Mars' gooey core will eventually solidify

By Dave Mosher

updated 7:16 p.m. ET May 31, 2007

Above ground, Mars is mostly a bone-chilling desert pocked with craters. Hundreds of miles below, however, a molten sea of iron, nickel and sulfur churns. And new research suggests the gooey core will eventually solidify — either from the outside-in, forming an iron-nickel core, or from the inside out, forming a core of a fool's-gold-like minerals.

Andrew Stewart, a planetary geochemist at the Swiss Federal Institute of Technology, said Mars' cooling core might restore magnetism to the Red Planet. "If liquid metal moves around a solid core, it could create a natural dynamo like the one found in Earth's core," said Stewart, who co-authored the study detailed in today's online edition of the journal Science.

Liquids turn solid at different temperatures when pressure or purity are changed. Dry ice, for example, is carbon dioxide gas squeezed under immense pressure. Add impurities to ice, and its freezing point is lowered (which is why roads are salted). Likewise, explained Stewart, sulfur mixes things up under Mars' crushing pressure of 5.8 million pounds per square inch.

To simulate the pressure at Mars' core, Stewart and his team used a synthetic diamond-making machine. Because the way Mars' entrails will freeze all depends on how much sulfur is mixed in with iron and nickel, Stewart crushed samples with different portions of sulfur. "Mars' core is made of anywhere between 10 and 16 percent sulfur," he told SPACE.com. "It doesn't sound like a significant range, but in a planet's core it makes all the difference."

After dissecting the samples with microscopes, Stewart and his colleagues discovered that a low amount of sulfur would cause nickel and iron to solidify in chunks near the outer edge of the core, which would sink to the center. Deemed the "snowing core" model, Stewart thinks it's the most likely scenario.

"On the other hand," Stewart said, "we found a heftier portion of sulfur would cause a fool's-gold-like mineral to form in the center of Mars and grow outward."

Stewart said he'll offer a better guess once the European Space Agency's ExoMars mission reaches the Red Planet in 2013 and the spacecraft's NetLander probes travel to Mars' surface. Designed to listen for Martian earthquakes and map out the inside of Mars, Stewart said the newly gathered information will be "the ultimate test for which of our conclusions is definitely wrong or definitely right," Stewart said. "Once we have seismic data from Mars, we'll be able to know the sulfur content and what's going to happen to Mars' core."

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