http://www.iht.com/articles/2009/03/03/america/space.php
The primary mirror of the Kepler telescope. The craft's mission, set to begin Friday, is to discover Earth-like planets in Earth-like places. (Ball Aerospace) Any more Earths out there? NASA hopes new mission will tell us By Dennis Overbye Published: March 3, 2009 Someday it might be said that this was the beginning of the end of cosmic loneliness. Presently perched on a Delta 2 rocket at Cape Canaveral, Florida, is a one-ton spacecraft called Kepler. If all goes well, the rocket will lift off about 10:50 p.m. Friday on a journey that will eventually propel Kepler into orbit around the Sun. There the spacecraft's mission will be to discover Earthlike planets in Earthlike places, that is to say, in the not-too-cold, not-too-hot Goldilocks zones around stars where liquid water can exist. The job, in short, is to find places where life as we know it is possible. "It's not E.T., but it's E.T.'s home," said William Borucki, an astronomer at the NASA Ames Research Center at Moffett Field in California, who is the lead scientist on the project. Kepler, named after the German astronomer who in 1609 published laws of planetary motion that now bear his name, will look for tiny variations in starlight caused by planets passing in front of their stars. Borucki and his colleagues say that Kepler could find dozens of such planets - if they exist. The point is not to find any particular planet, but to find out just how rare planets like Earth are in the cosmos. Jon Morse, director for astrophysics at NASA headquarters, calls Kepler the first planetary census-taker. Kepler's strategy is, in effect, to search for the shadows of planets. The core of the spacecraft, which carries a telescope 5.6 feet, or 1.7 meters, in diameter, is a 95-megapixel digital camera. For three-and-a-half years, the telescope will stare at the same patch of sky about 10 degrees, or 20 full moons, wide, in the constellation Cygnus. It will read out the brightness of 100,000 stars every half-hour, looking for the telltale blips when a planet crosses in front of its star, a phenomenon known as a transit. To detect something as small as the Earth, the measurements need to be done with a precision available only in space, away from the atmospheric turbulence that makes stars twinkle, and far from Earth so that our home world does not intrude on the view of shadow worlds in that patch of sky. It will take three or more years before astronomers know whether Kepler has found any distant Earths. If Kepler finds the planets, Borucki said, life could be common in the universe. The results will point the way for future missions aimed at getting pictures of what Carl Sagan, the late Cornell University astronomer and science popularizer, called "pale blue dots" out in the universe, and at the search for life and perhaps intelligence. But the results will be profound either way. If Kepler doesn't come through, that means Earth is really rare and we might be the only extant life in the universe, our loneliness just beginning. "It would mean there might not be Star Trek,"' Borucki said at a recent news conference. The need, even the possibility, of a planetary census is a recent development in cosmic history. It was only in 1995 that the first planet was detected orbiting another Sunlike star. In the years since then there has been a torrent of discoveries, 340 and counting, that have bewildered astronomers and captured the popular imagination. So far none of them qualify as prime real estate for life, and few of them reside in systems that resemble our solar system. Most of the planets have been found by what is called the wobble method, in which the presence of a planet is deduced by observing the to-and-fro gravitational tug it gives its star as it orbits. The closer a planet is to its star, the bigger the tug and the easier it is to detect. The smallest exoplanet - or planet that orbits a star that is not the Sun - discovered is about three times as massive as Earth, and most are in tight orbits. The fact that they are there suggests there are many more modest-size planets to be found in larger, more habitable orbits. As seen from outside the solar system, the Earth blocks only about 80 millionths of the Sun's light when it transits. Kepler has been built to detect changes in brightness as small as 1 part on 20 million, equivalent to a flea crawling across a car headlight. By measuring the diminution of a star's light during an exoplanet transit, astronomers in principle will be able to determine the size of the exoplanet. From the intervals between eclipses, astronomers will be able to determine its orbit. By combining this with other data, from, say, wobble measurements, they will be able to zero in on important properties like mass and density. Not all 100,000 stars in the field of Kepler's view would have their planetary systems oriented to provide transit eclipses from our particular point of view, of course. Borucki and his colleagues estimate that for an Earthlike star in its habitable zone, the stars would align to produce a blot-out in about one half of one percent of cases, yielding a few dozen to a few hundred new Earths out there. For planets that are closer in, however, the odds rise to about 10 percent, so there are ample reasons to expect a bumper crop of new planets. Borucki said the astronomers had set the goal of observing at least three such transits of a suspected planet, to confirm the period and rule out interference from starspots, the equivalent of sunspots. Then they would obtain backup observations from other telescopes, say, of wobble measurements, before announcing they had found a planet. "When we make a discovery, we want it to be bulletproof," Borucki said. That means that the first planets to be discovered and announced will be the biggest planets with the shortest orbits, the so-called hot Jupiters. Indeed, four stars with such planets are in the search area, and thus will be an early test of Kepler's acuity. "In the first six months, hot Jupiters are going to roll off the Kepler assembly line," said Debra Fischer of San Francisco State University, a veteran planet hunter who is not a member of the Kepler team. "These are bizarre planets; we don't understand how they form." The hardest and most exciting part of the mission, detecting bona fide Earths, will also take the longest. These should take about a year to circle a Sunlike star, producing only one blip a year in its starlight. So it would take more than three years to produce the requisite three blips and subsequent confirmation by ground-based telescopes before the discovery was announced. "We're not going to be able to tell you very quickly," Borucki said. Alan Boss, of the Carnegie Institution of Washington, who is a high-ranking member of the Kepler science team, said: "It really is going to count many Earths. About four years from now, we will have a really good estimate of how many Earths there are." If the history of exoplanet astronomy is any guide, there are likely to be surprises that geologists had not imagined - water worlds, for example. That could lead to the next series of questions: whether anywhere else in this galaxy the dust that once spewed from stars has come alive and conscious. James Fanson, the Kepler project manager, who will step down after the launching, said: "In my 25 years of working with NASA, this is the most exciting mission I've worked on. We are going to be able to answer for the first time a question that has been pondered since the time of the ancient Greeks: Are there other worlds like ours?" When a reporter departed from journalistic objectivity to venture a hope that other Earths were out there, Fanson happily joined in. "I hope the answer is yes," he said. "I hope the universe is teeming with planets like Earth." [Non-text portions of this message have been removed]
