NASA's Kepler space telescope's count of exoplanets has passed the magic 1,000 mark, including eight new "habitable" planets and 544 candidate planets.
The latest tally is based on Kepler's observations of 150,000 stars in the constellation of Lyra, from which the Kepler team and others have identified 4,175 candidate exoplanets and have confirmed 1,000. Until its primary mission was ended due to a reaction wheel malfunction, Kepler hunted for exoplanets by means of the transit method. That is, it would scan a predesignated area of the sky and measure the light coming from various stars. If a planet passed between the star and Kepler, the result would be a dip in the stars brightness. By recording the curve of the light intensity and making precise calculations, it is possible to determine if a planet is indeed the cause and deduce various characteristics of it, such as orbit and size.
One major find among the new planets are eight that are no more than twice the size of Earth and orbit in their stars' habitable zones, where the temperatures are in the region that allows liquid water to exist on the planet's surface. Of these eight, six orbit stars similar to the Sun, and of these, two are probably rocky terrestrial planets like those of the inner Solar System.
The two Earthlike planets are Kepler-438b, which is 475 light years away, 12 percent larger than the Earth, and circles its star in 35.2 days; and Kepler-442b, which is 1,100 light years away, 33 percent bigger, and has a "year" of 112 days. Though their shorter years indicate they are closer to their stars than the Earth, this still puts them in the habitable zone because their stars are smaller and cooler than the Sun.
One side benefit of having confirmed so many exoplanets and their characteristics is that it provides a database large enough to allow astronomers to carry out statistical analysis and make very rough predictions about how many planets there are in our galaxy, as well as the odds of finding another Earth.
"Kepler collected data for four years – long enough that we can now tease out the Earth-size candidates in one Earth-year orbits," says Fergal Mullally, SETI Institute Kepler scientist at Ames. "We're closer than we've ever been to finding Earth twins around other Sun-like stars.
The next task for the Kepler team will be to use the new confirmed planets to improve the estimates of how many habitable rocky planets there are orbiting Sun-like stars. In addition, they are working on the new catalog of Kepler's data recovered over four years, and will be subjecting the Kepler data to a more sophisticated software for detecting Earth-like planets.
The Kepler team's results will be published in The Astrophysical Journal.