Decode the mystery of Mercury's personality

Mercury tiny, the innermost planet of the solar system, seems to have a semi-solid nucleus. The finding may help explain the planet's weak magnetic field.

Scientists use a technique similar to measuring the light coming out of a sphere in a dance floor to find that Mercury is at least half liquid.(Photo: iStockphoto)

Due to its small size - Mercury is 40% smaller than the earth - the laws of physics assume that its nucleus must be cold and solidified long ago. However, a new improved radar technique measuring Mercury's speed found clear signs that the planet contained both solid and semi-solid matter.

"The liquid section tells us something very important about the temperature of this planet," astronomer Jean-Luc Margot, an assistant professor at Cornell University, said. "A planet of Mercury's size should have been cold. It should have radiated all of its heat for such a long time."

The discovery helped explain Mercury's weak magnetic field, discovered by the probe Mariner 10 during its close flight in the mid-1970s. That's because a principle for a magnetic field to be a has a metal core in liquid or semi-liquid form, like the earth.

The finding also raises new questions even more confusing: Those are the factors that keep Mercury's core hot enough to maintain semi-solid state for billions of years. One possibility is that light elements that keep heat, like sulfur, have played a role here. However, scientists are puzzled by how light elements can concentrate in a place close to the sun.

The next answers may come when NASA's Messenger probe flies to this tiny planet. The ship is expected to carry out three cross-over flights before flying into stable orbit for long-term research in 2011.

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