Metal-rich Stars - see note at foot ----------------------------------- Life, of course, needs planets just as much as stars to exist. And studies of the 50 or so extrasolar worlds detected since 1995 appear to confirm that metal-rich stars are more likely to be accompanied by solar systems. Our Sun is unusually metal-rich for a star of its age (4.5 billion years) and type (a yellow G-type "main sequence" star). [American astronomer Guillermo Gonzalez and other scientists aren't sure why. However, if this is pessimistic news, it does still leave billions of possible habitable solar systems. They may be fewer than we hoped, but they might also be easier to target in any future search for extraterrestrial life. Gonzalez's theories have so far won guarded acknowledgment from fellow planetary specialists. William Borucki, a research scientist at Nasa's Ames Research Center in California, said he was intrigued by how Gonzalez had imagined the consequences of planets existing in different parts of the galaxy. "I think this is a very, very interesting idea," he said. "Now scientists need to check the math to make sure it all adds up." Ian Brown 31 May 2001 http://news.independent.co.uk/uk/science/story.jsp?story=75486 ----------------------------------------------------------- Jan 2004 UPDATE Scientists say a ring-shaped region in the disc of the Milky Way shows the highest potential for life in our galaxy. The team of astronomers has identified stars that contain enough heavy elements to form terrestrial planets; are sufficiently distant from disastrous supernova explosions; and have existed for at least four billion years - the time it took for complex life to evolve on Earth. Using a sophisticated computer evolution model, they found that ten percent of the stars in our galaxy, located in a ring around the center of the Milky Way, meet those criteria."This is a crude first map of where life could be in our galaxy," said Charles Lineweaver, an astrophysicist at the University of New South Wales in Sydney, Australia, who led the study. The research also shows that 75 percent of the stars in this habitable zone are older than our sun; so if there is actually life there, it's probably more evolved than life on Earth. "Metallicity" Our galaxy, the Milky Way, contains more than 200 billion stars and countless other objects. It is one of billions of other galaxies in the universe. In their search for possible life, scientists look for favorable zones of "metallicity." A star with no heavy metals can't form terrestrial planets or life. "Anytime you can identify regions that have higher concentrations of metallicity, that's where you may find life," said Lineweaver. "In our model of the galaxy, we keep track of where and when these metals were produced. We can do that because we know how many massive stars went 'boom' as a function of time and place." The computer model used for the study is based on local observations. Scientists can look at stars all over the galaxy and determine the metallicity at the time they were formed. The region the researchers have concluded is the most favorable to host life is a ring that measures 21,000 to 27,000 light-years from the center of the galaxy. Created between four and eight billion years ago, this region is where 10 percent of the stars of the Milky Way were formed. The astronomers were also able for the first time to determine the age of the stars in the habitable zone. They found that 75 percent of them are older than our sun. "If people think that intelligent life will happen on these planets, then 75 percent of this intelligent life will have had a longer time to evolve than people that are circulating around our sun," said Lineweaver. "We're all trying to figure out how we compare to any life-forms that may exist in the universe," he added. "This study is the closest thing I can think of to answer that question. If there are aliens, 75 percent of them will have had longer time to evolve than we have. That may be the most fundamental take-home message of this study." Stefan Lovgren for National Geographic News ---------------------------------------- note: "metallicity" - not what we might think, Astronomers say a `metal' is anything more solid than hydrogen and helium; so it's stuff that has to come from inside stars, i.e. way after the big bang ('cos that just produced hydrogen / helium, or so they say). 2) Hyron Spinrad reported similar findings on `metallic stars' back in 1970 - and Isaac Asimov concluded "It is nine times to eighty one times more likely that intelligence has arisen earlier in the central region of our galaxy" fuller details - and lowdown on "habitable zones" - maybe check www.perceptions.couk.com/exosci.html#zone - it's in Google maybe for << perceptions exosci >> (no quotes) www.perceptions.couk.com/uef/setigift2.html#INTELLIGENCE maybe Google << setigift2 >> --------------------------------------------- FURTHER REFERENCES GO - "search perceptions" - in SEARCH-ENGINE file-ID www.perceptions.couk.com/uef/richsun.txt