![]() For instance, Mercury's surface possesses at least 10 times more sulfur, or brimstone, than Earth or the moon. The composition of Mercury's surface is substantially different from that of other terrestrial planets, according to Messenger's scans of the X-rays emanating from the planet. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington) ![]() This NASA illustration shows how the Messenger spacecraft uses its gamma-ray spectrometer to spot the gamma rays and neutrons, which allows it determine the chemical composition of the planet's surface. "It is exactly this kind of unexpected discovery that makes planetary exploration such an adventure." "Analysis of the images and estimates of the rate at which the hollows may be growing leads to the exciting possibility that they are actively forming today," Blewett told. This would suggest Mercury is loaded with higher levels of volatile materials than most scenarios of its formation predict. Planetary scientist David Blewett at Johns Hopkins' Applied Physics Laboratory and his colleagues suspect these hollows were created when volatile materials - perhaps sulfur-bearing compounds - were liberated from the surface through some combination of heating, outgassing, explosive volcanism, micrometeoroid bombardment or solar radiation. These hollows, ranging in diameter from tens of yards to a few miles, occur across Mercury and are commonly seen in clusters. These images of Mercury's surface also revealed an odd feature - shallow, rimless hollows of irregular shapes. (Image credit: Courtesy of Science/AAAS and Brown University) Red circles show the locations of impact craters larger than 20 km in diameter. This Mercury map shows the contiguous northern high-latitude smooth plains mapped by NASA's Messenger spacecraftfrom orbit (inside the black line) covers 4.7 million square kilometers, over 6 percent of the planet. "This one deposit is so huge, volcanism has got to be important elsewhere," Head said. Head and his colleagues expect that other parts of Mercury also experienced volcanism. "Now we're in orbit with Messenger, we're up close and personal, just going around and around and really building up our picture of Mercury." ![]() "When we flew by Mercury the first time with Mariner 10, we weren't really sure if volcanism caused these smooth plains," Head told. Mercury's northern high latitudes had largely escaped view until now. "We can't say if it took 2.7 days or 15 years or any exact time from orbit, but it wasn't hundreds of millions of years," Head added. Įarly in the planet's history, some 3.5 billion to 4 billion years ago, these gigantic volumes of lava poured from cracks in the surface as far as 125 miles (200 kilometers) outside the volcanic zone, flooding the surrounding, low-lying plains "like a bathtub," Head said.īased on the way this lava apparently eroded the underlying surface, the researchers suggest it rushed out rapidly. This once-molten rock filled craters more than a mile (1.6 kilometers) deep and covers 6 percent of Mercury's surface, an area equal to nearly 60 percent of the continental United States, explained planetary geoscientist James Head at Brown University. For instance, high-resolutionimages of Mercury's surface reveal that epic lava flows helped create the planet's smooth northern plains.
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