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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