Homework 7

1. Homework 7 Average: 38.5/40 (96.3%) High: 40/40 (100%)

2. Rest of Semester Thursday, December 6 – Finish Up Chapter 24/AstroJeopardy! Final Exam on Wednesday, December 12 – 8AM-10:30AM

3. Doppler Method - Extrasolar Planets • Doppler shift data tell us about a planet’s mass and the shape of its orbit.

4. Transits and Eclipses Planet passes behind star Planet passes in front of star • A transitis when a planet crosses in front of a star. • The resulting eclipse reduces the star’s apparent brightness and tells us planet’s radius. • Must be certain variability is not intrinsic to the star!

5. Transit Missions • NASA’s Kepler mission was launched in 2009 to begin looking for transiting planets around 100,000 stars. • Was designed to measure the 0.008% decline in brightness when an Earth-mass planet eclipses a Sun-like star.

6. The Kepler 11 system • The periods and sizes of Kepler 11's 6 known planets can be determined using transit data.

7. Calculating density • Using mass, determined using the Doppler technique, and size, determined using the transit technique, density can be calculated.  gas giant or terrestrial

8. Spectrum During Transit • Change in spectrum during a transit tells us about the composition of planet’s atmosphere. • Planet’s atmosphere absorbs more light at specific wavelengths

9. Surface Temperature Map HD 189733b • Measuring the change in infrared brightness during an eclipse enables us to map a planet’s surface temperature.

10. Direct Detection Brown dwarf 2M 1207 with a Jovian companion Glare much less from a brown dwarf • Special techniques like adaptive optics are helping to enable direct planet detection.

11. Direct Detection Bright star Fomalhaut (blocked out) with debris disk and Jupiter-sized planet (inset) orbiting at 115 AU. • Planet predicted from gravitational distortions in debris disk.

12. Direct Detection HR 8799 with four 7-10 Jupiter mass planets at distances 18 – 68 AU from the host star.

13. Direct Detection 2003 vs. 2009 β Pictoris May be forming carbon-rich planets 8 Jupiter masses at 8 AU

14. Direct Detection GJ 758 is very much like our Sun (G-dwarf). B is a 30-40 MJupiter brown dwarf C is a background star! GJ 758 Gas giant planet/brown dwarf boundary generally set at 17 Jupiter masses

15. Direct Detection κ Andromedae is a star with a mass of 2.5 solar masses (most massive star known to harbor a planet) b is a Super-Jupiter with a mass 13x that of Jupiter κ Andromedae

16. Orbits of Extrasolar Planets • Most of the detected planets have orbits smaller than Jupiter’s – biased! • Planets at greater distances are harder to detect with the Doppler technique. Does not include direct detections

17. Orbits of Extrasolar Planets • Orbits of some extrasolar planets are much more elongated (have a greater eccentricity) than those in our solar system.

18. Two Key Unexpected Features • Some extrasolar planets have highly elliptical orbits. • Some massive planets, called hot Jupiters, orbit very close to their stars. No analogs in our own Solar System.

19. Hot Jupiters

20. Can we explain the surprising orbits of many extrasolar planets?

21. Revisiting the Nebular Theory • The nebular theory predicts that massive Jupiter-like planets should not form inside the frost line (at << 5 AU). • The discovery of hot Jupiters has forced reexamination of nebular theory. • Planetary migrationor gravitational encounters may explain hot Jupiters.

22. Planetary Migration • A young planet’s motion can create waves in a planet-forming disk. • Models show that matter in these waves can tug on a planet, causing its orbit to migrate inward.

23. Gravitational Encounters and Resonances • Close gravitational encounters between two massive planets can also eject one planet while flinging the other into a highly elliptical orbit. • Multiple close encounters with smaller planetesimals can also cause inward migration. • Resonances may also contribute.

24. Modifying the Nebular Theory • Observations of extrasolar planets have shown that the nebular theory was incomplete (Hot Jupiters + highly elliptical orbits). • Effects like planetary migration and gravitational encounters might be more important than previously thought.

25. Chapter 24Life in the Universe

26. Earliest Life Forms • Major impacts from Heavy Bombardment period would vaporize the oceans and sterilize planet. • Heavy Bombardment period ended between 3.9 – 4.2 billion years ago. • Life probably arose on Earth more than 3.85 billion years ago, very fast after the end of heavy bombardment.

