Extraterrestrial life and extrasolar planets 5/1/07

Transcription

1 Extraterrestrial life and extrasolar planets

2 Announcements Final exam Thursday, May 10 11AM-1PM Brief review today Pick up past assignments! Office Hours Jade: not in this week John: as usual Me: as usual for times other than office hours

3 Have we Been Visited by Aliens? Check out:

4 A UFO panel convened to discuss all of the current evidence: The Sturrock Panel They concluded that the UFO problem is not a simple one No simple, universal answer Whenever there are unexplained observations, there is the possibility that scientists will learn something new by studying those observations. Example: ball lightning

5 Visual Evidence example: UFOs and Ball Lightning UFOs Not reported by scientists Scientists are skeptical Ball Lightning Often reported by scientists (and others who are deemed credible and believable) Never photographed! (confirmed to be authentic) Not produced in a laboratory and theoretical models are dubious (but a lot of effort has been put into studying this) A physiological effect?

6 Sprites observed over a thunderstorm in Kansas in August, 2000

7 Mission update #1

8 Life on Mars? The Viking Lander had a biological experiment package on board to search for life If life is confirmed to exist on Mars, this would be a scientific discovery of EPIC proportions! In fact, some reason that this alone supports the Humans-to-Mars initiative ALH48001 was there life on Mars in the past?

9 Labeled Release Experiment: Give them water Pyrolytic Release Experiment: Give them sunlight Gas Exchange Experiment: Give them food

10 Viking Results Summarized A key find came from the GCMS experiment Mars has NO organic compounds The surface of Mars is sterile The consensus opinion is that Viking found no evidence for life on Mars Better location? We know more about the surface of Mars now, perhaps a better site selection would help!

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13 A SNC meteorite found in 1984 in Alan Hills Antarctica The Story of ALH84001 Softball-sized meteorite weighing about 4 lbs. In a 1997 article in Science, David McKay indicated the meteorite showed evidence of primitive bacterial life on Mars

14 A separate class of meteorites. Igneous rocks crystallized from molten magma in a way which suggests they formed in a planetary-sized body, not an asteroid They show evidence of shock heating, presumably as a result of the impact which ejected them into space. Gas bubbles trapped in one meteorite, EETA79001, have a composition which matches the current Martian atmosphere SNC Meteorites Names after the first 3 places where they were found (Shergotty, Nakhla, Chassigny)

15 4.5 Billion years ago -- The original igneous rock solidified within Mars billion years ago -- the rock was fractured. Water then permeated the cracks, depositing carbonate minerals and allowing primitive bacteria to live in the fractures. 3.6 billion years ago -- the bacteria and their by-products became fossilized in the fractures. 16 million years ago -- a large meteorite struck Mars, dislodging a large chunk of this rock and ejecting it into space. 13,000 years ago -- the meteorite landed in Antarctica, where it was discovered in 1984 ALH84001 timeline

16 The Story of ALH84001 Simple organic compounds were found on the fracture surfaces Carbonate globules look like mineral alterations caused by primitive bacteria on Earth Concentric rings of different composition Magnetite was very pure Ovoids may be fossilized remains of bacteria Extremely small Smaller than even single cells Not life as we know it globules ovoids

17 Where do we stand on this? The original authors still maintain that this is evidence of life on Mars. Most scientists believe that the evidence can be explained by non-biological processes Need additional evidence The future? A sample-return mission would be important to resolve the issue of life on Mars Very expensive A multinational plan for 2005 was scrapped due to the back-to-back failures of The earliest launch of the next sample-return mission is 2014

18 Mission update #2

19 About 8 years ago, astronomers began finding extrasolar planets, or planets orbiting other stars More than 200 have been detected so far Extrasolar Planets They are not actually seen, instead, their effects on their parent star are oberved

20 Methods of detecting extrasolar planets Astrometry (changes in the star s location) Radial Velocity (changes in the star s velocity) Transit method (dimming caused by a transiting planet) Other methods: Pulsar timing, gravitational microlensing, circumstellar disks

21 Habitable zone a region of space where conditions are favorable for life as it can be found on Earth (water can exist as a liquid) This distance is centered on

22 The recent discovery of a new extrasolar planet that is within the habitable zone of its parent star It may be earth like but the diameter (and hence the density) is not known without modeling

