Maria Mitchell (1818-1889) Astronomer and first woman elected to the

1. We especially need imagination in science. It is not all mathematics, nor all logic, but is somewhat beauty and poetry. Maria Mitchell (1818-1889) Astronomer and first woman elected to the American Academy of Arts and Sciences

2. Sites of the Week • NASA Astrobiology Institute: • nai.arc.nasa.gov • Class Web Page • http://flash.uchicago.edu/~calder/teaching/life05/life_spring05.htm • Cassini mission to Saturn: • http://saturn.jpl.nasa.gov • Textbook • www.astonomyplace.com

3. Class # 1 • Outline of Course/Class business • Intro to Life in the Universe/SETI (Cosmos) • Science, scientific discovery, and the scientific method. • A Universe of life: Habitable worlds, extra-solar planets, SETI • History of the Universe • Tour of Solar System • Formation of Stars, planets, and Solar System

4. Outline of Course • Scientific method, Solar System, Astronomy, the greats- Kepler, Galileo, etc., habitability, space exploration • Life as we know it (DNA, Organic Chemistry) • Geologic history of Earth • Origin and evolution of Life on Earth • The possibility of Life in the Solar System, Mars, Jovian moons (Titan). • Nature and evolution of Habitability • Extra-solar planets • SETI and the Drake Equation • Interstellar communication and travel • Fermi Paradox and implications of Contact.

5. Class Business • Syllabus • astronomyplace.com • Reading: • Chapt. 1, • Chapt. 2 • Homework (Due Feb 11): • Chapt. 1: Review questions 2, 6, 7, 10, 13, Problems 3,5,7,14 • Chapt. 2: Review questions 1, 2, 4, 5, 9, 12

6. Class Business • This is an exciting time to be studying life in the Universe! All are encouraged to bring new items to class for discussion. The instructor will smile! NASA ESA, NASA

7. Aside: Scientific Visualization: an Art Which best describes coalescing neutron stars?

8. Scientific Visualization: an Art Visualization: Dave Bock, NCSA More info: books by Tufte

9. Definitions • Astronomy- The study of the Universe and its contents beyond the bounds of the Earth’s Atmosphere • Astrophysics- The physical theory of astronomical objects and phenomena • Cosmology- The branch of astro concerned with the origins, properties, and evolution of the Universe • Astrobiology- The study of Life in the Universe • SETI- Search for Extraterrestrial Intelligence

10. Science and the Scientific Method • The first thing to note is that there is not agreement on exactly what the scientific method is! • The scientific method relies on testing and validation. Any assertion is tested (or even attacked), and only after reliable, repeatable experiments demonstrate the assertion is the assertion accepted. • Most everything presented on issues related to SETI is really informed opinion. • The key, however, is to base those opinions on scientific fact as much as is possible.

11. Science and the Scientific Method • A scientific “fact” begins as an observation. This may be a discovery of some sort such as the recent Huygens data. • A hypothesis is an educated guess at an explanation for the observation. • An experiment is a test of a hypothesis. Experiments can easily disprove a hypothesis, but cannot prove a hypothesis. • Once a hypothesis has been subjected to a battery of experimental tests, none of which reliably disprove it, then the hypothesis becomes accepted. We can then consider the hypothesis a theory. • Many theories are called laws, but these laws are not always the most accepted. (Newton’s laws of gravity vs. Einstein’s theory of general relativity)

12. Science v. Pseudoscience • Can an assertion survive scientific scrutiny? • ``... only provided further evidence that a technological civilization once existed on Mars and that the artifacts of that civilization are still visibly present. '' -- P. Gersten, Formal Action Committee for Extra-Terrestrial Studies

13. Hallmarks of Science (Text) • The Universe is inherently understandable, and we can figure out how it works by observing it and examining the processes that affect it. • Science progresses through the creation and testing of models (hypotheses), and the best models are the simplest. • A scientific model should be testable so that we can indeed test its validity and if necessary rethink the model.

14. Science in a nutshell (Calder) • The Universe is inherently understandable. • Scientific knowledge is durable. • Scientific ideas may change. • Science explains and predicts. • Science demands evidence. • Science may not be able to answer all questions, particularly why.

15. A Universe of Life: Questions we want to address • Are there other habitable worlds? • Is biology universal? • Should we expect other star systems to be like ours? • NASA’s three fundamental questions (nai.arc.nasa.gov/): • How does life begin and develop? • Does life exist elsewhere in the Uni? • What is life’s future on Earth and beyond? • We begin by studying what we know about the Uni and life in the Uni.

