About 500 light-years away in the constellation Cygnus lives a star, which, though smaller and redder than the sun, has a planet that may look awfully familiar.
With a diameter just 10 percent bigger than Earth's, the newly found world is the first of its size found basking in the benign temperature region around a parent star where water, if it exists, could pool in liquid form.
Scientists on the hunt for Earth's twin are focused on worlds that could support liquid surface water, which may be necessary to brew the chemistry of life.
There once were two planets, new to the galaxy and inexperienced in life. Like fraternal twins, they were born at the same time, about four and a half billion years ago, and took roughly the same shape. Both were blistered with volcanoes and etched with watercourses; both circled the same yellow dwarf star—close enough to be warmed by it, but not so close as to be blasted to a cinder. Had an alien astronomer swivelled his telescope toward them in those days, he might have found them equally promising—nurseries in the making. They were large enough to hold their gases close, swaddling themselves in atmosphere; small enough to stay solid, never swelling into gaseous giants. They were "Goldilocks planets," our own astronomers would say: just right for life.