For the first time, scientists have definitively discovered an “invisible” alien planet by noticing how its gravity affects the orbit of a neighboring world, a new study reports.
NASA’s Kepler space telescope detected both alien planets, which are known as Kepler-19b and Kepler-19c. Kepler spotted 19b as it passed in front of, or transited, its host star. Researchers then inferred the existence of 19c after observing that 19b’s transits periodically came a little later or earlier than expected. The gravity of 19c tugs on 19b, changing its orbit.