天文学科普知识详说 (32).ppt

1、An experiment to detect life in other planets,Name: Hung Shui Ki A A a,Introduction Why search for life in exoplanets?,Since the beginning of the Space Age, one of the chief drivers has been the search for life beyond Earth. But why do human search for life in exoplanets?,Any Aliens?,In every age an

2、d in every place where humans have left records, we see evidence of a marvelous instinct. As soon as societies obtained even a little product beyond the needs of bare survival, they began to create arts, languages, cultures, philosophy, religion, science and also, to wonder and theorize about the un

3、iverse. It seems that human beings are born with creativity, wonder and intelligence. They are instinctive to explore the universe, the future and themselves. That is also why human societies became civilized and modern sciences and philosophy are developed.,What are the essential requirements for l

4、ife survival?,Water (and in extreme cases on Earth Ice) Energy (Sunlight OR other energy sources) Raw Materials (Organic matters) Nutrients Biological activities,Experiments to Search for Water Evidence of Liquid Water,Geographically Meandering channels River beds Oceans Gullies & Cliffs shaped by w

5、ater flow Below ice lakes (e.g. Europa) Rock Layers shaped by water flow,Liquid water below the cracks?,Geologically Carbonates Provided that the surface of the planet contains carbon dioxide. If carbonate minerals were formed on the surface by chemical reactions between water and the atmosphere, th

6、e presence of these minerals would be a clue that water had been present for a long time-perhaps long enough for life to have developed. Difficulties in searching for Water Searching for water is in fact very difficult, and it is a major obstacle to look for life right now. Until now, liquid water h

7、as not been found on the surface of Mars and other planets. Even if there is water, liquid water is going to be underground or under thick sheets of ice, which are hardly detectable.,Experiments to Search for Organic Matters Evidence of Organic Matters,The Pyrolytic Release Experiment: Aim: This exp

8、eriment would detect the existence of organic materials in the soil. Procedures: Following a five-day incubation period under a xenon-lamp, during which it was exposed to radioactive CO2, surface samples were heated to high temperatures to determine if any of the radioactive CO2 had been incorporate

9、d into molecular compounds.,Drawbacks of the PR Experiment:,Even though small concentrations of micro-organisms may be detected, the results are subsequently discounted on the basis that indigenous life-forms in the planet would have been killed by the relatively high temperatures they were exposed

10、to in the initial incubation period.,The Gas Chromatograph - Mass Spectrometer:,Aim: This experiment aims to determine the chemical composition of a soil sample on the surface of the planet. Apart from the primary interest for geological investigations, this experiment could also be used to detect c

11、oncentrations of organic compounds that would be the constituents of micro-organisms.,Results: The amount of water and organic compounds can be obtained. An absence of organic compounds may suggest the presence of some mechanisms that were destroying the carbon compounds in meteorites that reach the

12、 planet surface.,Tagish Lake meteorite - Traces of organic matter,Experiments to Search for Biological activity,1. The Gas Exchange Experiment Aim: To detect alterations in the composition of the gases in the test chamber as a result of biological activity. Results: This experiment detects the chang

13、e in the level of oxygen in the test chamber, yet the results should be investigated to see of they are consistent with biological activity.,2. The Labeled Release Experiment,Aims: To detect the uptake of the nutrient by micro-organisms, by used a liquid nutrient tagged (labeled) with radioactive Ca

14、rbon-14. Expected Result: A positive result would be that the soil, when wetted by the nutrient tagged (labeled) with radioactive Carbon-14, rapidly releases significant volumes of labeled gases over a period of time, e.g. several days. Also, the rate of gas release should be in a manner that is con

15、sistent with either chemical or biological activity.,Experiments to Search for Energy sources beyond Sunlight,Sunlight is NOT compulsory for Life Existence! Scientists have discovered an isolated community of bacteria nearly two miles underground that derives all of its energy from the decay of radi

16、oactive rocks rather than from sunlight. They have been isolated from the Earths surface for several million years, depending exclusively on geologically produced hydrogen and sulfur compounds for nourishment. This shows that LIFE CAN INDEED EXIST IN EXTREME CONDITIONS FAR BEYOND HUMANS IMAGINATIONS

17、.,Therefore, to search for extreme life-forms is indeed equivalent to search for energy sources that can be utilized by organisms. These possible energy forms include:,decay of radioactive rocks. e.g. uranium, thorium and potassium geothermal energy. e.g. hydrothermal vents sulfur compounds and geol

18、ogically produced hydrogen energy-rich food (instead of organic matters) EM wave Oxidation-Reduction Kinetic Energy Magnetic Field Gravitional Forces Tectonic Stress Pressure Gradients,hydrothermal pools & Mars microbes?,Experiments to Search for Fossils An easier alternative to search for Liquid Wa

19、ter,We have mentioned the Difficulties in searching for Water. On the other hand, fossilized bacteria might just be right there on the surface of planets, waiting for a rover to scoop it up and analyze it. Procedure: Find a location where water once existed for some period of time. For example, wher

20、e the Mars Exploration Rovers, Spirit and Opportunity, are currently roaming. In order to see fossilized bacteria, the rovers would need to be equipped with extremely sensitive microscopes and organic chemistry laboratories to analyze promising rocks.,Also, based on the experience of finding fossils

21、 on Earth, it is known only certain environments and types of deposits provide good places for fossil preservation. Therefore, regions of similar deposits on the exoplanets become targets for searching fossils. Advantages: On Earth, fossils in sedimentary rock leave a record of past life. Therefore, by finding fossils, we can determine the past life on the planets. Also, it would be easier than getting to liquid water.,Conclusion,Humans are still unable to find any kinds of life-forms on planets other