Essay 3

3. Final Exam…  Friday, 2:45 PM, here.  2 hours  100 multiple choice questions  Comprehensive  50% on chapters 10, 11 & Essay 3  50% on material covered in the first three exams  Review sheet on Oncourse

4. Today’s Topics  How likely it is that life exists elsewhere than Earth? (Drake Equation)  Searching for life elsewhere

5. The Habitable Zone The planet needs to be the right distance from the star. WHY? The star needs to have the right mass. WHY? Too hot! Too cold!

6. 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. A planet needs the right star!

7. You are here There are 400 Billion Stars in our Galaxy. How many harbor life?

8. 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

9. The Drake Equation  Start with 10 11 stars in the Milky Way…  What fraction are similar to the Sun?  What fraction of sun-like type stars have planets?  What fraction have planets in the HZ?  On what fraction will life emerge?  On what fraction will intelligence emerge?  What fraction will develop technology?  How long will a technological civilization survive?

10. 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? All stars in the Milky Way fraction with planets? fraction in the habitable zone? fraction with simple life? with intelligence? with technical society? with long-lasting technology? Make your own calculation of the number of intelligent, communicative, technologically advanced civilizations in the Milky Way.

11. We do not know the values for the Drake Equation N HP : probably billions. f life : ??? Hard to say (near 0 or near 1) f civ : ??? It took 4 billion years on Earth f now : ??? Can civilizations survive long-term? = N HP  f life  f civ  f now

12. SETI experiments look for deliberate signals from E.T. Search for Extra-Terrestrial Intelligence

13. 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.

14. Searching for ET  NASA funded SETI until 1993  Present efforts all privately funded  SETI Institute (Frank Drake)  seti@home -- help analyze SETI data seti@home  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 non- random patterns in the signals (most of the signals come from natural sources such as stars)  250 megabytes of data each second

15. Your computer can help! SETI @ Home: a screensaver with a purpose.

16. 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

17. Message to M13 Nov 1974  Message was beamed from the Arecibo radio telescope  toward the M13 star cluster  24,000 light-years away  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 extra-terrestrials.

18. 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

19. 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

20. 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 30,000 pc

21. The Fermi Paradox Emil Konopinski Enrico Fermi LANL Fuller Lodge Cafeteria LANL Tech Area  Enrico Fermi  Edward Teller  Herbert York  Emil Konopinski

22. The Fermi Paradox The Drake Equation – A few hundred technical civilizations 150,000,000 million years to colonize the Galaxy WHERE IS EVERYBODY?????

23. 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 self- destruct?  Is no one more advanced than we are?  The Zoo hypothesis…

24. 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

25. 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…

26. 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

27. 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

28. Horse Train Automobile Plane Space Shuttle Maximum Speed Achieved

29. 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

30.  Reading, homework, quiz next week  HAND IN HOMEWORK  HAND IN ACTIVIES Dates to Remember