Saturday, November 15, 2008
Moon's volcanic history has more to tell than first thought by scientists
According to a report in National Geographic News, until recently, the prevailing belief was that lunar volcanism started soon after the moon formed, about 4.5 billion years ago, and ended about 3 billion years ago. KAGUYA, which was launched and began orbiting the moon in the fall of 2007, has sent back some of the first high-resolution images of the moon's dark side.
Using these images, the research team was able to manually count craters in several regions. Scientists can determine the age of a lunar landscape by counting the craters that have been blasted into its surface by meteors. The older a region, the more craters it has. There are fewer craters on the far side's lunar maria, or seas, than expected, meaning they're younger than presumed.
"The finding will lead the scientific community to reconsider the early geology of the moon," said lead study author Jun'ichi Haruyama of the Japan Aerospace Exploration Agency.Scientists believe that early in the moon's formation, which was probably caused when a Mars-sized planet hit the Earth, light minerals floated to the top of a magma, or molten-rock, ocean, forming a harder crust. Even after the crust had been fully formed, by about 3.2 billion years ago, the mantle melted occasionally and lava flowed on the lunar surface.
Sometimes, meteor hits could trigger eruptions. Most of the volcanism occurred on the near side in several phases, according to Carle Pieters, a geologist at Brown University and a study co-author. But, there are relatively few basalts-glassy rocks formed by cooling magma-on the far side of the moon, so it was thought that volcanic activity had ended early in that hemisphere. According to the study, the volcanism that formed the few maria on the far side "lasted longer than previously considered and may have occurred episodically."
"The thermal history of the moon is certainly more complex than originally thought," Pieters said. "After a great data famine, this feast of quality new information about the moon will open a renaissance of scientific exploration and new understanding of Earth's nearest neighbor," he added.