27. Earliest Fossils • The oldest fossils show that bacteria-like organisms (stromatolites) were present over 3.5 billion years ago. • Carbon isotope (12C and 13C, not 14C) evidence dates the origin of life to more than 3.85 billion years ago • Life more easily incorporates 12C more easily than 13C; 3.85 billion year old rocks have elevated 12C/13C Modern, living stromatolites off coast of Australia (formed from trapping, binding and cementation of rock grains by microbes, notably cyanobacteria)

28. The Geological Time Scale 4.4 billion years - early oceans form 3.5 billion years - cyanobacteria start releasing oxygen  key! 2.0 billion years - oxygen begins building up in atmosphere 540–500 million years - Cambrian Explosion 225–65 million years - dinosaurs and small mammals (dinosaurs ruled) Few million years - earliest hominids

29. Studies suggest that the earliest life on Earth may have resembled the bacteria today found near deep ocean volcanic vents (black smokers) and geothermal hot springs. Extremophiles – don’t necessarily rely on sunlight – life is robust!

30. What Defines Life? The necessary but not sufficient conditions: ➢ Order – organisms are structured ➢but so are your socks! crystalline structures ➢ Reproduction – continuation of kind ➢but not viruses, computer code can reproduce ➢ Growth ➢but so do crystals ➢Utilization of fuel: energy for growth, organization, etc. ➢but so does your car ➢ Environmental response ➢but snow melts in response to heating ➢Evolutionary Adaptation  BINGO!

31. Must Life be Carbon-Based? Carbon is versatile; H has one bond, O two, C four: can get a vast array of C-based scaffoldings, to which other simple atomic groupings may attach, making complex organic molecules such as lipids, carbohydrates, amino acids. Is there a substitute for carbon? Silicon has four bonds, but... ➢the bonds are weak ➢ Si-based molecules will not survive long in water ➢only single, not double bonds, so ➢ fewer chemical reactions than for C-molecules ➢ less rich set of molecular structures There is a high probability that “life elsewhere” is carbon-based. “No kill I”

32. How Did Life Arise on Earth? • It formed here. • Life originated elsewhere and was transported to Earth via meteorites, comets, or asteroids (panspermia).

33. Laboratory Experiments Start with just water, methane, ammonia, hydrogen, carbon dioxide, carbon monoxide: CO2 → CO + [O] (atomic oxygen) CH4 + 2[O] → CH2O + H2O CO + NH3 → HCN + H2O CH4 + NH3 → HCN + 3H2 CH2O + HCN + NH3 → NH2-CH2-CN + H2O NH2-CH2-CN + 2H2O → NH3 + NH2-CH2-COOH (glycine) 21 other amino acids also formed, plus RNA and DNA nucleobases. • The Miller-Urey experiment (and more recent experiments) show that the building blocks of life form easily and spontaneously under the conditions of early Earth.

34. Could life have migrated to Earth? • Venus, Earth, Mars have exchanged tons of rock (blasted into orbit by impacts). • Comets have been shown to contain organic material. • Some microbes can survive years in space.

35. Murchison Meteorite • Fell in Australia September 28, 1969. • Carbonaceous chondrite contains over 100 kinds of amino acids

36. What are the necessities of life?

37. Hardest to find on other planets Necessities for Life • A nutrient source • Energy (sunlight, chemical reactions, internal heat) – thermophiles (tube worms around black smokers) don’t need sunlight • Liquid water (or possibly some other liquid)

38. Why is Liquid Water Important? Liquid water is an invaluable solvent: ➢it facilitates reactions by bringing together the chemical components ➢ in ice, no transport occurs ➢ in vapor the chemicals are dispersed ➢it transports chemicals to and from cells Water actually participates in key reactions.

39. Could there be life on Mars?

40. Searches for Life on Mars • Mars had liquid water in the distant past. • Still has subsurface ice; possibly subsurface water near sources of volcanic heat

41. The Martian Meteorite debate Composition indicates origin on Mars. • 1984: meteorite ALH84001 found in Antarctica • 13,000 years ago: fell to Earth in Antarctica • 16 million years ago: blasted from surface of Mars • 4.4 billion years ago: rock formed on Mars

42. ALH84001 • Highly magnified images reveal rod-shaped structures, some of which are segmented. • Look like fossilized remains of actual bacteria. • Problems: • inorganic processes can sometimes produce elliptical and tubular structures • ancient bacteria on Earth were hundreds of times larger, but some “nanobacteria” has been discovered.

43. Could there be life on Europa or other jovian moons?

44. Europa and Ganymede show some evidence for subsurface oceans. • Relatively little energy available for life, but there still may be enough. • Intriguing prospect of two potential homes for life around Jupiter. Europa Ganymede

45. Titan • The surface is too cold for liquid water (but there may be some deep underground). • Has lakes of liquid ethane/methane on its surface.

46. Enceladus • Ice fountains suggest that Enceladus may have a • subsurface ocean.