<http://schema.org/alternativeHeadline>
"Scientists are flummoxed by the lack of methane on the planet, and wonder if they're monitoring a place that doesn't leak the gas often."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.mnn.com/earth-matters/space/stories/no-methane-on-mars-so-what-does-that-mean>