A bevy of backward-orbiting exoplanets could challenge theories of planet formation, new research suggests. The planets’ wonky orbits might also rule out the presence of Earthlike bodies in some planetary systems.
The wrong-way planets got where they are by cartwheeling over their stars’ heads, Andrew Collier Cameron of the University of St Andrews in Scotland proposed in an April 13 presentation at the Royal Astronomical Society’s National Astronomy Meeting in Glasgow, Scotland.
Planets are thought to form from the disk of gas and dust that surrounds a young star. Because the star and the disk both coalesce from the same cloud of material, theory holds that both should spin in the same direction — and so should any planets that arise. The “disk migration theory” posits that some planets should end up close to their stars by gently migrating inward over time, maintaining an orbital plane in line with the star’s rotation.