The tilt of a star's spin is obviously an important feature, but knowing it first requires knowing the orbit of its planets. One amazing and serendipitous result of the Kepler mission and its powerful ability to find transiting planets is its ability - by characterizing planetary systems - to address the issue of stellar tilts. Stellar tilts measured so far in exoplanetary systems display a surprising diversity, from very small values like our Sun's to strongly tilted stars, and even some "retrograde" stars whose direction of rotation is opposite to the planetary orbital revolution. These stars also happen to be somewhat young; indeed most of the stars hosting planets in the Kepler program have not evolved past the hydrogen burning stage of their lives. Almost all of the tilted stars host hot Jupiters—planets about the mass of Jupiter (that is, large planets) but that orbit very close to the star and so are hot. The wide range of observed tilts suggests that they arose not from a standard sudden collision, but rather from some more intricate process that transports a normal Jupiter from its orbit far out (as in our solar system) to an orbit very close to the star.
CfA astronomers Josh Carter and Dave Latham, along with a team of collaborators, have found that the star known as Kepler-56 is the most evolved star observed by Kepler so far known to have more than one planet in its system. Kepler-56 is a red-giant star about 3.5 billion years old (it is now burning helium as fuel), has more than four times the diameter of the Sun, and is about 30% more massive. Its two planets, neither one a hot Jupiter, are much less massive with only about 22 and 181 Earth-masses, respectively. Notably, they orbit their star in nearly circular, coplanar orbits . It turns out that Kepler-56 is also tilted, and with a large angle of 47+-6 degrees. The result shows for the first time that the tilt of a star is not necessarily associated with the process of making hot Jupiters. What did tilt Kepler-56 is not yet known. The authors suggest that a third, distant massive companion, either a planet or another star, could be responsible, and indeed the data suggest the presence of such a third orbiting body. Additional observations are needed to confirm this conclusions, which already demonstrates the remarkable power of Kepler and the diversity of exoplanet systems.