The 18 new planets recently discovered by ground telescopes were upstaged by NASA's space telescope, Kepler, which also recently announced a new cache of planetary discoveries, including the most promising Earth-like planet yet.
NASA's newest habitable-zone planet, dubbed Kepler-22b, is much more likely to host an advanced civilization than its previous candidates, which have orbits on the fringe of habitability, like Venus and Mars. Although NASA's newly discovered planet is twice as big as the Earth, Kepler-22b has a star in the same G-class as our sun; plus, its orbit is 290 days, very similar to the Earth's 365-day year.
So far NASA's space telescope has discovered 2,326 new planets--207 approximately Earth-sized--but only a handful of these are in the same habitable zone around their stars as the Earth, Mars and Venus.
As G-class stars age, however, they expand into Red Giants (A-class), which engulf their closer planets--like Mercury--and incinerate the rest with radiation, a stage that will occur after billions of years of further evolution by our sun. The spate of new planets recently discovered by ground telescopes, however, concentrated on "retired" stars that have already evolved to the cusp of changing into Red Giants. Consequently, any Earth-like planets accompanying these 18 new gas giants have been evolving for billions of years longer than on Earth, potentially hosting civilizations more advanced than our own.
The California Institute of Technology (Caltech) scientists leading the survey team, however, were not looking for advanced civilizations, but were merely trying to maximize their successes with the methods amenable to discovering planets by ground-based telescopes.
The 18 new planets were confirmed using the Keck Observatory in Hawaii with follow-ups at the McDonald Observatory (Mt. Davis, Texas) and the Fairborn Observatory (Paradise Valley, Ariz.). The teams surveyed more than 300 retired stars (A-type), most of which had just begun their evolution to Red Giants with diameters about 50 percent larger than our sun. Eventually, these stars will grow to be a hundred times larger than the sun, engulfing nearby planets and burning off the atmospheres and oceans of any Earth-like planets that do not get engulfed. Of course, any advanced civilizations there will be looking to relocate to nearby star systems with habitable planets like Earth.
The scientists’ motivation, however, was to study retired stars because any planet-induced wobble from gas giants can be detected with ground-based telescopes. In more detail, the star's spectra exhibits Doppler shifts of signals coming from them, which can only be caused by planets with masses about the size of Jupiter. The teams confirmed 18 gas-giant planets are circling these retired stars. Any smaller Earth-like planets that might circle these stars, unfortunately, cannot be detected by the Doppler method, leaving it up to NASA's Kepler to potentially detect them in the future.
Now, the scientists are cataloging the characteristics of the 18 new gas giants--which is half as many as have been previously detected in the complete history of astronomy before Kepler--to determine if they can reveal any new facts about planetary evolution. So far, they seem to indicate that the oblong elliptical orbits typical of some gas giants will evolve to be closer to symmetrical circles as observed in the 18 new ones.