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Stars 59 sufficient abundance. Until recently, searches had focused on stars similar to the Sun (spectral types F, G, and K), about 10% of the stars in our galaxy. Recent observations have challenged this view. The onset of star forma- tion and related element production seems to have been very rapid after the Big Bang. Heavy elements, including those necessary for life as we know it, appeared much earlier in universal history than astronomers once thought. One analysis suggested that 30% of the stars harboring life in our galaxy are, on the average, 1 billion years older than our Sun.‘ Mind-Stretcher. The peaking of the universe’s stellar birth rate about 5 billion years ago roughly coincided with the birth of our own solar system. If the evolution of life and intelligence in our case is typical, this may imply a flowering of intelligence in our own era. Astronomer Martin Rees even suggested that the unfolding of intelligence is near its cosmic beginnings.” We now have a broader view of the types of stars that might have planets with life. SETI researchers have extended the range to include the smaller and dimmer M-class stars that may make up 85-90% the stellar inventory—perhaps 300 billion of them in our galaxy.® A recent census of stars within 10 parsecs (32.6 light-years) of our Sun raised the count to 341. These include 4 white A stars, 6 yellow F stars, 21 G stars like our Sun, 45 orange K dwarfs, 20 white dwarfs, 9 brown dwarfs, and a whopping 236 cool, orange-red M dwarfs like Proxima Centauri, our closest neighbor.’ At a minimum, this widens the scope for simple life. Drake saw even greater promise: The types of stars that might harbor civilizations are much more extensive than we used to think.* Astronomers already have found a large dust disk around a nearby M- class star. As such circumstellar disks are signposts for extrasolar planetary systems, this discovery provides clues as to how the majority of planetary systems might evolve. “The habitable zone around a red dwarf is much thinner than around a sun-like star,” observed astronomer Todd Henry, “but since their number is so much larger, I believe that the first exo-Earth will be found around a nearby red dwarf.”° In place of the traditional sharp dividing line between stars and planets, we now have a continuum, with the apparent gaps filling in. Astronomers have discovered hundreds of dim stars known as brown dwarfs. These bodies, which occupy the mass range between 10 and 75 Jupiters, share some characteristics with stars and others with planets. Astronomers have detected bodies orbiting some brown dwarf stars, suggesting that they too might have planetary companions." As far back as 1979, astronomer Virginia Trimble concluded that stars with both ages and heavy element abundances comparable with those of