23 Mission update #3

24 Format: Final Exam 6 short answer questions (4 pts each) 38 multiple choice questions (2 pts each) Closed book, closed note, no electronic devices (including a calculator!) Bring a #2 Pencil You will have 2 full hours to take the exam What will it cover? Mostly material discussed in the lectures (75%) Reading (25 %) 75% of the exam will be from Chapters % from topics covered throughout the course A brief review of these follows

25 Final Exam What should you study? Go over lecture slides Go over questions at the beginning of each chapter Go over key ideas and review questions at the end of each chapter Go over in-class activities, quizzes, and homework (except for mathematical questions) The solutions are on the website A practice exam is now posted on the website

26 Final Exam: A brief review of comprehensive material (25% of exam) Chapters 1-4 : Basic Astronomy The motion and position of objects in the sky Diurnal motion, retrograde motion Reason for seasons Moon phases Kepler orbits and gravity Chapter 5: The Nature of Light and Atoms Wien slaw Stefan-Boltzman law The Electromagnetic Spectrum Kirchoff s Laws (emission and absorption lines in spectra)

27 Final Exam: A brief review of comprehensive material (25% of exam) Chapters 7 and 8: The layout, nature, origin, age, and formation of the Solar System Basic solar-system properties Terrestrial planets and gas giants All planets orbit the Sun in the same direction and in the same plane Density of the planets The Solar Nebula The nebular hypothesis of the formation of the solar system

28 Final Exam: A brief review of comprehensive material (25% of exam) Basic Planetary processes Interiors and Surfaces Review the rules of thumb discussed in the textbook p. 156 (in box 7-2) p. 159 p. 161 Planetary Magnetic Fields Atmospheres Chapter 9: The Earth Plate tectonics Structure of the interior PTYS/ASTR Greenhouse 206 effect

29 Final Exam: A brief review of comprehensive material (25% of exam) Chapter 18: The Sun Basic Structure (interior and atmosphere) Radiative zone NOT radioactive zone! Energy Source Sun-Earth connection Sunspots and the sunspot cycle Sunspots are dim against the Sun, but still very bright! What is a geomagnetic storm? What is a cosmic ray? Chapters 10 and 11: The Moon and Mercury Lots of craters why? Basic surface geology (highlands, mare) No atmosphere why? Synchronous rotation (due to tidal forces)

30 Final Exam: A brief review of comprehensive material (25% of exam) Chapter 12: Venus Why does it exhibit phases? And why is it so bright? Runaway greenhouse effect Chapter 13: Mars Why is it at opposition every 2 years (nearly)? Evidence for Water Atmosphere Basic geology (northern vs southern regions)

31 Final Exam: A brief review of Chapters (75% of exam) Chapters 14 : Jupiter and Saturn Orbits composition Rotation Both are rapid and exhibit differential rotation Oblateness (Saturn is the most oblate) Features of the upper atmosphere Belts, and Zones, Giant Red Spot (Jupiter) Interiors Magnetic Fields Jupiter extremely strong Saturn aligned with rotation axis Planetary Rings (formation, gaps, which planets have them? Saturn s rings, etc.)

32 Final Exam: A brief review of Chapters (75% of exam) Chapter 15: Jupiter and Saturn s Moons Galilean Satellites: A Solar system in miniature Io, Europa, Ganymede, and Callisto Titan and Enceladus Tidal forces (tidal heating of the moons) Connection to the Jovian Magnetosphere Io torus

33 Final Exam: A brief review of Chapters (75% of exam) Chapter 16: The Outer Worlds Uranus and Neptune How were they discovered? Why are they blue-green in color? Uranus has an unusual tilt Both have unusual magnetic fields Pluto Discovery Orbit Charon Kuiper-belt objects

34 Final Exam: A brief review of Chapters (75% of exam) Chapter 17: Asteroids/Comets/Meteorites Asteroid Belt Kuiper Belt Oort Cloud Kirkwood Gaps Trojan Asteroids Asteroids shapes and brightness Rubble piles

35 Final Exam: A brief review of Chapters (75% of exam) Chapter 17: Asteroids/Comets/Meteorites (cont.) Meteorites Stony, irons, stony-irons, carbonaceous chondrites Comets Basic structure Orbits Meteor showers