astroengine writes "The Kepler space telescope has spotted an extra-solar planet with a very odd orbit. Sometimes Kepler-19b slows down by five minutes during its 9-day orbit. Other times it speeds up by five minutes. Johannes Kelper's laws of orbital dynamics never said a celestial body can arbitrarily speed up and slow down; another planetary body must therefore be gravitationally acting on Kepler-19b. Enter Kepler-19c, a world that hasn't been observed, but its gravitational effects have. This is an unprecedented discovery, one that could potentially be used in multi-planetary star systems to discover more 'phantom' worlds that would have otherwise gone unnoticed."