<http://schema.org/alternativeHeadline>
"Scientists debate whether there's a single, Jupiter-like planet pulling space rocks toward it, or if two Mars-sized planets crashed together to create the gravitational pull."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.mnn.com/earth-matters/space/stories/swarm-of-comets-hint-at-mysterious-undiscovered-alien-planet>