astroengine writes: Speaking at the 223rd meeting of the American Astronomical Society in Washington D.C., astronomers have announced the discovery of an Earth-mass exoplanet that has a thick, puffed-up atmosphere making it 60% bigger than Earth. The exoplanet's mass is the first to be derived using transit timing variation (TTV) data from NASA's Kepler space telescope. “Rather than looking for a wobbling star, we essentially look for a wobbling planet,” said co-investigator David Nesvorny, of the Southwest Research Institute (SwRI). “Kepler saw two planets transiting in front of the same star over and over again. By measuring the times at which these transits occurred very carefully, we were able to discover that the two planets are locked in an intricate dance of tiny wobbles giving away their masses.” With this information, astronomers are now trying to understand how such a planet (with a very compact orbit around its star) evolved. The leading idea is that it might have been a Neptune-like gas giant that had the bulk of its atmosphere ripped away by stellar radiation.