Dr. Henry Throop / University of Colorado Astronomy 1110 July 5, 2000 Lecture 21: Astrobiology Announcements ------------- HW #5 -- due Thursday Final: review tomorrow Office Hours: extended office hours: Wednesday afternoon 2-4, Thursday afternoon 2-4 Friday morning (really desparate) 10-11 Similar format to current exams. But, will also have slides. Identify & discuss the the planet, feature, or process. Observing: tonight. For people who haven't been to SBO yet, 9-11 PM. Hand out grade sheets Exam #2 ------- Astrobiology ------------ One of deep questions of our time: are we along. We are the first generation to be able to a) think about it in a quantitative way, b) be able to answer it o we _have_ answered it to some degree, regarding planets o we have tried to answer it regarding ET's 'snobbery of chronology' -- w. safire Every era thinks they're in a `golden age' and the best so far Q's --- What is life? Group answers: o Moves o Reproduces o Mutates o Uses energy o Grows o Communicates o Has intelligence (?) o (Has radios) (?) What do we need for life? o Energy o Food o Organic molecules (chains of C, H, O, N -- all lots of interactions, lots of bonds) o UV / cosmic rays to mutate o Water -- never seen life without it o Right temperature On Earth, we see life: o Deep within the crust, km deep o In space, bombarded by cosmic rays for many years (e.g., tomato seeds put in orbit by shuttle) o In ice o In 125 degree hot, smoking vents Search for ET can take several paths o Q: How does life work on earth A: it starts fast and easily, everywhere we look o Can we find life elsewhere in SS? A: We're trying, suggestive evidence, but no proof yet. o Can we find other planets like Earth elsewhere? A: Almost -- come back in 10 years o Can we detect evidence for life anywhere in galaxy? A: Long shot, but we're trying (listening for radio transmissions) How did life start on earth? Planetarium show: talked about Mars rock from Antarctica, ALH84001 ALH84001: formed 4.5 bya, ejected 16 mya, landed 13 kya Evidence: o PAH's (also in barbecued foods) o PAH's denser further in o Magnetite grains o `Look like bugs' o Carbonates younger than rocks ie, four weak arguments which -- when put together -- form one slightly stronger argument. C. Sagan -- 'Extraordinary claims require extraordinary evidence' "In examining the martian meteorite ALH84001 we have found that the following evidence is compatible with the existence of past life on Mars: (i) an igneous Mars rock (of unknown geologic context) that was penetrated by a fluid along fractures and pore spaces, which then became the sites of secondary mineral formation and possible biogenic activity; (ii) a formation age for the carbonate globules younger than the age of the igneous rock; (iii) SEM and TEM images of carbonate globules and features resembling terrestrial microorganisms, terrestrial biogenic carbonate structures, or microfossils; (iv) magnetite and Fe-sulfide particles that could have resulted from oxidation and reduction reactions known to be important in terrestrial microbial systems; and (v) the presence of PAHs associated with surfaces rich in carbonate globules. None of these observations is in itself conclusive for the existence of past life. Although there are alternative explanations for each of these phenomena taken individually, when they are considered collectively, particularly in view of their spatial association, we conclude that they are evidence for primitive life on early Mars." http://www-curator.jsc.nasa.gov/curator/antmet/marsmets/alh84001/sample.htm Major questions with ALH rock: o Is it really life? o Was that life put there while on Mars, or Earth? o Where did it come from originally? o If it is life, did more advanced life ever exist on Mars? Paper was 3 years ago. Since then, o JSC group: found more evidence that these are bugs, eg pictures o Other people: found more evidence that this is hokey -- eg, small rocks on Earth that look like same bugs Collab Q's ---------- If it turns out that evidence for life in ALH84001 is disproven, what does this mean? o Life on Mars never existed o Life is rare in the solar system o Nothing o Water existed on Mars' surface o Life on Earth probably started on Mars Poll: There are 100 billion stars in our galaxy. How many besides our Sun have planets with intelligent life? 0 a few thousands millions+ how many people thing vg: Arecibo plot vg: hale-bopp image