It took humans thousands of years to understand our own planet, and centuries 1 our neighboring planets. Nowadays, new worlds are being 2 every week.
Up to the present time, astronomers have 3 more than 370 "exoplanets"—planets orbiting (绕……运动) outer space stars (恒星) other than our sun. There is a "hot Saturn (土星)" 260 light-years from Earth that orbits its parent star so 4 that a year there lasts less than three days. 5 another star 150 light-years out is a burning "hot Jupiter (木星)," where upper atmosphere (大气层) is being burning to form a huge comet-like tail. Astronomers have found another three 6 orbiting a pulsar (脉冲星)—the remains of a once huge star shrinking (收缩) into a small atomic nucleus the 7 of a city. Some planets have obviously fallen into their suns. Others have been thrown out of their 8 to become "floaters" that float in the darkness of the universe.
Among all these, scientists are eager to find a clue of the 9 : planets like the Earth. That is, planets orbiting their stars at just the right distance—neither too hot nor too cold—to 10 life as we know it. We have not yet found planets that are quite like our own, 11 because they're inconspicuous (不起眼的). To see a planet as 12 and slim as ours among the brightness of its star is like trying to see a firefly in a fireworks display. 13 by pushing technology to the 14 , astronomers are rapidly approaching the day when they can find another Earth. And when they do, they can examine it for 15 of life.