16. The Scientific History of the Universe

17. How would the Universal post office find us? Address: Earth

18. Star A large, glowing ball of gas that generates heat and light through nuclear fusion

19. Planet A moderately large object which orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition.

20. Moon An object that orbits a planet.

21. Asteroid A relatively small and rocky object which orbits a star.

22. Comet A relatively small and icy object which orbits a star.

23. Solar (Star) System A star and all the material which orbits it, including its planets and moons

24. Galaxy A great island of stars in space, all held together by gravity and orbiting a common center

25. Universe The sum total of all matter and energy; that is, everything within and between all galaxies

26. The Solar System Distances not to scale! • The Sun and the objects that orbit it.

27. The Layout of the Solar System • Large bodies in the Solar System have orderly motions • planets orbit counterclockwise in same plane • orbits are almost circular • the Sun and most planets rotate counterclockwise • most moons orbit counterclockwise

28. The Layout of the Solar System • Planets fall into two main categories • Terrestrial (i.e. Earth-like) • Jovian (i.e. Jupiter-like or gaseous)

29. Mars Neptune Terrestrial Jovian

30. The Layout of the Solar System • Swarms of asteroids and comets populate the Solar System

32. A Few Exceptions to the Rules… • Both Uranus & Pluto are tilted on their sides. • Venus rotates “backwards” (i.e. clockwise). • Triton orbits Neptune “backwards.” • Earth is the only terrestrial planet with a relatively large moon.

33. The Sun – King of the Solar System • How does the Sun influence the planets? • Its gravity regulates the orbits of the planets. • Its heat is the primary factor which determines the temperature of the planets. • It provides practically all of the visible light in the Solar System. • High-energy particles streaming out from the Sun influence planetary atmospheres and magnetic fields. This streaming of particles is known as the solar wind.

34. Apply the scientific method to formation of the Solar system! • Make observations about the solar system • Hypothesize • Test or experiment • Draw conclusions about the validity of our hypothesis • Repeat

35. What is density? density = mass/volume typical units: [ g/cm3] Density of water is defined as 1 g/cm3.

36. Definitions • meteor- a flash of light caused when a particle from space burns up upon entering our atmosphere • meteorite- a rock from space that lands on the Earth • nebula- a cloud of gas in space (usually glowing) • isotopes- elements with the same number of protons but differing numbers of neutrons • Asteroid- a small rocky body orbiting the Sun. • Comet- a small icy body orbiting the Sun. • Astronomical Unit (AU)- the average Earth-Sun distance, about 15O million km (93 million miles)

37. Observation: Patterns of Motion • All planets orbit the Sun in the same direction: counterclockwise when seen from above the Earth’s North Pole. • All planetary orbits lie in nearly the same plane. • Almost all the planets travel on nearly circular orbits, with a spacing that increases with distance according to a fairly regular trend.

38. Patterns of Motion • Most planets rotate in the same direction they orbit: counterclockwise when viewed from above the Earth’s North Pole. • The Sun rotates in the same direction in which the planets orbit. • Almost all moons orbit their planet in the same direction as the planet’s rotation and near the planet’s equatorial plane.

39. Patterns of Motion • Most planets have fairly small axis tilts, usually less than 25º. Question #1:Why are the observed motions in the solar system generally so orderly?

40. Observation: Categorizing Planets Can we categorize the planets into groups? How many categories do we need?

41. Categorizing Planets Question #2:Why do the inner and outer planets divide so neatly into two classes?

42. Observation: Asteroids & Comets • No formation theory would be complete without an explanation of the most numerous objects in the solar system: asteroids and comets. • Asteroids are small rocky bodies that orbit the Sun between the orbits of Mars and Jupiter, primarily in the asteroid belt.

43. Observation: Asteroids & Comets • Their orbits generally lie close to the plane of the planetary orbits, although they are usually tilted a bit more. Some have quite large eccentricities. • Almost 10,000 asteroids have been identified; these are probably only the largest ones. The largest asteroids have a radius of about 200 km - much less than half of the Moon’s radius.

44. Asteroids & Comets • Comets are small, icy bodies residing in one of two regions, the Kuiper Belt and the Oort Cloud.

45. Asteroids & Comets Question #3: Why are there a large number of asteroids & comets in two different locations?

46. Observation: Exceptions to the patterns • Some objects don’t fit the general patterns: • Mercury and Pluto have much larger eccentricities and inclinations. • The rotational axes of Uranus and Pluto are substantially tilted.

47. Exceptions • Venus rotates backwards - clockwise, rather than counterclockwise,as viewed from above Earth’s North Pole. • Earth has an exceptionally large moon. Pluto’s moon is almost as big as Pluto. • While most jovian moons orbit with the same orientation as the planet’s rotation, a few orbit in the opposite direction.

48. Exceptions Question #4: Why are there exceptions to the general patterns?

49. Four principal characteristics of the Solar System • Patterns of motion • Two types of planets • Asteroids and comets • Exceptions to the patterns A theory of the formation of the Solar System must include these.

50. Solar nebula theory • In the last 20 years, a lot of evidence has accumulated in support of a model called“solar nebula theory”. • Originally proposed by Kant (1755) and Laplace (~1795) • This model holds that our solar system formed from a giant swirling interstellar cloud of gas and dust. “Nebula” is the Latin word for cloud. Orion Nebula : an active star-forming region.