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Messenger's message from Mercury: Time to rewrite the textbooks

Scientists with the Messenger mission to Mercury unveiled their findings Thursday, which are answering some decades-old mysteries – but also creating new ones.

These images from the Messenger spacecraft show candidates for ancient lava flows and vents on Mercury. At upper left and right, the image and sketch map show volcanic flow-related features. At lower left, the pits could be source vents. At lower right, the teardrop-shaped hills could have been shaped by lava erosion.

AAAS/Science

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The Messenger spacecraft has already begun to rewrite textbooks about Mercury only six months after it settled into orbit around the first planet from the sun.

Its findings, presented at a press conference Thursday, challenge prevailing theories on planetary formation and paint a picture of a planet long ago convulsed by massive lava flows.

As the least studied of the solar system's four inner planets, Mercury is ready for a scientific facelift. But the relative dearth of information about it means that scientists are struggling to make sense of everything Messenger is telling them. For now, the data are raising more questions than answers. But 36 years after humanity's only other visits to Mercury – two Mariner 10 flybys in 1974 and 1975 – scientists are at least learning which questions to ask.

"Mercury is not the planet described in the textbooks," said James Head III, a mission team member and geologist at Brown University in Providence, R.I.

In Messenger's first months orbiting Mercury, the mission has focused on the questions raised by Mariner 10 decades ago.

Foremost among them was Mercury's curious construction. The iron core of Mercury is much larger relative to the planet's total size than the cores of any other inner planet – Venus, Earth, or Mars.

Since Mariner 10's flybys, several theories emerged as to why this could be. Perhaps Mercury was once two to three times bigger and much of its outer surface was blown away by the intensity of the sun. Or perhaps the outer surface of a once-larger was removed in a cataclysmic collision.

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