Astronomers aided by a precocious amateur have discovered two more planets orbiting sun like stars, including one with the most Earth like orbit of any of the new worlds detected so far. The discovery brings the total number of confirmed extrasolar planets to a dozen. But, until now, all the planets were in orbits much closer to, or much farther from, their stars than is Earth, whose distance from the sun's warmth is within the so-called life zone, where conditions are neither too hot nor too cold for life to evolve.