At last count, astronomers had identified more than 400 planets orbiting stars beyond the Sun, and Gliese 581 was host to no fewer than four of them. Now a team of astronomers have found two more planets circling the star. It sits smack in the middle of the so-called habitable zone, orbiting at just the right distance from the star to let water remain liquid rather than freezing solid or boiling away. [Source: Time]
