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Mars-orbiting probes have spied hundreds of mounds, some up to 500 meters across and dozens of meters tall, inside an ancient crater near the planet's equator. In the 15 April issue of Earth and Planetary Science Letters, researchers make the case that these enigmatic features (depicted in blue in the main image) are mud volcanoes. For one thing, the near-circular mounds weren't formed by molten-rock volcanoes because there are no deposits of volcanic ash or lava nearby. Instead, the mounds contain boulders and other chunks of material apparently stripped from underlying layers of sediments (depicted in yellow-green), which range from 200 to 500 meters thick. Also, most of the mounds inside the 90-kilometer-wide Firsoff crater (inset) are found on slopes inside the crater rim and were likely created when mud under high pressure—which likely formed during a warmer, wetter phase on the Red Planet—oozed to the surface through a network of cracks there. Other teams have claimed finding mud volcanoes elsewhere on Mars, but the researchers contend that the new finds are the first that definitively link material in the mounds to underlying sediments. |
火星轨道探测器发现，在火星赤道附近的一个火山口内，存在几百个土丘，有的直径达500米，高度有几十米。在4月15日即将出版的一期《地球与行星科学通讯》上，研究人员说明了情况：这些神秘的地貌（见主图像中描绘成的蓝色部分）属于泥火山。一方面，这些近乎圆形的土丘不是由于火山熔岩形成的，因为附近没有火山灰和熔岩构成的沉积层；而另一方面，土丘中包含卵石和其他的块状物质，很明显是从地表下面的沉积层中脱落出来的，沉积层（见黄绿色区域）的厚度从200米到500米不等。此外还发现，90米宽的佛索夫火山口（见图中插图）内部土丘位于火山口边缘的斜坡上，很可能是泥浆在高压力的情况下通过网状裂缝慢慢渗出地表后而形成的。高压力可能曾经形成于火星的一个比较温暖和湿润的时期。其他的研究小组称，曾经在火星的其他地方发现过泥火山。但是这组研究人员争辩说，他们的新发现是第一次明确地将土丘中的物质跟地下沉积层联系起来。 |
