October 18, 2013
A long-standing puzzle in the study of exoplanets is the formation of hot Jupiters, gas giant planets that snuggly orbit their host star. To explain their short orbital periods, theory suggests that hot Jupiters form in long orbits and then quiescently migrate through the protoplanetary disc, the flat ring of dust and debris that circles a newly fashioned star and coalesces to form the planets.
This theory was challenged when the orbital plane of hot Jupiters were discovered to be frequently misaligned with the equator of their host stars. Scientists interpreted this as evidence that hot Jupiters are the result of chaotic close encounters with other planets.
A decisive test between the two theories are systems with more than one planet: if misalignments are indeed caused by dynamical perturbations which lead to the creation of hot Jupiters, then multi-planet systems without hot Jupiters should be preferentially aligned. What new research reveals is quite different.