"When I began searching for exoplanets," Geoff Marcy told me last year, "everybody said I was crazy." Back then—in the 1990s, when "planet hunting" was new and, as its name might suggest, somewhat exotic—the notion of finding planets that existed outside our solar system seemed to have as much to do with science fiction as with science. The Times wrote articles noting that "a few skeptics still question whether these objects, called exoplanets, qualify as true planets."
All of which makes new research, published today in the Proceedings of the National Academy of Sciences, fairly mind-boggling. Marcy and his co-authors, Erik Petigura and Andrew Howard, surveyed 42,000 sun-like stars, searching for the tell-tale visual sign of a planet: the periodic dimming that occurs when that planet crosses in front of its host star. The trio discovered, from that analysis, 603 planets, 10 of which are Earth-sized and orbit their host stars in the habitable zone (the range of distance from a host star that allows the surface temperature of a planet to be suitable for liquid water). The nearest of those planets may be within 12 light-years—a relatively close neighbor in the cosmic scheme of things.