  The Sun's equator and the planets' orbital planes are nearly aligned, which
is presumably a consequence of their formation from a single spinning gaseous
disk. For exoplanetary systems this well-aligned configuration is not
guaranteed: dynamical interactions may tilt planetary orbits, or stars may be
misaligned with the protoplanetary disk through chaotic accretion, magnetic
interactions or torques from neighbouring stars. Indeed, isolated 'hot
Jupiters' are often misaligned and even orbiting retrograde. Here we report an
analysis of transits of planets over starspots on the Sun-like star Kepler-30,
and show that the orbits of its three planets are aligned with the stellar
equator. Furthermore, the orbits are aligned with one another to within a few
degrees. This configuration is similar to that of our Solar System, and
contrasts with the isolated hot Jupiters. The orderly alignment seen in the
Kepler-30 system suggests that high obliquities are confined to systems that
experienced disruptive dynamical interactions. Should this be corroborated by
observations of other coplanar multi-planet systems, then star-disk
misalignments would be ruled out as the explanation for the high obliquities of
hot Jupiters, and dynamical interactions would be implicated as the origin of
hot Jupiters.
