Announcements

1. Announcements • Observing on the roof of Van Allen Hall, “clear sky patrol”, will begin on Tuesday, September 7th. For that week, it will run from Tuesday to Thursday from 9 pm to 11 pm on clear nights.

2. Planets beyond the solar system • Yesterday’s news • Life • The habitable zone • Evolution of life on Earth • Communicating with intelligent life Reading: all of chapter 27

5. Researchers don't know the composition of these new, smaller planets or what they actually look like. In our solar system, Neptune and Uranus are of similar size and they are composed of an icy, rocky core enveloped in a thick atmosphere of hydrogen and helium. But they sit in the farthest coldest reaches of our solar system. By contrast, both of the new planets are very close to their stars, making them difficult to spot.

7. One of them orbits very close to the star named 55 Cancri, which is about the same size as our sun and located 41 light-years away in the constellation Cancer. The new planet was located by University of Texas-Austin astronomers using the Hobby-Eberly telescope in the Davis Mountains southeast of El Paso. The star already had three known gas giant planets looping it in orbits that take anywhere from 14 to 4,520 days. The new planet is the innermost of the quartet, zooming around the star in 2.8 days from a distance of about 3 million miles. Researchers acknowledged there probably are several different types of solar systems orbiting distant stars. But for now, the 55 Cancri system bears the closest resemblance to ours.

9. 55 Cancri • Star 60% as bright as the Sun and only 5% less massive than the Sun. • Outermost known planet has an orbit similar to that of Jupiter, but is 4 times the mass of Jupiter. • Inner 3 planets all lie within the orbit of Mercury – one is about the mass of Jupiter.

10. The other new planet discovered by American scientists orbits a star called Gliese 436, that lies about 33 light-years from Earth in the direction of the constellation of Leo. This Neptune-sized planet also sits 3 million miles from its star and whips around in a tight circular orbit once every 2.64 days. Besides the exoplanet's size, what makes the discovery remarkable is that Gliese 436 is a red dwarf star that produces only 2 or 3 percent as much light as the Sun. Stars in this category account for 70 percent of the stars in the Milky Way galaxy, but until now, astronomers had not believed that such faint stars would yield new planets. "We estimate there is something like 20 billion planetary systems existing in our Milky Way galaxy alone," Butler said.

11. Two more exoplanets both gas giants also were spotted in the past week. One was by the same European team using a telescope in Chile. The other was discovered by a U.S.-based team using a network of small telescopes on California, Texas and the Canary Islands. Instead of measuring star wobbles, they measured the tiny amount that a star dims when a planet passes by in its orbit. So, a total of 4 new planets were discovered (really announced) last week.

12. What is Life? • What are the essential characteristics of life?

13. What is Life? Essential elements are: • Life reproduces itself • Life is able to adapt and pass changes to new generations This seems to require a genetic code which can stores information about how to grow new organism and is passed from generation to generation

14. Life on Earth • Is based on `organic’ molecules – those containing carbon atoms • Carbon can combine with hydrogen and other atoms to form complex molecules • Complex molecules appear necessary to store the information needed for a genetic code • Life on Earth uses DNA, a carbon-based molecule, to store the genetic code

15. Life on Earth • Life on Earth appears to require water • No life is know to exist in the complete absence of water • Water allows other molecules to dissolve, move around, and interact with each other

16. Habitable zone • The requirement for water suggests those planets which have liquid water may be the most promising havens for life. • In order to have liquid water, a planet must be “not too cold and not too hot”, i.e. at a temperature between freezing and boiling. • How warm a planet is depends on its distance from the sun.

18. Are there any exceptions to the habitable zone? • Yes, if there are sources of energy other than the sun to keep a planet (or moon) warm. • Possible energy sources • Radioactivity • Tides • Liquid water oceans are though to exist on Jupiter’s moon Europa

19. Are 55 Cancri’s planets in the habitable zone?

20. Evolution of Life on Earth • Even if we find life on another planet, is it likely to be a higher form of life such as mammals or something simpler? • What form of life occupied the Earth for most of its history?

21. Evolution of Life on Earth • 4.6 billion years ago – Earth formed • 3.96 “ “ “ – oldest rocks • 3.5 “ “ “ – oldest fossils – single celled life • 0.7 “ “ “ – multicellular life • 0.0001 “ “ “ – humans (homo sapiens)

22. History of life on Earth in 12 hours

23. Carl Sagan’s “Cosmic Calendar” The history of the Universe in one year Big bang Milky Way forms Sun and planets form Oldest known life - single cell First multicellular life

25. Search for Extraterrestrial Intelligence (SETI) • We could avoid this whole business of searching for planets and primitive forms of life, if extraterrestrials would just send us a message. • There are active searches for such signals, mainly in the radio, some using visible light. • One thing that is needed is more computing power. You can volunteer your computer to process SETI signals while the screen saver is on at the web site http://setiathome.ssl.berkeley.edu/