-- Chuck Hards asked on 8/15 ---
I recall that there are 2 bio-chemical "paths" (lacking the proper term at the moment) that photo-synthesis can take here on earth. Was wondering if there are any botanists on the list who would speculate on the possibility of a form of photosynthesis that could work under the spectrum of a non-G type star? -- and 8/16 he speculated that - [W]hile ET species may share a common chemistry, they may have totally different sensory organs, or similar organs that operate at different wavelengths/frequencies.
There are three paths. I'm not a botanist. I. For the blue end of the visible spectrum - The terresterial plants that predominte our local Intermountain city-scape use chlorophyll-b to drive photosynthesis because chlorophyll-b absorbs light from the higher wavelength energy blue end of the spectrum - and reflects unused green light. Because blue light contains more energy, it can drive more efficient higher energy photochemical cycles - http://www.sirinet.net/~jgjohnso/modphotopigments.jpg in - http://www.sirinet.net/~jgjohnso/photosynthesis.html http://www.biologie.uni-hamburg.de/b-online/ge24/03.jpg in - http://www.biologie.uni-hamburg.de/b-online/e24/24.htm Note that absorbtion stops in the visible spectrum and does not occur in the ultra-violet. The limiting factor is uv light is too energetic - it can break down proteins and degrade photochemical processes. Groups of chorophyll-b driven plants are shown as items 1,2 and 3 in this spectral diagram - http://www.bio.mtu.edu/~mrgretz/bl4140_www/taiz_art/Illustrations/ch07/PP070... in - http://www.bio.mtu.edu/~mrgretz/bl4140_www/photosn1.htm II. For the green middle of the visible spectrum - Another group of plants - the red alage - http://tolweb.org/tree?group=Florideophyceae - use the less efficient carotenes to drive photosynthesis. Carotene photosynthesis utilizes the lower engery green portion of the spectrum, reflects unused red light, and is represented by item 4 in the spectral diagram - http://www.bio.mtu.edu/~mrgretz/bl4140_www/taiz_art/Illustrations/ch07/PP070... III. For the red end of the visible spectrum Also, within the green leafed plants that we are most familiar with in our daily lives - there are two photosysthesis systems - http://www.sirinet.net/~jgjohnso/photosynthesis.html http://en.wikipedia.org/wiki/Light_reaction (cyclic photosynthesis using photosystem I, non-cyclic photosynthesis using photosystem II an photosytem I). Photosystem II utilizes chlorophyll-b to absorb blue light. But Photosystem I utilizes chlorophyll-a to absorb red light at the far end of the spectrum. See the red side of the spectrum in - http://www.sirinet.net/~jgjohnso/modphotopigments.jpg http://www.biologie.uni-hamburg.de/b-online/ge24/03.jpg So, the color of the leaves of plants (not the flowers) can tell you about what wavelengths of light the plant _is not using_. This implies whether it is using chlorophyll-b based photosynthesis or carotene based photosynthesis. IV. Speculative astrobiology. One speculative thought experiment implied by these three photosynthetic pathways, that utilize three separate portions of visible spectrum, is the existance of alternative ecologies around G and M class stars. One thought experiment proposes that there is a habitable zone around red drawf stars - stellar class M4-M6. http://www.emse.fr/~yukna/researchers/reddwarf.htm Red drawf stars are among the most prevalent type of star in our Local Neighborhood of the Milky Way galaxy - the M class. Numerically, the M-class comprises about 80% of the stars on the main sequence. http://anzwers.org/free/universe/startype.html Wolf 424A-B, Gliese 752B and Wolf 359 are nearby red drawf stars. http://www.solstation.com/stars/wolf424.htm http://www.solstation.com/stars/wolf359.htm - but are also flare stars. Our Sun is rich in blue light - hence chlorophyll-b plants dominate in the ecology. Because our blue-light photosynthesis-based ecology produces autotrophic plants with a high energy content, Earth's ecology can support more trophic levels in a food chain that contains more active, complex predators. http://en.wikipedia.org/wiki/Trophic_level http://en.wikipedia.org/wiki/Food_chain If there is a planet is around the red-light dominated star Wolf 359, would the ecology of that planet be based on plants that use carotene and/or chlorophyll-a photosynthesis? If there is a carotene based ecology around Wolf 359, what how many trophic levels of ecological predation would it support? Would the most complex predator be a red algae-eating marine iguana? http://www.junglewalk.com/info/iguana-information.htm Because Wolf 359 is a flare star - could life on a hypothetical planet around the star adapt to flare distruptions? In conclusion Chuck, ET may have a 6-foot bulbous head and look like one of these - http://tolweb.org/tree/ToLimages/flortitle1a.100a.jpg - and want to "interwine" some tenancles with you, instead looking like one of these - http://www.avp-movie.com/ - and want to "have you over" for lunch. V. Targets for tonight? Since this is an astronomy listserv, if I would like to take my scope out tonight and look for a Gliese star of brighter than mag. 11-12 in the M4-M6 class - what would I look for? Barnard's Star - M4Ve? - Peace - Canopus56 Further reading - http://nai.arc.nasa.gov/ NASA Astrobiology Institute http://www.astrobio.net/ Astrobiology net http://astrobiology.arc.nasa.gov/ Astrobiology web at NASA http://en.wikipedia.org/wiki/Astrobiology Wikipedia entry on astrobiology __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com