Hidden Alien Planet Revealed by Its Gravitational Effects

Astronomers have discovered at least one unseen alien planet, and possibly another, around a distant star by observing the odd behavior of a planet already known to orbit the same star. The newfound planet has about the mass of Saturn and orbits its host star once every 57 days. It was revealed by its gravitational effects on the previously known planet around the parent star KOI-872. The find is an apparent validation of what scientists call the transit timing variation method of finding extrasolar planets.When the researchers looked in more detail at the system, they found signs of yet another planet, one only a bit larger than our own world. This “super-Earth” is likely circling very close to the star with an orbital period of 6.8 days. The first look at data from NASA’s planet-hunting telescope Kepler had identified only one planet around the star KOI-872. But a closer inspection by scientists outside the Kepler team revealed telltale signs of an extra planet. As part of its systematic search for alien planets, Kepler looks for stars whose brightness dims periodically, a signal that something, presumably a planet, is passing in front of it and blocking its light. The Kepler team identified a light dip in KOI-872 and attributed it to a planet that orbited the star every 34 days. However, that timing appeared to vary by a few hours. Using a computer model, astronomer David Nesvorny of the Southwest Research Institute in Boulder, Colo., who led the new study and his colleagues concluded that the most likely explanation for the timing variations was the presence of another planet in the system, the Saturn-mass world. Their calculations suggested a likelihood greater than 99 percent that this mystery planet exists. Nesvorny and his team are now combing through the wealth of Kepler data for signs of exomoons, moons orbiting alien planets. So far none has been found.