Astronomy
Chapter 27 Homework
Homework
Chapter 27: Search for Extraterreatrial Life
Homework
- Reading Preparation
- Key Formulae to Know
- WebLecture
- Study Activity
- Chat Preparation Activities
- Chapter Quiz
- Lab Work
Reading Preparation
Reading: Astronomy, Chapter 27: The Search for Extraterrestrial Life
Study Guide
- Section 1: Life-as-we-know-it depends on two things: carbon compounds and liquid water. The abundance of carbon and oxygen from stellar nucleosynthesis supports formation of basic organic molecules in cool interstellar clouds, where the bonds will not be destroyed by high-energy radiation. Probes to comets and asteroids have detected not only simple carbohydrate compounds (containing carbon, oxygen, and hydrogen), but also amino acids. The Miller-Urey experiment showed that under specific conditions, amino acids can form from inorganic compounds.
- Section 2: Without liquid water, photosynthesis and cellular respiration cannot occur, so any search for ET life can focus on planets or moons with liquid water. While ice has been detected on Mercury and Mars, liquid water may exist in a subsurface ocean ocean on Europa, and Enceladus has salt water plumes. Detecting life in the subsurface water reservoirs poses many problems, not the least of which is the considerable risk of destroying a fragile ecosystem by investigative methods that break through the surface layers protecting the oceans of these atmosphere-free moons from high energy radiation. Investigating similar environments, such as Lak Vostok on Earth, may give us a way to estimate the possibility that life exists on these moons. Mars missions carry experiments designed to detect life signs, including gases released by metabolic processes, evidence of waste production, gas use during photosynthesis, 12C to 13C ratios, and an abundance of methane. So far, no experiments have conclusively shown life exists on any planet or moon other than Earth.
- Section 3: Meteors crashing into Mars send debris into space, some of which has reached Earth. These Martian meteorite chips show some evidence that liquid water existed on Mars around 16 million years ago, and may contain fossils of microorganisms as well as tunnels created by rock-eating microbes similar to such species on Earth.
- Section 4: The Drake equation is an effort to summarize the factors that contribute the development of advanced civilizations and estimate the number of such civilizations that exist now and could be detected by Earth's own technology. Each factor of the Drake equation limits the preceding factor. While we can assume reasonable values for the formation of Sol-type stars (1 per year) and the formation of planetary systems (about 100% of Sol-type stars should have planetary systems), we don't have enough informaiton to estimate the other factors.
- Section 5: Several attempts have been made to detect extraterrestrial intelligence, the most signifcant of which was the 1989 NASA HRMS project. Because of funding and computational limitations, the project was unsupported within a year, but millions of eager would-be astronomers continued to help the SETI project analyze data on their personal computers, an early example of computer-aided crowd-sourced science. The publicly-funded SETI Institute uses the Allen Telescope Array to study stars with likely planets discovered by the Kepler telescope survey for signs of intelligent life.
- Section 6: NASA's space-based Kepler telescope and other efforts have discovered over 1000 exoplanets or planets orbiting stars other than the sun, some of which have Earth-type masses and lie within the "habitable range" of their star's energy emissions.
Key Equations
| Drake Equation | N: number of civilizations R*: Rate of sol-type star formation fp: fraction of stars with planets nc: number of Earthlike planets per solar system fl: fraction of Earthlike planets with life fi: fraction of life-forms which are intelligent fc: fraction of species with adequate technology L: lifetime of technical civilizations. |
Web Lecture
Read the following weblecture before chat: Looking for ET
Study Activity
Use the Drake Equation calculator at the Information is Beautiful site to estimate the chances of finding another civilization in your lifetime.
- Check the defaults for the "optomisitic" estimation, then run the calculation.
- Vary the defaults to use the lowest possible number, the original Drake values, and today's current "skeptical" values.
- Put in your own estimates and make a calculation.
- Chose the optimistic default and vary each variable one at a time. Which one has the most influence on the outcome?
- Reset the calculator and use the higher estimates suggested by the scientific evidence. How does the number of habitable planets change?
UNL Tools Exercises
- ClassAction: ExtraSolar Planets
- On the main tab, anser the warmup, general, and challenge questions.
- Under Animations, Check out the Extrasolar Planet Radial Velocity Demonstrator to see how Doppler shifts can be used to detect planets.
- Under Outlines, read the brief introduction to Planet Hunting Techniques.
- NAAP Labs
- Look at Lab 12. Extra Solar Planets. Read the background materials and use the Simulators to study how velocities and transits can be used to discover exoplanets.
- Look at Lab 15. Habitable Zones. Read the background materials and use the Simulators to study how we can determine where life-as-we-know-it might have appeared in other solar systems or parts of our galaxy.
Website of the Week: The longest running public or crowd-sourced science project is the SETI "@home" project, which distributed a screen saver running on early Commodore 64 computers that would analyze radio telescope data for paterns. SETI continues to sponsor crowd-sources data analysis projects aimed at detecting possible transmissions that would give evidence of non-terrestrial life forms elsewhere in the Universe.
Chapter Quiz
- Required: Complete the Mastery exercise with a passing score of 85% or better.
- Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!
Lab Work
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
- Lab instructions: Curvature of Space
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