Spacecraft reveal Mars’ molten heart

The core of Mars is at least partially liquid, planetary scientists have concluded. The Red Planet hasn’t completely cooled since its formation 4.5 billion years ago, and its core is made either entirely of liquid iron or has a solid iron center surrounded by molten iron, researchers report in an upcoming Science.

INSIDE MARS. Drawing shows Mars with a liquid core about one-half the radius of that of the planet. The dark layer under the crust is the mantle. JPL/NASA

Because the sun exerts a slightly stronger tug on the near side of Mars than on the far side, it causes the planet to bulge slightly. Charles Yoder of NASA’s

Jet Propulsion Laboratory in Pasadena, Calif., and his colleagues have now measured that bulge. It’s just under a centimeter. That, the researchers say, is enough to indicate that Mars must be relatively flexible, which means the planet’s core must be at least partially molten.

Yoder’s group made the bulge measurements by monitoring the motion of the Mars Global Surveyor spacecraft as it orbited the planet over the past 3 years. A tiny drift in Surveyor’s orbit results from the planet’s bulge.

The scientists also drew upon data from another spacecraft, Mars Pathfinder, regarding the rate at which the Red Planet’s rotation axis slowly wobbles, like that of a top. This rate is proportional to the density of Mars’ core. The findings also reveal other details about the core: It’s radius is half that of the planet’s, as in the case of Earth and Venus. What’s more, the core contains a significant fraction of an element lighter than iron, such as sulfur.


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